Structure of H(D)TaO3 determined by powder X-ray and neutron diffraction

Pure crystalline samples of HTaO₃ and DTaO₃ have been prepared. The crystal structure has been solved using powder X-ray and neutron diffraction (at 2 K and room temperature) and has been shown to consist of Ta(O,OH)₆ octahedra sharing vertices with the oxygen atoms displaced toward the vacant perovskite A sites. The compound is isomorphous with HNbO₃, D_xWO₃, and D_xReO₃ and contains hydrogen atoms as hydroxide groups.     

Thermal degradation and oxidation of polystyrene studied by factor-jump thermogravimetry

Factor-jump thermogravimetry has been used to study the activation energy of polystyrene degrading in a vacuum, in N₂ flowing at 4 mm/s and in $\text{N}{}_2\text{O}{}_2$ mixtures. The results show the activation energy to be 44·9 ± 0·2 kcal/mole (188 ± 0·8 kJ/mole) for degradation above 350°C in vacuum or in flowing N₂. This agrees well with work reported in 1949 by Jellinek⁷ but with few results reported subsequently.The apparent activation energy for polystyrene losing weight above 280°C in an atmosphere of abundant O₂ is 21·5 ± 0·2 kcal/mole (90·2 ± 0·8 kJ/mole). In all cases where O₂ was deliberately introduced (partial pressures >4 mm Hg), the sample degraded to a black tar and the activation energy was ≤30 kcal/mole, depending on the amount of oxygen present and on the thermal history of the sample.     

Substitution in barium-fluoride apatite: The crystal structures of Ba10(PO4)6F2, Ba6La2Na2(PO4)6F2 and Ba4Nd3Na3(PO4)6F2

The crystal structures of the apatites Ba₁₀(PO₄)₆F₂(I), Ba₆La₂Na₂(PO₄)₆F₂(II) and Ba₄Nd₃Na₃(PO₄)₆F₂ (III) have been determined by single-crystal X-ray diffraction. All three compounds crystallize in a hexagonal apatite-like structure. The unit cells and space groups are: I, a = 10.153(2), c = 7.733(1)Å, $\text{P6}{}_3\text{m}\text{; a = 9.9392(4), c = 7.4419(5)}$Å, $\text{P}\text{6}$; III, a = 9.786(2), c = 7.281(1)Å, $\text{P}\text{3}$. The structures were refined by normal full-matrix crystallographic least squares techniques. The final values of the refinement indicators R_w and R are: I, R_w = 0.026, R = 0.027, 613 observed reflections; II, R_w = 0.081, R = 0.074, 579 observed reflections; III, R_w = 0.062, R = 0.044, 1262 observed reflections.In I, the Ba(1) atoms located in columns on threefold axes, are coordinated to nine oxygen atoms; the Ba(2) sites form triangles about the F site and are coordinated to six oxygen atoms and one fluoride ion. The fluoride ions are statistically displaced ～0.25 Å from the Ba(2) triangles. This displacement of the F ions is analogous to the displacement of OH ion in Ca₁₀(PO₄)₆(OH)₂.The structures of II and III contain disordered cations. In II there is disorder between La and Na in the column cation sites as well as triangle sites. In III, Nd and Na ions are ordered in the column sites, but there is disorder among Ba and the remaining Nd and Na ions in the triangle sites to give an average site population of $\text{2}\text{3}\text{Ba}\text{,}\text{1}\text{6}\text{Nd}\text{,}\text{1}\text{6}\text{Na}$. The coordination of the rare earth ions and Na ions in the ordered column sites are nine and six oxygens, respectively, in accord with the greater charge of the rare earth ions as compared with Na. The F ions in both II and III suffer from considerable disorder in position, and their locations are not precisely known.     

Calculation of vibrational relaxation times in gaseous cyanogen

A calculation of vibrational relaxation times in gaseous cyanogen at 300°K is presented. It is suggested that two well separated dispersion regions should be found in sound velocity measurements at ultrasonic frequencies, the higher frequency region being associated with the relaxation of the combined vibrational specific heat contributions of the two lowest modes and the lower frequency region being associated with the relaxation of the corresponding contribution of the next highest mode.     

Effects of ZnS:Mn concentrated vinyl ester matrices under flexural loading on the triboluminescent yield

This paper investigates the feasibility of using zinc sulfide manganese (ZnS:Mn) concentrated vinyl ester resin as a photon emitter for damage monitoring of polymer composites under flexural loading. Unreinforced vinyl ester resins doped with optical emitting materials (ZnS:Mn phosphors) in ratios of 5–50% by weight were cast, and subjected to flexural loading using standard 3-point bend tests. The intent of this work was to observe the transient response of triboluminescence (TL) throughout the failure cycle. Results indicate TL crystals emit light at various intensities corresponding to crystal concentration and imminent matrix fracture. Consequently, concentrated samples showed nearly 50% reductions of mechanical moduli. Scanning electron microscopy (SEM) revealed particulate inclusions with shearing bands and semblance of particle to resin adhesion. Despite significant parasitic effect to mechanical properties, the triboluminescent properties occur at yielding and point of matrix fracture.     

Temperature variation of phonon frequency distribution in the fast ion conductor lead fluoride

A weighted phonon frequency distribution has been measured in PbF₂ at temperatures 10, 302, 660 and 910 K, using a neutron scattering technique. At 10 K good agreement is found between the measured distribution and the phonon density-of-states calculated from the low temperature dispersion relation of PbF₂. At the higher temperatures, near the ionic conductivity transition temperature, T_c ～ 700 K, the optic modes are observed to broaden into a high energy tail consistent with strong anharmonicity or extensive disorder. A low energy peak arising from transverse acoustic modes remains well defined even at temperatures above T_c.     

A new method of preparation of 1H-1,2-benzodiazepines by the rearrangement of 2,4,6-trichlorophenylhydrazones

A new method for preparing 1H-1,2-benzodiazepines is described. Hydrazones of generalised structure 1 undergo base catalysed cyclisation to form 4-imidazolyl-4,5-dihydro-1H-1,2-benzodiazepines of general structure 2 . These compounds readily eliminate imidazole to form 1H-1,2-benzodiazepines of general structure 3 .