Abstract
The heats of solution were measured for As-S glasses in aqueous solutions of NaOH, NH3, (NH4)2 S and Na2S. The anion species formed after the dissolution were identified by TLC and the composition dependence of heats of solution were discussed by assuming the dissolution mechanism.
The enthalpy change in each solution was negative, i. e., exothermic for every glass. The exothermic heat per formula weight of AsSm, in NaOH and NH3 solutions linearly decreased with an increase of mole fraction of AsS1.5, in the pseudo-binary system AsS1.5-AsS2.5. TLC examinations showed that AsO33- and AsOnS4-n3- (n=1, 2 or 3) were the anion species formed on dissolution in NaOH solution. The glass of high sulfur content formed anions of low n values and gave higher heat on dissolution. In NH3 solution, the four-coordinated anions were not formed and the heats were fairly low.
The heats of solution in sulfide solutions did not depend on the galss composition and were nearly equal to the heat of solution of AsS2.5 glass in NaOH solution. This behavior can be interpreted by assuming that the major species of four-coordinated anion is AsS43- formed by coordination of S2- which exists in large excess in the sulfide solutions.
