Die Systeme Arsen-Schwefel und Arsen-Selen und die thermodynamischen Daten ihrer Verbindungen

The Systems Arsenic-Sulphur and Arsenic-Selenium and the Thermodynamical Data of their Compounds The phase diagrams As? S and As? Se were determined by differential scanning calorimetry. The cage molecules As₄S₃ and probably As₄S₃ were found in the equilibrium systems. The different modifications of As₄S₄, As₄S₃, and As₄Se₃ were investigated by DSC and high temperatur X-ray methods. The transition β → β- As₄S₄ is reversible with extrem slow cooling rates. β- As₄S₃ transform to β- As₄S₃ at 404 K. The plastic phase of all A₄B₃ cages is probably of tetragonal symmetry. At still higher temperatures the melt of As₄S₃ resp. solid As₄S₃ polymerizes. The thermodynamic data – C_p, ΔHu, ΔHm – of the compounds in the system As? S and As? Se were determined.