A calorimetric study of the thermodynamic properties of potassium molybdate

The low-temperature heat capacity of K₂MoO₄ was measured by adiabatic calorimetry. The smoothed heat capacity values, entropies, reduced Gibbs energies, and enthalpies were calculated over the temperature range 0–330 K. The standard thermodynamic functions determined at 298.15 K were C _p ^° (298.15 K) = 143.1 ± 0.2 J/(mol K), S°(298.15 K) = 199.3 ± 0.4 J/(mol K), H°(298.15 K)-H°(0) = 28.41 ± 0.03 kJ/mol, and Φ°(298.15 K) = 104.0 ± 0.4 J/(mol K). The thermal behavior of potassium molybdate at elevated temperatures was studied by differential scanning calorimetry. The parameters of polymorphic transitions and fusion of potassium molybdate were determined.     

Pac studies of the electric quadrupole interaction of181Ta in yttrium and copper oxides and in super conducting ceramics YBa2Cu3O7−δ

The electric quadrupole interaction of¹⁸¹Ta in Y₂O₃, CuO, and in the YBa₂Cu₃O_7−δ high temperature superconductors, doped with¹⁸¹Hf, has been studied by the time-differential perturbed angular correlation method (TDPAC). In Y₂O₃, two distinct fractions of the probe nuclei were detected, which were attributed to the substitutional positions at the two cation sites in the lattice. In CuO, and in the ceramic samples, broad distributions of quadrupole frequencies were observed. Possible configurations of the probe nuclei in these substances are discussed.     

PAC studies of hyperfine interactions of181Ta in YBa2Cu3O7-δ and of140Ce in La2CuO4 and La1.85Sr0.15CuO4

Results of TDPAC studies of hyperfine interaction in high temperature superconducting ceramics are reported. The γ-ray cascade of 329–487 keV in¹⁴⁰Ce excited in the decay of¹⁴⁰La in La_2-xSr_xCuO₄ samples (x=0 and 0.15), and 133–482 keV cascade in¹⁸¹Ta excited in the decay of¹⁸¹Hf in YBa₂Cu₃O_7-δ samples were used. The procedure of introducing radioactive¹⁸¹Hf into the ceramics is described and indirect evidence for the occupation of Cu sites by the¹⁸¹Hf-¹⁸¹Ta probe is presented.     

Nucleophilic coaction during one-electron oxidation of hydroxyaromatic compounds

Conclusions The role of internal catalysis during one-electron oxidation of hydroxyaromatic compounds by mercuric salts, the possibility of which is determined by the nature of the salt anion, was shown.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2601–2603, November, 1974.     

Optical study of parameters of the passage of a shock wave from air to water

A study is made of the penetration of shock waves from air into water. The shock wave in air is generated as a result of dielectric breakdown induced by pulsed CO₂-laser radiation. A combination of the double-exposure shadow method and holographic interferometry is used to measure the shock-wave parameters. Density and pressure profiles behind the wave front are obtained at different times after onset of breakdown. It is shown experimentally that as the wave passes through the interface from the air to the water, there is a fourfold amplification of the pressure in the shock wave front. Estimates of the width of the shock wave front formed in the water are given in the context of studies of large-scale explosion processes. It is shown that simple empirical dependences, established in the course of studies of large-scale explosions, are also valid with certain corrections for microscopic laboratory experiments. Zh. Tekh. Fiz. 68, 39–43 (August 1998)