Synthesis of Sodium Borohydride Dihydrate and Specific Features of Its Thermolysis

Process of thermolysis of sodium borohydride dihydrate samples produced from solution and via a vapor was considered. A study of an acetonitrile solution made by the method of nuclear magnetic resonance demonstrated that the stoichiometry is observed in both cases. An X-ray diffraction analysis evidenced that the sample produced via a vapor is defective. It was found that, in both cases, the process begins after the reaction of peritectic decomposition of the starting compound occurs and a liquid phase is formed. The enthalpy of the peritectic reaction was determined to be ΔHreact = 18.6 ± 1.5 kJ mol−1 for the sample crystallized from an alkaline solution. For the sample produced via a vapor, this quantity is substantially smaller. The kinetics of a low-temperature thermolysis (40–80°C) of both samples is described by the Avrami—Erofeev equation.