Heat content of sodium borohydride and of potassium borohydride from 0-degrees-C to 400-degrees-C

Abstract

The heat conten t of sodium bo rohyd rid e, NaBH, a nd of potass iulYl bo roh vdrid c KI3H" was m eas ured , relative to t hat at 0 0 C, at 50-de'g ree intervals from 0 0 to 400 0 c: The so-called " drop" method was used wit h a precision Bunsen ice calorimeter a nd a sil ver-co re furnace . Preliminary tests showed t hat sponta neous decomposit ion of t hese co m-pounds IS ver y slow at temperat.u res up to 400 0 C. ~eas ure men ts we re made on two samples of eac h compound, t hose of socl1um borohydnde hav mg been obtained from differen t sources. Smoothed valu es of t he ~ eat-co n ten t function, heat capac ity, en tropy, a nd t he Gibbs fr ee-e ne rgy funct ion were derI ved from t he data. These values were increased b y 0.5 p erce n t to correct for the presence of a n estimated 1 percent of t he corresponding metaborate in eac ll sampl e. The heat capacity of sodi um borohydride inc reases monotoni cally with te mpera-t ure ln t he range mves tJgated ; that of potasS IUm borohydrIde passes t hrough a point of in-fl ection, whi ch suggests that t he re may be a b road second-order t ransit ion in the neig hbor-hood of r oo m te mperature.