Biomedical Engineering Reference
In-Depth Information
181.7°
79.1°
190.5°
182.0°
60.2°
180.3°
186.2°
91.8°
65.0°
188.3°
193.9°
180.3°
49.0°
182.8°
204.3°
74.2°
174.1°
182.9°
67.9°
188.8°
193.8°
57.0°
182.2°
(a)
(b)
2.5
(a) Atomic arrangement in polyethylene oxide determined by
XRD Molecular model of PEO with the helical symmetry D7.
(b) molecular structure of PEO. The fi gures give the internal rotation
angles. (Source: Reprinted with permission from Ref. 4. Copyright 1973.
American Chemical Society.)
hydroxyapatite, Ca
5
(PO
4
)
3
OH, the scan of which from a reference powder is
also shown in the fi gure. One of the scans from the implanted pericardium
has a small crystalline peak at 2
θ
~ 20° that could be due to a small amount
of Brushite (Ca PO
4
· 2H
2
O). This type of detailed identifi cation of the crys-
talline phases is extensively discussed in textbooks on powder diffraction.
2.3.3 Structure function analysis
If the material is amorphous, then the structure cannot be determined
using crystallographic techniques. In these cases, pair distribution function
(PDF) is calculated from the X-ray diffraction data to determine the atomic
