The thermal decompositions of NH4VO3 and NH4VO3-TiO2 mixtures were investigated by mass-spectrometry and DTA. Three stages of decomposition were distinguished, in which the contribution of redox-type reactions increased successively. The bulk of the decomposition was independent of the nature of the atmosphere; only the third stage displayed a variation. In vacuo and in argon there was continuous reduction of the vanadium oxide system, but in air its reoxidation took place.
The Avrami model of solid-state reactions or transformations has frequently been presented and compared with other stochastic models. The equation often applied is shown to be merely a simplification of the full Avrami model equation (FAME). A convenient procedure for application of the FAME to the kinetics of solid-state reactions is proposed.
The concept of labile lattice oxygen (LLO) as a consequence of the Mars-Van Krevellen model was reminded, and contrasted with the surface oxygen species. Methods of characterizing of the Me-O bond strength were reviewed emphasizing the temperature-programmed limited thermal decomposition (TPLTD). A series of AgxV2MoyOz was characterized by TPLTD. Two forms of LLO were distinguished. The weaker form is independent on Ag-doping, in contrast to the stronger one. Activation energy of TPLTD of the stronger bound LLO was a linear function of the anion vacancy concentration.
Sulphur substitution of oxygen in LiMn2O4
spinel destroyed the ideal symmetry of MnO6 octahedrons.
In consequence, the phase change at about room temperature is strongly retarded,
manifested by lowering heat of the transition and hysteresis of the temperature
dependence of electrical conductivity. The optimal conditions for preparation
of sulphur substituted spinel LiMn2O4–ySy
have been determined.
Authors:R. Dziembaj, S. Hodorowicz, and G. Ciembroniewicz
Temperature-programmed decomposition, thermal analysis, thermogravimetry and high-temperature X-ray analysis have been used to investigate a commercial catalyst for the selective oxidation of benzene into maleic anhydride. It was shown that phase transformations took place in the vanadia-molybdena alkali-promoted catalyst. The transformations were caused either by high-temperature treatment or by catalytic work in an industrial plant. As a result, theβ-bronze phase was formed. In the high-temperature region a reversible transformation of the bronze phase was observed. This was interpreted as theβ⇋β′ phase transformation.
Authors:A. Kochanowski, R. Dziembaj, M. Molenda, A. Izak, and E. Bortel
Key issue in the gelcasting method is the way water is released from
the ceramic–hydrogel system. It is the first step to the formation of
ceramic materials called green body.
The purpose of the presented
investigations is to establish the range of temperatures in which dehydration
of the various hydrogels takes place, and at what temperatures the eight prepared
hydrogels are disintegrated.
The set of hydrogels polymers was
obtained by radical polymerization from ionic and non-ionic monomers. The
polymers were solved in water causing formation of clear gels. The dehydration
and thermal decomposition of the obtained hydrogel samples was studied using
thermal analysis techniques. The amount of water contained in hydrogels was
determined as well as the temperature and products of polymer disintegration.
Enthalpies of dewatering were also determined.
Authors:M. Molenda, R. Dziembaj, Z. Piwowarska, and M. Drozdek
A series of conductive composite
materials were obtained by polymerization of acrylonitrile in water suspensions
of Al2O3 powder followed by
further carbonization of the polymeric films covering the Al2O3
grains. The electrical conductivity and activation energy of the composites
were measured in relation to the parameters used in preparation of the samples.
This highly effective procedure can be used to improve electrical conductivity
of the cathodes in lithium ion batteries.
Authors:L. Chmielarz, M. Zbroja, P. Kuśtrowski, B. Dudek, A. Rafalska-Łasocha, and R. Dziembaj
Alumina, zirconia and titania pillared montmorillonites additionally modified with silver were tested as catalysts of NO reduction
with NH3 or C2H4. Ammonia was much more effective reducer of NO than ethylene. The silver containing TiO2-pillared clay has been found to be the most active catalyst for NO reduction both with NH3 or C2H4. Oxidation of the reducing agents by oxygen limited the NO conversion in the high temperature region. The ammonia and nitric
oxide adsorption sites were studied by the temperature programmed desorption methods (TPD).