Diffraction Diffractometry

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. 

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. 

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]. 

X-ray powder diffractometry can be used to study solid state reactions, provided the powder pattern of the reactant is different from that of the reaction product. The anhydrous and hydrated states of many pharmaceutical compounds exhibit pronounced differences in their powder x-ray diffraction patterns. Such differences were demonstrated earlier in the case of fluprednisolone and carbamazepine. Based on such differences, the dehydration kinetics of theophylline monohydrate (CvHgN H20) and ampicillin trihydrate (Ci6H19N304S 3H2O) were studied [66]. On heating, theophylline monohydrate dehydrated to a crystalline anhydrous phase, while the ampicillin trihydrate formed an amorphous anhydrate. In case of theophylline, simultaneous quantification of both the monohydrate and the anhydrate was possible. It was concluded that the initial rate of this reaction was zero order. By carrying out the reaction at several... 

Another characteristic point is the special attention that in intermetallic science, as in several fields of chemistry, needs to be dedicated to the structural aspects and to the description of the phases. The structure of intermetallic alloys in their different states, liquid, amorphous (glassy), quasi-crystalline and fully, three-dimensionally (3D) periodic crystalline are closely related to the different properties shown by these substances. Two chapters are therefore dedicated to selected aspects of intermetallic structural chemistry. Particular attention is dedicated to the solid state, in which a very large variety of properties and structures can be found. Solid intermetallic phases, generally non-molecular by nature, are characterized by their 3D crystal (or quasicrystal) structure. A great many crystal structures (often complex or very complex) have been elucidated, and intermetallic crystallochemistry is a fundamental topic of reference. A great number of papers have been published containing results obtained by powder and single crystal X-ray diffractometry and by neutron and electron diffraction methods. A characteristic nomenclature and several symbols and representations have been developed for the description, classification and identification of these phases. 

Recent developments and prospects of X-ray powder diffraction methods. In the preceding paragraph a few comments have been made about diffractometry and its uses in the analysis of materials. However it is not possible to give here an account of this subject its principles and underlying theories, its experimental techniques and... 

Techniques used in the research examined In the period examined the most widely used technique was X-ray diffraction, even though neutron diffractometry has recently become popular. 

There are three methods of collecting high-resolution X-ray diffraction data diffractometry, photographically, and by electronic area detector. Each method has advantages and disadvantages for a particular crystalline protein, but for very accurate data acquisition beyond 2 A... 

Key words electron diffraction, precession method, electron diffractometry, structure determination... 

Electron diffractometry system with the combination of the precession technique can be very perspective experimental instrumentation for precise structural investigations. The technique can now be adapted in a commercial TEM (previously applied uniquely to electron diffraction cameras) taking advantage of the small beam size and can measure reflections in the ED pattern with same required precision for structure analysis. 

PbO is more stable in alkaline solutions. Anodic oxidation of Pb leads to the selective growth of /I-PbO, which transforms into a-PbO in the course of prolonged polarization, as supported by X-ray diffraction studies and photoelectrochemical experiments [172]. In the presence of sulfate ions, simultaneous formation of basic lead sulfate with PbO has been observed, until the formation of 4Pb0-PbS04. At higher potentials, the oxide film in sulfate ions solution has a strong (110) orientation with microporous structure. X-ray diffractometry and photocurrent measurements have confirmed the presence of... 

Diffractometry provides an excellent tool for examining structure so we turn now to low-energy electron diffraction to study the order at a specific face of a single crystal, with and without adsorbed molecules. For the remainder of the chapter, we focus attention on the faces of the metal crystals. There are several reasons for this choice ... 

In LEED a beam of low-energy electrons rather than x-rays is used to form the diffraction pattern, but otherwise many of the concepts, relationships, and vocabulary are based on x-ray diffraction (Van Hove and Tong 1979). Accordingly, our discussion of LEED includes a review of pertinent aspects of this topic. Since diffractometry can get quite involved, we tailor our review to those subjects most helpful in getting us started and leave more advanced concepts for further study. 

Chapters 9 and 10 of the second edition (dealing with physical adsorption at gas/ solid interfaces and microscopy, spectroscopy and diffractometry of metal surfaces, respectively) have been pared down and consolidated into one chapter (new Chapter 9, on adsorption on gas/solid interfaces). The outdated materials or materials extraneous to the main thrust of the book from the old Chapter 10 have been eliminated and only the discussion of low-energy electron diffraction (LEED) has been retained. 

This kind of diffractometry gives highly accurate intensity measurement but is slow in comparison with methods that record many reflections at once. In addition, the total irradiation time is long, so crystals may deteriorate and have to be replaced. While one reflection is being recorded, there are usually other unmeasured reflections present, so a considerable amount of diffracted radiation is wasted. Diffractometers can be teamed up with area detectors, as shown in Fig. 4.22, giving substantial increases in the efficiency of data collection. 

These examples illustrate how to obtain results about crystallinity and disorder for a better understanding of the relationships between structure and properties. The reader is, however, cautioned that crystallinity and disorder parameters determined by x-ray diffractometry are average values and that they should be carefully compared with local order measured by electron diffraction on ultra-thin cross sections of textile fibers (9) with differing crystallite sizes (10,11). 

The SiC-coated diamond particles can be characterized by X-ray powder diffractometry. The diffraction peak appears at 35.6° which is assigned as the /J-SiC (111) plane. 

A7.11 X-ray diffraction characterisation of GaN-based materials triple axis diffractometry... 

Refs. [i] West AR (1988) Basic solid state chemistry. Wiley New York, pp 323 [ii] Nazri GA, Pistoia G (eds) (2004) Lithium batteries Science and technology Kluwer, Boston, parts I-III [Hi] David WIF, Shank-land K, McCusker LB, Baerlocher C (eds) (2002) Structure determination from powder diffraction data. Oxford University Press, Oxford, pp 337 [iv] Jenkins R, Snyder RL (1996) Introduction to X-ray powder diffractometry. Wiley, New York, pp 403 [v] Baehtz C, Buhrmester T, Bramnik NN, Nikolowski K, Ehrenberg H (2005) Solid State Ionics 176 1647... 

We discuss the combined use of high-resolution electron microscopy, electron diffraction, optical diffractometry and computer graphics for investigating zeolitic structure. Particular attention is given to twinned faujasitic materials and to intergrowth structures in ZSM-5 and ZSM-11 catalysts. 

In this paper we shall describe how high resolution electron microscopy (HREM) can be used in conjunction with selected area electron diffraction (SAED) to probe the local structure of zeolitic solids (2, 5 8) which are often microcrystalline, multi-phasic or twinned. We shall also refer to the application of optical diffractometry (4, 9-11) as a supplemental procedure either for interpretation of electron micrographs, or for analogue diffraction studies of model systems. 

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