Search

A new route for the preparation of electron-loaded mayenites using vanadium foils as deoxygenating agent is reported. The findings reveal that mayenite subjected to prolonged heating at 1373 K decompose to give C5A3 and C3A to yield a mayenite with higher amount of free electrons in it.

Research has been conducted on the nitrilotris(methylenephosphonic acid) complexes. The synthesis of these complexes has been carried out via the reaction of nitrilotris(methylenephosphonic acid) with the divalent transition metal and the possibility of forming open structures with H-bonding has been investigated and is discussed.

Layered materials of six aluminum phenylphosphonates always exhibit a strong diffraction peak at ~15 angstroms, similar to an organic bilayer of phenyl groups between an inorganic layer formed by the metal-phosphonate bonding. This was revealed by single-crystal or powder diffraction data of the crystal structures of this family of compounds. Thermal analysis, infrared spectroscopy, and nuclear magnetic resonance spectroscopy were also used to examine the structure and thermal stability of these metal phosphonates.

Research was conducted to examine the polymorphism and phase transition in nanotubular uranyl phenylphosphonate, (UO2)3(HO3PC6H5)2(O3PC6H5)2*H2O. Two very related microporous uranyl phosphonates, delta- and epsilon-(UO2)3(HO3PC6H5)2(O3PC6H5)2*H2O, were studied. X-ray powder diffraction data, powder thermodiffractometry and P MAS NMR techniques were used for the characterization of both polymorphs and the phase transition between them.

A simple new solid, MnAsO4, in a sample containing 20% Mn2As2O7, was examined using a low-temperature time-of-flight neutron powder diffraction method. MnAsO4 orders magnetically at 14.5(5)K and the unusual antiferromagnetic structure below this temperature was determined. Results show that only half of the Mn3+ spins are ordered and the remaining idle spins show some spin-glass behavior evidenced by susceptibility measurements.

The crystal structure of the complex tubular uranyl phosphonate, (UO2)(HO3PC6H5)2(O3PC6H5)2.H20, has been determined ab initio by X-ray powder diffraction techniques. The structure has been shown to consist of phosphonate oxygens bridging the metal ions to form one-dimensional channels, which are held together by stacking forces of the phenyl groups arranged on the outer periphery of the channels.

Three forms of bismuth phosphate are synthesized and characterized by infrared spectroscopy, powder X-ray diffraction and thermal analysis. Two phases, having monoclinic and trigonal systems, are obtained at room temperature. The third type is obtained by heating monoclinic type BiPo4 above 600 degrees Celsius. Rietveld method is used to analyze the crystal structure and the similarities between the three forms.

MnXO4.nH2O (X = P, As; n = 1.0-1.5) phases were characterized by electron microscopy, density measurements and X-ray powder diffraction. The results suggest that samples with n greater than 1 are intergrowths of crystalline MnXO4.H2O and amorphous MnXO4.4H2O. This compound adopts a monoclinically-distorted CuSO4 type structure in which chains of edge-sharing MnO6 octahedra displaying cooperative (4 + 2) and (2 + 2 + 2) Jahn-Teller distortions are linked through distorted AsO4 groups.

The structure of vanadyl dihydrogen arsenate VO(H2AsO4)2 was refined in space group 14/mcm using laboratory x-ray powder diffraction data by the Rietveld method. Thus, R(sub wp) = 10.1% and R(sub F) = 5.5%. Meanwhile, the structure of the lithium derivative Li4VO(As)4-2 has a P4/ncc symmetry because of the partial ordering between vanadyl chains. Refinement results in R(sub wp) = 13.8% and R(sub F) = 9.3%. Lithium ions are positioned at irregular five-coordinate sites between vanadyl arsenate layers.

Single-crystal low-temperature synchrotron X-ray diffraction is used for providing an accurate structural study for three members of the series [[Ca.sub.12][Al.sub.14][O.sub.32]][O.sub.1-[delta]][e.sub.2[delta]] ([delta] = 0, 0.15, and 0.45). The studies have indicated that the final electron density map for [delta] = 0.45 black mayenite has shown electron density localized into the center of the cages, which is the first experimental proof of their electride nature.

Fabrication of portland cements commonly depends on X-ray fluorescence (XRF), which measures the elemental compositions. XRF is used to adjust the raw material proportions and to control the process conditions. However, to predict the mechanical strength of the resulting concrete, it is essential to know the phase composition which is, so far, indirectly inferred by the Bogue method. Here, we report a phase analysis of an industrial portland clinker containing six crystalline phases, [Ca.sub.3]Si[O.sub.5], [Ca.sub.2]Si[O.sub.4], [Ca.sub.4][Al.sub.2][Fe.sub.2][O.sub.10], [Ca.sup.3][Al.sup.2][O.sup.6], Na[K.sup.3][([SO.sup.4]).sup.2], and CaO, by Rietveld refinement of synchrotron X-ray powder diffraction data ([Lambda] = 0.442 377 [Angstrom]). Even the minor component, CaO 0.45(2)% was readily analyzed. We have also carried out a phase study of the same clinker with laboratory X-rays to characterize the changes in the detection limit and errors. Furthermore, by adding a suitable crystalline standard to the same clinker, we have determined the overall amorphous phase content. The procedure established for this state-of-the-art phase analysis shows the high precision that can be achieved by using penetrating X-rays, which is of interest not only in cement chemistry but in other industrially important multiphase systems such as slags, superalloys, or catalysts.

There are numerous studies in the management literature that analyze specific aspects of the implementation of information technology (IT) in organizations. Meanwhile, the global IT management area has emerged as a dynamic field of investigation of IT impact in a global environment. However, after reviewing the management/international business literature and the global IT literature, we detect the need to integrate the theoretical frameworks of both streams in order to advance in this field. As a result, we connect the areas of advance in IT general management with the main lines of research in global IT management. The synthesis of both fields allows us to suggest new areas of research that we discuss in the final section. [ABSTRACT FROM AUTHOR]