Influence of the Processes Parameters on the Properties of The ...

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