Sodium borohydride reacts slowly with water ultimately to liberate 4 moles of hydrogen per mole of the compound at room temperature, or 2.4 1. per gram. The reaction is greatly accelerated by rise of temperature or by the addition of acidic substances, for which latter purpose boric oxide is convenient and effective when the objective is the generation of hydrogen. Particularly striking is the catalytic effect of certain metal salts, especially that of eobalt(II) chloride. Thus pellets of sodium borohydride containing only 5% of the cobalt salt react as rapidly as those containing 10 times that amount of boric oxide. The effect of the cobalt salt is ascribed to the catalytic action of a material of empirical composition, Co2B, which is formed in the initial stages o'f the reaction.
No measurable shift is observed in the boundary between the hexagonal (A) and monoclinic (B) phases, but stability of the monoclinic phase relative to the cubic phase is enhanced by increased pressure as well as higher temperature. The C-B phase transformations are shown to be reversible. Lattice parameters are given for 11 monoclinic sesquioxides-Y203 and Sm203 through Lu203. The entropy increase involved in the transformation from the cubic to monoclinic structure is estimated to be 1.5 eu.
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