Diffraction methods X-ray

According to Bragg s law, the difference in path length between X-ray beams scattered from two adjacent lattice planes of a crystal will be a multiple of the X-ray wavelength. A  

Annealing at a higher temperature can dramatically increase the amount of crystallinity in polymers, including nanofibers (Inai et al. 2005a). On annealing PDLA noncrystaUine PEO nanofibers electrospun from CH2CI2/DMF (1 5), at a temperature of 55°C for 24 h, two characteristic crystalline 

Besides the use of X-ray absorption for the elucidation of adsorbates and adsorbate-surface interactions (see Chap. 5), X-ray diffraction is a tool that is useful particularly for the determination of structural data at a very high level of precision provided the presence of a minimum level of structuring. The advent of synchrotron radiation that provides an intense source of electromagnetic radiation in the range of X-rays has greatly stimulated the application of X-ray diffraction methods. A broad 

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The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

The formation of such materials may be monitored by several techniques. One of the most useful methods is and C-nmr spectroscopy where stable complexes in solution may give rise to characteristic shifts of signals relative to the uncomplexed species (43). Solution nmr spectroscopy has also been used to detect the presence of soHd inclusion compound (after dissolution) and to determine composition (host guest ratio) of the material. Infrared spectroscopy (126) and combustion analysis are further methods to study inclusion formation. For general screening purposes of soHd inclusion stmctures, the x-ray powder diffraction method is suitable (123). However, if detailed stmctures are requited, the single crystal x-ray diffraction method (127) has to be used. 

The mineralogical, structural, physical, and thermodynamic properties of the various crystalline alumiaa hydrates are Hsted ia Tables 1, 2, and 3, respectively. X-ray diffraction methods are commonly used to differentiate between materials. Density, refractive iadex, tga, and dta measurements may also be used. 

X-ray studies indicate that the vinyl chloride polymer as normally prepared in commercial processes is substantially amorphous although some small amount of crystallinity (about 5% as measured by X-ray diffraction methods) is present. It has been reported by Fuller d in 1940 and Natta and Carradini in 1956 that examination of the crystalline zones indicates a repeat distance of 5.1 A which is consistent with a syndiotactic (i.e. alternating) structure. Later studies using NMR techniques indicate that conventional PVC is about 55% syndiotactic and the rest largely atactic in structure. 

Crystallinity of 9 in solid dispersions with polyethylene glycol (PEG 400) and urea was measured by IR and X-ray diffraction methods (00JPS79). 

The X-ray diffraction method is applicable to solids and provides such detailed views of crystal geometry as those shown for sodium chloride solid in Figure 5-10, p. 81. 

As has been shown by the X-ray diffraction method the parent metals (i.e. Pd or Ni), the a-phase, and /3-phase all have the same type of crystal lattice, namely face centered cubic of the NaCl type. However, the /9-phase exhibits a significant expansion of the lattice in comparison with the metal itself. Extensive X-ray structural studies of the Pd-H system have been carried out by Owen and Williams (14), and on the Ni-H system by Janko (8), Majchrzak (15), and Janko and Pielaszek (16). The relevant details arc to be found in the references cited. It should be emphasized here, however, that at moderate temperatures palladium and nickel hydrides have lattices of the NaCl type with parameters respectively 3.6% and 6% larger than those of the parent metals. Within the limits of the solid solution the metal lattice expands also with increased hydrogen concentration, but the lattice parameter does not depart significantly from that of the pure metal (for palladium at least up to about 100°C). 

A rough estimation of the critical temperatures of coexistence of the (a + /3)-phases in two Ni-Cu-H systems containing 59 at. % and 63 at. % nickel was made by Majchrzak (26). Both phases, a and /8, were identified by the X-ray diffraction method. The presence of the /3-phase was not seen above 47°C for the alloy with 63 at. % Ni and above 20°C for the alloy with 59 at.% Ni. Though this method gives only approximative numerical values, one can make conclusions of a general character, e.g. that the critical temperature of the Ni-Cu-H system increases sharply with a growing content of nickel in the Ni-Cu alloy, and that one might expect the critical temperature of the coexistence of the a- and /8-phases... 

The direct proof of hydride formation in situ in a reaction vessel is in principle possible. One can follow changes of resistance (of a film, a wire, etc.) or of magnetic susceptibility of a catalyst. Hydride identification by means of the X-ray diffraction method requires a catalyst sample to be taken out from a reaction vessel, and eventually frozen in order to avoid a rapid decomposition of the hydride under ambient conditions (67). 

Zirconocene dichloride 121 derived from (l-phenylethyl)cyclopentadienyl ligand is formed as a mixture of diastereomers from which the racemic form can be isolated by fractional crystallization. This complex was studied by X-ray diffraction methods and revealed a virtually chiral C2-symmetrical conformation in which the chiral ring-substituents are arranged in a synclinal position relative to the five-membered ring. It was proposed that this conformation is preserved in solution. Using 121 as catalyst the influence of double stereodifferentiation during isospecific polymerization of propylene (Eq. 32) was demonstrated for the first time [142],... 

A good deal was learned about plutonium metal, including the determination of its density by both capillary displacement and x-ray diffraction methods, its melting point and vapor pressure. 

XAFS (EXAFS and XANES) methods X-ray diffraction method Biological investigations Flydrolysis of [OrganotinllV)]" Cations Interactions of [OrganotinllV)]" with Biological Molecules... 

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 Ca-Cu system has been reexamined using thermal analysis and x-ray diffraction methods an independent study of the CaCuj-Cu section has also been completed. The resultant phase diagram, although similar to that in ref. 3 at the Cu-rich end, differs markedly for Ca-rich alloys. Supporting evidence for the modifications has been obtained from the Ca-Mg-Cu ternaiy system. Three intermediate compounds are formed in the system CaCuj (950 C) melts congruently, whereas CajCu (488 C) and CaCu (567°C) are formed in peritectic reactions. Single-crystal x-ray diffraction studies verify the stoichiometry of CajCu and examine the polymorphism of CaCu. ... 

Molecular Structures of Phosphazenes Determined by X-Ray Diffraction Methods... 

As a result of compelling three-dimensional models and remarkably high levels of precision, it is often assumed that structural elucidation by single crystal X-ray diffraction is the ultimate structural proof. Spatial information in the form of several thousands of X-ray reflection intensities are used to solve the position of a few dozen atoms so that the solution of a structure by X-ray diffraction methods is highly overdetermined, with a statistically significant precision up to a few picometers. With precise atomic positions, structural parameters in the form of bond distances, bond... 

Oxidation of aknadinine with silver nitrate gave a pair of dimeric compounds, one of which was identical to the naturally occurring bisaknadinine (8) and the other assumed to be a stereoisomer arising from an axial chirality concerning the mode of biphenyl linkage (21,22). It was impossible, however, to determine from ORD and CD measurements whether the isomer is of natural bisaknadinine (8). Therefore, unambiguous proof of the stereochemistry was achieved, using the X-ray diffraction method, and the... 

Turner, W. E. S. and H. P. Rooksby (1961), Further historical studies based on X-ray diffraction methods on the reagents employed in making opal and opaque glass, Jahrbuch des Romisch-Germanischen Zentralmuseums (Mainz) 8, 1-6. 

X-Ray Diffraction Methods in Polymer Science", Alexander, Leroy E. Wiley-Interscience, New York, 1969. 

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