o-Benzoquinones and their polarographic reduction

Conclusions Some alkyl-substituted o-benzoquinones were synthesized and a study was made of their polarographic reduction at a dropping mercury electrode.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1380–1382, June, 1973.The authors express their gratitude to L. P. Lebedeva for determining the oxidation induction period.     

Kinetics of the Kola Apatite Rock Interaction With H3PO4

Abstract

Besides the production of fertilizers, Kola phosphate rock may be used as a source of lanthanides, strontium and fluorine. It implies the necessity to carry out a study of kinetics and mechanisms of the process in order to choose optimal conditions for the realization of the technological scheme [1]. The fluorapatite concentrate used had the following composition: ?Ln₂O₃ - 0.89; Y₂O₃ - 0.04; SrO - 2 80; CaO - 45.40; Fe₂O₃ -0.42; Al₂O₃ - 0.86; MgO - 0 10; F - 2.80; SiO₂ - 1.80; P₂ ^O ₅ - 39.40 weight %; molar ratio CaO : P₂O₅ = 1.5; the content of the apatite - 98.5%. The reaction of H₃PO₄ with fluorapatite was studied using a laboratory reactor with a stationary layer. The following parameters were varied: H₃PO₄ concentration (20, 30 and 50 weight % P₂O₅), temperature (20, 75, 150, 200 and 250°C) and time of contact (1–180 min.). A multimethod approach was used. X-ray diffraction, electron probe microanalysis and paper chromatography were applied to follow the bulk structural aspects of the apatite powders. It was shown that at the first stage of reaction a thin film of calcium monophosphate Ca(H₂PO₄)₂ H₂O is deposited on the apatite particles (avg. diameter 150 nm). The reaction is thought to proceed at the interphase solid/liquid and its kinetics may be described by the equation     

Phase formation in the Ag3VO4-ScVO4 quasi-binary system

Subsolidus phase formation in the Ag₃VO₄-ScVO₄ quasi-binary system was studied using X-ray powder diffraction and DTA in air under atmospheric pressure over the entire range of component concentrations in 5 mol % steps between 20 and 800°C. Two compounds were found to form: Ag₃Sc(VO₄)₂ and Ag₃Sc₂(VO₄)₃, both melting incongruently at 750 ± 5 and 960 ± 5°C, respectively. A T-x diagram of the Ag₃VO₄-ScVO₄ quasi-binary system was constructed. A eutectic (T _m = 450 ± 5°C) is between the compounds Ag₃VO₄ and Ag₃Sc(VO₄)₂; Ag₃VO₄ concentration is ～5 mol %.     

A statistical comparison of non-isothermal methods of kinetic investigation

A statistical analysis of some non-isothermal kinetic techniques is given. Comparison of the kinetic parameter values obtained by different techniques has shown them to be statistically non-equivalent. Hypotheses of significance or non-significance of discrepancies in the kinetic parameter values should therefore be tested using two-dimensional normal distributions. Comparisons of the results obtained by various techniques using activation energy values only lead to erroneous conclusions.