Production of anhydrous sodium sulfide crystal

TLDR: In this paper, the phase transition temperature from highly hydrated sodium sulfide to monohydrate + or -10 deg.C under =2hr is discussed. And the transition from high-level to low-level sulfide is achieved without melting of the highly-hydrated crystal.

Abstract: PURPOSE:To obtain dense cubic system anhydrous sodium sulfide crystal having little deliquescence and liability to be oxidized by heating highly hydrated sodium sulfide crystal under a specified combination of pressure, temp. and time. CONSTITUTION:The highly hydrated sodium sulfide crystal is heated at the phase transition temp. from highly hydrated sodium sulfide to sodium sulfide monohydrate + or -10 deg.C under =2hr. Then it is heated at 90-200 deg.C under atmospheric or reduced pressure for >=2hr to obtain the targeted crystal. As raw highly hydrated sodium sulfide crystal, Na2S.6H2O, Na2S.5.5H2O, Na2 S.5H2O, etc., are used. These highly hydrated sodium sulfide crystals are obtd. by concentrating or cooling an aq. soln. of sodium sulfide. The transition from highly hydrated to monohydrated crystal proceeds without melting of the highly hydrated crystal. Therefore, lumping or sticking to a vessel of the raw material is prevented and thus uniform stirring can be easily carried out.