Study of phase transition and volume thermal expansion in a rare-earth (RE) oxyfluoride system by high-temperature XRD (RE=La, Nd, Sm, Eu and Gd)

Volume thermal expansion behaviour of a number of rare-earth oxyfluorides (REOF) have been studied using high-temperature X-Ray diffractometry (HT-XRD) in the 298–1075 K range in air. The studies revealed an anomalous expansion for each compound associated with phase transition. The phase transition temperature and the coefficient of volume thermal expansion of five compounds in REOF series determined by this method are reported and compared with our earlier results obtained by dilatometry.     

Synthesis of Linearly Fused Tetracyclic Heterocycles Through a Novel Base Catalyzed Intramolecular Rearrangement Involving Scission of N-N Bond

Synthesis of s-triazolothiadiazepinoquinolines 4a-f and the base catalyzed intramolecular facile rearrangement of 4a-f to s-triazolothiazinoquinolines 5a-f involving scission of N-N bond is reported.     

Operator algebras and a theorem of Dieudonne

LetA be aC*-algebra with second dualA″. Let (φ _n)(n=1,...) be a sequence in the dual ofA such that limφ _n(a) exists for eacha εA. In general, this does not imply that limφ _n(x) exists for eachx εA″. But if limφ _n(p) exists whenever p is the range projection of a positive self-adjoint element of the unit ball ofA, then it is shown that limφ _n(x) does exist for eachx inA″. This is a non-commutative generalisation of a celebrated theorem of Dieudonné. A new proof of Dieudonné’s theorem, for positive measures, is given here. The proof of the main result makes use of Dieudonné’s original theorem.     

The effect of substitution on the thermo-physical properties of LaMnxV1−xO4−δ

LaMn_xV_1−xO_4−δ(0≤x≤1) samples were characterized using thermogravimetry, thermo-dilatometry, high-temperature X-ray diffraction (HTXRD) and temperature-programmed reduction techniques, with an objective to explore the role of substitution on their thermo-physical properties, which may have a direct bearing on their catalytic behavior. Even though the substituted compositions (x<0.8) were of a single phase, their reduction occurred in two steps, a lower temperature step corresponding to Mn⁴⁺→Mn³⁺/Mn²⁺ and another higher temperature one related to V⁵⁺→V³⁺. The dilatometric measurements gave similar values of linear thermal expansion coefficient (α₁) at temperatures up to 600 °C, both for LaVO₄ and substituted samples. A different behavior was, however, observed at higher temperatures, whereas thermal contraction was observed in case of LaVO₄ for measurements at temperatures above 700 °C, the value of α₁ remained almost constant in case of the substituted samples. Furthermore, the HTXRD data revealed expansion in cell volume for all temperatures up to 950 °C, irrespective of the substitution. These results therefore point to a higher degree of sintering in LaVO₄ as compared to Mn-doped samples on heating at temperatures above 700 °C. It is inferred that the resistance to sintering and the lowering of the reduction temperature are both responsible to the higher catalytic activity of the substituted samples and their compositional stability during the repeated cycles of reduction-reoxidation, as reported earlier [Appl. Catal. A 205 (2001) 295].     

AgNbO3 dispersed Ag2SO4 composite for potentiometric SO2 gas sensor application

Composite electrolytes of Ag₂SO₄ is prepared by dispersing fine particles, average particle size <40 microns (350 mesh), of ferroelectric AgNbO₃ in varying weight fraction. Enhancement in the conductivity is observed in β-phase of host system. The effect of dispersion on the conductivity, activation energy and transition temperature is studied as a function of weight % of the dispersoid in the host. Two distinct conduction mechanisms, viz. conduction through electrolyte bulk in parallel with conduction along the inter-grain interaction layer (R _b ^‖ ‖R_∞) and perpendicular to the interface (R _b ^⊥ ) could be resolved in the frequency range of 5 Hz to 13 MHz at temperatures below 300 °C. The interface interaction is found to be nucleophilic increasing the concentration of Ag⁺ vacancies at the interface. Potentiometric SO₂ gas sensors are tested with this composite electrolyte as an auxiliary phase. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Adsorption and expression of penicillin G acylase immobilized onto methacrylate polymers generated with varying pore generating solvent volume

Adsorption and expression of penicillin G acylase was studied on macroporous methacrylate polymer beads of differing pore volume, generated with kerosene. The absorption and expression of the penicillin G acylase was dependent on pore volume. Maximum expression of 57% of adsorbed enzyme was obtained on beads synthesized with 40 mL of kerosene, indicating minimum pore-diffusion limitations.     

Deep inelastic collisions of32S +27Al reaction at 130 MeV bombarding energy

The³²S +²⁷Al reaction was studied to investigate the deep inelastic collisions at a bombarding energy of 130 MeV which is well above the Coulomb barrier. The energy distributions of the binary decay products of 6⩽Z⩽10 were determined using a large area position sensitive ionization chamber. The average kinetic energies of the reaction products indicate that the exit shapes correspond to highly stretched scission configurations in the deep-inelastic processes.