Powder mixtures diffraction pattern

Fig. 14.15 Comparative powder neutron diffraction pattern measured for Lio.6peP04 measured at 620 K (solid-solution) and at room temperature (two-phase mixture of LiFeP04 and FeP04) using the same diffractometer HERMES...

Additionally, Powder X-ray diffraction patterns for the same anthracene (1) + pyrene (2) system were also obtained. Figure 4 shows that the crystal structure of the eutectic mixture is similar to that of pyrene because peaks at 10.6, 11.6, 14.9, 16.3, 18.2, 23.3, 24.7 and 28.0 degree are all retained in the mixture diffraction pattern. This is consistent with the DSC result that implies that the AfusH of the eutectic is very close to that of pure pyrene, and indicates that the crystal structures of the eutectic mixture and pure pyrene are similar. Likewise, Figure 4 shows that the crystal structure of a mixture at Xi = 0.90 is comparable to that of pure anthracene. 

The dichlorodibenzo-p-dioxin component was isolated by passing a dioxane solution of the mixture through acetate ion exchange resin to remove phenolics. The eluted product was recrystallized from benzene. The x-ray powder diffraction pattern of the precipitate was identical with that of 2,7-dichlorodibenzo-p-dioxin. Analysis of the mother liquor by GLC showed a singular peak consistent with 2,7-dichlorodibenzo-p-dioxin. The mother liquor was cooled to 5°C and yielded transparent crystals. This material had an x-ray diffraction pattern congruent to a sample of 2,8-dichlorodibenzo-p-dioxin obtained from A. E. Pohland (FDA). The two patterns were quite distinct from each other 14, 15). 

Other hand, when an equimolar mixture of 2,5-DSP and l OEt is recrystallized from benzene, yellow crystals, comprising 2,5-DSP and l OEt in a molar ratio of 1 2, deposit. In the DSC curve of this crystal, a single endothermic peak is observed at 166°C, which is different from the melting point of either 2,5-DSP (223°C) or l OEt (156°C). Furthermore, the X-ray powder diffraction pattern of the crystal is quite different from those of the homocrystals 2,5-DSP and l OEt. Upon irradiation the cocrystal 2,5-DSP-l OEt affords a crystalline polymer (77i h = 1.0 dl g in trifluoroacetic acid). The nmr spectrum of the polymer coincides perfectly with that of a 1 2 mixture of poly-2,5-DSP and poly-1 OEt. In the dimer, only 2,5-DSP-dimer and l OEt-dimer are detected by hplc analysis, but the corresponding cross-dimer consisting of 2,5-DSP and l OEt is not detected at all (Hasegawa et al., 1993). These observations by nmr and hplc indicate that the photoproduct obtained from the cocrystal 2,5-DSP-l OEt is not a copolymer but a mixture of poly-2,5-DSP and poly-l OEt in the ratio 1 2. 

X-ray analysis of the various samples that were produced indicated that the system ZnO-ZnClj-HjO includes four crystalline phases, two of which, ZnO and ZnClj. l HjO, are essentially the starting materials. Sorrell also found the 4 1 5 phase, reported by Droit, with an identical X-ray powder diffraction pattern to that reported by Nowacki Silverman (1961, 1962), and a 1 1 2 phase. Since neither the 1 1 2 nor the 4 1 5 phase lost or gained weight on exposure to air at about 50% relative humidity and 22 °C and no changes developed in the X-ray diffraction pattern following this exposure, he concluded that the previously reported 1 1 1 phase cannot be formulated from mixtures of ZnO and aqueous ZnCl,. 

X-ray diffraction has been applied to certain AB cements. For example. Crisp et al. (1979), in a study of silicate mineral-poly(acrylic acid) cements, used the technique both to assess the purity of the powdered minerals employed and to monitor mineral decomposition in mixtures with poly(acrylic acid), in order to indicate whether or not cement formation had taken place. They employed Cu radiation passed through a nickel filter for most of the samples, a seven-hour exposure time was found to be adequate for the development of a discernible diffraction pattern. Samples were identified by reference to published powder diffraction data. 

In the bulk crystalline phases, large differences exist in the properties of the racemic mixture and the pure enantiomers. X-ray powder diffraction patterns showed that the racemic mixture was a true racemate, and the melting transition points and heats of fusion of the racemate were markedly different from those of the pure enantiomers [which were identical (Arnett and Thompson, 1981)]. 

The /3-polymorphic form of anhydrous carbamazepine is official in the USP [3], The USP stipulates that, The X-ray diffraction pattern conforms to that of USP Carbamazepine Reference Standard, similarly determined. No limits have been set in the USP for the other polymorphs of anhydrous carbamazepine. Although several polymorphic forms of anhydrous carbamazepine have been reported, only the a- and /3-forms have been extensively studied and characterized [49]. A comparison of the powder x-ray diffraction patterns of these two forms revealed that the 10.1 A line (peak at 8.80° 26) was unique to a-carbamazepine, and so this line was used for the analysis (Fig. 5). It was possible to detect a-carbamazepine in a mixture where the weight fraction of a-carbamazepine was 0.02 at a signal-to-noise ratio of 2. Much greater sensitivity of this technique has been achieved in other systems. While studying the polymorphism of l,2-dihydro-6-neopentyl-2-oxonicotinic acid, Chao and Vail [50] used x-ray diffractometry to quantify form I in mixtures of forms I and II. They estimated that form I levels as low as 0.5% w/w can be determined by this technique. Similarly the a-inosine content in a mixture consisting of a- and /3-inosine was achieved with a detection limit of 0.4% w/w for a-inosine [51]. 

A similar development in this direction is the synthesis of a mixed-phase material containing both micro- and mesopores (Ti-MMM-1) (223). This material was synthesized by the addition of organic templates for mesopores (cetyltrimethylammonium bromide, CTABr) and micropores (tetrapropylammo-nium bromide, TPABr) at staggered times and the variation of the temperature of a single reaction mixture. Ti-MMM-1 is more selective (for oxidation of cyclohexane and of n-octane) than either Ti-MCM-41 or TS-1. The powder X-ray diffraction pattern indicates that the material contains both MCM-41 and MFI structures. The mixed phase contains framework Ti species and more atomic order within its walls than Ti-doped MCM-41. 

The last method for producing standard patterns for phases not in the PDF is more involved. In many instances single crystals of unknown phases can be removed from reaction mixtures. If this is the case, a full three dimensional crystal structure analysis will yield the positions of all atoms in the structure. Once the crystal structure is known, it can be used to calculate the X-ray powder diffraction pattern for the phase. This powder diffraction information can then be used with confidence as a standard powder pattern. 

X-Ray powder diffraction patterns are catalogued in the JCPDS data file,7 and can be used to identify crystalline solids, either as pure phases or as mixtures. Again, both the positions and the relative intensities of the features are important in interpretation of powder diffraction patterns, although it should be borne in mind that diffraction peak heights in the readout from the photon counter are somewhat dependent on particle size. For example, a solid deposit accumulating in a heat exchanger can be quickly identified from its X-ray powder diffraction pattern, and its source or mechanism of formation may be deduced—for instance, is it a corrosion product (if so, what is it, and where does it come from) or a contaminant introduced with the feedwater ... 

Tables II and III are presented as an initial attempt to establish a broad correlation between crystallization and structure in terms of cation composition. The extensive assumptions and uncertainties involved are well recognized including acceptance of assignment of framework type based on similarity of x-ray powder diffraction patterns, exclusion of some polyhedral cages found in zeolite structures (62) f the relative concentrations of cations in mixtures, variables other than cation, and the possible presence of impurity cations not reported but derived from reagents or reaction vessels.

Both powders collected from the reactor wall and from the reactor bottom showed similar diffraction patterns (Fig. 5.) indicating the presence of spinel as the dominant phase (amount of sample C was negligible in these experiments). Composition of the spinel phase was estimated from the lattice parameters (a), assuming, that the increase of lattice parameter due to Zn incorporation is proportional to the Zn concentration. From these calculations the compositions of sample R and sample RB were Zno.7Fe2.3O4 and Zno.4Fe2.6O4, respectively. Consequently, some of the Zn content of the starting mixture could not build into the spinel structure and left the system through the exhaust in the form of very fine ZnO powder. 

Spreading of polycrystalline M0O3 in powder mixtures with y-ANOi and TiC>2 (anatase) was indicated by the disappearance of the X-ray diffraction pattern of M0O3 after thermal treatment, provided that the M0O3 content remained below a certain limit [8, 85, 86]. This limiting M0O3 content was determined as... 

Ruthenium Dioxide (by Pichler).190 A mixture of 1 g of ruthenium powder, 10 g of potassium hydroxide, and 1 g of potassium nitrate is fused in a silver (or a nickel) crucible. It is recommended that the potassium nitrate be added not simultaneously but in portion after portion. In 1-2 h the fusion is complete. After cooling, the mass is dissolved with water into a solution. The dark red solution of potassium ruthenate is heated to boiling, and methanol is added to this dropwise. Immediately after the first drop of methanol has been added, the reduction of the ruthenate to ruthenium dioxide takes place and the reduction is completed in a few minutes. After leaving the precipitate for 1-2 h, the precipitate is collected on a glass filter, washed 7 times with a dilute nitric acid solution and then 18 times with distilled water, and dried at 110°C for 24 h in a desiccator. Pichler s dioxide thus prepared does not show any distinct diffraction patterns corresponding to the oxide of ruthenium and is partly soluble into hot concentrated hydrochloric acid. These facts suggest that Pichler s dioxide is a mixture of the oxide and the hydroxide of ruthenium.191... 

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