Influence of the Processes Parameters on the Properties of The ...
Influence of the Processes Parameters on the Properties of The ...
Influence of the Processes Parameters on the Properties of The ...
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Chapter 3.<br />
Analytical Methods and Designs <str<strong>on</strong>g>of</str<strong>on</strong>g> Experiments<br />
median pore diameter. As example for P L LA, a Hg typical distributi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> pores is presented in Figure 3.12-B<br />
[Ho et al., 2004].<br />
5.1.3 X-ray Microtomography<br />
Trater et al. [2005] have investigated <str<strong>on</strong>g>the</str<strong>on</strong>g> use <str<strong>on</strong>g>of</str<strong>on</strong>g> n<strong>on</strong>-invasive 3-D X-ray microtomography (XMT)<br />
for microstructure characterizati<strong>on</strong>. Moreover, XMT generated images were more c<strong>on</strong>ducive to digital<br />
image processing than SEM images because <str<strong>on</strong>g>of</str<strong>on</strong>g> ‘razorthin’ depth <str<strong>on</strong>g>of</str<strong>on</strong>g> focus and sharp c<strong>on</strong>trast between solid<br />
and void areas. This technique has been widely used for <str<strong>on</strong>g>the</str<strong>on</strong>g> in vivo imaging <str<strong>on</strong>g>of</str<strong>on</strong>g> plants, insects, animals and<br />
humans. X-ray microtomography is a n<strong>on</strong> destructive technique that provides a reas<strong>on</strong>able level <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
resoluti<strong>on</strong> (~ 5 – 20 m). <strong>The</strong> X-ray microtomography approach is an extensi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> computer aided<br />
tomography (CT) medical imaging technique. X-rays are directed from a high-power source toward a<br />
sample, and a detector <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> opposite side <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> sample measures <str<strong>on</strong>g>the</str<strong>on</strong>g> intensity <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> transmitted X-rays<br />
(see Figure 3.13-A).<br />
(A)-Schematic reprensati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> CT. (B)-Example <str<strong>on</strong>g>of</str<strong>on</strong>g> analysis with P L LA/Silica.<br />
Figure 3.13: CT principle and images <str<strong>on</strong>g>of</str<strong>on</strong>g> P L LA/Silica sample.<br />
[Collins et al., 2010; Hancock and Mullarney, 2005]<br />
A two-dimensi<strong>on</strong>al “shadow” image is produced by accurately rastering <str<strong>on</strong>g>the</str<strong>on</strong>g> X-ray beam across <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
sample. <strong>The</strong> sample <str<strong>on</strong>g>the</str<strong>on</strong>g>n is carefully moved relative to <str<strong>on</strong>g>the</str<strong>on</strong>g> X-ray beam, and <str<strong>on</strong>g>the</str<strong>on</strong>g> process is repeated to<br />
produce additi<strong>on</strong>al two-dimensi<strong>on</strong>al images from various view points. Using a Fourier transform algorithm,<br />
<str<strong>on</strong>g>the</str<strong>on</strong>g> two-dimensi<strong>on</strong>al images <str<strong>on</strong>g>the</str<strong>on</strong>g>n are combined to generate a complete three-dimensi<strong>on</strong>al map <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> sample.<br />
<strong>The</strong> intensity <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> X-rays reaching <str<strong>on</strong>g>the</str<strong>on</strong>g> detector is c<strong>on</strong>trolled by <str<strong>on</strong>g>the</str<strong>on</strong>g> sample path length and <str<strong>on</strong>g>the</str<strong>on</strong>g> X-ray<br />
attenuati<strong>on</strong> coefficient <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> material that it encounters <strong>on</strong> that path [Cao et al., 2003]. <strong>The</strong> varying levels <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
signal intensity provide a gray-scale in <str<strong>on</strong>g>the</str<strong>on</strong>g> images (see Figure 3.13-B) from which informati<strong>on</strong> about <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
thickness, and attenuati<strong>on</strong> properties <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> sample can be deduced.<br />
5.2 Scanning Electr<strong>on</strong> Microscopy Observati<strong>on</strong>s<br />
Electr<strong>on</strong> microscopy is a technique based <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> principle <str<strong>on</strong>g>of</str<strong>on</strong>g> electr<strong>on</strong>-matter interacti<strong>on</strong>s, capable<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> producing high-resoluti<strong>on</strong> images <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> surface <str<strong>on</strong>g>of</str<strong>on</strong>g> a sample. A focused electr<strong>on</strong> beam is deflected<br />
through electromagnetic lenses, scans <str<strong>on</strong>g>the</str<strong>on</strong>g> surface <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> sample for analysis which, in resp<strong>on</strong>se, re-emits<br />
different types <str<strong>on</strong>g>of</str<strong>on</strong>g> emissi<strong>on</strong>s (cf. Figure 3.14). <strong>The</strong> signals that derive from electr<strong>on</strong>-sample interacti<strong>on</strong>s<br />
reveal informati<strong>on</strong> about <str<strong>on</strong>g>the</str<strong>on</strong>g> sample including external morphology (texture), chemical compositi<strong>on</strong>, and<br />
pore size, pore structure and orientati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> materials making up <str<strong>on</strong>g>the</str<strong>on</strong>g> sample. In most applicati<strong>on</strong>s, data are<br />
collected over a selected area <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> surface <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> sample, and a 2-dimensi<strong>on</strong>al image is generated that<br />
displays spatial variati<strong>on</strong>s in <str<strong>on</strong>g>the</str<strong>on</strong>g>se properties. magnificati<strong>on</strong> ranging from 20× to approximately 30,000×.<br />
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