Phase Composition X-ray Diffraction

In general, the diffraction technique is based on the fact that if a thin beam of electromagnetic radiation of an appropriately small wavelength (X-rays, electrons, y-rays) is incident to a crystal lattice, the beam is scattered ( diffracted ) in specific directions and angles depending on the distances of atoms in the scattering crystal lattice, thus forming a diffraction pattern . 

If the dimensions of the scattering particles fall below about 500 nm the interference pattern shows line broadening. Hence, the full width at half maximum (F WHM) value, /) is dependent on particle size D. This relation has been expressed by the Scherrer equation (Scherrer, 1918) as 

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Phase composition X-ray diffraction Philips diffractometer with Cu fine-focus tube... 

The number of course programmes is directly proportional to the demand made by trade and industry. Many factors have been of influence on this instruction, among others the Gibbs phase rule (see the chapter on Phase rule), X-ray diffraction to clarify the structure of solids and the development of synthetic barium titanate and other ceramic materials whose properties could be influenced by controlling composition and process conditions. As early as 1900 it became clear that the study of ceramics required much knowledge of other subjects, as appears from the Ohio State University s course programme of that year. 

Gas composition CO Hs Total time, hours Atom ratios Phases from x-ray diffraction ... 

Six compositions of TiCrV ternary alloys were synthesized as is shown in Table 1. After the heat treatment, all of the alloys were found to be BCC single phase by X-ray diffraction analysis. The lattice constants of them are shown in Table 1. PC isotherms at 298K of the alloys are shown in Fig.2. Dissociation pressure of the alloy increases with the decrease of the lattice size. This trend is consistent with a general one often observed for other metal hydrides. However, the effective hydrogen capacity decreases with the increase of the lattice constant. As a result, in TiCrV ternary alloys, both high effective hydrogen capacity and high dissociation pressure are not satisfied simultaneously. 

The previous discussion has focused primarily on determining the number of phases present. The specific nature of these phases other than crystallographic structure has not been considered. Although establishing the number of phases by X-ray diffraction is also closely connected with their identification and bonding, mere determination of the pattern characteristic of a particular structure, such as spinel or perovskite, does not establish its chemical composition. The existence of many solid solutions gives rise to very similar patterns derived from totally different chemical compositions. 

The distribution of hydrogen atoms among the available interstitial sites of the metal host structure is of both fundamental and practical interest with regards to the stabilities and compositions of the various hydride phases. Although x-ray diffraction is commonly used to determine hydride structures, this technique cannot identify the hydrogen site occupancy except under extremely favorable conditions (which are quite rare). Powder neutron diffraction is the conventional method to locate deuterium atoms in metal deuterlde structures. Because the Incoherent... 

We have already seen the direct measurement of the composition of a solid phase by X-ray diffraction. This measiuement can be used to quantify the disappearance or the appearance of sohd phases, that is, the fractional extent and the rates relative to A or B (see sections 11.2.4 and 11.2.5). 

Nylon-6. Nylon-6—clay nanometer composites using montmorillonite clay intercalated with 12-aminolauric acid have been produced (37,38). When mixed with S-caprolactam and polymerized at 100°C for 30 min, a nylon clay—hybrid (NCH) was produced. Transmission electron microscopy (tern) and x-ray diffraction of the NCH confirm both the intercalation and molecular level of mixing between the two phases. The benefits of such materials over ordinary nylon-6 or nonmolecularly mixed, clay-reinforced nylon-6 include increased heat distortion temperature, elastic modulus, tensile strength, and dynamic elastic modulus throughout the —150 to 250°C temperature range. 

X-ray Diffraction (XRD) is a powerful technique used to uniquely identify the crystalline phases present in materials and to measure the structural properties (strain state, grain size, epitaxy, phase composition, preferred orientation, and defect structure) of these phases. XRD is also used to determine the thickness of thin films and multilayers, and atomic arrangements in amorphous materials (including polymers) and at inter ces. 

Solid state NMR is a relatively recent spectroscopic technique that can be used to uniquely identify and quantitate crystalline phases in bulk materials and at surfaces and interfaces. While NMR resembles X-ray diffraction in this capacity, it has the additional advantage of being element-selective and inherently quantitative. Since the signal observed is a direct reflection of the local environment of the element under smdy, NMR can also provide structural insights on a molecularlevel. Thus, information about coordination numbers, local symmetry, and internuclear bond distances is readily available. This feature is particularly usefrd in the structural analysis of highly disordered, amorphous, and compositionally complex systems, where diffraction techniques and other spectroscopies (IR, Raman, EXAFS) often fail. 

The phase composition of products obtained from the thermal treatment of LiNbOF4 and NaNbOF4 was investigated using X-ray diffraction and vibration spectroscopy, as reported in [379]. Compounds with the following structures were found M2NbOF5, MNb02F2 and MNbC>3, where M = Li or Na. 

A first study of the Li-Ag system showed only two phases of fixed composition however, a much more complex system of phases was found later using thermal, micrographic and x-ray diffraction methods. 

The phase diagram of the Li-Au system reveals a great deal of complexity, with separate intermetallic phases being formed based on thermal analysis supported by x-ray diffraction at specific compositions. Annealing, sometimes over long time periods, has been undertaken in some cases. 

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