instrumental techniques applied to mineralogy and geochemistry

More documents

Recommendations

Info

Raman, Conventional Infrared and Synchrotron Infrared Spectroscopy in Mineralogy and Geochemistry: Basics and Applications 77 a minimal coupling between vibrations involving Ca with those arising from the silicate anionic structure is assumed. This allows the identification of the internal vibrations of the silicate anions. Finite silicate chains (Q 2 ) dominate the structures of the samples at Ca/Si ratios 0.2-1.0, the spectra showing characteristic symmetric stretching (SS) bands between 1010 and 1020 cm -1 (Raman, Fig. 10) and antisymmetric stretching (ASS) ~965 cm -1 (IR, Fig. 10). The main characteristic feature of the Raman spectra is the Si- O-Si symmetric bending (SB) vibration at ~670 cm -1 . Comparisons with bending frequencies of some known crystalline phases composed of single silicate chains has led to an estimation of the mean Si-O-Si angles in the C-S-H phases to be ~140°, which is the energetically favored bond angle (Garbev et al., 2007). The shift of the SB vibration to a higher frequency (668-672 cm -1 , Raman) indicates narrowing of the Si-O br -Si angle with silicate depolymerization. For Ca/Si>1, silicate depolymerization occurs and dimeric silicate units are formed witnessed further in the IR spectra by the increasing intensity of the SS vibration of Si-O Q 1 units ~806 cm -1 and the increased splitting of the n 2 /n 4 SiO 4 bending around 470 cm -1 with increasing Ca/Si ratio. Considering the frequency, intensity, and width of the Raman stretching vibration bands of Q 1 and Q 2 silicate units it was possible to reconstruct some characteristic structural features, such as the chain length of the silicate species as a function of the Ca/Si ratio. The variation in the frequency of the broad OH stretching bands for the different samples is also Ca/Si ratio specific thus implying that the role of H 2 O in the structure is essential. The broad shoulder around 3245 cm -1 in the Raman spectra is assigned to collective in-phase stretching motions of OH involved in a network of hydrogen bonds. On the other hand, the appearance of a relatively well defined peak at ~3565 cm -1 in the Raman spectra of Ca/Si 1.33 and 1.5 suggests increasing ordering of Ca-bonded OH groups. Similarly, increased ordering of the Ca environment is seen in the increase and sharpening of the Ca-O bands at 332 cm -1 (Raman) and 255 cm -1 (IR). The prominent sharp band at 3618 cm -1 (Raman) and 3640 cm -1 (IR) due to O-H stretching in portlandite, Ca(OH) 2 , which first appear in the sample with Ca/Si 1.33 (Raman) and 1.5 (IR) point to excess Ca indicating an upper limit for the incorporation of Ca into the C-S- H structure of less than 1.33 (probably ~1.25). Additional OH band at 3740 cm -1 in the IR spectra due to surface silanol (Si-)OH groups is indicative for surface charge, which is also Ca/Si dependent.
78 Biliana Gasharova Abs (a.u.) C/S 1.5 1.3 1.0 0.83 0.75 0.67 0.5 0.4 0.2 SiO2 (Aerosil) 255 LV C-S-H 318 Ca(OH)2 455 2 / 4 (SiO 4 ) 470 490 Abs (a.u.) 666 SB Si-O-Si 805 806 840 SS Si-O (Q1) 860 (OH Ca ) / SS Si-O (Q2) 2 (CO 3 ) 945 Si motion against the oxygen cage SiO2 (Aerosil) ASS Si-O (Q1) ASS Si-NBO (Q2) 965 ASS Si-BO (Q2) 1005 1095 (OH Si(Q2) ) (A)SS Q3 / Q4 C/S 1.5 1.3 1.0 0.83 0.75 0.67 0.5 0.4 0.2 Abs (a.u.) C/S 1.5 1.3 1.0 0.83 0.75 0.67 0.5 0.4 0.2 C-H 3240 H2O 3365 3405 H2O H2O SiO2 (Aerosil) 3520 H2O 3640 (Ca(OH)2) 3740 (Si)O-H 200 300 400 wavenumber (cm -1 ) 500 700 800 900 1000 1100 wavenumber (cm -1 ) 1200 1300 2800 3000 3200 3400 wavenumber (cm -1 ) 3600 3800 FIGURE 10. The Raman and IR spectra of C-S-H samples of type C-S-H(1) with Ca/Si ratios ranging from 0.2 to 1.5 reveal changes in structure dependent upon Ca/Si ratio. Surface carbonation of fresh C-S-H samples starts immediately upon exposure to air. The n 1 CO 3 bands overlap with the silicate Raman scattering around ~1080 cm -1 . For unambiguous Raman band assignment of C-S-H phases, it is thus imperative to avoid exposure to CO 2 , which was assured in the above study by analyzing the samples in sealed quartz glass capillaries. A 40x objective with an adjustable cover-slip correction lens helped minimizing the scattering from the capillary. Further, the effect of carbonation of the same C-S-H samples under ambient conditions for up to 6 months have been investigated by Raman spectroscopy (Black et al., 2007). The technique’s sensitivity toward the various CaCO 3 polymorphs illuminates the sequence of carbonation and decalcification processes during aging of C-S-H. Amorphous calcium carbonate hydrate is formed within minutes upon exposure to air as indicated by a broad band ~1080 cm -1 . It crystallizes, over time, to give primarily vaterite at Ca/Si 0.67 (e.g.
Page 2 and 3:
SEMINARIOS DE LA SOCIEDAD ESPAÑOLA
Page 4 and 5:
FOREWORD On the occasion of the Spa
Page 6 and 7:
INDEX Electron back-scattered diffr
Page 8 and 9:
8 Elisabetta Mariani et al Introduc
Page 10 and 11:
10 Elisabetta Mariani et al success
Page 12 and 13:
12 Elisabetta Mariani et al number
Page 14 and 15:
14 Elisabetta Mariani et al FIGURE
Page 16 and 17:
16 Elisabetta Mariani et al FIGURE
Page 18 and 19:
18 Elisabetta Mariani et al In-situ
Page 20 and 21:
TEM in Geology. Basics and applicat
Page 22 and 23:
Page 24 and 25:
Page 26 and 27: TEM in Geology. Basics and applicat
Page 42 and 43: X-ray Absorption Spectroscopy in Mi
Page 56 and 57: Raman, Conventional Infrared and Sy
Page 82 and 83: 84 Clemente Recio Isotope Terminolo
Page 84 and 85: 86 Clemente Recio collector gas sou
Page 86 and 87: 88 Clemente Recio Something similar
Page 88 and 89: 90 Clemente Recio beers. Some brand
Page 90 and 91: 92 Clemente Recio The source of the
Page 92 and 93: 94 Clemente Recio By using GC-C-IRM
Page 94 and 95: 96 Clemente Recio about 25% of tota
Page 96 and 97: 98 Clemente Recio such as blood and
Page 98 and 99: 100 Clemente Recio relatively simpl
Page 100 and 101: 102 Clemente Recio following admini
Page 102 and 103: 104 Clemente Recio and high N in dr
Page 104 and 105: 106 Clemente Recio although 15 N d
Page 106 and 107: 108 Clemente Recio spectrometers th
Page 108 and 109: 110 Clemente Recio O’Brien, D.M.
Page 110 and 111: 112 Kjell Bilström time in old geo
Page 112 and 113: 114 Kjell Bilström ratios ( 204 Pb
Page 114 and 115: 116 Kjell Bilström Certain samples
Page 116 and 117: 118 Kjell Bilström Molybdenite is
Page 118 and 119: 120 Kjell Bilström analyzed with r
Page 120 and 121: 122 Kjell Bilström radiogenic sign
Page 122 and 123: 124 Kjell Bilström plants inherits
Page 124 and 125: 126 Kjell Bilström in some cases a
Page 126 and 127:
128 Kjell Bilström Besides, minera
Page 128 and 129:
130 Kjell Bilström References Bear
Page 130 and 131:
Analytical techniques applied to fl
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
show all

instrumental techniques applied to mineralogy and geochemistry

Create successful ePaper yourself

Delete template?

Save as template?