Chemical kinetics study of the sol-gel processing of GeS2

A chemical kinetics study of the functional groups -OC2H5, SH-, and S2- was carried out for the sol-gel processing of GeS2 from hydrogen sulfide and germanium ethoxide in toluene. A mass balance of the reaction components was monitored by potentiometric titrations of SH- and S2- with the Ag/Ag2S ion-selective electrode. The study was performed for different concentrations of precursors at different molar ratios and temperatures. The results indicate that the proposed reaction mechanism was simplified under appropriate reaction conditions. Experimentally determined rate constants of thiolysis and condensations demonstrate that thiolysis is slow and that condensations are fast steps, regardless of reaction conditions (concentration, rate, and temperature). A study of the temperature effect on the reaction rate constants shows that they increase with temperature in accord with both Arrhenius law and transition-state theory. Activation energies, E,, and activation parameters DeltaS(double dagger), DeltaH(double dagger), and DeltaG(double dagger) were determined for thiolysis and condensation reactions.