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The creep behavior of a TiCxN1-x-Co-Mo2C cermet has been investigated at temperatures between 1100-1200ºC in an inert atmosphere to assess the one step mechanically induced self-sustaining reaction synthesis and pressureless sintering process, and the influence of the Mo2C additive in the high temperature mechanical properties of this cermet. The samples deform plastically at the chosen temperatures, and values of the stress exponent (n=1.70.6) and activation energy (Q= 4.30.5 eV) have been estimated from uniaxial compression tests. No significant grain growth has been detected after deformation. The reproducibility of the creep tests compared to other compositions indicates that the Mo2C addition contributes to increase notably the resistance to high temperature oxidation of the samples, so that the plastic behavior is not affected by oxidation when deformation experiments are performed in an inert atmosphere.

A nanometric BaTiO3powder sample with a medium crystallite sizeD= 157 Å has been prepared from the thermal decomposition of BaTiO(C2O4) · 4.5H2O by constant rate thermal analysis (CRTA). Rietveld analysis of the XRD pattern shows that this BaTiO3sample presents a crystalline cubic structure. The evolution of the texture, the structure, and the ferroelectric → paraelectric enthalphy transition as a function of the annealing temperature of BaTiO3has been followed from XRD and DSC experiments. A relationship has been found between the reaction enthalphy of the tetragonal → cubic polymorphic transition and the tetragonality of the sample, as measured from thec/aratio. Therefore, the calorimetric data can be used for predicting the structure of this material. The Curie temperature seems to independent of the crystallite sizeD, provided that it is higher than about 400 Å.

This work deals with the evolution of a mechanical mixture of Fe2(MoO4)3and α-Sb2O4(prepared separately) during calcination in air at 500°C over a period of six days. The samples were studied by X-ray diffraction, X-ray photoelectron spectroscopy, BET surface area, CTEM, analytical electron microscopy and selected area electron diffraction. A reaction occurs between the two phases, leading to a mixture of Fe2(MoO4)3, Sb2O4, FeSbO4and MoO3with a significant increase of the surface area. Ta king into account previous results, the present work suggests that the ability of α-Sb2O4to produce oxygen spillover facilitates the oxidation of Sb3+to Sb5+allowing the solid state transformation to FeSbO4to take place.

AbstractBarium titanyl oxalate tetrahydrate, Ba(TiO)(C2O4)2.4H2O, has been investigated by means of X-ray powder diffraction. Precise powder diffraction data were obtained by a conventional diffractometer with strictly monochromatic radiation. Unit cell dimensions were determined by an indexing program based on the variation of parameters by successive dichotomies. A monoclinic cell was found, a=14.044(2)?, b=13.812(2)?, c=13.382(2)?, ?=91.48(1); V=2594.9?3, which is characterized by the figures of merit M20=46.5 and F30=107(0.0056, 50). The complete powder pattern was reviewed by means of the program NBS*AIDS83 and the 81 first lines were indexed. Structural imperfections were not detected from the diffraction line widths, which are comparable to the instrumental resolution.