Diffractometry

The main book dealing with single crystal diffractometry is that of Arndt and Willis (1966). For a detailed treatment of angle settings for four-circle diffractometers the reader is referred to Hamilton (1974). For up-to-date details of area detector diffractometry see Howard, Nielsen and Xuong (1985) and Hamlin (1985). In this section we will describe the following related diffractometer configurations  

The purpose of the diffractometer goniostat is to bring a selected reflected beam into the detector aperture (see figure A1.6) or a number of reflected beams onto an area detector of limited aperture (i.e. an aperture which does not intercept all the available diffraction spots at one setting of the area detector. 

In this geometry (figure A1.6) the crystal is oriented specifically so as to bring the incident and reflected beam, for a given hk plane, into the equatorial plane. In this way the detector is moved to intercept the reflected beam by a single rotation movement about a vertical axis (the 20-axis). The value of 6 is given by Bragg s law as sin 1(rf /2). 

The x circle is a relatively bulky object whose thickness can stop the measurement of diffracted beams at high 6. Also, collision of the x circle with the collimator or X-ray tube housing has to be avoided. An alternative is the Kappa goniostat geometry. In the Kappa diffractometer (see figure A1.8) the Kappa axis is inclined at 50° to the tu-axis and can be rotated about the tu-axis the K-axis is an alternative to x therefore. The 

From Wycoff (1985) p. 334 and with courtesy of Enraf-Nonius Ltd. 

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R. Jenkins and R. L. Snyder, Introduction to X-ray Powder Diffractometry, John Wiley Sons, Inc., New York, 1996. 

The structure of PP-g-polystyrene was studied by wide and narrow angle x-ray diffractometry. The polystyrene component formed discrete amorphous structures, which were identified after chloromethylation [143]. Structure of Rayon-Styrene graft copolymer was characterized by IR, wide angle x-ray, and SEM, grafting occurred mainly in the amorphous regions of rayon [1441. 

Crystalline material will diffract a beam of X-rays, and X-ray powder diffractometry can be used to identify components of mixtures. These X-ray procedures are examples of non-destructive methods of analysis. 

Person, A., Bocherens, H., Saliege, J.-F, Paris, F., Zeitoun, V. and Gerard, M. 1995 Early diagenetic evolution of bone phosphate an x-ray diffractometry analysis. Journal of Archaeological Science 22. 211-221. 

Vol. 138. Introduction to X-Ray Powder Diffractometry. By Ron Jenkins and Robert L. Snyder... 

Several methods based on the utilization of x-rays are nsed to study LB fihn structure. Diffractometry and reflectometry are the nsnal ones. Diffractometry is nsed mainly when well-ordered periodic strnctnre is under the investigation and several Bragg reflections are in the x-ray pattern. The position of these reflections is determined by the Bragg eqnation ... 

Suhtnicion nickel powders luive been synthesized successfully from aqueous NiCh at various tempmatuTKi and times with ethanol-water solvent by using the conventional and ultrasonic chemical reduction method. The reductive condition was prepared by flie dissolution of hydrazine hydrate into basic solution. The samples synthesized in various conditions weae claractsiz by the m ins of an X-ray diffractometry (XRD), a scanning electron microscopy (SEM), a thermo-gravimetry (TG) and an X-ray photoelectron spectroscopy (XPS). It was found that the samples obtained by the ultrasonic method were more smoothly spherical in shape, smaller in size and narrower in particle size distribution, compared to the conventional one. 

Bulk characterization of calcined precursors and reduced catalysts was carried out by X-ray diffractometry using Cu K radiation. Reduced catalysts were first passivated by exposure to N2O as described above. Line-broadening analysis was carried out on the Fe(llO) reflection to obtain the iron particle size. Overlap with the MgO(200) reflection limited its usefulness to the more highly-loaded catalysts. 

In the cements of this type a number of phases are known to be present. For example, in the zinc oxychloride cement two discrete phases, corresponding to the composition ZnO. ZnCl. H O in the ratios 4 1 5 and 1 1 2 respectively, are known to occur (Sorrell, 1977). Similarly, in the magnesium oxychloride cement, phases corresponding to Mg(OH)a. MgClj. HjO in the ratios 5 1 8 and 3 1 8 have been shown to exist and have been studied by X-ray diffractometry (Sorrell Armstrong, 1976). 

Detailed TEM investigations as well as small-angle X-ray diffractometry show the clusters organized via their edges, as is indicated in Figure 17b. 

Overviews [321] and monographs [322,323] dealing with X-ray powder diffractometry are available. 

Test measurements were performed on Cuprite, Cu20, for various reasons it has a well-known structure (cubic, space group Pn3m, a = 4.2696, Z = 2) and has been examined by conventional X-ray single crystal diffractometry [5, 6] and by synchrotron radiation in the Tow energy regime [7]. As a consequence of the... 

Brown, PJ. and I orsylh, J.B. (1964) The determination of beam polarisation and flipping efficiency in polarised neutron diffractometry, Brit. J. Appl. Phys., 14, 1529-1532. 

The boron nitride obtained in this study was characterized by infrared spectroscopy, powder x-ray diffractometry and transmission electron microscopy. Trace elemental analyses were also performed by energy dispersive x-ray analysis and carbon arc emission spectroscopy. Representative spectra are displayed in Figures 2-4. 

In this paper we present results from independent studies on the stage 2 to stage 1 transition area that show some unexpected features (anomalies). The results are obtained by electrochemical impedance spectroscopy (EIS), entropy measurements (AS(x)) and in situ x-ray diffractometry (XRD). The aim is to understand the mechanism of stage transition dealing with the observed anomalies. 

X-ray powder patterns can be obtained using either a camera or a powder diffractometer. Currently, diffractometers find widespread use in the analysis of pharmaceutical solids. The technique is usually nondestructive in nature. The theory and operation of powder diffractometers is outside the purview of this chapter, but these topics have received excellent coverage elsewhere [1,2]. Instead, the discussion will be restricted to the applications of x-ray powder diffractometry (XPD) in the analysis of pharmaceutical solids. The U.S. Pharmacopeia (USP) provides a brief but comprehensive introduction to x-ray diffractometry [3],... 

X-ray powder diffractometry is widely used for the identification of solid phases. The x-ray powder pattern of every crystalline form of a compound is unique, making this technique particularly suited for the identification of different polymorphic forms of a compound. The technique can also be used to identify the solvated and the unsolvated (anhydrous) forms of a compound, provided the... 

II, and III), two were monohydrates (termed a-monohydrate and /3-monohydrate) and one was a ferf-butylamine disolvate. The differences in the powder patterns of the phases were readily evident (Table 1). This study demonstrates the unique ability of x-ray diffractometry for the identification of (1) anhydrous compound existing in both crystalline and amorphous states, (2) different polymorphic forms of the anhydrate, (3) the existence of solvates where the solvent of crystallization is water (hydrate) or an organic solvent (in this case, /m-butylamine), and (4) polymorphism in the hydrate. 

Depending on the water vapor pressure, cephalexin can exist as an anhydrate (C16Hi7N304S), a monohydrate (C16H17N304S H20) or a dihydrate (C16H17N304S 2H20) at 25°C [10]. The monohydrate and the dihydrate were characterized by the pronounced differences in their powder x-ray diffraction patterns. Thus, x-ray diffractometry can be used to characterize several hydrated states of a compound. 

X-ray powder diffractometry is widely used to determine the degree of crystallinity of pharmaceuticals. X-ray diffractometric methods were originally developed for determining the degree of crystallinity of polymers. Many polymers exhibit properties associated with both crystalline (e.g., evolution of latent heat on cooling from the melt) and noncrystalline (e.g., diffuse x-ray pattern) materials. This behavior can be explained by the two-state model, according to which polymeric materials consist of small but perfect crystalline regions (crystallites) that are embedded within a continuous matrix [25]. The x-ray methods implicitly assume the two-state model of crystallinity. 

X-ray powder diffractometry offers a unique advantage in the quantitative analyses of mixtures consisting of the anhydrous and hydrated forms of a compound. In order to appreciate this, it is necessary to understand the interaction of water with solids. There are four possible states of water in solids [48] (1) adsorbed on the solid surface, (2) absorbed or dissolved in the solid, (3) associated... 

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