Quantitative analysis of phase composition

A substance with different chemical compositions and structures is called different phases. Chemical composition difference can be resulted from phase. With the 

Since the 1980s, with wide applications of the highly automated X-ray spectrometer, scientists have used X-ray spectrometry to perform quantitative analysis of phase. This analysis principle is based on the relationship between phase content and diffraction intensity, and the method is simple and fast. Its accuracy can also meet the requirements if its component is not too complex. There are more than 20 quantitative methods such as internal standards, external standards, nil standards, adiabatic methods and theoretical calculations etc. Generally speaking, the more mature internal standard method requires a lot of time to draw the standard curve, and the curve can only apply to one matter, so this method has certain restrictions in quantitative analysis. In 1974, F. H. Chung proposed a skeleton washing method , also called as if-value method, which greatly simplified the X-ray quantitative analysis method, and has been widely used in various research fields. 

Standard K value method is essentially the internal standard method, but with a difference that K value method does not require drawing the standard curve and it is very suitable of a large number of samples for analysis. When determining the content of one phase (a) in mixture contained N phases, it can be added a new known standard phase (s) to the sample which is not present in the sample, making a complex sample containing IV 4-1 phases. If the intensity of strongest diffraction line of phase (a) is la, the intensity of the standard material (s) is Ig, based on quantitative analysis of the basic equation, we can obtain  

Kg is unrelated to the content of standard material and the diffraction conditions. The existence of the other phases only act as the role of thinner, or the absorption, but the impact of absorbing can be eliminated by using the ratio of two-phase diffraction intensity. Thus Kg only relates with the crystal structure and the selected anode target. When selecting the same radiation, Kg only relates with phase (a) and phase (s), and therefore. Kg is a characteristic constant of phase (a) and phase (s). 

When Kg and Wg are known, as long as la/Ig is measured, Wa can be obtained by Eq. (7.127). If the sum of mass fraction of added standard material and various phase in the sample equals to one, the sum of the mass fraction of various phase in the sample equals to (1 — Wg), and therefore mass fraction of various phase in the sample can be obtained by equation of Wa = Wa/(1 — Wg). 

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To illustrate the utility of TG analysis for such determinations, a series of calibration samples were prepared at levels approximately 90% or 10% in the monohydrate phase, using anhydrous /1-lactose as a diluent in bulk a-monohydrate.48 These were subjected to a standard TG evaluation, and the results of the analysis are shown in Table 1. The results indicate that the TG method yields reasonable estimations of the phase composition, but that the difference between measured and found compositions could be unacceptably large for some applications. The data appear to indicate the existence of a small positive bias, which was found to be worse in the 10% monohydrate samples. In a properly controlled and validated system, however, it is highly likely that method limitations could be overcome and TG analysis appropriately used for quantitative analysis of phase composition. 

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