1. X-Ray Diffraction (XRD)

1.1 Principle

The basic principle of XRD is using regular atomic cells as X-ray diffraction gratings, because the distance between atoms is on the same order of magnitude as the wavelength of an X-ray, X-ray will have diffraction between different atom and finally get the different diffraction intensity value correspond to the different diffraction angle which is closely related to the crystal structure. Through XRD, the crystal structure can be characterized by using the equation

2dsinθ=nλ

(d: distance between crystal face; θ: diffraction angle; λ: the wave length of X-ray)

The X-ray wavelength after diffraction and the diffraction angle can be used to characterize the interplanar spacing and the value of diffraction intensity can be used to characterize the concentration of different interplanar.

1.2 Accuracy and precision

Due to the X-ray focusing issue, the XRD has ~25 micrometres accuracy, if the sample is in nanoscale, the XRD cannot characterize the sample accurately. During the sample rotation in the diffraction part, the angular accuracy of XRD is 0.01°. The XRD precision is related to the substance content, phase cannot be characterized by XRD when the content is lower than 5%^[4].

1.3 Characterization result

In the characteristic of β-TCP, the sample is made into powder. During the rotation of the sample from 2θ=20 degree to 2θ=50 degree, the intensity of diffraction is shown in Figure 2. By analyzing the XRD diffraction pattern, the following information about crystal can be characterized:

Phase and composition: By comparing the intensity with the standard cards, there are two phases in the sample which are β-TCP and β-Ca2P2O7, and from the number of the intensity peak, the concentration of each phase can be shown that the concentration of β-TCP is 71.2% and the rest, which was 28.8% of beta-calcium pyrophosphate.
Crystal face concentration: From the analyze of intensity and diffraction angle, the highest peak corresponding to the crystallinity of beta phase was found at 2θ=31.5°, which corresponding to the (0 2 1 0) planes, so it means the most abundant crystal face is (0 2 1 0)
Unit cell structure: The XRD also can reach the cell parameters of β-TCP, which are a=10.42497A ̊ and c=37.34332A ̊ and with the data of interplanar spacing, the structure of beta-TCP can be fully characterized^[5].

Figure 2: The XRD diffraction patterns of β-TCP powders ^[5]

Link Webpages for β-TCP

Link Webpages for β-TCP

Characterisation Data

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