Thermal Analysis of a Hydrated Silica–Sodium Thiosulfate–Sulfur System

Abstract

A system formed by concerted action of orthosilicic acid gelation and decomposition of sodium thiosulfate to afford highly dispersed elemental sulfur was studied by simultaneous methods, DTA, TG and DTG. A typical curve has been found to be an outcome of thermal processes associated with desorption of physically adsorbed water, condensation of surface silanol groups and thermal degradation of sodium thiosulfate. A large loss in mass over the lower temperature range was assigned to the loss of physically adsorbed water and condensation of silanol groups of the gel as indicated by accompanying strong endothermic effects. Subsequent strong exothermic effects were attributed to combustion of elemental sulfur embedded in the gel. Experiments were also conducted to control the extent of decomposition of the thiosulfate and generation of elemental sulfur by varying pH of thesilicic acid solution. These have shown that acidification of the silicic acid - sodium thiosulfate system with sulfuric acid fostered decomposition of the thiosulfate and raised the quantity of elemental sulfur.