Physicochemical investigations of potassium, rubidium and cesium hydrophosphates and hydroarsenates

Results of investigations into K, Rb, Cs hydrophosphates and hydroarsenates, conducted by the methods of differential thermal and X-ray phase analyses in 25-400 deg C range are presented. It was established that water is completely removed at 300-400 deg C under conditions of dynamic heating; all compounds at that are transformed into corresponding metaphosphates and metaarsenates. Investigated hydrophosphates and hydroarsenates melt congruently on heating in closed volume in water vapor presence. Measurements of melting temperatures of Rb(Dsub(0.95)Hsub(0.05))sub(2)AsOsub(4) and Cs(Dsub(0.95)Hsub(0.05))sub(2)AsOsub(4) showed that their values increase slightly and equal 273+-3 and 295+-3 deg C respectively as compared to RbH2AsO4 and CsH2AsO4. Polymorphous transformations with formation of phases with the lower syngony were revealed for all compounds. Temperatures and the character of polymorphous transformations as well as X-ray characteristics of high-temperature modifications of all investigated compounds are presented. It was noted that polymorphous transitions from low temperatures up to high ones are accompanied by the decrease of lattice cell volume for CsH2AsO4, which is probably related to the change of hydrogen bond character