Identification of crystalline

Identification of crystalline phases determination of strain, and crystallite orientation and size accurate determination of atomic arrangements... 

Raman spectroscopy is a very convenient technique for the identification of crystalline or molecular phases, for obtaining structural information on noncrystalline solids, for identifying molecular species in aqueous solutions, and for characterizing solid—liquid interfaces. Backscattering geometries, especially with microfocus instruments, allow films, coatings, and surfaces to be easily measured. Ambient atmospheres can be used and no special sample preparation is needed. 

Crystals produce different diffraction patterns when subjected to bombardment of monochromatic X-ray sources and thereby provide unequivocal identification of crystalline materials. 

Although its main use is still the identification of crystalline phases, X-ray diffraction is also the most used technique for the determination of the location of extraframework cations. XRD is well suited to perform structural characterisation of dehydrated zeolites since the framework is highly crystallised and the extraframework cations are often heavy elements. 

CA 41, 6105(1947) (X-ray diffraction patterns for the identification of crystalline constituents of explosives) (Includes GuPicr)... 

ASTM D 934-80 (reapproved 1994), Standard Practices for Identification of Crystalline Compounds in Water-Formed Deposits by X-Ray Diffraction, ASTM, Philadelphia, PA, 1994. 

ASTM D 5380-93, Standard Test Method for Identification of Crystalline Pigments and Extenders in Paint by X-ray Diffraction Analysis, ASTM, Philadelphia, PA, 1993. 

Crystals thus have a greater wealth and variety of measurable characteristics than liquids or gases. This circumstance can be turned to good account we can use these varied directional properties for the identification of crystalline substances. Since there are more characteristic magnitudes to determine, identification by physical methods is often mu h more cert tin for crystals than it is for liquids or gases. 

More sensitive space-based studies with Spitzer helped secure identification of crystalline silicate peaks in PAH-free spectra of Sun-like stars, resolving this problem (e.g. Sargent et al. 2006 Bouwman et al. 2008 Watson et al. 2009). These studies, however, could all but reinforce the lack of strong correlations with age,... 

Although x-ray diffraction has been used for many years in the identification of crystalline materials, its special application to the study of ceramic temper and paste minerals is relatively recent. Because many tem-... 

Porter, M. W. and Spiller, R. C. (1951). Crystals of the tetragonal, hexagonal, trigonal and orthorhombic systems. In The Barker index of crystals. A method for the identification of crystalline substances, Vol. 1, W. Heffer Sons, Cambridge. [14, 95] Porter, M. W. and Spiller, R. C. (1956). Crystals of monoclinic system. In The Barker index of crystals. A method for the identification of crystalline substances, Vol. 2, W. Heffer Sons, Cambridge. [14]... 

Campins H. and Ryan E. (1989) The identification of crystalline olivine in cometary silicates. Astrophys. J. 341, 1059-1066. 

There are two broad applications of X-rays in the characterization of materials (i) X-ray spectrometry and (ii) X-ray diffractometry. The former technique is used for chemical analysis and has found only limited use in the characterization of pharmaceuticals. On the other hand, X-ray diffractometry, by providing a means for the study of the structure of crystalline materials, is extensively used to characterize pharmaceutical solids. There are two principal applications of X-ray diffractometry. X-ray crystallography is concerned with the structure determination of crystalline phases. Single crystals are usually used for this purpose. On the other hand, in X-ray powder diffractometry, the sample is usually in the form of a powder. X-ray powder diffractometry is recognized as a powerful technique for the identification of crystalline phases. The technique can also be used for the quantitative analyses of solids. This article will be restricted to the principles and applications of X-ray powder diffractometry (XRD) in the characterization of pharmaceutical solids. 

The use of a cooling accessory permits XRD patterns to be obtained under subambient conditions. In pharmaceutical systems, the greatest utility of the technique is to monitor the crystallization of solutes in frozen solutions. Conventionally, differential scanning calorimetry has been the most popular technique for the characterization of frozen systems. However, as mentioned earlier, this technique has some drawbacks (i) It does not enable direct identification of crystalline solid phase(s). Moreover, it is difficult to draw any definitive conclusions about the degree of crystallinity, (ii) The interpretation of DSC curves is very difficult if there are overlapping thermal events. Low temperature XRD was found to be an excellent complement to differential thermal analysis in the characterization of water-glycine-sucrose ternary systems. " ... 

International Centre for Diffraction Data, (ICDD ) is a non-profit scientific organization dedicated to collecting, editing, publishing, and distributing powder diffraction data for the identification of crystalline materials. ICDD on the Web http //www.icdd.com/. 

Identification of crystalline substance and crystalline phases in a specimen is achieved by comparing the specimen diffraction spectrum with spectra of known crystalline substances. X-ray diffraction data from a known substance are recorded as a powder diffractionfile (PDF). Most PDFs are obtained with CuKa radiation. Standard diffraction data have been published by the International Centre for Diffraction Data (ICDD), and they are updated and expanded from time to time. For one crystalline substance, there may be more than one file. The most recently updated file is recommended for phase identification. The early PDFs may contain errors in data obtained experimentally. More recently published PDFs are either obtained by more accurate experimental measurements or by theoretical calculation. A specimen to be identified should be in a powder form for most accurate matching. When we need to identify the crystal structure of a specimen that cannot be prepared as powder, matches of peak positions and relative intensities might be less than perfect. In this case, other information about the specimen such as chemical composition should be used to make a judgment. 

The computer based identification of crystalline phases in powder diffraction patterns normally requires two separate components (a) a powder diffraction database containing reference information and (b) a search-match program that loads the diffractogram and accesses the database to attempt to match the diffraction data to known phases in the database. 

X-ray or electron diffraction allows Identification of crystalline species by the long-used Hannawalt-Dow-ASTM-JCPDS system(4). Small particles can be removed for analysis in a small rotating specimen X-ray powder camera, or by extraction replication and selected area diffraction in a Transmission Electron Microscope (5). For those specimens where a residue of reactant or corrosion product is too adherent, the material may be removed for analysis by micro-bulldozing (with a microhardness Indentor), micro-jack hammering (with a needle attached to a small piezoelectric crystal on a pencil-like rod), and micro-boring (with a precision controlled dental drill)(5). 

XRD is used for the identification of crystalline materials such as pigments, metal powders, organic materials and salts. Non-crystalline materials lacking a regular crystal lattice, such as glass, do not produce a clear pattern. 

There are some difficulties of the identification of crystalline phases for the samples after reduction, by using XRD data. Moreover, it is very important to know not only phase composition of crystalline part of the samples but also oxidation states of iron and cobalt. In view of these circumstances the investigations of EPR and XPS spectra of the samples before and after their reduction in H2 atmosphere were performed to detect main features of degradation. 

International Centre for Diffraction Data — Maintains and distributes the Powder Diffraction File (PDF), a file of over 500,000 X-ray powder diffraction patterns used for identification of crystalline materials. The ICDD also distributes the NIST Crystal Data file, which contains lattice parameters for over 235,000 inorganic, organic, metal, and mineral crystalline materials. Address 12 Campus Blvd., Newton Square, PA 19073-3273 [www.icdd.com]. 

X-ray diffraction also provides a convenient and practical means fur the qualitative identification of crystalline compounds. The X-ray powder diffractiott method is the only analytical method thtit is capable of... 

Crystalline materials, in which the atomic spacing is about the same magnitude as x-ray wavelengths, are capable of diffracting x-rays. This serves as the basis of x-ray diffraction analysis qualitative identification of crystalline materials is readily made from a measurement of the angles of diffraction. X-ray diffraction also serves as a means for isolating x-rays of a particular wavelength in an x-ray spectrometer. 

The automatic identification of crystallinity with stereoregularity should be avoided however, as they are not necessarily synonymous, and whereas highly stereoregular polymers tend to be crystalline, the existence of any polymer in a crystalline state does not automatically mean the sample is markedly stereoregular. 

For the identification of crystalline polymorphs, IR spectroscopy and X-ray diffraction are the most commonly used techniques, while a combination of DSC-TGA or DTA-TGA are useful for analysing solvates. 

X-ray Powdar Diffraction. X-ray powder diffraction (XRD) is a routine technique for the identification of crystalline phases present in a catalyst material (17), which routinely utilizes the comparing of an observed set of reflections from the catalyst sample with those of pure reference phases, or with a database. These XRD studies can now be carried out under in situ conditions on a working catalyst, in particular with the use of synchrotron radiation, which allows for the acquisition of data in real time (18). Time-resolved studies on the time scale... 

Most paints do not usually display as much diversity in chemistry, color, and layer structure as do automotive ones. Therefore, a wider variety of analytical instruments are often used to characterize them. Along with microscopy and IR spectroscopy, other methods frequently used are pyrolysis GC/MS and inorganic elemental analysis by X-ray spectroscopy in the SEM. X-ray diffraction is also of use in the identification of crystalline pigments and fillers. 

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