Influence of nitrate on fining and Sn redox in alkali free aluminoborosilicate glass melts

摘要

Alkali free aluminoborosilicate melts were prepared from batches with different five nitrate contents. The fining ability of each glass batch was estimated using the profiled melting and fining method, and the redox equilibrium of Sn in each fined melt was examined by square wave voltammetry. The fining ability expressed as residual seed number increased up to 3 wt% nitrate content and decreased with further nitrate additions. According to the voltammograms, the peak potential due to reduction of Sn~(4+) to Sn~(2+) initially tended towards a negative direction (oxidation state) with an increase of nitrate content. On passing through 3 wt% nitrate the peak potential moved in a positive direction. In relation to the dependence on nitrate content, the voltammetry results showed a similarity to the fining ability. Based on the oxygen solubility determined from the redox ratio the decay of fining ability when 3 wt% nitrate was exceeded was explained.