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.     

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.     

Nanostructured microspheres of silver @ zinc oxide: an excellent impeder of bacterial growth and biofilm

Au@TiO₂ core–shell hollow nanoparticles were prepared by a simple hydrothermal method without surfactants or templates. The core–shell structure materials were characterized by transmission electron microscopy, X-ray powder diffraction, scanning electron microscopy, and specific surface area of the test (BET). The catalytic activity was tested in a stainless reactor with a fixed bed and connected with a gas chromatograph. The results show that the microstructure, crystallography, and morphology were correlated with the hydrothermal reaction time and temperature, and the properties of the solvent. The crystallinity degree of TiO₂ and the particle size increased with the reaction time and temperature. Particles with different morphologies can be obtained when using different solvents. The size of microsphere can be controlled easily by changing the amount of TiF₄. This material exhibited the complete CO conversion temperature to be about 130 °C and no deactivation was observed after 1,000 min reaction.     

Dilatometric and high temperature X-ray diffractometric studies of La1−xMxCrO3 (M=Sr, Nd, x=0.0, 0.05, 0.10, 0.20 and 0.25) compounds

The phase transition, bulk and lattice thermal expansion behaviour of the strontium and neodymium substituted lanthanum chromites have been studied by dilatometry and high temperature X-ray powder diffractometry from room temperature to 1123 and 1073 K, respectively, in static air. The studies revealed that the temperature of the orthorhombic to rhombohedral phase transition, which occurred at 550 K in undoped LaCrO₃, decreased on substitution of Sr²⁺ ions and increased on substitution of Nd³⁺ ions, systematically. However, the coefficients of average linear and volume thermal expansion (_l and _v) of LaCrO₃ showed a marginal increase on Sr²⁺ substitution to different extent, whereas a reverse trend was observed with Nd³⁺ substitution. The phase transition temperatures and _l and _v of the compounds as determined by dilatometric and high temperature X-ray diffractometric methods are reported.     

Galvanic CO2 sensor with Li2O: B2O3 glass ceramics based composite

In order to develop an electrolyte with better thermal-stability, a new composite is prepared by partially crystallizing the lithium borate glass along the grain boundaries of Li₂CO₃: BaCO₃ binary system. Highly dense material is obtained on controlled partial crystallization. The structural and electrical characterization proved its composite nature with enhancement in conductivity. A few potentiometric CO₂ gas sensors prepared by using optimized composite electrolyte with lithium titanate as the reference electrode. This configuration resulted in a device of high mechanical strength with ease of fabrication and free from interfacial failures. Reproducible and reversible response is obtained for these sensors over a long-term operation at lower temperatures (275 – 450 °C). The sensor response found to obey Nernst relation with sensitivity and emf approaching the theoretical value. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.