Phase analysis, diffraction

Quantitative Phase Analysis. Once the identity of the components in a sample are known, it is possible to determine the quantitative composition of the sample. There are several different methods for doing a quantitative analysis, but the most rehable method is to use mixtures of known composition as standards. The computer can determine quantitatively the relative amounts of each component in the unknown sample. For accurate calculations of relative amounts in the unknown sample, it is necessary that the sample and standards have uniform distributions of crystaUites. Often the sample and standards are rotated during data collection to provide a more even distribution of crystaUites which diffract. 

The use of Equation (22) is very general, but it is also possible, with accurate measurements and data treatment, to perform the quantitative phase analysis in semi-crystalline materials without using any internal standard. This procedure is possible only if the chemical compositions of all the phases, including the amorphous one, are known. If the composition of the amorphous phase is unknown, the quantitative analysis without using any internal standard can still be used provided that the chemical composition of the whole sample is available [51]. This approach, until now, has been developed only for the XRD with Bragg-Brentano geometry that is one of the most diffused techniques in powder diffraction laboratories. 

It must however be pointed out that a sound experimental definition of a phase diagram can be obtained from the results of a number of concerted investigations such as thermal analysis, thermodynamic analysis, micrographic examination and phase analysis and identification by means of techniques such as X-ray diffraction measurements, microprobe analysis, etc. 

The success of the gas phase electron diffraction analysis of cis-and /ra 5-decalin (123) is another example of the use of MM calculations as an auxiliary technique. Minimum energy conformations and vibrational ampUtudes were calculated by both the Lifson and Boyd force fields (30,31) and were used as the starting values for refinement of the geometrical and vibrational parameters for the least-squares analysis. The results revealed no appreciable strain in cj5-decalin (123) other than that expected from gauche interactions. 

When all the phases present were identified, we can quantify their volume fraction in the analyzed volume similarly to the way the Rietveld-method is used for phase analysis in XRD. A whole profile fitting is used in ProcessDifraction, modeling background and peak-shapes, and fitting the shape parameters, thermal parameters and volume fractions. Since the kinematic approximation is used for calculating the electron diffraction intensities, the grain size of both phases should be below 10 nm (as a rule of... 

Figure 3.32 shows XRD patterns of (MgH -i-LiAlH ) composites after DSC testing up to 500°C. The primary phases present are Mg and Al. Peaks of MgO and (LiOH) HjO arise from the exposure of Mg and Li (or possibly even some retained LiH) to the environment during XRD tests. Apparently, XRD phase analysis indicates that a nearly full decomposition of original MgH and LiAlH hydride phases has occurred to the elements during a DSC experiment. In addition, no diffraction peaks of any intermetallic compound are observed in those XRD patterns. That means that no intermetallic compound was formed upon thermal decomposition of composites in DSC. Therefore, the mechanism of destabilization through the formation of an intermediate intermetallic phases proposed by Vajo et al. [196-198] and discussed in the beginning of this section seems to be ruled out of hand. 

Singh, A.K. Ericsson,T. Haggstrom, L. (1985) Mossbauer and X-ray diffraction phase analysis of rusts from atmospheric test sites with different environments in Sweden. Corrosion Sd. 25 931-945... 

Tetrafluoro-1,3,2-dithiazoldine (7) has an envelope conformation in the gas phase (electron diffraction study) and in the crystal (x-ray structural analysis) <93JPC9625). The S atom is located in the flap in the first case S and N play the part alternatively in the second case, both conformational varieties comprising the unit cell while being interconnected by N H—N bonds. A quantum chemical calculation was made to rationalize these structural features (Section 4.12.2). 

Phase analysis and texture of the metal particles. Over the whole composition range, whatever the particle diameter, a face-centered cubic (fee) phase is always observed (Fig. 9.2. J 3) by x-ray diffraction (XRD) either as a single phase (Ni and CovNi) v with x < 0.35) or beside a hexagonal close-packed (hep) phase with broad lines (Co and Co,Ni (with x 2 0.35). The lattice parameter of the fee phase shows... 

An ongoing study of sulfur materials taken from an Icelandic Norse-trading site context (55) has used this combination of simultaneous co-incident X-ray micro-fluorescence and micro-diffraction analyses. The compositional data from the fluorescence results are used to constrain the multi-phase analysis of the diffraction data. This approach reduces the requirement for accuracy in the... 

Peplinski B, Schultze D, Wenzel J (2001) Interlaboratory comparison (round robin) on the application of the Rietveld method to quantitative phase analysis by X-ray and neutron diffraction. In Delhez R, Mittemeijer EJ (eds) Proc 7th European powder diffraction conference (EPDIC-7), Barcelona, Spain, 20th 23rd May 2000, Trans Tech Publications Ltd, Switzerland, p 124... 

Table 1 Structural data of five-membered heterocycles a (X = N), c, g (X= N) derived from X-ray structure analysis and gas-phase electron diffraction...

The tridentate mode of attachment is also rather common. The first structural report of this arrangement appeared in 1967, when the X-ray analysis of Zr(BH4)4 (Fig. 19) was described by Bird and Churchill99). However, the twelve bridging H atoms could not be located in that study. The correctness of the tridentate-bridged model was later confirmed by two independent gas-phase electron diffraction investigations 10°), which came up with measurements of Zr-H = 2.21 (4) A, B—H =... 

A simple example of the use of XRD for quantitative phase analysis is as follows the phase composition of a perovskite was determined using the obtained XRD diffraction pattern. The x-ray diffractograms were obtained in a Siemens D5000 x-ray diffractometer, in a vertical setup 0-20 geometry in the range 15° < 20 < 75°, with a Cu Ka radiation source, Ni filter, and graphite monochromator [32],... 

The compounds in Table 2 have been structurally analyzed by gas-phase electron diffraction or by X-ray crystal structure analysis and confirm the calculated effects of the substituents85,87,88. 

Produced by the EW technique CNM were subjected to investigation using XRD analysis, electron microscopy, and mass-spectrometer analysis. The typical XRD patterns for the exploded materials in different conditions are shown in Fig. 1 and Fig. 2. It is immediately obvious that there is a presence of additional diffraction peaks at small angle values besides those typical for common graphite. This fact clearly demonstrates the appearance of new structural compositions in the synthesis products. A phase analysis performed shows that these diffraction peaks correspond to those for carbonic spatial materials with the fullerene-like structure of the C60-C70 types. 

X-ray diffraction patterns of three obtained samples are plotted in Fig. 2. Their phase analysis showed follows. The pattern of pure catalyst sample (Fig. 2a) contains the structural peaks of magnesium oxide MgO, and also the weak, strongly widened peaks which correspond to MgFe204 Calculated MgO particles... 

The common copper wavelength is a good compromise between the loss of intensity by absorption from the gas or liquid environment and the precision of the determination of the diffraction pattern that is attainable. The use of hard radiation (e.g., Mo, W, Ag) is advantageous only in limited cases as it helps enormously in the penetration of the X-rays, but it severely limits the resolution of the information essential to phase analysis. 

For floppy systems, such as many metal halide molecules, the rg/re differences may be even much greater than those listed in Table 3. Alkaline earth metal, zinc, and transition metal dihalides, for example, have been extensively investigated by gas-phase electron diffraction (see e.g., [33-36]). The structure determinations have involved a joint electron diffraction/vibrational spectroscopic analysis (cf. [37]). Depending on the model potential used, and among them on the manner in which anharmonic effects are taken into account, even the r distances are rather different. This is illustrated by the data of Table 4. The re distances obtained from experimental data applying various model potentials [32] have the following... 

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