Raportul Stiintific si Tehnic (RST) in extenso
Raportul Stiintific si Tehnic (RST) in extenso
Raportul Stiintific si Tehnic (RST) in extenso
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<strong>Raportul</strong> <strong>Sti<strong>in</strong>tific</strong> <strong>si</strong> <strong>Tehnic</strong> (<strong>RST</strong>) <strong>in</strong> <strong>extenso</strong><br />
Cupr<strong>in</strong>s<br />
1. Analiza chimica elementara pr<strong>in</strong> EDS <strong>si</strong> analiza compozitiei fazelor cristal<strong>in</strong>e pr<strong>in</strong> DRX ale<br />
pulberilor de BNT-BTx, unde x=0,08, preparate pr<strong>in</strong> sol-gel<br />
1.1. Analiza compozitiei chimice pr<strong>in</strong> spectroscopie EDS (<strong>si</strong> SEM) a pulberilor de<br />
BNT-BT0,08 preparate pr<strong>in</strong> sol-gel<br />
1.2. Analiza compozitiei de faze pr<strong>in</strong> DRX a pulberilor de BNT-BT0,08 preparate pr<strong>in</strong><br />
sol-gel<br />
2. Analiza chimica elementara pr<strong>in</strong> EDS <strong>si</strong> analiza morfologiei cu ajutorul microscopiei<br />
electronice cu baleiaj (SEM) pentru pulberile de BNT-BT0,08, preparate pr<strong>in</strong> metoda<br />
atomizarii<br />
2.1. Analiza chimica pr<strong>in</strong> EDS a pulberilor de BNT-BT0,08 preparate pr<strong>in</strong> metoda<br />
pirosol<br />
2.2. Analiza morfologiei cu ajutorul SEM a pulberilor de BNT-BT0,08 preparate pr<strong>in</strong><br />
metoda pirosol<br />
3. Analiza granulometriei pulberilor de BNT-BTx, unde x=0,08 preparate pr<strong>in</strong> cele doua<br />
metode chimice <strong>in</strong> solutie cu ajutorul microscopului cu transmi<strong>si</strong>e (TEM) <strong>si</strong> a<br />
granulometrului cu laser<br />
3.1. Analiza morfologiei cu ajutorul microscopiei electronice cu transmi<strong>si</strong>e a<br />
pulberilor de BNT-BT0,08 preparate pr<strong>in</strong> sol-gel<br />
3.2. Analiza morfologiei cu ajutorul granulometrului cu laser a pulberilor de BNT-<br />
BT0,08 preparate pr<strong>in</strong> sol-gel<br />
3.3. Analiza morfologiei cu ajutorul microscopiei electronice cu transmi<strong>si</strong>e a<br />
pulberilor de BNT-BT0,08 preparate pr<strong>in</strong> metoda pirosol<br />
3.4. Analiza morfologiei cu ajutorul granulometrului cu laser a pulberilor de BNT-<br />
BT0,08 preparate pr<strong>in</strong> metoda pirosol<br />
3.5. Activitati suport <strong>si</strong> de implementare a rezultatelor cercetarii.<br />
4. Concluzii<br />
5. Bibliografie<br />
1
Obiectivele generale<br />
Obiectivul general al proiectului MPPC propus este prepararea materialelor ceramice de<br />
compozitie (1-x)(Bi0.5Na0.5TiO3)-xBaTiO3 unde 0.05≤x≤0.15, cu proprietati piezoelectrice cel<br />
put<strong>in</strong> egale cu cele ale materialelor piezo cu plumb (PZT).<br />
O atentie deosebita va fi acordata controlului compozitiei chimice <strong>in</strong> vederea evitarii<br />
pierderilor de Bi <strong>si</strong> Na pr<strong>in</strong> evaporare <strong>in</strong> timpul <strong>si</strong>nterizarii <strong>si</strong>, morfologiei pulberilor <strong>in</strong> scopul<br />
obt<strong>in</strong>erii unor pulberi nanometrice care imbunatatesc procesul de den<strong>si</strong>ficare a ceramicii de<br />
BNT-BTx.<br />
In acest sens, noi propunem utilizarea a doua metode chimice de <strong>si</strong>nteza (sol-gel <strong>si</strong><br />
pirosol) pentru prepararea elementelor presate piezoceramice, compararea rezultatelor lor <strong>si</strong><br />
alegerea metodei care da cele mai bune performante pentru ceramica piezoelectrica de BNT-<br />
BTx. Metoda sol-gel va fi folo<strong>si</strong>ta <strong>si</strong> pentru obt<strong>in</strong>erea filmelor subtiri de compozitie BNT-<br />
BTx, cu proprietati piezoelectrice.<br />
Obiectivele etapei de executie<br />
Caracterizarea microstructurala <strong>si</strong> morfologica a pulberilor <strong>si</strong> a filmelor subtiri de<br />
BNT-BTx, unde x=0,08, preparate pr<strong>in</strong> sol-gel <strong>si</strong> atomizare.<br />
Analiza chimica elementara pr<strong>in</strong> EDS <strong>si</strong> analiza compozitiei fazelor cristal<strong>in</strong>e pr<strong>in</strong><br />
DRX ale pulberilor de BNT-BTx, unde x=0,08, preparate pr<strong>in</strong> sol-gel.<br />
Analiza chimica elementara pr<strong>in</strong> EDS <strong>si</strong> analiza morfologiei pulberilor de BNT-BTx,<br />
unde x=0,08,preparate pr<strong>in</strong> metoda atomizarii, cu ajutorul microscopiei electronice cu baleiaj<br />
(SEM).<br />
Analiza granulometriei pulberilor de BNT-BTx, unde x=0,08, preparate pr<strong>in</strong> cele doua<br />
metode chimice <strong>in</strong> solutie cu ajutorul microscopului cu transmi<strong>si</strong>e (TEM) <strong>si</strong> a granulometrului<br />
cu laser.<br />
Activitati suport <strong>si</strong> de implementare a rezultatelor cercetarii.<br />
2
Rezumatul etapei (maxim 2 pag<strong>in</strong>i)<br />
In acord cu scopul Etapei IIa: „Caracterizarea microstructurala <strong>si</strong> morfologica a<br />
pulberilor <strong>si</strong> a filmelor subtiri de BNT-BTx, unde x=0,08 preparate pr<strong>in</strong> sol-gel <strong>si</strong> atomizare”,<br />
sunt prezentate <strong>in</strong> acest raport sti<strong>in</strong>tific, rezultatele caracterizarii microstructurale <strong>si</strong><br />
morfologice a pulberilor de BNT-BTx, unde x=0,08, preparate pr<strong>in</strong> metodele sol-gel <strong>si</strong><br />
pirosol. Gelul precursor a fost calc<strong>in</strong>at la temperaturi diferite 200, 500, 600, 700 <strong>si</strong> 900 °C <strong>si</strong><br />
apoi analizat.<br />
Fig.41. Imag<strong>in</strong>i SEM,TEM, HR-TEM <strong>si</strong> SAED ale pulberii de BNT-BT0,08 preparata pr<strong>in</strong><br />
calc<strong>in</strong>area gelului precursor la 600 °C.<br />
Gelul tratat la 600 °C, 3 ore prez<strong>in</strong>ta granule cu dimen<strong>si</strong>unile <strong>in</strong> domeniul 45-95 nm<br />
iar cel calc<strong>in</strong>at la 700 °C, 2 ore <strong>in</strong> aer, <strong>in</strong>dica o morfologie omogena, granulele avand<br />
diametrul <strong>in</strong> domeniul 30-65 nm.<br />
Inten<strong>si</strong>tatea (a. u.)<br />
*<br />
x<br />
o<br />
o<br />
*<br />
* - (Bi 0.5 Na 0.5 )TiO 3 (structura perovskitica)<br />
o - Bi 2 O 3 hexagonal<br />
x- Bi O tetragonal<br />
2 3<br />
* *<br />
20 25 30 35 40 45 50 55 60<br />
3<br />
2θ<br />
1150 o C<br />
700 o C<br />
600 o C<br />
500 o C<br />
400 o C<br />
200 o C<br />
Fig.7. Difractogramele de raze X ale precursorului gel de Bi1/2Na1/2TiO3 dopat cu 8<br />
mol.% BaTiO3, calc<strong>in</strong>at la 200, 400, 500, 600, 700 <strong>si</strong> 1150 °C<br />
Analiza pr<strong>in</strong> DRX arata ca gelul <strong>in</strong>calzit la 200 °C a fost amorf <strong>si</strong> cristalizeaza ca faza<br />
unica la 600 °C. Pulberea obt<strong>in</strong>uta pr<strong>in</strong> metoda pirosol a fost cristalizata, prezentand doua faze<br />
cristal<strong>in</strong>e.<br />
*
Fig.16. Imag<strong>in</strong>ea SEM, distributia elementelor chimice <strong>si</strong> spectrul EDS pentru pulberea de<br />
BNT-BT0,08, calc<strong>in</strong>ata la 600 °C<br />
Rezultatele analizei cu EDS pun <strong>in</strong> evidenta o pulbere omogena compozitional.<br />
Fig.53. Imag<strong>in</strong>i SEM <strong>si</strong> TEM/HR-TEM ale pulberii crude de BNT-BT0,08 obt<strong>in</strong>uta pr<strong>in</strong> pirosol<br />
(imag<strong>in</strong>ea d<strong>in</strong> stanga), calc<strong>in</strong>ata ulterior la 700 °C, 3 ore (cele doua imag<strong>in</strong>i d<strong>in</strong> dreapta)<br />
Analizele cu ajutorul microscopiei electronice SEM <strong>si</strong> TEM, EDAX <strong>si</strong> difractia de<br />
raze X au aratat ca se obt<strong>in</strong>e un material monofazic, stoichiometric BNT-BT0,08, complet<br />
cristalizat <strong>in</strong> conditii termice avantajoase daca se foloseste metoda sol-gel pentru <strong>si</strong>nteză <strong>si</strong><br />
polifazic <strong>in</strong> cazul metodei pirosol.<br />
În concluzie, rezultatele cupr<strong>in</strong>se <strong>in</strong> raport sti<strong>in</strong>tific complet, priv<strong>in</strong>d caracterizarea<br />
microstructurala <strong>si</strong> morfologica a pulberii <strong>si</strong> filmelor de BNT-BT0,08 obt<strong>in</strong>ute pr<strong>in</strong> sol-gel <strong>si</strong><br />
pirosol, <strong>in</strong>dica faptul ca obiectivele Etapei II a au fost realizate.<br />
Aceste rezultate prelim<strong>in</strong>are constituie o bază de date utile pentru etapele urmatoare<br />
ale Contractului PNCDI II nr. 72 153/2008.<br />
4
1. Analiza chimica elementara pr<strong>in</strong> EDS <strong>si</strong> analiza compozitiei fazelor cristal<strong>in</strong>e pr<strong>in</strong><br />
DRX ale pulberilor de BNT-BT0,08 preparate pr<strong>in</strong> metoda sol-gel<br />
Studiul pr<strong>in</strong> microscopie electronica, difractie de electroni <strong>si</strong> microanaliza de raze X<br />
permite obt<strong>in</strong>erea unor <strong>in</strong>formatii calitative priv<strong>in</strong>d porozitatea, dimen<strong>si</strong>unea de graunti, de<br />
particule, precum <strong>si</strong> a unor <strong>in</strong>formatii microstructurale <strong>si</strong> microcompozitionale. In plus,<br />
studiile cu ajutorul microscopiei electronice (SEM <strong>si</strong>/sau TEM), asociate cu microanaliza de<br />
raze X disper<strong>si</strong>va <strong>in</strong> energie (EDS) pot oferi <strong>in</strong>formatii utile pentru <strong>in</strong>telegerea unor fenomene<br />
fizice d<strong>in</strong> domeniul materialelor micro sau nanostructurate.<br />
In cazul nostru, vom folo<strong>si</strong> microscopia electronica <strong>si</strong> analiza pr<strong>in</strong> EDS pentru a<br />
evidentia dimen<strong>si</strong>unile nanometrice ale pulberilor de BNT-BT0,08 preparate atat pr<strong>in</strong> sol-gel<br />
cat <strong>si</strong> pr<strong>in</strong> metoda pirosol <strong>si</strong>, de asemenea, pentru confirmarea stoichiometriei pulberilor astfel<br />
preparate.<br />
Analiza cu ajutorul difractiei de raze X, este utilizata <strong>in</strong> acest studiu pentru ga<strong>si</strong>rea<br />
acelor conditii de tratament termic (temperatura, durata) care sa conduca laobt<strong>in</strong>erea unui<br />
material monofazic (compus d<strong>in</strong> faza cu proprietatile electrice dorite).<br />
1.1. Analiza compozitiei chimice pr<strong>in</strong> spectroscopie EDS (<strong>si</strong> SEM) a pulberilor de<br />
BNT-BT0,08 preparate pr<strong>in</strong> sol-gel<br />
Proprietatile materialelor sunt direct dependente de microstructura lor, adica de factori<br />
cum ar fi: den<strong>si</strong>tatea <strong>si</strong> tipul defectelor retelei cristal<strong>in</strong>e, dimen<strong>si</strong>unea, distributia <strong>si</strong> compozitia<br />
fazelor prezente <strong>in</strong> materiale, segregarea localizata a impuritatilor <strong>si</strong> elementelor de dopare. O<br />
buna <strong>in</strong>telegere a acestor probleme se obt<strong>in</strong>e pr<strong>in</strong> aplicarea exten<strong>si</strong>va a microscopiei<br />
electronice pr<strong>in</strong> transmi<strong>si</strong>e (TEM) <strong>si</strong> microscopiei electronice cu baleiaj (SEM) <strong>in</strong> studiul<br />
materialelor.<br />
In cadrul acestei etape de cercetare, am utilizat analiza SEM iar pentru toate pulberile,<br />
iar pentru cele care au avut dimen<strong>si</strong>uni nanometrice am folo<strong>si</strong>t <strong>si</strong> analiza cu ajutorul metodei<br />
de analiza TEM.<br />
Asa cum am evidentiat <strong>si</strong> pr<strong>in</strong> experimentarile prelim<strong>in</strong>are d<strong>in</strong> prima etapa a<br />
proiectului MPPC, pentru obt<strong>in</strong>erea unei pulberi monofazice de BNT-BT0,08, gelul precursor a<br />
fost calc<strong>in</strong>at <strong>in</strong> mai multe etape, la temperaturi diferite. In cadrul acestei faze, prezentam o<br />
caracterizare caracterizare chimica, structurala <strong>si</strong> morfologica a materialului rezultat d<strong>in</strong> gelul<br />
calc<strong>in</strong>at la temperaturi diferite (200, 500, 600, 700 <strong>si</strong> 900 °C ). Pentru o cat mai fidela<br />
5
prezentare a morfologiei pulberilor obt<strong>in</strong>ute, am prezentat mai multe imag<strong>in</strong>i SEM, obt<strong>in</strong>ute<br />
pentru zone cat mai variate ale probei analizate, pentru fiecare temperatura de calc<strong>in</strong>are <strong>in</strong><br />
parte. In figura 1 sunt prezentate cateva imag<strong>in</strong>i SEM ale precursorului gel uscat la 200 °C<br />
Fig.1. Imag<strong>in</strong>i SEM ale precursorului gel uscat la 200 °C<br />
Datorita faptului ca gelul precursor a fost obt<strong>in</strong>ut porn<strong>in</strong>d de la acetat de bismut, acetat<br />
de sodiu, acetat de bariu, şi izopropoxid de titan, tipul de gel obt<strong>in</strong>ut este gel polimeric. Asa<br />
cum se vede <strong>in</strong> figura 1, structura de polimer a pulberii provenite d<strong>in</strong> uscarea gelului la 200<br />
°C, se pastreaza <strong>si</strong> la aceasta temperatura. De fapt, elim<strong>in</strong>area partii organice a gelului<br />
polimeric nu este realizata complet la aceasta temperatura.<br />
Imag<strong>in</strong>ile SEM arata fragmente de structura polimerica monolitica, fragmente cu<br />
forme <strong>si</strong> dimen<strong>si</strong>uni variate. In functie de viteza de <strong>in</strong>calzire, descompunerea <strong>si</strong> piroliza cu aer<br />
a componentilor gelului vor fi mai rapide sau mai lente putand sa se ajunga chiar la piroliza cu<br />
6
flacara. In acest d<strong>in</strong> urma caz, pulberea rezultata va fi de culoare neagra datorata grafitizarii<br />
ei.<br />
Figura 2 prez<strong>in</strong>ta imag<strong>in</strong>i SEM ale precursorului gel uscat la 500 °C. La aceasta<br />
temperatura, partea organica a fost elim<strong>in</strong>ata completa <strong>si</strong> s-a obt<strong>in</strong>ut o pulbere compusa d<strong>in</strong><br />
granule <strong>si</strong> nu d<strong>in</strong> fragmente de material cu microstructura polimerica.<br />
(a) (b)<br />
(c)<br />
Fig.2. Imag<strong>in</strong>i SEM ale gelului calc<strong>in</strong>at la 500 °C<br />
Imag<strong>in</strong>ile SEM obt<strong>in</strong>ute pe esantioane de pulberi rezultate d<strong>in</strong> mai multe <strong>si</strong>nteze,<br />
evidentiaza pulberi nanometrice. Se remarca pulberi cu diametrul granulelor <strong>in</strong> domeniul 20-<br />
25 nm (Fig.2b) <strong>si</strong> pulberi cu diametrul cupr<strong>in</strong>s <strong>in</strong>tre 20 <strong>si</strong> 32 nm (Fig.2 c,d). Pulberea obt<strong>in</strong>uta<br />
d<strong>in</strong> gelul calc<strong>in</strong>at la 500 °C este caracterizata de o granulatie omogena d<strong>in</strong> punct de vedere<br />
dimen<strong>si</strong>onal.<br />
Figura 3 prez<strong>in</strong>ta imag<strong>in</strong>i SEM ale precursorului gel uscat la 600 C.<br />
7<br />
(d)
Fig.3. Imag<strong>in</strong>i SEM ale gelului calc<strong>in</strong>at la 600 °C<br />
Gelul tratat la 600 °C, timp de 3 ore <strong>in</strong> aer, se prez<strong>in</strong>ta sub forma de pulbere cu granule<br />
avand dimen<strong>si</strong>unile <strong>in</strong> domeniul 45-95 nm. Pr<strong>in</strong> cresterea temperaturii de calc<strong>in</strong>are cu 100 °C<br />
<strong>si</strong> ment<strong>in</strong>and constanta durata calc<strong>in</strong>arii, granulele au crescut de la ~30 nm la ~90 nm. Deja, la<br />
aceasta temperatura, materialul este complet cristalizat, monofazic. BNT-BT0.08 a cristalizat<br />
pe structura cubica a titanatului de bismut <strong>si</strong> sodiu (Bi0,5Na0,5TiO3).<br />
Figura 4 prez<strong>in</strong>ta imag<strong>in</strong>i SEM ale precursorului gel uscat la 700 C.<br />
8
Fig.4. Imag<strong>in</strong>i SEM ale gelului calc<strong>in</strong>at la 700 °C<br />
Imag<strong>in</strong>ile SEM obt<strong>in</strong>ute pe o pulbere de gel precursor de BNT-BT0,08, calc<strong>in</strong>at la 700<br />
°C, 2 ore <strong>in</strong> aer, <strong>in</strong>dica o morfologie omogena, granulele avand diametrul <strong>in</strong> domeniul 30-65<br />
nm. Pulberea rezultata la aceasta temperatura are tend<strong>in</strong>ta de aglomerare asemanator celor<br />
obt<strong>in</strong>ute la temperaturi sub 700 °C. In cazul utilizarii metodelor sol-gel pentru <strong>si</strong>nteza<br />
materialelor, pulberile obt<strong>in</strong>ute prez<strong>in</strong>ta o tend<strong>in</strong>ta moderata de agomerare.<br />
Figura 5 prez<strong>in</strong>ta imag<strong>in</strong>i SEM ale precursorului gel uscat la 900 °C.<br />
9
Fig.5. Imag<strong>in</strong>i SEM ale gelului calc<strong>in</strong>at la 900 °C<br />
Microfotografiile SEM obt<strong>in</strong>ute pentru pulberile de BNT-BT0,08, care au fost calc<strong>in</strong>ate<br />
la 900 °C, sugereaza un material neomogen d<strong>in</strong> punct de vedere al dimen<strong>si</strong>unilor granulelor.<br />
Granule cu diametrul <strong>in</strong> domeniul 50-195 nm coexista cu granule poliedrice cu dimen<strong>si</strong>uni de<br />
pana la 250-300 nm. Aceasta crestere bimodala a granulelor s-a realizat pr<strong>in</strong> difuzie de masa<br />
de la granulele mai mici catre cele mai mari.<br />
Analiza cu ajutorul microscopiei electronice cu baleiaj a pulberilor rezultate d<strong>in</strong><br />
calc<strong>in</strong>area gelului la diferite temperaturi, a scos <strong>in</strong> evidenta faptul ca pr<strong>in</strong> sol-gel se ont<strong>in</strong>e o<br />
pulbere de BNT-BT0,08 cu morfologie uniforma <strong>si</strong> granule nanometrice sau submicronice. In<br />
general, pulberile cu astfel de morfologie, se caracterizeaza pr<strong>in</strong>tr-o aptitud<strong>in</strong>e buna la<br />
den<strong>si</strong>ficare pr<strong>in</strong> <strong>si</strong>nterizare.<br />
Deoarece, literatura de specialitate remarca faptul ca titanatul de bismut <strong>si</strong> sodiu poate<br />
pierde pr<strong>in</strong> evaporare, o parte d<strong>in</strong> cont<strong>in</strong>utul sau de sodiu <strong>si</strong> bismut, am analizat compozitia<br />
chimica a materialului rezultat dupa fiecare de tratament termic.<br />
Microanaliza de raze X <strong>in</strong> microscopia electronica (EDAX)<br />
Microanaliza de raze X foloseste emi<strong>si</strong>a de raze X caracteristice, pentru a identifica <strong>si</strong><br />
cuantifica elementele prezente <strong>in</strong> zona de proba ilum<strong>in</strong>ata. Pr<strong>in</strong> urmare, constituie un mijloc<br />
de identificare <strong>in</strong> <strong>si</strong>tu a compozitiei chimice microvolumice, conjugata cu localizarea precisa a<br />
regiunii exam<strong>in</strong>ate, precum <strong>si</strong> analizarea sa microstructurala <strong>si</strong> morfologica.<br />
Acest procedeu nece<strong>si</strong>ta <strong>in</strong>corporarea unor detectori de raze X <strong>in</strong> <strong>si</strong>stemul electronooptic,<br />
fara a compromite alte facilitati de exam<strong>in</strong>are a probelor. Rolul acestor detectori este de<br />
a capta cat mai mult d<strong>in</strong> radiatia X emisa de zona d<strong>in</strong> proba bombardata de fasciculul <strong>in</strong>cident<br />
10
de electroni accelerati, precum <strong>si</strong> de a analiza energiile sau lungimile de unda ale acestor<br />
radiatii pentru a identifica elementele care le-au generat.<br />
In SEM se folosesc pentru detectia razelor X caracteristice emise de proba detectori<br />
cu cristal solid disper<strong>si</strong>v <strong>in</strong> lungimea de unda ( <strong>si</strong>stemul WDS) cat <strong>si</strong> detectori cu cristal solid<br />
disper<strong>si</strong>v <strong>in</strong> energie (<strong>si</strong>stemul EDS).<br />
In TEM, datorita particularitatilor constructive ale coloanei <strong>si</strong> lentilei obiectiv <strong>in</strong><br />
campul careia se afla proba, nu se pot adapta decat detectori cu cristal solid disper<strong>si</strong>v <strong>in</strong><br />
energie.<br />
Sistemul este controlat de un calculator cu programe adecvate care <strong>in</strong>registreaza<br />
spectrul, aplica corectiile necesare <strong>si</strong> calculeaza concentratiile elementelor detectate.<br />
Cuantificarea cupr<strong>in</strong>de extragerea fondului, <strong>in</strong>tegrarea maximelor caracteristice, compararea<br />
cu <strong>in</strong>ten<strong>si</strong>tatile maximelor obt<strong>in</strong>ute pe standarde (etapa elim<strong>in</strong>ata la <strong>si</strong>stemele dotate cu<br />
programe de calcul ce cupr<strong>in</strong>d subrut<strong>in</strong>e de analiza rapida fara standarde) <strong>si</strong> calculul<br />
concentratiilor cu aplicarea corectiei ZAF.<br />
Analiza se poate efectua <strong>in</strong>tr-un punct cu diametru egal cu diametrul fasciculului de<br />
electroni <strong>in</strong>cident pe proba sau pe o suprafata cu dimen<strong>si</strong>uni variabile care pot fi selectate de<br />
operator. Analiza este rapida, se obt<strong>in</strong>e <strong>si</strong>multan tot spectrul cu radiatiile caracteristice ce<br />
permit identificarea compozitiei <strong>in</strong> zona analizata.<br />
Sistemul este put<strong>in</strong> susceptibil la modificarile parametrilor de analiza <strong>si</strong> nu nece<strong>si</strong>ta<br />
suprafete plane. Permite analiza calitativa <strong>si</strong> cantitativa a elementelor de la sodiu (Z = 11) la<br />
uraniu (Z=92). Sistemele mai moderne sunt prevazute cu fereastra de beriliu ce se poate<br />
<strong>in</strong>departa astfel <strong>in</strong>cat pot fi detectate <strong>si</strong> elementele mai usoare, de la bor (Z=5).<br />
In acest studiu, am folo<strong>si</strong>t spectrometria disper<strong>si</strong>va <strong>in</strong> energia radiatiei X (EDS) pentru<br />
a pune <strong>in</strong> evidenta prezenta tuturor tipurilor de ioni implicati <strong>in</strong> <strong>si</strong>nteza BNT-BT0,08, pentru a<br />
ga<strong>si</strong> rapoartele atomice d<strong>in</strong>tre ele <strong>si</strong> pentru a obt<strong>in</strong>e distributia atomilor <strong>in</strong> proba, corelat cu<br />
imag<strong>in</strong>ea SEM a zonei respective d<strong>in</strong> proba. Au fost analizat compozitional pr<strong>in</strong> EDAX<br />
pulberile de calc<strong>in</strong>ate la 500, 600 <strong>si</strong> 700°C.<br />
1) BNT-BT0,08 obt<strong>in</strong>ut la 500 °C<br />
Pulberea de BNT-BT0,08 obt<strong>in</strong>uta la 500 °C a fost analizata cu ajutorul microscopiei SEM plus<br />
EDAX <strong>in</strong> trei zone diferite.<br />
Zona 1:<br />
11
Fig.6. Imag<strong>in</strong>ea SEM obt<strong>in</strong>uta pe pulberea de BNT-BT0,08,<br />
(zona 1), calc<strong>in</strong>ata la 500 °C<br />
Fig.7. Imag<strong>in</strong>ea SEM, distributia elementelor chimice <strong>si</strong> spectrul EDS pentru pulberea de<br />
BNT-BT0,08, calc<strong>in</strong>ata la 500 °C<br />
12
Tabelul 1. Compozitia chimica a BNT-BT0,08 obt<strong>in</strong>ut la 500 °C, zona 1<br />
Elementul % At % <strong>Raportul</strong>-K Z A F<br />
NaK 5.83 9.34 0.0111 1.0661 0.1785 1.0001<br />
BaL 0.00 0.00 0.0000 0.8538 0.8292 1.0000<br />
TiK 18.03 13.86 0.1240 0.9960 0.6904 1.0000<br />
BiL 46.31 8.16 0.3854 0.8048 1.0340 1.0000<br />
O K 29.83 68.64 0.0477 1.1357 0.1408 1.0001<br />
Total 100.00 100.00<br />
Elementul Net Inte. (P) Backgrd (B) Inte. Error P/B<br />
NaK 50.21 20.76 4.29 2.42<br />
BaL 0.00 26.92 0.00 0.00<br />
TiK 418.33 26.92 1.17 15.54<br />
BiL 142.09 18.23 2.11 7.79<br />
O K 116.63 8.44 2.23 13.83<br />
Pentru evidentierea distributiei elementelor chimice componente ale BNT-BT0,08, prezentam<br />
separat imag<strong>in</strong>ile cu repartitia fiecarui element pe suprafata d<strong>in</strong> figura 6.<br />
Ti Ba<br />
13
Fig.8. Distributia elementelor Ti, Ba, Bi, Na <strong>si</strong> O <strong>in</strong><br />
portiunea de proba prezentata <strong>in</strong> Fig.6<br />
Se poate observa o distributie uniforma a tuturor elementelor <strong>in</strong> zona exam<strong>in</strong>ata a<br />
probei. Chiar <strong>si</strong> bariul apare <strong>in</strong> microfotografia distributiei acestui element, ceea ce conduce la<br />
ideea ca totu<strong>si</strong> bariul estesub limita de separare a lui de titan, asa cum reiese <strong>si</strong> d<strong>in</strong> spectrul<br />
EDAX. De<strong>si</strong> dupa <strong>si</strong>nterizari la temperaturi mari, literatura de specialitate con<strong>si</strong>dera separarea<br />
bariului la marg<strong>in</strong>ea granulelor, pentru pulberile calc<strong>in</strong>ate la 500 °C nu se observa acest<br />
fenomen.<br />
Zona 2:<br />
Bi Na<br />
O<br />
14
Fig.9. Imag<strong>in</strong>ea SEM obt<strong>in</strong>uta pe pulberea de BNT-BT0,08,<br />
(zona 2), calc<strong>in</strong>ata la 500 °C<br />
Fig.10. Imag<strong>in</strong>ea SEM, distributia elementelor chimice <strong>si</strong> spectrul EDS pentru pulberea de<br />
BNT-BT0,08, calc<strong>in</strong>ata la 500 °C<br />
15
Tab. 2. Compozitia chimica a BNT-BT0,08 obt<strong>in</strong>ut la 500 °C, zona 2<br />
Elementul % At % <strong>Raportul</strong>-K Z A F<br />
NaK 5.92 9.39 0.0113 1.0649 0.1787 1.0001<br />
BaL 0.00 0.00 0.0000 0.8526 0.8330 1.0000<br />
TiK 18.29 13.93 0.1261 0.9945 0.6935 1.0000<br />
BiL 45.69 7.98 0.3796 0.8034 1.0343 1.0000<br />
O K 30.11 68.69 0.0481 1.1344 0.1408 1.0001<br />
Total 100.00 100.00<br />
Elementul Net Inte. (P) Backgrd (B) Inte. Error P/B<br />
NaK 54.16 24.01 2.06 2.26<br />
BaL 0.00 29.02 0.00 0.00<br />
TiK 452.57 28.84 0.55 15.70<br />
BiL 148.86 21.77 1.03 6.84<br />
O K 125.02 10.75 1.07 11.63<br />
Ti Ba<br />
16
Bi Na<br />
O<br />
Fig.11. Distributia elementelor Ti, Ba, Bi, Na <strong>si</strong> O <strong>in</strong><br />
portiunea de proba prezentata <strong>in</strong> Fig.9<br />
Ca <strong>si</strong> <strong>in</strong> cazul zonei 1, <strong>in</strong> zona 2 se observa o distributie omogena a elementelor chimice ale<br />
solutiei solide BNT-BT0,08 <strong>si</strong> impo<strong>si</strong>bilitatea separarii bariului de titan <strong>in</strong> spectrul EDS.<br />
Zona 3:<br />
Fig.12. Imag<strong>in</strong>ea SEM obt<strong>in</strong>uta pe pulberea de BNT-BT0,08, (zona 3), calc<strong>in</strong>ata la 500 °C<br />
17
Fig.13. Imag<strong>in</strong>ea SEM, distributia elementelor chimice <strong>si</strong> spectrul EDS pentru pulberea de<br />
BNT-BT0,08, calc<strong>in</strong>ata la 500 °C<br />
Tabelul 3. Compozitia chimica a BNT-BT0,08 obt<strong>in</strong>ut la 500 °C, zona 3<br />
Elementul % At % <strong>Raportul</strong>-K Z A F<br />
NaK 5.89 9.30 0.0112 1.0643 0.1789 1.0001<br />
BaL 0.00 0.00 0.0000 0.8521 0.8320 1.0000<br />
TiK 17.68 13.41 0.1218 0.9940 0.6927 1.0000<br />
BiL 45.89 7.97 0.3812 0.8030 1.0346 1.0000<br />
O K 30.54 69.31 0.0493 1.1337 0.1424 1.0001<br />
Total 100.00 100.00<br />
18
Elementul Net Inte. (P) Backgrd (B) Inte. Error P/B<br />
NaK 48.62 22.41 3.87 2.17<br />
BaL 0.00 25.15 0.00 0.00<br />
TiK 393.71 24.99 1.04 15.75<br />
BiL 134.68 18.66 1.90 7.22<br />
O K 115.49 9.94 1.96 11.62<br />
Ti Ba<br />
Bi Na<br />
O<br />
Fig.14. Distributia elementelor Ti, Ba, Bi, Na <strong>si</strong> O <strong>in</strong> portiunea de proba prezentata <strong>in</strong> Fig.12<br />
19
Distributia elementelor compusului BNT-BT0,08 <strong>in</strong> zona 3 conduce la observatia generala ca<br />
pulberea calc<strong>in</strong>ata la 500 °C, este un compus monofazal, stoichiometric.<br />
2) BNT-BT0,08 obt<strong>in</strong>ut la 600 °C<br />
Zona 1:<br />
Figura 15 prez<strong>in</strong>ta imag<strong>in</strong>ea SEM a zonei1, a unei pulberi de BNT-BT0,08 calc<strong>in</strong>ata la 600 °C.<br />
Fig.15. Imag<strong>in</strong>ea SEM obt<strong>in</strong>uta pe pulberea de BNT-BT0,08, (zona 1), calc<strong>in</strong>ata la 600 °C<br />
Fig.16. Imag<strong>in</strong>ea SEM, distributia elementelor chimice <strong>si</strong> spectrul EDS pentru pulberea de<br />
BNT-BT0,08, calc<strong>in</strong>ata la 600 °C<br />
20
Tabelul 4. Compozitia chimica a BNT-BT0,08 obt<strong>in</strong>ut la 600 °C, zona 1<br />
Elementul % At % <strong>Raportul</strong>-K Z A F<br />
NaK 5.94 10.18 0.0112 1.0747 0.1761 1.0001<br />
BaL 0.00 0.00 0.0000 0.8612 0.8230 1.0000<br />
TiK 21.47 17.66 0.1477 1.0048 0.6845 1.0000<br />
BiL 46.87 8.84 0.3928 0.8125 1.0313 1.0000<br />
O K 25.72 63.32 0.0384 1.1449 0.1303 1.0001<br />
Total 100.00 100.00<br />
Elementul Net Inte. (P) Backgrd (B) Inte. Error P/B<br />
NaK 46.76 15.33 4.14 3.05<br />
BaL 0.00 24.52 0.00 0.00<br />
TiK 459.60 24.52 1.08 18.75<br />
BiL 133.60 20.02 2.17 6.67<br />
O K 86.00 11.07 2.66 7.77<br />
Ti Ba<br />
21
Zona 2:<br />
Bi Na<br />
O<br />
Fig.17. Distributia elementelor Ti, Ba, Bi, Na <strong>si</strong> O <strong>in</strong><br />
portiunea de proba prezentata <strong>in</strong> Fig.15<br />
Fig.18. Imag<strong>in</strong>ea SEM obt<strong>in</strong>uta pe pulberea de BNT-BT0,08,<br />
(zona 2), calc<strong>in</strong>ata la 600 °C<br />
22
Fig.19. Imag<strong>in</strong>ea SEM, distributia elementelor chimice <strong>si</strong> spectrul EDS pentru pulberea de<br />
BNT-BT0,08, calc<strong>in</strong>ata la 600 °C<br />
Tabelul 5. Compozitia chimica a BNT-BT0,08 obt<strong>in</strong>ut la 600 °C, zona 1<br />
Elementul % At % <strong>Raportul</strong>-K Z A F<br />
NaK 5.86 9.88 0.0111 1.0729 0.1768 1.0001<br />
BaL 0.00 0.00 0.0000 0.8599 0.8196 1.0000<br />
TiK 19.58 15.85 0.1339 1.0032 0.6817 1.0000<br />
BiL 47.57 8.83 0.3984 0.8115 1.0321 1.0000<br />
O K 27.00 65.44 0.0416 1.1430 0.1347 1.0001<br />
Total 100.00 100.00<br />
23
Elementul Net Inte. (P) Backgrd (B) Inte. Error P/B<br />
NaK 42.32 14.82 5.36 2.86<br />
BaL 0.00 24.20 0.00 0.00<br />
TiK 381.57 24.20 1.45 15.77<br />
BiL 124.09 15.47 2.68 8.02<br />
O K 85.33 8.02 3.16 10.64<br />
Ti Ba<br />
Bi Na<br />
O<br />
Fig.20. Distributia elementelor Ti, Ba, Bi, Na <strong>si</strong> O <strong>in</strong> portiunea de proba prezentata <strong>in</strong> Fig.18<br />
24
Zona 3:<br />
Fig. 21. Imag<strong>in</strong>ea SEM obt<strong>in</strong>uta pe pulberea de BNT-BT0,08,<br />
(zona 3), calc<strong>in</strong>ata la 600 °C<br />
Fig. 22. Imag<strong>in</strong>ea SEM, distributia elementelor chimice <strong>si</strong> spectrul EDS pentru pulberea de<br />
BNT-BT0,08, calc<strong>in</strong>ata la 600 °C (zona 3)<br />
25
Tabelul 6. Compozitia chimica a BNT-BT0,08 obt<strong>in</strong>ut la 600 °C, zona 3<br />
Elementul % At % <strong>Raportul</strong>-K Z A F<br />
NaK 5.44 8.73 0.0103 1.0664 0.1773 1.0001<br />
BaL 0.00 0.00 0.0000 0.8541 0.8285 1.0000<br />
TiK 18.41 14.19 0.1264 0.9963 0.6890 1.0000<br />
BiL 46.30 8.18 0.3854 0.8051 1.0340 1.0000<br />
O K 29.86 68.90 0.0474 1.1361 0.1397 1.0001<br />
Total 100.00 100.00<br />
Elementul Net Inte. (P) Backgrd (B) Inte. Error P/B<br />
NaK 39.55 14.73 6.81 2.69<br />
BaL 0.00 20.51 0.00 0.00<br />
TiK 363.84 20.30 1.79 17.92<br />
BiL 121.28 17.04 3.33 7.12<br />
O K 98.28 8.20 3.53 11.98<br />
Ti Ba<br />
Bi Na<br />
26
O<br />
Fig.23. Distributia elementelor Ti, Ba, Bi, Na <strong>si</strong> O <strong>in</strong><br />
portiunea de proba prezentata <strong>in</strong> Fig.21<br />
D<strong>in</strong> figura 16, 19 <strong>si</strong> 22 se observa ca toate elementele care constituie solutia solida<br />
BNT-BT0,08 adica, Bi, Na, Ti, Ba <strong>si</strong> O sunt prezente <strong>in</strong> proba supusa analizei. Compozitia<br />
chimica exprimata <strong>in</strong> procente de masa <strong>si</strong> <strong>in</strong> procente atomice a probei de BNT-BT0,08,<br />
obt<strong>in</strong>uta <strong>in</strong> urma analizei EDS efectuate <strong>in</strong> trei zone diferite ale pulberii de analizat, este<br />
redata <strong>in</strong> tabelele 4, 5 <strong>si</strong> 6. Rezultatele analizei cu EDS pun <strong>in</strong> evidenta o pulbere omogena<br />
compozitional, <strong>in</strong> toate cele trei zone analizate. Calc<strong>in</strong>area gelului precursor la 600 °C, ajuta la<br />
cresterea gradului de cristalizare a materialului pulverulent <strong>si</strong> pastreaza omogenitatea chimica<br />
observata la pulberea obt<strong>in</strong>uta pr<strong>in</strong> calc<strong>in</strong>are la 500 °C.<br />
3) BNT-BT0,08 obt<strong>in</strong>ut la 700 °C<br />
Zona 1:<br />
Fig. 24. Imag<strong>in</strong>ea SEM obt<strong>in</strong>uta pe pulberea de BNT-BT0,08,<br />
(zona 1), calc<strong>in</strong>ata la 700 °C<br />
27
Fig. 25. Imag<strong>in</strong>ea SEM, distributia elementelor chimice <strong>si</strong> spectrul EDS pentru pulberea de<br />
BNT-BT0,08, calc<strong>in</strong>ata la 700 °C (zona 1)<br />
Tabelul 7. Compozitia chimica a BNT-BT0,08 obt<strong>in</strong>ut la 700 °C, zona 1<br />
Elementul % At % <strong>Raportul</strong>-K Z A F<br />
NaK 5.73 9.85 0.0109 1.0756 0.1762 1.0001<br />
BaL 0.00 0.00 0.0000 0.8624 0.8102 1.0000<br />
TiK 18.73 15.45 0.126 9 1.0064 0.6733 1.0000<br />
BiL 49.04 9.27 0.4122 0.8147 1.0317 1.0000<br />
O K 26.50 65.43 0.0411 1.1459 0.1354 1.0001<br />
Total 100.00 100.00<br />
Elementul Net Inte. (P) Backgrd (B) Inte. Error P/B<br />
28
NaK 61.08 22.44 3.02 2.72<br />
BaL 0.00 28.05 0.00 0.00<br />
TiK 535.38 27.86 0.81 19.22<br />
BiL 190.03 25.49 1.46 7.46<br />
O K 124.31 9.78 1.73 12.71<br />
Ti Ba<br />
Bi<br />
O<br />
Fig.26. Distributia elementelor Ti, Ba, Bi, Na <strong>si</strong> O <strong>in</strong><br />
portiunea de proba prezentata <strong>in</strong> Fig.24<br />
29<br />
Na
Zona 2:<br />
Fig. 27. Imag<strong>in</strong>ea SEM obt<strong>in</strong>uta pe pulberea de BNT-BT0,08,<br />
(zona 2), calc<strong>in</strong>ata la 700 °C<br />
Fig. 28. Imag<strong>in</strong>ea SEM, distributia elementelor chimice <strong>si</strong> spectrul EDS pentru pulberea de<br />
BNT-BT0,08, calc<strong>in</strong>ata la 700 °C (zona 2)<br />
30
Tabelul 8. Compozitia chimica a BNT-BT0,08 obt<strong>in</strong>ut la 700 °C, zona 2<br />
Elementul % At % <strong>Raportul</strong>-K Z A F<br />
NaK 5.73 9.85 0.0109 1.0756 0.1762 1.0001<br />
BaL 0.00 0.00 0.0000 0.8624 0.8102 1.0000<br />
TiK 18.73 15.45 0.1269 1.0064 0.6733 1.0000<br />
BiL 49.04 9.27 0.4122 0.8147 1.0317 1.0000<br />
O K 26.50 65.43 0.0411 1.1459 0.1354 1.0001<br />
Total 100.00 100.00<br />
Elementul Net Inte. (P) Backgrd (B) Inte. Error P/B<br />
NaK 61.08 22.44 3.02 2.72<br />
BaL 0.00 28.05 0.00 0.00<br />
TiK 535.38 27.86 0.81 19.22<br />
BiL 190.03 25.49 1.46 7.46<br />
O K 124.31 9.78 1.73 12.71<br />
Ti Ba<br />
Bi Na<br />
31
Zona 3:<br />
O<br />
Fig.29. Distributia elementelor Ti, Ba, Bi, Na <strong>si</strong> O <strong>in</strong><br />
portiunea de proba prezentata <strong>in</strong> Fig.27<br />
Fig. 30. Imag<strong>in</strong>ea SEM obt<strong>in</strong>uta pe pulberea de BNT-BT0,08,<br />
(zona 3), calc<strong>in</strong>ata la 700 °C<br />
32
Fig. 31. Imag<strong>in</strong>ea SEM, distributia elementelor chimice <strong>si</strong> spectrul EDS pentru pulberea de<br />
BNT-BT0,08, calc<strong>in</strong>ata la 700 °C (zona 3)<br />
Tabelul 9. Compozitia chimica a BNT-BT0,08 obt<strong>in</strong>ut la 700 °C, zona 3<br />
Elementul % At % <strong>Raportul</strong>-K Z A F<br />
NaK 5.30 8.93 0.0100 1.0732 0.1761 1.0001<br />
BaL 0.00 0.00 0.0000 0.8603 0.8125 1.0000<br />
TiK 18.13 14.68 0.1229 1.0039 0.6752 1.0000<br />
BiL 48.78 9.05 0.4092 0.8125 1.0324 1.0000<br />
O K 27.79 67.34 0.0437 1.1433 0.1376 1.0001<br />
Total 100.00 100.00<br />
Elementul Net Inte. (P) Backgrd (B) Inte. Error P/B<br />
NaK 51.57 22.34 4.64 2.31<br />
BaL 0.00 24.06 0.00 0.00<br />
TiK 474.93 24.30 1.17 19.54<br />
BiL 172.79 19.19 2.05 9.00<br />
O K 121.09 9.74 2.39 12.43<br />
33
Ti<br />
Fig. 32. Distributia elementelor Ti, Ba, Bi, Na <strong>si</strong> O <strong>in</strong><br />
portiunea de proba prezentata <strong>in</strong> Fig.30<br />
Daca facem o comparatie <strong>in</strong>tre cont<strong>in</strong>utul de Na <strong>in</strong> cele trei zone, se constata ca pentru zonele<br />
1<strong>si</strong> 2 cont<strong>in</strong>utul de sodiu este acela<strong>si</strong> (9,85 at% Na) <strong>si</strong> este mai mare decat cel d<strong>in</strong> zona 3 (8,93<br />
at% Na). Comparand <strong>si</strong> cu rezultatele obt<strong>in</strong>ute pentru pulberea calc<strong>in</strong>ata la 500 <strong>si</strong> 600 °C,<br />
cont<strong>in</strong>utul de Na variaza <strong>in</strong>tre acelea<strong>si</strong> limite. Am analizat cu atentie elementul Na deoarece el<br />
are temperatura de evaporare cea mai mica d<strong>in</strong>tre toate elementele solutiei solide BNT-BT0,08.<br />
34<br />
Ba<br />
Bi Na<br />
O
Se constata ca pr<strong>in</strong> calc<strong>in</strong>are pana la 700 °C, compozitia elementara a BNT-BT0,08, se ment<strong>in</strong>e<br />
constanta, <strong>in</strong> limitele stoichiometrice.<br />
De<strong>si</strong> apare problema <strong>in</strong>separarii peak-urilor de Ti <strong>si</strong> Ba, metoda EDAX ofera rezultate<br />
reproductibile pentru celelalte elemente (Bi <strong>si</strong> O) d<strong>in</strong> BNT-BT0,08. In concluzie, rezultatele<br />
analizelor SEM <strong>si</strong> EDAX pun <strong>in</strong> evidenta o pulbere omogena d<strong>in</strong> punct de vedere chimic <strong>si</strong><br />
morfologic, <strong>in</strong> cazul prepararii ei pr<strong>in</strong> metoda sol-gel, urmata de calc<strong>in</strong>are <strong>in</strong> <strong>in</strong>tervalul termic<br />
500-700 °C.<br />
1.2. Analiza compozitiei de faze pr<strong>in</strong> DRX a pulberilor de BNT-BT0,08 preparate pr<strong>in</strong><br />
sol-gel<br />
Difractia de raze X este o metoda de analiza structurala, curent folo<strong>si</strong>ta <strong>in</strong> studiul<br />
monocristalelor sau policristalelor pentru determ<strong>in</strong>area structurii cristal<strong>in</strong>e, determ<strong>in</strong>ari<br />
calitative <strong>si</strong> cantitative de faze, transformari de faze, determ<strong>in</strong>ari ale parametrilor de retea, ale<br />
ten<strong>si</strong>unilor <strong>in</strong>terne, ale dimen<strong>si</strong>unii de graunti. Figura 33 prez<strong>in</strong>ta curbele de difractie de raze<br />
X ale pulberii de BNT-BT0.08 preparate pr<strong>in</strong> metoda sol-gel <strong>si</strong> calc<strong>in</strong>ata la 200, 400, 500, 600<br />
<strong>si</strong> 700 ºC.<br />
Inten<strong>si</strong>tatea (a. u.)<br />
*<br />
x<br />
o<br />
o<br />
*<br />
* - (Bi 0.5 Na 0.5 )TiO 3 (structura perovskitica)<br />
o - Bi 2 O 3 hexagonal<br />
x- Bi O tetragonal<br />
2 3<br />
* *<br />
20 25 30 35 40 45 50 55 60<br />
35<br />
2θ<br />
1150 o C<br />
700 o C<br />
600 o C<br />
500 o C<br />
400 o C<br />
200 o C<br />
Fig.33. Difractogramele de raze X ale precursorului gel de Bi1/2Na1/2TiO3 dopat cu 8<br />
mol.% BaTiO3, calc<strong>in</strong>at la 200, 400, 500, 600, 700 <strong>si</strong> 1150 °C<br />
*
Gelul <strong>in</strong>calzit la 200 °C a prezentat structura amorfa. Curba de difractie de raze X a<br />
gelului calc<strong>in</strong>at la 400 °C, 2h a <strong>in</strong>dicat un material amorf <strong>si</strong> aparitia unui peak corespunzator<br />
fazei hexagonale a oxidului de bismuth (Bi2O3) (fisa ASTM: 51-1161) [1].<br />
Fazele Bi2O3 hexagonal, Bi2O3 tetragonal (fisa ASTM: 78-1793) [2] <strong>si</strong> Bi1/2Na1/2TiO3<br />
dopat cu 8 mol% BaTiO3 cristalizat pe structura perovskitica a Bi1/2Na1/2TiO3 au fost<br />
identificate <strong>in</strong> pulberile calc<strong>in</strong>ate la 500 °C (Fig.33).<br />
La temperaturi mai mari de 600 °C, a fost identificata o <strong>si</strong>ngura faza cristal<strong>in</strong>a cu<br />
structura perovskitica a fazei Bi1/2Na1/2TiO3.<br />
Rezultatele analizei pr<strong>in</strong> difractie de raze X arata ca pentru obt<strong>in</strong>erea unui material de<br />
compozitie BNT-BT0,08, cristalizat monofazic, derivat d<strong>in</strong> sol-gel, este suficienta o<br />
temperatura de calc<strong>in</strong>are de 600 °C. Acest aspect constituie avantajul major al utilizarii<br />
metodei sol-gel fata de metoda cla<strong>si</strong>ca a calc<strong>in</strong>arii amestecului de oxizi, care <strong>in</strong> cazul BNT-<br />
BT0,08 nece<strong>si</strong>ta o temperatura de peste 1100 °C [3-5].<br />
Pr<strong>in</strong> obt<strong>in</strong>erea BNT-BT0,08 la 600 °C, se evita pierderea de Na <strong>si</strong> Bi, ca <strong>in</strong> cazul<br />
calc<strong>in</strong>arii la temperaturi mai mari de 1100 °C.<br />
In ceea ce priveste formele de cristalizare a materialului de baza (Bi1/2Na1/2TiO3),<br />
studiile sunt <strong>in</strong> curs de desfasurare. Se cunosc doua faze cristal<strong>in</strong>e ale compusului<br />
Bi1/2Na1/2TiO3 , <strong>si</strong> anume: forma cubica <strong>si</strong> forma romboedrica. Diferentierea lor este dificila,<br />
asa cum reiese <strong>si</strong> d<strong>in</strong> fisele lor ASTM, redate <strong>in</strong> cont<strong>in</strong>uare.<br />
Fisa ICSD nr.43769, [6] arata ca primele trei peak-uri ca <strong>in</strong>ten<strong>si</strong>tate ale Bi1/2Na1/2TiO3<br />
cubic sunt: (110) la 32.525° (2 θ); (200) la 46.662° <strong>si</strong> (211) la 58.031°.<br />
Pentru forma cristal<strong>in</strong>a monocl<strong>in</strong>ica a Bi1/2Na1/2TiO3, Fisa ICSD nr. 46-0001, [7]<br />
<strong>in</strong>dica: (102) <strong>si</strong> (121) la 32.452° (2 θ) <strong>si</strong> 32.618; (220) la 46.698° <strong>si</strong> (003) la 58.165°.<br />
Mai exista <strong>si</strong> forma cristalizata <strong>in</strong> <strong>si</strong>stemul romboedral care corespunde compozitiei<br />
chimice (Na0,5Bi0,5TiO3)2. Fisa corespunzatoare nr. 20786 prez<strong>in</strong>ta urmatoarele picuri de<br />
difractie.<br />
Fisa ICSD nr.20786, [8] pentru reteaua romboedrala a Na0,5Bi0,5TiO3: (110) la 20.921°<br />
(2 θ); (202) la 29.757° <strong>si</strong> (300) la 36.658°.<br />
Mai recent a fost publicata o lucrare [9] care pune <strong>in</strong> evidenta forma tetragonala a<br />
Na0.5Bi0.5TiO3 cu structura perovskitica. Fisa ICSD nr. 280381 [9] <strong>in</strong>dica peak-uri<br />
asemanatoare cu forma cubica: (110) la 32.50° (2 θ); (100) la 22.74° <strong>si</strong> (111) la 40.05°.<br />
Se remarca dificultatea separarii fazei cubice de cea tetragonala datorita <strong>si</strong>militud<strong>in</strong>ii<br />
pozitiilor maximelor de difractie pentru cele doua faze. S<strong>in</strong>gura cale de diferentiere a acestor<br />
forme cristalografice ramane, compararea parametrilor celulei cristal<strong>in</strong>e elementare. In plus<br />
36
mai exista o faza cu retea tetragonala <strong>in</strong> care raportul Na/Bi nu mai este 0,5/0,5 care conduce<br />
la ideea trecerii fazei cubice la faza tetragonala pr<strong>in</strong> pierderea unei parti d<strong>in</strong> Na.<br />
Forma tetragonala a Na0.5Bi0.5TiO3 a fost observata atunci cand materialul a fost supus<br />
unei ten<strong>si</strong>uni [5]. In prezenta unor dopanti, adaugati <strong>in</strong>tr-o anumita concentratie, s-a observat<br />
de asemenea, aparitia fazei tetragonale. Si <strong>in</strong> acest caz, explicatia pentru trecerea de la faza<br />
cubica la cea tetragonala, se bazeaza tot pe ten<strong>si</strong>onarea mecanica a retelei pr<strong>in</strong> <strong>in</strong>serarea<br />
dopantului.<br />
Este importanta cunoasterea conditiilor <strong>in</strong> care se poate obt<strong>in</strong>e faza tetragonala pentru<br />
ca <strong>in</strong> cazul perovskitilor, faza tetragonala este cea care a<strong>si</strong>gura o permitivitate mare. Un calcul<br />
foarte exact al parametrilor de retea ai materialului BNT-BT0.08 cristalizat pe structura<br />
Na0.5Bi0.5TiO3 poate face separarea <strong>in</strong>tre formele de cistalizare am<strong>in</strong>tite.<br />
Datele de literatura arata ca solutia solida (1-x)Na1/2Bi1/2TiO3-xBaTiO3 (NBT-BTx)<br />
prez<strong>in</strong>ta <strong>si</strong>militud<strong>in</strong>i structurale cu <strong>si</strong>stemele PZT <strong>si</strong> PZN-PT (PbZn1/3Nb2/3O3-PbTiO3). In<br />
conditiile mediului ambiant, toate cele trei solutii solide au proprietati comune chiar daca<br />
unele au <strong>si</strong>metrie romboedrala iar altele au <strong>si</strong>metrie tetragonala.<br />
Proprietatile piezoelectrice cele mai bune au fost observate <strong>in</strong> regiunea compozitiilor<br />
morfotropice (MPB= morphotropic phase boundary). Pentru BNT-BTx faza MPB este <strong>si</strong>tuata<br />
<strong>in</strong> jurul lui x~0,07 dar <strong>si</strong>metria nu a fost <strong>in</strong>ca determ<strong>in</strong>ata [10,3]. Raman <strong>in</strong>ca multe<br />
controverse despre natura <strong>si</strong> ord<strong>in</strong>ea tranzitiei de faza cu temperatura chiar <strong>si</strong> pentru compusul<br />
Na1/2Bi1/2TiO3.<br />
In particular, natura feroelectrica <strong>si</strong> antiferoelectrica a fazei tetragonale de temperatura<br />
<strong>in</strong>alta atat <strong>in</strong> BNT cat <strong>si</strong> <strong>in</strong> solutia sa solida cu BT ramane controversabila asa cum sugereaza<br />
Jones <strong>si</strong> Thomas [11]. Ei au remarcat pe baza rezultatelor de difractie de neutroni <strong>si</strong><br />
masuratori de generare a armonicii a doua ca forma tetragonala este o faza polara <strong>in</strong> timp ce<br />
alti autori [10] con<strong>si</strong>dera aceasta faza anti-feroelectrica, d<strong>in</strong> masuratori de histerezis.<br />
O controversa <strong>si</strong>milara exista <strong>si</strong> despre natura fazelor <strong>in</strong> BNT-BT [3,12]. Datele de<br />
difractie de raze X obt<strong>in</strong>ute pe monocristale au demonstrat o splitare clara a picului (200)<br />
pentru compozitii nom<strong>in</strong>ale de 10% BaTiO3 <strong>si</strong> 15% BaTiO3. Aceste splitari sunt corelate cu<br />
schimbarile asteptate ale <strong>si</strong>metriei pr<strong>in</strong> trecerea de la romboedral la tetragonal odata cu<br />
cresterea cont<strong>in</strong>utului de bariu.<br />
Valorile parametrilor retelei pseudocubice arata ca aceasta retea este avantajata de un<br />
cont<strong>in</strong>ut redus <strong>in</strong> Ba [13]. Curbele de difractie pentru compozitiile tetragonale cu x≥ 0.1<br />
corespund <strong>si</strong>metriei P4mm. Pulberile de analizat au fost obt<strong>in</strong>ute pr<strong>in</strong> mac<strong>in</strong>area<br />
monocristalului de BNT-BTx.<br />
37
2. Analiza chimica elementara pr<strong>in</strong> EDS <strong>si</strong> analiza morfologiei cu ajutorul microscopiei<br />
electronice cu baleiaj (SEM) ale pulberilor de BNT-BT0,08 preparate pr<strong>in</strong> metoda<br />
atomizarii<br />
2.1. Analiza chimica pr<strong>in</strong> EDS a pulberilor de BNT-BT0,08 preparate pr<strong>in</strong> metoda<br />
pirosol<br />
Fig. 34. Imag<strong>in</strong>e SEM a unei pulberi de BNT-BT0,08, preparata pr<strong>in</strong><br />
metoda pirosol <strong>si</strong> apoi calc<strong>in</strong>ata la 700 °C, 3 ore<br />
Fig. 35. Imag<strong>in</strong>ea SEM, distributia elementelor chimice <strong>si</strong> spectrul EDS pentru pulberea de<br />
BNT-BT0,08, preparata pr<strong>in</strong> metoda pirosol <strong>si</strong> apoi calc<strong>in</strong>ata la 700 °C, 3 ore; zona 1<br />
38
Tabelul 10. Compozitia chimica a pulberii de BNT-BT0,08, preparata pr<strong>in</strong> metoda pirosol <strong>si</strong><br />
apoi calc<strong>in</strong>ata la 700 °C, 3 ore; zona 1<br />
Elementul % At % <strong>Raportul</strong>-K Z A F<br />
NaK 4.78 9.72 0.0091 1.0980 0.1739 1.0001<br />
BaL 0.00 0.00 0.0000 0.8833 0.7658 1.0000<br />
TiK 17.46 17.04 0.1149 1.0316 0.6380 1.0000<br />
BiL 57.06 12.76 0.4914 0.8395 1.0259 1.0000<br />
O K 20.70 60.48 0.0316 1.1699 0.1305 1.0001<br />
Total 100.00 100.00<br />
Elementul Net Inte. (P) Backgrd (B) Inte. Error P/B<br />
NaK 68.46 22.80 2.80 3.00<br />
BaL 0.00 33.59 0.00 0.00<br />
TiK 643.86 33.59 0.74 19.17<br />
BiL 300.82 39.53 1.16 7.61<br />
O K 127.95 10.59 1.72 12.08<br />
Fig. 36. Spectrul EDS pentru pulberea de BNT-BT0,08, preparata pr<strong>in</strong> metoda pirosol <strong>si</strong> apoi<br />
calc<strong>in</strong>ata la 700 °C, 3 ore; zona 2<br />
39
Tabelul 11. Compozitia chimica a pulberii de BNT-BT0,08, preparata pr<strong>in</strong> metoda pirosol <strong>si</strong><br />
apoi calc<strong>in</strong>ata la 700 °C, 3 ore; zona 2<br />
Elementul % At % <strong>Raportul</strong>-K Z A F<br />
NaK 4.71 10.16 0.0090 1.1058 0.1721 1.0001<br />
BaL 1.60 0.58 0.0108 0.8904 0.7595 1.0000<br />
TiK 17.25 17.85 0.1135 1.0401 0.6329 1.0000<br />
BiL 57.82 13.72 0.5015 0.8474 1.0235 1.0000<br />
O K 18.62 57.69 0.0284 1.1784 0.1296 1.0001<br />
Total 100.00 100.00<br />
Elementul Net Inte. (P) Backgrd (B) Inte. Error P/B<br />
NaK 72.58 24.17 2.60 3.00<br />
BaL 22.94 35.85 7.26 0.64<br />
TiK 685.71 35.85 0.69 19.13<br />
BiL 330.96 43.13 1.06 7.67<br />
O K 124.24 10.53 1.66 11.80<br />
Ti Bi<br />
40
Na Ba<br />
O<br />
Fig.37. Distributia elementelor Ti, Ba, Bi, Na <strong>si</strong> O <strong>in</strong><br />
portiunea de proba prezentata <strong>in</strong> Fig.34<br />
Compozitia chimica rezultata <strong>in</strong> urma analizei EDS pe o pulbere de BNT-BT0,08,<br />
preparata pr<strong>in</strong> metoda pirosol <strong>si</strong> apoi calc<strong>in</strong>ata la 700 °C, 3 ore prez<strong>in</strong>ta un raport atomic<br />
Bi/Na destul de aproipiat de stoichiometria dorita d<strong>in</strong> start <strong>si</strong> anume 50/50, t<strong>in</strong>and cont <strong>si</strong> de<br />
precizia metodei EDAX.<br />
Distributia atomilor constituienti ai BNT-BT0,08, reprezentata <strong>in</strong> Fig.37, <strong>in</strong>dica o<br />
distributie uniforma a tuturor atomilor pe <strong>in</strong>treg domeniul analizat (<strong>in</strong> zonele 1 <strong>si</strong> 2).<br />
Rezultatele analizei EDS sunt <strong>in</strong> buna concordanta cu rezultatele difractiei de raze X. Astfel,<br />
comparand rezultatele EDAX pentru pulberile de BNT-BT0,08 preparate pr<strong>in</strong> sol-gel <strong>si</strong> pr<strong>in</strong><br />
metoda pirosol, se constata ca raportul atomic Na:Bi este mai apropiat de cel stoichiometric<br />
1:1 <strong>in</strong> pulberile obt<strong>in</strong>ute pr<strong>in</strong> sol-gel decat la cele obt<strong>in</strong>ute cu ajutorul metodei pirosol.<br />
Spre exemplificare, raportul atomic (%) Na:Bi este: 9,85/9,27 (Tab.8); 8,93/9,05<br />
(Tab.9) <strong>in</strong> cazul metodei sol-gel <strong>si</strong> respectiv, 9,72/12,76 (Tab.10) <strong>in</strong> cazul metodei pirosol.<br />
41
Acest rezultat este sust<strong>in</strong>ut de analiza pr<strong>in</strong> difractie de raze X deoarece pulberea de BNT-<br />
BT0,08 tratata termic la 700 °C, este faza unica <strong>in</strong> cazul <strong>si</strong>ntezei sol-gel <strong>si</strong> bifazica <strong>in</strong> cazul<br />
pirosolului. Faza unica cere un raport Na/Bi de 1/1.<br />
2.2. Analiza morfologiei cu ajutorul SEM a pulberilor de BNT-BT0,08 preparate pr<strong>in</strong><br />
metoda pirosol<br />
Imag<strong>in</strong>ile SEM de mai jos sunt obt<strong>in</strong>ute pentru o pulbere de BNT-BT0.08 preparata pr<strong>in</strong><br />
metoda pirosol, <strong>in</strong> urmatoarele conditii de lucru:<br />
- pulberea cruda, asa cum a fost obt<strong>in</strong>uta pr<strong>in</strong> metoda pirosol (temperatura <strong>in</strong> cuptor<br />
= 700 °C); proba (a);<br />
- pulberea cruda calc<strong>in</strong>ata ulterior la 700 °C, 3 ore, proba (b)<br />
(a) Analiza SEM a pulberii crude de BNT-BT0,08<br />
42
Fig. 38. Imag<strong>in</strong>i SEM a unei pulberi de BNT-BT0,08, preparata pr<strong>in</strong><br />
metoda pirosol la 700 °C<br />
Imag<strong>in</strong>ile SEM obt<strong>in</strong>ute d<strong>in</strong> mai multe zone ale probei de pulbere ofera o reprezentare<br />
cupr<strong>in</strong>zatoare a distributiei formei <strong>si</strong> dimen<strong>si</strong>unilor granulelor pulberii obt<strong>in</strong>ute la 700 °C. Ca<br />
forma, se remarca forma sferica a granulelor, dar exista <strong>si</strong> forme rezultate d<strong>in</strong> coliziunea<br />
picaturilor de sol, forme de tip crater (calota sferica sau chiar <strong>in</strong>el). Pr<strong>in</strong> uscare s-au obt<strong>in</strong>ut<br />
granule cu sau fara contact cu sfera de impact.<br />
Ca dimen<strong>si</strong>uni, granulele sferice au diametrul cupr<strong>in</strong>s <strong>in</strong>tre 170 nm <strong>si</strong> 1 µm, asa cum<br />
reiese d<strong>in</strong> imag<strong>in</strong>ile SEM. Coexistenta granulelor mici cu granule mari este datorata<br />
conditiilor de lucru d<strong>in</strong> timpul <strong>si</strong>ntezei (pulverizarea solului <strong>in</strong> cuptor, temperatura <strong>in</strong> cuptor,<br />
43
etc). La mariri mai mari, imag<strong>in</strong>ile SEM <strong>in</strong>dica o suprafata neregulata (nu este neteda) a<br />
granulelor.<br />
Acest fapt se poate explica pr<strong>in</strong> transformarea picaturii de sol <strong>in</strong> gel pulbere pr<strong>in</strong>tr-un<br />
proces de evaporare a solventilor, <strong>in</strong> trepte <strong>si</strong> cu viteze diferite. Rugozitatea suprafetei<br />
granulelor este pusa mai b<strong>in</strong>e <strong>in</strong> evidenta cu ajutorul microscopiei electronice cu transmi<strong>si</strong>e<br />
TEM <strong>si</strong> HRTEM.<br />
(b) Analiza SEM a pulberii crude de BNT-BT0,08,calc<strong>in</strong>ate ulterior la 700 °C, 3 ore<br />
- Proba 1-<br />
44
- Proba 2-<br />
Fig. 39. Imag<strong>in</strong>e SEM a unei pulberi de BNT-BT0,08, preparata pr<strong>in</strong><br />
metoda pirosol <strong>si</strong> apoi calc<strong>in</strong>ata la 700 °C, 3 ore; proba1<br />
45
Fig. 40. Imag<strong>in</strong>e SEM a unei pulberi de BNT-BT0,08, preparata pr<strong>in</strong><br />
metoda pirosol <strong>si</strong> apoi calc<strong>in</strong>ata la 700 °C, 3 ore; proba 2<br />
Figurile 39 <strong>si</strong> 40 arata un material cu granule de forma cubica, cu dimen<strong>si</strong>unile cupr<strong>in</strong>se <strong>in</strong><br />
<strong>in</strong>tervalul 300-400 nm, cu morfologie omogena. Aceste poliedre se unesc cu ajutorul unei<br />
pelicule de faza topita <strong>si</strong> formeaza agregate cu forme <strong>si</strong> dimen<strong>si</strong>uni diferite. Aceste granule<br />
cubice se obt<strong>in</strong> d<strong>in</strong> granulele sferice pr<strong>in</strong>tr-un proces de cristalizare. Pe imag<strong>in</strong>ile SEM se mai<br />
pot vedea cateva granule sferice. Si aceste imag<strong>in</strong>i SEM se coreleaza b<strong>in</strong>e cu faza care<br />
cristalizeaza a BNT-BT0,08, pusa <strong>in</strong> evidenta pr<strong>in</strong> spectrele de difractie. Prezenta acestor<br />
granule sferice sugereaza ca procesul de cristalizare a materialului obt<strong>in</strong>ut pr<strong>in</strong> metoda pirosol<br />
nu este complet, la aceasta temperatura.<br />
3. Analiza granulometriei cu ajutorul microscopului cu transmi<strong>si</strong>e (TEM) <strong>si</strong> a<br />
granulometrului cu laser a pulberilor de BNT-BT0,08 preparate pr<strong>in</strong> cele doua metode<br />
chimice <strong>in</strong> solutie<br />
3.1. Analiza morfologiei cu ajutorul microscopiei electronice cu transmi<strong>si</strong>e a pulberilor<br />
de BNT-BT0,08 preparate pr<strong>in</strong> sol-gel<br />
Nece<strong>si</strong>tatea valorificarii proprietatilor fizice deosebite ale materiei nanostructurate au<br />
impus utilizarea exten<strong>si</strong>va a microscopiei electronice de <strong>in</strong>alta rezolutie (HRTEM) ce permite,<br />
datorita rezolutiei de sub 2A, vizualizarea retelei cristal<strong>in</strong>e <strong>si</strong> a defectelor acesteia, studiul<br />
<strong>in</strong>terfetelor nanocristal<strong>in</strong>e, nanocompozitelor, nanodomeniilor, etc.<br />
46
Investigarea structurii acestor materiale pare a fi o cer<strong>in</strong>ta necesara pentru <strong>in</strong>telegerea<br />
functionalitatii lor. Deoarece trasaturile structurale de <strong>in</strong>teres sunt <strong>in</strong> domeniul dimen<strong>si</strong>unal<br />
nanometric, microscopia electronica de <strong>in</strong>alta rezolutie este foarte <strong>in</strong>dicata pentru<br />
<strong>in</strong>vestigarea structurii acestora.<br />
In studiul de fata, imag<strong>in</strong>ile TEM (<strong>in</strong> stanga) <strong>si</strong> HR-TEM (<strong>in</strong> dreapta) obt<strong>in</strong>ute pentru<br />
gelul <strong>in</strong>calzit la 600 °C, 3h <strong>in</strong> aer, sunt prezentate <strong>in</strong> figura 41.<br />
47
(a)<br />
(b)<br />
Fig.41. Imag<strong>in</strong>i TEM <strong>si</strong> HR-TEM ale pulberii de BNT-BT0,08 preparata pr<strong>in</strong> calc<strong>in</strong>area gelului<br />
precursor la 600 °C. (a) reprez<strong>in</strong>ta o imag<strong>in</strong>e SAED.<br />
Imag<strong>in</strong>ile TEM d<strong>in</strong> Fig.41 ne permit sa apreciem dimen<strong>si</strong>unea medie a cristalitelor ca<br />
fi<strong>in</strong>d de aproximativ 30 nm.<br />
De asemenea, pe aceste imag<strong>in</strong>i se observa ca pulberea este compusa d<strong>in</strong> particule cu<br />
structuri aglomerate. Tend<strong>in</strong>ta de aglomerare a granulelor pulberii de BNT-BT0.08 este<br />
obisnuita <strong>in</strong> cazul <strong>si</strong>ntezelor chimice <strong>in</strong> solutie <strong>si</strong> este datorata prezentei gruparilor OH, care<br />
sunt elim<strong>in</strong>ate complet la temperaturi <strong>in</strong> jur de 900 °C. Aceste grupari OH sunt elim<strong>in</strong>ate mai<br />
greu deoarece sunt grupe structurale care nu au fost hidrolizate. Se stie ca <strong>in</strong> cazul <strong>si</strong>ntezei solgel,<br />
cand se folosesc reactivi organometalici, nu toate gruparilor OH ajung sa fie hidrolizate,<br />
chiar daca se folosesc agenti modificatori moleculari ai alcoxizilor sau cataliza acida/bazica.<br />
48
Pr<strong>in</strong> microscopie electronica cu transmi<strong>si</strong>e de <strong>in</strong>alta rezolutie (Fig.41) se pun <strong>in</strong><br />
evidnta planele atomice ale structurii cristal<strong>in</strong>e a BNT-BT0.08. Distantele <strong>in</strong>terplanare d=0.279<br />
nm pot fi atribuite planelor cristalografice (102) ale formei cubice a Bi0.5Na0.5TiO3.<br />
Succe<strong>si</strong>unea regulata a planelor atomice <strong>in</strong>dicata de HR-TEM sugereaza o structura cristal<strong>in</strong>a<br />
uniforma.<br />
Avand <strong>in</strong> vedere ca BNT-BT0.08 este un material cu proprietati feroelectrice, pe<br />
imag<strong>in</strong>ile HR-TEM se evidentiaza <strong>si</strong> domeniile feroelectrice. De<strong>si</strong>, pr<strong>in</strong> difractie de raze X nu<br />
se pune <strong>in</strong> evidenta <strong>si</strong> o parte amorfa (foarte mica d<strong>in</strong> punct de vedere cantitativ) a probei, pe<br />
imag<strong>in</strong>ile HR-TEM se observa totu<strong>si</strong>, acea parte amorfa (fara plane atomice vizibile).<br />
Imag<strong>in</strong>ea SAED (Fig.41,a) arata un material b<strong>in</strong>e cristalizat, <strong>in</strong> buna concordanta cu<br />
rezultatele analizei pr<strong>in</strong> difractie cu raze X.<br />
Inten<strong>si</strong>ty (a.u.)<br />
(c)<br />
(b)<br />
(a)<br />
(100)<br />
(110)<br />
(111)<br />
10 20 30 40 50 60 70 80<br />
49<br />
(200)<br />
2θ ( o )<br />
(210)<br />
(211)<br />
(220)<br />
1200 o C<br />
900 o C<br />
700 o C<br />
Fig.42. Difractogramele de raze X ale pulberii de BNT-BT0,08, obt<strong>in</strong>uta pr<strong>in</strong><br />
metoda pirosol la 700 °C (a) <strong>si</strong> apoi calc<strong>in</strong>ata la 900 <strong>si</strong> 1200 °C<br />
Datorita procesului de atomizare a solutiei precursoare a BNT-BT0,08 este dificil sa se<br />
obt<strong>in</strong>a un material monofazic pr<strong>in</strong> pulverizare <strong>in</strong> cuptor, la o temperatura de 700 °C,<br />
(Fig.42,a). Picurile <strong>in</strong>dexate apart<strong>in</strong> fazei monocl<strong>in</strong>ice a Bi0,5Na0,5TiO3 pe structura careia a<br />
cristalizat BNT-BT0,08.<br />
Proba tratata la 900 °C, prez<strong>in</strong>ta faza cubica a Bi0,5Na0,5TiO3 <strong>in</strong>dicand trecerea de la<br />
faza monocl<strong>in</strong>ica la faza cubica (Fig.42,b). Aceasta transformare plimorfa este <strong>in</strong>dicata pe<br />
difractograma pr<strong>in</strong> disparitia peak-urilor mici care dublau peak-urile mari de difractie.
Peak-ul de la 2θ=30 o , care se ment<strong>in</strong>e <strong>si</strong> la 1200 °C (Fig.42,c), poate fi atribuit fazei<br />
hexagonale a Bi2O3 [1].<br />
Se constata ca <strong>in</strong> comparatie cu metoda sol-gel, obt<strong>in</strong>erea fazei unice de BNT-BT0,08<br />
este mai dificila pr<strong>in</strong> metoda pirosol.<br />
3.2. Analiza morfologiei cu ajutorul granulometrului cu laser a pulberilor de BNT-BT0,08<br />
preparate pr<strong>in</strong> sol-gel<br />
Proprietatile electrice, optice <strong>si</strong> mecanice ale elementelor presate <strong>si</strong> <strong>si</strong>nterizate dep<strong>in</strong>d<br />
de cantitatea de defecte prezente <strong>in</strong> materialul den<strong>si</strong>ficat. Aceste proprietati sunt <strong>in</strong>fluentate<br />
negativ de prezenta porilor. Pr<strong>in</strong> procesele de presare <strong>si</strong> <strong>si</strong>nterizare se urmareste sa se obt<strong>in</strong>a o<br />
den<strong>si</strong>tate cat mai apropiata de cea teoretica.<br />
Procesul de den<strong>si</strong>ficare pr<strong>in</strong> presare dep<strong>in</strong>de <strong>in</strong> primul rand de distributia<br />
granulometrica a pulberii supuse presarii. D<strong>in</strong> acest motiv, prezentam rezultatele analizei<br />
granulometrice pentru pulberea de BNT-BT0.08 preparata pr<strong>in</strong> metoda sol-gel. Deoarece,<br />
dimen<strong>si</strong>unile granulelor dep<strong>in</strong>d de temperatura de calc<strong>in</strong>are a gelului pentru obt<strong>in</strong>ea fazei<br />
dorite, am analizat distributia dimen<strong>si</strong>unii granulelor pulberilor obt<strong>in</strong>ute la diferite temperaturi<br />
(600 <strong>si</strong> 700 °C).<br />
Pentru realizarea acestei analize, am utilizat un granulometru cu laser tip Master<strong>si</strong>zer<br />
2000 de la Malvern Instruments.<br />
Caracteristicile echipamentului folo<strong>si</strong>t pentru analiza granulometrica sunt:<br />
- <strong>in</strong>tervalul dimen<strong>si</strong>unilor granulelor care pot fi masurate:
Pr<strong>in</strong>cipiul de lucru cu granulometrul cu laser este urmatorul:<br />
- se prepara o suspen<strong>si</strong>e diluata, de ord<strong>in</strong>ul 0,0001 la 1,0% v/v, folo<strong>si</strong>nd agenti de<br />
udare <strong>si</strong>/sau dispersare;<br />
- uneori se foloseste ultrasonarea pentru dezaglomerarea granulelor.<br />
Se foloseste o cantitate de 2 sau 3 mL de suspen<strong>si</strong>e pentru efectuarea analizei granulometrice.<br />
Aceasta suspen<strong>si</strong>e se pune <strong>in</strong> nacele d<strong>in</strong> material plastic, atunci cand dispersantul este apa sau<br />
un alcool <strong>si</strong>mplu. Se poate folo<strong>si</strong> <strong>si</strong> o nacela d<strong>in</strong> sticla pentru dispersanti mai corozivi. Sunt<br />
necesare doar cateva m<strong>in</strong>ute pentru proba <strong>si</strong> nacela pentru echilibrarea automata a<br />
temperaturii cu temperatura mediului d<strong>in</strong> <strong>in</strong>teriorul aparatului.<br />
Pentru prezentarea datelor, sunt po<strong>si</strong>bile trei po<strong>si</strong>bilitati. Determ<strong>in</strong>area diametrului<br />
median <strong>si</strong> masurarea <strong>in</strong>tervalelor de distributie sunt suficiente, de obicei. O alta po<strong>si</strong>bilitate<br />
consta <strong>in</strong> fitarea acestor valori pentru a obt<strong>in</strong>e o distributie logaritmica, cumulativa <strong>si</strong><br />
diferentiala. A treia po<strong>si</strong>bilitate, care se foloseste pentru distributia pulberilor multimodale,<br />
are la baza un algoritm numeric care t<strong>in</strong>e cont de teoria Mie. In timpul masurarii, trecerea de<br />
la un mod de reprezentare la altul se face <strong>in</strong>teractiv.<br />
Imprastierea lum<strong>in</strong>ii are loc atunci cand particulele polarizabile d<strong>in</strong>tr-o proba sunt<br />
<strong>in</strong>troduse <strong>in</strong>tr-uncamp electric al unui flux de lum<strong>in</strong>a. Variatia campului <strong>in</strong>duce dipoli<br />
oscilanti <strong>in</strong> particule <strong>si</strong> astfel radiatia lum<strong>in</strong>oasa este imprastiata <strong>in</strong> toate directiile. Acest<br />
fenomen universal important este utilizat <strong>in</strong> multe domenii ale sti<strong>in</strong>tei pentru determ<strong>in</strong>area<br />
marimii particulei, masei moleculare, forma, coeficientilor de difuzie, etc.<br />
Modul de lucru <strong>in</strong> cazul utilizarii granulometrului cu laser tip Master<strong>si</strong>zer 2000 este<br />
urmatorul: pulberea de analizat (<strong>in</strong> cazul nostru Na0,5Bi0,5TiO3 dopat cu 8mol%BaTiO3;<br />
prescurtat BNT-BT0.08) se <strong>in</strong>troduce <strong>in</strong>tr-un vas cu apa, <strong>in</strong> cantitatea necesara realizarii unei<br />
suspen<strong>si</strong>i de concentratie 0,0023 vol %. La aceasta solutie se poate adauga <strong>si</strong> un dispersant<br />
organic (metacrilatul de metil).<br />
Pentru comparatie am facut analiza granulometrica a BNT-BT0,08 <strong>in</strong> suspen<strong>si</strong>e apoasa<br />
<strong>si</strong> <strong>in</strong> suspen<strong>si</strong>a apoasa la care s-a adaugat dispersantul organic. Suspen<strong>si</strong>a se <strong>in</strong>troduce <strong>in</strong> baia<br />
cu ultrasunete <strong>si</strong> se t<strong>in</strong>e 5 m<strong>in</strong>ute. Apoi, cu ajutorul unei ser<strong>in</strong>gi, se picura suspen<strong>si</strong>a <strong>in</strong> <strong>in</strong>c<strong>in</strong>ta<br />
de analiza. Rezultatele sunt date subforma de diagrama <strong>si</strong> tabel. Am analizat esantioane de<br />
pulberi de BNT-BT0.08 obt<strong>in</strong>ute <strong>in</strong> urma calc<strong>in</strong>arii gelului precursor la 500, 600 <strong>si</strong> 700 °C <strong>si</strong><br />
pulbere de BNT-BT0.08 obt<strong>in</strong>uta pr<strong>in</strong> metoda pirosol.<br />
51
Pulbere de BNT-BT0.08 calc<strong>in</strong>ata la 700 °C<br />
Volume (%)<br />
5<br />
4<br />
3<br />
2<br />
1<br />
Particle Size Distribution<br />
0<br />
0.01 0.1 1 10<br />
Particle Size (µm)<br />
100 1000 3000<br />
BNTBT7001,5h - Average, Thursday, November 12, 2009 9:19:51 AM<br />
Fig.43. Curba de variatie a volumului granulelor de pulbere <strong>in</strong> functie de diametrul<br />
particulelor de BNT-BT0.08 calc<strong>in</strong>ata la 700 °C; suspen<strong>si</strong>e apoasa<br />
Tab.12. Distributia granulometrica a pulberii de BNT-BT0.08 calc<strong>in</strong>ata la 700 °C; suspen<strong>si</strong>e<br />
apoasa<br />
Size (µm) Volume In %<br />
0.010<br />
0.00<br />
0.011<br />
0.00<br />
0.013<br />
0.00<br />
0.015<br />
0.00<br />
0.017<br />
0.00<br />
0.020<br />
0.00<br />
0.023<br />
0.00<br />
0.026<br />
0.00<br />
0.030<br />
0.00<br />
0.035<br />
0.00<br />
0.040<br />
0.00<br />
0.046<br />
0.00<br />
0.052<br />
0.00<br />
0.060<br />
0.00<br />
0.069<br />
0.00<br />
0.079<br />
0.00<br />
0.091<br />
0.00<br />
0.105<br />
Size (µm) Volume In %<br />
0.105<br />
0.00<br />
0.120<br />
0.07<br />
0.138<br />
0.25<br />
0.158<br />
0.55<br />
0.182<br />
0.83<br />
0.209<br />
1.18<br />
0.240<br />
1.55<br />
0.275<br />
1.95<br />
0.316<br />
2.35<br />
0.363<br />
2.70<br />
0.417<br />
2.97<br />
0.479<br />
3.14<br />
0.550<br />
3.21<br />
0.631<br />
3.20<br />
0.724<br />
3.12<br />
0.832<br />
3.01<br />
0.955<br />
2.88<br />
1.096<br />
Size (µm) Volume In %<br />
1.096<br />
2.78<br />
1.259<br />
2.73<br />
1.445<br />
2.76<br />
1.660<br />
2.90<br />
1.905<br />
3.12<br />
2.188<br />
3.43<br />
2.512<br />
3.78<br />
2.884<br />
4.14<br />
3.311<br />
4.47<br />
3.802<br />
4.71<br />
4.365<br />
4.83<br />
5.012<br />
4.80<br />
5.754<br />
4.61<br />
6.607<br />
4.26<br />
7.586<br />
3.78<br />
8.710<br />
3.21<br />
10.000<br />
2.58<br />
11.482<br />
Size (µm) Volume In %<br />
11.482<br />
1.97<br />
13.183<br />
1.33<br />
15.136<br />
0.75<br />
17.378<br />
0.09<br />
19.953<br />
0.00<br />
22.909<br />
0.00<br />
26.303<br />
0.00<br />
30.200<br />
0.00<br />
34.674<br />
0.00<br />
39.811<br />
0.00<br />
45.709<br />
0.00<br />
52.481<br />
0.00<br />
60.256<br />
0.00<br />
69.183<br />
0.00<br />
79.433<br />
0.00<br />
91.201<br />
0.00<br />
104.713<br />
0.00<br />
120.226<br />
52<br />
Size (µm) Volume In %<br />
120.226<br />
0.00<br />
138.038<br />
0.00<br />
158.489<br />
0.00<br />
181.970<br />
0.00<br />
208.930<br />
0.00<br />
239.883<br />
0.00<br />
275.423<br />
0.00<br />
316.228<br />
0.00<br />
363.078<br />
0.00<br />
416.869<br />
0.00<br />
478.630<br />
0.00<br />
549.541<br />
0.00<br />
630.957<br />
0.00<br />
724.436<br />
0.00<br />
831.764<br />
0.00<br />
954.993<br />
0.00<br />
1096.478<br />
0.00<br />
1258.925<br />
Size (µm) Volume In %<br />
1258.925<br />
1445.440<br />
1659.587<br />
1905.461<br />
2187.762<br />
2511.886<br />
2884.032<br />
3311.311<br />
3801.894<br />
4365.158<br />
5011.872<br />
5754.399<br />
6606.934<br />
7585.776<br />
8709.636<br />
10000.000<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
Rezultatele analizei granulometrice a pulberii de BNT-BT0.08 calc<strong>in</strong>ata la 700 °C<br />
(suspen<strong>si</strong>e apoasa) sunt: diametrul median = 3,544 µm <strong>si</strong> suprafata specifica = 7,73 m 2 /g.<br />
Volume (%)<br />
6<br />
5<br />
4<br />
3<br />
2<br />
1<br />
Particle Size Distribution<br />
0<br />
0.01 0.1 1 10<br />
Particle Size (µm)<br />
100 1000 3000<br />
BNT BT 700 1,5h D - Average, Thursday, November 12, 2009 9:28:49 AM<br />
Fig.44. Curba de variatie a volumului granulelor de pulbere <strong>in</strong> functie de diametrul<br />
particulelor de BNT-BT0.08 calc<strong>in</strong>ata la 700 °C; suspen<strong>si</strong>e apoasa plus aditiv organic
Tab.13. Distributia granulometrica a pulberii de BNT-BT0.08 calc<strong>in</strong>ata la 700 °C; suspen<strong>si</strong>e<br />
apoasa plus aditiv organic<br />
Size (µm) Volume In %<br />
0.010<br />
0.00<br />
0.011<br />
0.00<br />
0.013<br />
0.00<br />
0.015<br />
0.00<br />
0.017<br />
0.00<br />
0.020<br />
0.00<br />
0.023<br />
0.00<br />
0.026<br />
0.00<br />
0.030<br />
0.00<br />
0.035<br />
0.00<br />
0.040<br />
0.00<br />
0.046<br />
0.00<br />
0.052<br />
0.00<br />
0.060<br />
0.00<br />
0.069<br />
0.00<br />
0.079<br />
0.00<br />
0.091<br />
0.00<br />
0.105<br />
Size (µm) Volume In %<br />
0.105<br />
0.00<br />
0.120<br />
0.05<br />
0.138<br />
0.18<br />
0.158<br />
0.42<br />
0.182<br />
0.64<br />
0.209<br />
0.91<br />
0.240<br />
1.21<br />
0.275<br />
1.53<br />
0.316<br />
1.85<br />
0.363<br />
2.12<br />
0.417<br />
2.34<br />
0.479<br />
2.48<br />
0.550<br />
2.54<br />
0.631<br />
2.53<br />
0.724<br />
2.47<br />
0.832<br />
2.38<br />
0.955<br />
2.28<br />
1.096<br />
Size (µm) Volume In %<br />
1.096<br />
2.20<br />
1.259<br />
2.17<br />
1.445<br />
2.21<br />
1.660<br />
2.36<br />
1.905<br />
2.60<br />
2.188<br />
2.94<br />
2.512<br />
3.36<br />
2.884<br />
3.81<br />
3.311<br />
4.28<br />
3.802<br />
4.70<br />
4.365<br />
5.02<br />
5.012<br />
5.22<br />
5.754<br />
5.24<br />
6.607<br />
5.07<br />
7.586<br />
4.70<br />
8.710<br />
4.18<br />
10.000<br />
3.54<br />
11.482<br />
Size (µm) Volume In %<br />
11.482<br />
2.86<br />
13.183<br />
2.19<br />
15.136<br />
1.59<br />
17.378<br />
1.10<br />
19.953<br />
0.74<br />
22.909<br />
0.50<br />
26.303<br />
0.36<br />
30.200<br />
0.29<br />
34.674<br />
0.26<br />
39.811<br />
0.23<br />
45.709<br />
0.18<br />
52.481<br />
0.12<br />
60.256<br />
0.06<br />
69.183<br />
0.00<br />
79.433<br />
0.00<br />
91.201<br />
0.00<br />
104.713<br />
0.00<br />
120.226<br />
53<br />
Size (µm) Volume In %<br />
120.226<br />
0.00<br />
138.038<br />
0.00<br />
158.489<br />
0.00<br />
181.970<br />
0.00<br />
208.930<br />
0.00<br />
239.883<br />
0.00<br />
275.423<br />
0.00<br />
316.228<br />
0.00<br />
363.078<br />
0.00<br />
416.869<br />
0.00<br />
478.630<br />
0.00<br />
549.541<br />
0.00<br />
630.957<br />
0.00<br />
724.436<br />
0.00<br />
831.764<br />
0.00<br />
954.993<br />
0.00<br />
1096.478<br />
0.00<br />
1258.925<br />
Size (µm) Volume In %<br />
1258.925<br />
1445.440<br />
1659.587<br />
1905.461<br />
2187.762<br />
2511.886<br />
2884.032<br />
3311.311<br />
3801.894<br />
4365.158<br />
5011.872<br />
5754.399<br />
6606.934<br />
7585.776<br />
8709.636<br />
10000.000<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
Rezultatele analizei granulometrice a pulberii de BNT-BT0.08 calc<strong>in</strong>ata la 700 °C<br />
(suspen<strong>si</strong>e apoasa plus aditiv organic) sunt: diametrul median = 5,289 µm <strong>si</strong> suprafata<br />
specifica = 3,67 m 2 /g.<br />
Pulbere de BNT-BT0.08 calc<strong>in</strong>ata la 600 °C<br />
Volume (%)<br />
6<br />
5<br />
4<br />
3<br />
2<br />
1<br />
Particle Size Distribution<br />
0<br />
0.01 0.1 1 10<br />
Particle Size (µm)<br />
100 1000 3000<br />
BNT BT 600 2h D - Average, Thursday, November 12, 2009 9:37:07 AM<br />
Fig.45. Curba de variatie a volumului granulelor de pulbere <strong>in</strong> functie de diametrul<br />
particulelor de BNT-BT0.08 calc<strong>in</strong>ata la 600 °C; suspen<strong>si</strong>e apoasa
Tab.14. Distributia granulometrica a pulberii de BNT-BT0.08 calc<strong>in</strong>ata la 600 °C; suspen<strong>si</strong>e<br />
apoasa<br />
Size (µm) Volume In %<br />
0.010<br />
0.00<br />
0.011<br />
0.00<br />
0.013<br />
0.00<br />
0.015<br />
0.00<br />
0.017<br />
0.00<br />
0.020<br />
0.00<br />
0.023<br />
0.00<br />
0.026<br />
0.00<br />
0.030<br />
0.00<br />
0.035<br />
0.00<br />
0.040<br />
0.00<br />
0.046<br />
0.00<br />
0.052<br />
0.00<br />
0.060<br />
0.00<br />
0.069<br />
0.00<br />
0.079<br />
0.00<br />
0.091<br />
0.00<br />
0.105<br />
Size (µm) Volume In %<br />
0.105<br />
0.00<br />
0.120<br />
0.00<br />
0.138<br />
0.02<br />
0.158<br />
0.14<br />
0.182<br />
0.51<br />
0.209<br />
0.96<br />
0.240<br />
1.55<br />
0.275<br />
2.24<br />
0.316<br />
2.98<br />
0.363<br />
3.68<br />
0.417<br />
4.28<br />
0.479<br />
4.70<br />
0.550<br />
4.92<br />
0.631<br />
4.93<br />
0.724<br />
4.76<br />
0.832<br />
4.42<br />
0.955<br />
3.96<br />
1.096<br />
Size (µm) Volume In %<br />
1.096<br />
3.44<br />
1.259<br />
2.92<br />
1.445<br />
2.48<br />
1.660<br />
2.15<br />
1.905<br />
1.97<br />
2.188<br />
1.92<br />
2.512<br />
2.02<br />
2.884<br />
2.24<br />
3.311<br />
2.54<br />
3.802<br />
2.89<br />
4.365<br />
3.22<br />
5.012<br />
3.49<br />
5.754<br />
3.65<br />
6.607<br />
3.66<br />
7.586<br />
3.50<br />
8.710<br />
3.21<br />
10.000<br />
2.79<br />
11.482<br />
Size (µm) Volume In %<br />
11.482<br />
2.31<br />
13.183<br />
1.81<br />
15.136<br />
1.34<br />
17.378<br />
0.93<br />
19.953<br />
0.58<br />
22.909<br />
0.31<br />
26.303<br />
0.17<br />
30.200<br />
0.13<br />
34.674<br />
0.11<br />
39.811<br />
0.08<br />
45.709<br />
0.05<br />
52.481<br />
0.01<br />
60.256<br />
0.00<br />
69.183<br />
0.00<br />
79.433<br />
0.00<br />
91.201<br />
0.00<br />
104.713<br />
0.00<br />
120.226<br />
54<br />
Size (µm) Volume In %<br />
120.226<br />
0.00<br />
138.038<br />
0.00<br />
158.489<br />
0.00<br />
181.970<br />
0.00<br />
208.930<br />
0.00<br />
239.883<br />
0.00<br />
275.423<br />
0.00<br />
316.228<br />
0.00<br />
363.078<br />
0.00<br />
416.869<br />
0.00<br />
478.630<br />
0.00<br />
549.541<br />
0.00<br />
630.957<br />
0.00<br />
724.436<br />
0.00<br />
831.764<br />
0.00<br />
954.993<br />
0.00<br />
1096.478<br />
0.00<br />
1258.925<br />
Size (µm) Volume In %<br />
1258.925<br />
1445.440<br />
1659.587<br />
1905.461<br />
2187.762<br />
2511.886<br />
2884.032<br />
3311.311<br />
3801.894<br />
4365.158<br />
5011.872<br />
5754.399<br />
6606.934<br />
7585.776<br />
8709.636<br />
10000.000<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
Rezultatele analizei granulometrice a pulberii de BNT-BT0.08 calc<strong>in</strong>ata la 600 °C<br />
(suspen<strong>si</strong>e apoasa) sunt: diametrul median = 3,869 µm <strong>si</strong> suprafata specifica = 6,34 m 2 /g.<br />
Volume (%)<br />
5<br />
4<br />
3<br />
2<br />
1<br />
Particle Size Distribution<br />
0<br />
0.01 0.1 1 10<br />
Particle Size (µm)<br />
100 1000 3000<br />
BNT BT 600 2h - Average, Thursday, November 12, 2009 9:45:23 AM<br />
Fig.46. Curba de variatie a volumului granulelor de pulbere <strong>in</strong> functie de diametrul<br />
particulelor de BNT-BT0.08 calc<strong>in</strong>ata la 700 °C; suspen<strong>si</strong>e apoasa plus aditiv organic<br />
Tab.15. Distributia granulometrica a pulberii de BNT-BT0.08 calc<strong>in</strong>ata la 700 °C; suspen<strong>si</strong>e<br />
apoasa plus aditiv organic<br />
Size (µm) Volume In %<br />
0.010<br />
0.00<br />
0.011<br />
0.00<br />
0.013<br />
0.00<br />
0.015<br />
0.00<br />
0.017<br />
0.00<br />
0.020<br />
0.00<br />
0.023<br />
0.00<br />
0.026<br />
0.00<br />
0.030<br />
0.00<br />
0.035<br />
0.00<br />
0.040<br />
0.00<br />
0.046<br />
0.00<br />
0.052<br />
0.00<br />
0.060<br />
0.00<br />
0.069<br />
0.00<br />
0.079<br />
0.00<br />
0.091<br />
0.00<br />
0.105<br />
Size (µm) Volume In %<br />
0.105<br />
0.03<br />
0.120<br />
0.23<br />
0.138<br />
0.56<br />
0.158<br />
0.91<br />
0.182<br />
1.34<br />
0.209<br />
1.83<br />
0.240<br />
2.39<br />
0.275<br />
3.01<br />
0.316<br />
3.62<br />
0.363<br />
4.16<br />
0.417<br />
4.56<br />
0.479<br />
4.77<br />
0.550<br />
4.77<br />
0.631<br />
4.59<br />
0.724<br />
4.26<br />
0.832<br />
3.81<br />
0.955<br />
3.28<br />
1.096<br />
Size (µm) Volume In %<br />
1.096<br />
2.74<br />
1.259<br />
2.25<br />
1.445<br />
1.87<br />
1.660<br />
1.64<br />
1.905<br />
1.56<br />
2.188<br />
1.63<br />
2.512<br />
1.84<br />
2.884<br />
2.15<br />
3.311<br />
2.51<br />
3.802<br />
2.89<br />
4.365<br />
3.24<br />
5.012<br />
3.51<br />
5.754<br />
3.66<br />
6.607<br />
3.68<br />
7.586<br />
3.55<br />
8.710<br />
3.28<br />
10.000<br />
2.89<br />
11.482<br />
Size (µm) Volume In %<br />
11.482<br />
2.42<br />
13.183<br />
1.90<br />
15.136<br />
1.37<br />
17.378<br />
0.91<br />
19.953<br />
0.32<br />
22.909<br />
0.07<br />
26.303<br />
0.00<br />
30.200<br />
0.00<br />
34.674<br />
0.00<br />
39.811<br />
0.00<br />
45.709<br />
0.00<br />
52.481<br />
0.00<br />
60.256<br />
0.00<br />
69.183<br />
0.00<br />
79.433<br />
0.00<br />
91.201<br />
0.00<br />
104.713<br />
0.00<br />
120.226<br />
Size (µm) Volume In %<br />
120.226<br />
0.00<br />
138.038<br />
0.00<br />
158.489<br />
0.00<br />
181.970<br />
0.00<br />
208.930<br />
0.00<br />
239.883<br />
0.00<br />
275.423<br />
0.00<br />
316.228<br />
0.00<br />
363.078<br />
0.00<br />
416.869<br />
0.00<br />
478.630<br />
0.00<br />
549.541<br />
0.00<br />
630.957<br />
0.00<br />
724.436<br />
0.00<br />
831.764<br />
0.00<br />
954.993<br />
0.00<br />
1096.478<br />
0.00<br />
1258.925<br />
Size (µm) Volume In %<br />
1258.925<br />
1445.440<br />
1659.587<br />
1905.461<br />
2187.762<br />
2511.886<br />
2884.032<br />
3311.311<br />
3801.894<br />
4365.158<br />
5011.872<br />
5754.399<br />
6606.934<br />
7585.776<br />
8709.636<br />
10000.000<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00
Rezultatele analizei granulometrice a pulberii de BNT-BT0.08 calc<strong>in</strong>ata la 600 °C (suspen<strong>si</strong>e<br />
apoasa plus aditiv organic) sunt: diametrul median = 5,289 µm <strong>si</strong> suprafata specifica = 4,66<br />
m 2 /g.<br />
Pulbere de BNT-BT0.08 calc<strong>in</strong>ata la 500 °C<br />
Volume (%)<br />
6<br />
5<br />
4<br />
3<br />
2<br />
1<br />
Particle Size Distribution<br />
0<br />
0.01 0.1 1 10<br />
Particle Size (µm)<br />
100 1000 3000<br />
BNT BT 500 3h - Average, Thursday, November 12, 2009 9:52:52 AM<br />
Fig.47. Curba de variatie a volumului granulelor de pulbere <strong>in</strong> functie de diametrul<br />
particulelor de BNT-BT0.08 calc<strong>in</strong>ata la 500 °C; suspen<strong>si</strong>e apoasa<br />
Tab.16. Distributia granulometrica a pulberii de BNT-BT0.08 calc<strong>in</strong>ata la 500 °C; suspen<strong>si</strong>e<br />
apoasa<br />
Size (µm) Volume In %<br />
0.010<br />
0.00<br />
0.011<br />
0.00<br />
0.013<br />
0.00<br />
0.015<br />
0.00<br />
0.017<br />
0.00<br />
0.020<br />
0.00<br />
0.023<br />
0.00<br />
0.026<br />
0.00<br />
0.030<br />
0.00<br />
0.035<br />
0.00<br />
0.040<br />
0.00<br />
0.046<br />
0.00<br />
0.052<br />
0.00<br />
0.060<br />
0.00<br />
0.069<br />
0.00<br />
0.079<br />
0.00<br />
0.091<br />
0.00<br />
0.105<br />
Size (µm) Volume In %<br />
0.105<br />
0.00<br />
0.120<br />
0.00<br />
0.138<br />
0.00<br />
0.158<br />
0.07<br />
0.182<br />
0.19<br />
0.209<br />
0.38<br />
0.240<br />
0.60<br />
0.275<br />
0.87<br />
0.316<br />
1.19<br />
0.363<br />
1.50<br />
0.417<br />
1.80<br />
0.479<br />
2.05<br />
0.550<br />
2.25<br />
0.631<br />
2.40<br />
0.724<br />
2.51<br />
0.832<br />
2.58<br />
0.955<br />
2.62<br />
1.096<br />
Size (µm) Volume In %<br />
1.096<br />
2.65<br />
1.259<br />
2.70<br />
1.445<br />
2.79<br />
1.660<br />
2.93<br />
1.905<br />
3.13<br />
2.188<br />
3.38<br />
2.512<br />
3.68<br />
2.884<br />
4.00<br />
3.311<br />
4.33<br />
3.802<br />
4.63<br />
4.365<br />
4.88<br />
5.012<br />
5.05<br />
5.754<br />
5.09<br />
6.607<br />
5.01<br />
7.586<br />
4.77<br />
8.710<br />
4.40<br />
10.000<br />
3.90<br />
11.482<br />
Size (µm) Volume In %<br />
11.482<br />
3.32<br />
13.183<br />
2.70<br />
15.136<br />
2.08<br />
17.378<br />
1.51<br />
19.953<br />
1.01<br />
22.909<br />
0.63<br />
26.303<br />
0.29<br />
30.200<br />
0.11<br />
34.674<br />
0.01<br />
39.811<br />
0.00<br />
45.709<br />
0.00<br />
52.481<br />
0.00<br />
60.256<br />
0.00<br />
69.183<br />
0.00<br />
79.433<br />
0.00<br />
91.201<br />
0.00<br />
104.713<br />
0.00<br />
120.226<br />
55<br />
Size (µm) Volume In %<br />
120.226<br />
0.00<br />
138.038<br />
0.00<br />
158.489<br />
0.00<br />
181.970<br />
0.00<br />
208.930<br />
0.00<br />
239.883<br />
0.00<br />
275.423<br />
0.00<br />
316.228<br />
0.00<br />
363.078<br />
0.00<br />
416.869<br />
0.00<br />
478.630<br />
0.00<br />
549.541<br />
0.00<br />
630.957<br />
0.00<br />
724.436<br />
0.00<br />
831.764<br />
0.00<br />
954.993<br />
0.00<br />
1096.478<br />
0.00<br />
1258.925<br />
Size (µm) Volume In %<br />
1258.925<br />
1445.440<br />
1659.587<br />
1905.461<br />
2187.762<br />
2511.886<br />
2884.032<br />
3311.311<br />
3801.894<br />
4365.158<br />
5011.872<br />
5754.399<br />
6606.934<br />
7585.776<br />
8709.636<br />
10000.000<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
Rezultatele analizei granulometrice a pulberii de BNT-BT0.08 calc<strong>in</strong>ata la 600 °C<br />
(suspen<strong>si</strong>e apoasa) sunt: diametrul median = 3,595 µm <strong>si</strong> suprafata specifica = 5,72 m 2 /g.<br />
Pentru toate pulberile de BNT-BT0.08 analizate, se observa ca o granulometrie mai<br />
buna a pulberii se obt<strong>in</strong>e atunci cand suspen<strong>si</strong>a se realizeaza folo<strong>si</strong>nd numai apa. Aceasta<br />
<strong>in</strong>seamna ca dispersantul organic actioneaza ca un coagulant, reu<strong>si</strong>nd sa mareasca<br />
aglomerarea particulelor.
Se constata ca exista o diferenta <strong>in</strong>semnata <strong>in</strong>tre dimen<strong>si</strong>unile granulelor observate cu<br />
ajutorul microscopiilor electronice SEM <strong>si</strong> TEM. Aceasta diferenta este pusa pe seama<br />
faptului ca apa <strong>si</strong> dispersantul organic nu reusesc sa distruga agregatele granulelor. Mai mult,<br />
<strong>in</strong> prezenta solventului apos <strong>si</strong> a dispersantului organic, se produce o aglomerare a granulelor,<br />
daca ne referim la microscopia SEM, unde nu se foloseste un mediu lichid pentru analiza.<br />
Aceste rezultate, de<strong>si</strong> par orientative, sunt foarte utile mai ales pentru materialele<br />
pulverulente care nu prez<strong>in</strong>ta aptitud<strong>in</strong>e buna la presare, caz <strong>in</strong> care, pentru obt<strong>in</strong>erea unei<br />
den<strong>si</strong>tati a materialului presat de peste 40% d<strong>in</strong> cea teoretica, se folosesc aditivi de presare d<strong>in</strong><br />
aceea<strong>si</strong> gama (apa, substanta organica).<br />
Mai mult, repartizarea cantitativa (procente volumetrice) a granulelor cu diametrul<br />
cupr<strong>in</strong>s <strong>in</strong>tr-un anumit <strong>in</strong>terval dimen<strong>si</strong>onal) reprez<strong>in</strong>ta un parametru important pentru<br />
realizarea unui material dens pr<strong>in</strong> presare.<br />
3.3. Analiza morfologiei cu ajutorul microscopiei electronice cu transmi<strong>si</strong>e a pulberilor<br />
de BNT-BT0,08 preparate pr<strong>in</strong> metoda pirosol<br />
Imag<strong>in</strong>ile TEM de mai jos sunt obt<strong>in</strong>ute pentru o pulbere de BNT-BT0.08 preparata pr<strong>in</strong><br />
metoda pirosol, <strong>in</strong> urmatoarele conditii de lucru:<br />
- pulberea cruda, asa cum a fost obt<strong>in</strong>uta pr<strong>in</strong> metoda pirosol (temperatura <strong>in</strong> cuptor<br />
= 700 °C); proba (a);<br />
- pulberea cruda calc<strong>in</strong>area ulterior la 700 °C, 3 ore, proba (b)<br />
(a) Analiza TEM a pulberii crude de BNT-BT0,08<br />
- Proba 1-<br />
56
Fig.48. Imag<strong>in</strong>i TEM ale pulberii crude de BNT-BT0,08 preparata pr<strong>in</strong> metoda pirosol<br />
la 700 °C<br />
57
- Proba 2-<br />
Fig.49. Imag<strong>in</strong>i HR-TEM ale pulberii crude de BNT-BT0,08 preparata pr<strong>in</strong> metoda<br />
pirosol la 700 °C<br />
58
Fig.50. Imag<strong>in</strong>i TEM ale pulberii crude de BNT-BT0,08 preparata pr<strong>in</strong> metoda pirosol<br />
la 700 °C<br />
59
Fig.51. Imag<strong>in</strong>i SAED ale pulberii crude de BNT-BT0,08 preparata pr<strong>in</strong> metoda pirosol<br />
la 700 °C<br />
Fig.52. Spectrul EDS al pulberii crude de BNT-BT0,08 preparata pr<strong>in</strong> metoda pirosol la<br />
700 °C<br />
Imag<strong>in</strong>ile TEM obt<strong>in</strong>ute pentru pulberea de BNT-BT0,08 asa cum rezulta pr<strong>in</strong> metoda pirosol<br />
arata granule sferice, de diferite marimi (<strong>in</strong> stransa legatura cu dimen<strong>si</strong>unile picaturilor de sol<br />
d<strong>in</strong> care prov<strong>in</strong>). In completarea <strong>in</strong>formatiilor despre microstructura pulberii obt<strong>in</strong>ute pr<strong>in</strong><br />
<strong>si</strong>nteza pirosol v<strong>in</strong> imag<strong>in</strong>ile HR-TEM. Aceste ultime imag<strong>in</strong>i <strong>in</strong>dica granule sferice formate<br />
d<strong>in</strong> mai multe cristalite de aproximativ 10 nm. Aceste imag<strong>in</strong>i sugereaza ca d<strong>in</strong> granula<br />
sferica, pr<strong>in</strong> cristalizare se vor forma acele granule cu forma poliedrala (<strong>in</strong> spacial cubica)<br />
60
evidentiate pr<strong>in</strong> microscopie SEM la pulberea calc<strong>in</strong>ata ulterior 3 ore, la 700 °C. Imag<strong>in</strong>ile<br />
SAED pun <strong>in</strong> evidenta cristalizarea <strong>in</strong>completa a pulberii de BNT-BT0,08 <strong>in</strong> momentul imediat<br />
dupa <strong>si</strong>nteza. Spectrul EDAX <strong>in</strong>dica prezenta tututror speciilor atomice care formeaza<br />
compusul BNT-BT0,08.<br />
(b) Analiza SEM a pulberii crude de BNT-BT0,08,calc<strong>in</strong>ata ulterior la 700 °C, 3 ore<br />
- Proba 1<br />
Fig.53. Imag<strong>in</strong>i TEM ale pulberii crude de BNT-BT0,08,calc<strong>in</strong>ata ulterior la 700 °C, 3 ore<br />
61
Fig.54. Imag<strong>in</strong>i HR-TEM ale pulberii crude de BNT-BT0,08,calc<strong>in</strong>ata ulterior la 700 °C, 3 ore<br />
62
Fig.55. Imag<strong>in</strong>ea SAED a pulberii crude de BNT-BT0,08,calc<strong>in</strong>ata ulterior la 700 °C, 3 ore<br />
Imag<strong>in</strong>i TEM ale pulberii de BNT-BT0,08, calc<strong>in</strong>ata dupa <strong>si</strong>nteza, la 700 °C, 3 ore <strong>in</strong>dica un<br />
material cu granule care nu mai sunt sferice. De fapt, aceste granule apar ca fi<strong>in</strong>d niste<br />
agregate constituite d<strong>in</strong> componente sferice cu diametrul de 10-20 nm (Fig.54; HR-TEM).<br />
Analiza SAED sugereaza un material mai b<strong>in</strong>e cristalizat decat cel obt<strong>in</strong>ut <strong>in</strong> conditiile<br />
termice ale <strong>in</strong>stalatiei pirosol. Succe<strong>si</strong>unea regulata a planelor atomice (Fig. 54) sugereaza<br />
faptul ca nanocristalitele au structura uniforma d<strong>in</strong> punct de vedere cristalografic.<br />
3.4. Analiza morfologiei cu ajutorul granulometrului cu laser a pulberilor de BNT-BT0,08<br />
preparate pr<strong>in</strong> metoda pirosol<br />
Pentru analiza granulometrica cu lase a pulberii de BNT-BT0.08 obt<strong>in</strong>uta pr<strong>in</strong> metoda<br />
pirosol a fost utilizat acela<strong>si</strong> echipament; modul de lucru fi<strong>in</strong>d acela<strong>si</strong>. Deoarece rezultate mai<br />
bune au fost obt<strong>in</strong>ute <strong>in</strong> suspen<strong>si</strong>e apoasa, prezentam <strong>in</strong> cont<strong>in</strong>uare numai rezultatele obt<strong>in</strong>ute<br />
folo<strong>si</strong>nd suspen<strong>si</strong>a apoasa.<br />
63
Volume (%)<br />
6<br />
5<br />
4<br />
3<br />
2<br />
1<br />
Particle Size Distribution<br />
0<br />
0.01 0.1 1 10<br />
Particle Size (µm)<br />
100 1000 3000<br />
BNTBT700Pirosol - Average, Thursday, November 12, 2009 9:59:07 AM<br />
Fig.56. Curba de variatie a volumului granulelor de pulbere <strong>in</strong> functie de diametrul<br />
particulelor de BNT-BT0.08 calc<strong>in</strong>ata la 700 °C; suspen<strong>si</strong>e apoasa<br />
Tab.17. Distributia granulometrica a pulberii de BNT-BT0.08 calc<strong>in</strong>ata la 700 °C; suspen<strong>si</strong>e<br />
apoasa<br />
Size (µm) Volume In %<br />
0.010<br />
0.00<br />
0.011<br />
0.00<br />
0.013<br />
0.00<br />
0.015<br />
0.00<br />
0.017<br />
0.00<br />
0.020<br />
0.00<br />
0.023<br />
0.00<br />
0.026<br />
0.00<br />
0.030<br />
0.00<br />
0.035<br />
0.00<br />
0.040<br />
0.00<br />
0.046<br />
0.00<br />
0.052<br />
0.00<br />
0.060<br />
0.00<br />
0.069<br />
0.00<br />
0.079<br />
0.00<br />
0.091<br />
0.00<br />
0.105<br />
Size (µm) Volume In %<br />
0.105<br />
0.00<br />
0.120<br />
0.00<br />
0.138<br />
0.00<br />
0.158<br />
0.05<br />
0.182<br />
0.15<br />
0.209<br />
0.31<br />
0.240<br />
0.49<br />
0.275<br />
0.72<br />
0.316<br />
0.98<br />
0.363<br />
1.25<br />
0.417<br />
1.51<br />
0.479<br />
1.72<br />
0.550<br />
1.90<br />
0.631<br />
2.03<br />
0.724<br />
2.11<br />
0.832<br />
2.17<br />
0.955<br />
2.19<br />
1.096<br />
Size (µm) Volume In %<br />
1.096<br />
2.20<br />
1.259<br />
2.22<br />
1.445<br />
2.27<br />
1.660<br />
2.35<br />
1.905<br />
2.49<br />
2.188<br />
2.68<br />
2.512<br />
2.92<br />
2.884<br />
3.21<br />
3.311<br />
3.54<br />
3.802<br />
3.89<br />
4.365<br />
4.26<br />
5.012<br />
4.61<br />
5.754<br />
4.92<br />
6.607<br />
5.14<br />
7.586<br />
5.25<br />
8.710<br />
5.21<br />
10.000<br />
5.02<br />
11.482<br />
Size (µm) Volume In %<br />
11.482<br />
4.67<br />
13.183<br />
4.17<br />
15.136<br />
3.57<br />
17.378<br />
2.89<br />
19.953<br />
2.22<br />
22.909<br />
1.55<br />
26.303<br />
0.92<br />
30.200<br />
0.25<br />
34.674<br />
0.00<br />
39.811<br />
0.00<br />
45.709<br />
0.00<br />
52.481<br />
0.00<br />
60.256<br />
0.00<br />
69.183<br />
0.00<br />
79.433<br />
0.00<br />
91.201<br />
0.00<br />
104.713<br />
0.00<br />
120.226<br />
64<br />
Size (µm) Volume In %<br />
120.226<br />
0.00<br />
138.038<br />
0.00<br />
158.489<br />
0.00<br />
181.970<br />
0.00<br />
208.930<br />
0.00<br />
239.883<br />
0.00<br />
275.423<br />
0.00<br />
316.228<br />
0.00<br />
363.078<br />
0.00<br />
416.869<br />
0.00<br />
478.630<br />
0.00<br />
549.541<br />
0.00<br />
630.957<br />
0.00<br />
724.436<br />
0.00<br />
831.764<br />
0.00<br />
954.993<br />
0.00<br />
1096.478<br />
0.00<br />
1258.925<br />
Size (µm) Volume In %<br />
1258.925<br />
1445.440<br />
1659.587<br />
1905.461<br />
2187.762<br />
2511.886<br />
2884.032<br />
3311.311<br />
3801.894<br />
4365.158<br />
5011.872<br />
5754.399<br />
6606.934<br />
7585.776<br />
8709.636<br />
10000.000<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
0.00<br />
Rezultatele analizei granulometrice a pulberii de BNT-BT0.08 calc<strong>in</strong>ata la 600 °C<br />
(suspen<strong>si</strong>e apoasa) sunt: diametrul median = 6,861 µm <strong>si</strong> suprafata specifica = 3,13 m 2 /g.<br />
Asa cum s-a aratat la comentariul pentru pulberile <strong>si</strong>ntetizate pr<strong>in</strong> metoda sol-gel, nu<br />
se pot face comparatii <strong>in</strong>tre rezultatele obt<strong>in</strong>ute pe pulberile cu aceea<strong>si</strong> compozitie chimica dar<br />
tratate termic la temperaturi <strong>si</strong> durate egale dar obt<strong>in</strong>ute pr<strong>in</strong> metode de <strong>si</strong>nteza diferite (solgel<br />
<strong>si</strong> pirosol) deoarece scopul a fost obt<strong>in</strong>erea unui material monofazic la o a numita<br />
temperatura. Aceasta <strong>in</strong>seamna ca duratele de tratament termic au fost cele care au <strong>in</strong>fluentat<br />
obt<strong>in</strong>erea fazei dorite fara a lua <strong>in</strong> con<strong>si</strong>deratie <strong>in</strong>fluenta duratei de calc<strong>in</strong>are asupra cresterii<br />
dimen<strong>si</strong>unilor granulelor.<br />
De asemenea, se poate spune <strong>si</strong> faptul ca aceasta metoda de analiza granulometrica<br />
scoate <strong>in</strong> evidenta gradul de aglomerare <strong>si</strong> taria legaturilor care produc aglomerarea<br />
granulelor. Aceste rezultate pot servi ca <strong>in</strong>formatii prelim<strong>in</strong>are pentru analizele cu ajutorul<br />
microscopiei electronice.
3.5. Activitati suport <strong>si</strong> de implementare a rezultatelor cercetarii<br />
Participari la confer<strong>in</strong>te<br />
1. Mar<strong>in</strong> Cernea, Carmen Galas<strong>si</strong>, Ecater<strong>in</strong>a Andronescu, Roxana Radu, Roxana Trusca, “Solgel<br />
synthe<strong>si</strong>s and characterization of BaTiO3 doped-(Bi1/2Na1/2)TiO3 piezoelectric ceramics”,<br />
Poster P2.7, E-MRS 2009 SYMPOSIA, June 8-12, 2009, Strasbourg, France.<br />
2. Roxana Radu, Mar<strong>in</strong> Cernea, Bogdan Stefan Va<strong>si</strong>le, Crist<strong>in</strong>a Dragoi, “Ferroelectric<br />
properties and microstructure of (Bi1/2Na1/2)0.95 Ba 0.05 TiO3 (BNT-BT0.05) ceramic prepared by<br />
sol-gel”, Romanian Conference on Advanced Materials - ROCAM 2009 (August 25-28th,<br />
2009), Brasov, Romania.<br />
Articole publicate<br />
M. Cernea, E. Andronescu, R. Radu, F. Fochi, C. Galas<strong>si</strong>, “Sol-gel synthe<strong>si</strong>s and<br />
characterization of BaTiO3 doped-(Bi1/2Na1/2)TiO3 piezoelectric ceramics”, Journal of Alloys<br />
and Compound Materials, (2009), acceptat.<br />
4. Concluzii<br />
Analiza morfologiei pulberilor de BNT-BT0,08 preparate pr<strong>in</strong> metoda sol-gel a <strong>in</strong>dicat<br />
o pulbere nanometrica. Se remarca faptul ca aceasta compozitie (BNT-BT0,08) se obt<strong>in</strong>e <strong>in</strong><br />
conditii de lucru avantajoase (se obt<strong>in</strong>e o pulbere monofazica, complet cristalizata, la o<br />
temperatura relativ joasa (600 °C) fata de metoda reactiei <strong>in</strong> faza solida (1100 °C)).<br />
Morfologia pulberii astfel obt<strong>in</strong>ute este omogena, fi<strong>in</strong>d <strong>in</strong>fluentata <strong>in</strong> pr<strong>in</strong>cipal, de conditiile<br />
termice de procesare ulterioara a solului precursor.<br />
In cazul pulberilor de BNT-BT0,08 preparate pr<strong>in</strong> metoda pirosol, omogenitatea<br />
morfologiei este <strong>in</strong>fluentata <strong>in</strong> mai mare masura de conditiile de procesare d<strong>in</strong> timpul <strong>si</strong>ntezei.<br />
Avand <strong>in</strong> vedere mecanismul diferit de cel al metodei sol-gel, <strong>si</strong> morfologia pulberilor,<br />
atat d<strong>in</strong> punct de vedere al dimen<strong>si</strong>unilor dar mai ales al formei, este complet diferita la<br />
pulberea obt<strong>in</strong>uta pr<strong>in</strong> tehnica pirosol.<br />
Forma obisnuita a granulelor este sferica dar distributia granulometrica este larga.<br />
Pulberile obt<strong>in</strong>ute de noi nu mai sunt <strong>in</strong> domeniul nanometric (ca la sol-gel) ci, submicronic.<br />
Aceasta forma sferica a granulelor dispare <strong>in</strong> urma tratamentelor termice de cristalizare <strong>si</strong><br />
rezulta granule poliedrale, <strong>in</strong> mare masura cubice.<br />
65
Analizele cu ajutorul microscopiei electronice SEM <strong>si</strong> TEM, EDAX <strong>si</strong> difractia de<br />
raze X au aratat ca se obt<strong>in</strong>e un material monofazic, stoichiometric BNT-BT0,08, complet<br />
cristalizat <strong>in</strong> conditii termice avantajoase daca se foloseste metoda sol-gel pentru <strong>si</strong>nteză <strong>si</strong><br />
polifazic <strong>in</strong> cazul metodei pirosol.<br />
Alegerea conditiilor de transformare a pulberilor de BNT-BT0,08 obt<strong>in</strong>ute pr<strong>in</strong> cele<br />
doua metode, <strong>in</strong> elemente comprimate <strong>si</strong> den<strong>si</strong>ficate pr<strong>in</strong> <strong>si</strong>nterizare, va trebui sa t<strong>in</strong>a cont de<br />
rezultatele experimentale obt<strong>in</strong>ute <strong>in</strong> cadrul acestei faze.<br />
În concluzie, rezultatele cupr<strong>in</strong>se <strong>in</strong> raport sti<strong>in</strong>tific complet, priv<strong>in</strong>d caracterizarea<br />
microstructurala <strong>si</strong> morfologica a pulberii <strong>si</strong> filmelor de BNT-BT0,08 obt<strong>in</strong>ute pr<strong>in</strong> sol-gel <strong>si</strong><br />
pirosol, <strong>in</strong>dica faptul ca obiectivele Etapei IIa au fost realizate.<br />
Aceste rezultate prelim<strong>in</strong>are constituie o bază de date utile pentru Etapa IIb a<br />
Contractului PNCDI II nr. 72 153/2008.<br />
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