Evolution structurale sous haute pression des phases K2MO3 (M = Zr,Hf, Sn,Pb)

The study of the high-pressure modifications of the oxides K₂MO₃ (M = Zr, Hf, Sn, Pb) confirms the tendency of potassium to adopt the trigonal prismatic coordination in layer oxides: The β form is characterized by layers of (K, M)O₆ octahedra with common edges, between which other potassium atoms are inserted with prismatic coordination. For M = Zr and Hf, an increase of pressure or temperature transforms β to the γ or δ variety, both derived from the NaCl structure. The influence of the electronegativity of M on the potassium coordination in layer structures is discussed.     

NMR study of catechol and some catecholamines

The proton magnetic resonance spectra of catechol, epinephrine, dopamine, synephrine, tyramine and amphetamine have been analysed by computer simulation. The chemical shifts and coupling constants are discussed, with their molecular implications. Convenient parameters are introduced for the additivity of substituent effects on chemical shifts of aromatic protons. The additivity rule of coupling constants is extended to these compounds.     

Polybenzoylenebenzimidazoles

A polyamide amino acid was prepared by the solution condensation of 3,3′-diaminobenzidine and pyromellitic dianhydride. This polymer was cast as a film and converted to a polybenzoylenebenzimidazole. The gross conversion path was elucidated by spectroscopy and was substantiated by model compound studies. A novel ladder polymer was prepared from 1,2,4,5-tetraaminobenzene and pyromellitic dianhydride.     

Perturbed Arcs in Turbulent Axial Gas Flow IV. Thermal Reignition Experiments

By means of the short-circuiting of electric arcs burning in turbulent axial gas coolant flow and their reaction on a (recovering) voltage ramp the reignition in circuit breakers is modelled. Strong stochasticity of thermal reignition is demonstrated even under relatively weak conditions. Channels or nozzles showing flow detachment are further deteriorated by that. Corresponding low-current test experiments are recommended for in-scale circuit breaker development tests.