Abstract: This article has studied the influence of the boric acid on sintering and crystallization of the fused silica. The microstructure of the sintered fused silica was studied by XRD, SEM. The results showed that the sinter ability of the fused silica could be improved by the addition of boric acid. When the boric acid content is smaller than 0.5wt%,with the boric acid content's increase, the effect is obvious; When the boric acid content is between 0.5wt% and 1.0wt%, the sinterability of the fused silica changes little; When the boric acid content is greater than 1.0wt%, the effect is much more obvious. It was also found that adding boric acid promoted the crystallization of fused silica. As the boric acid content's increasing, the crystallization is more serious, and its crystalline grows at an exponential rate. When the boric acid content is not more than 1.0wt%, the crystalline phase is all the low-temperature cristobalite phase; when boric acid was higher than 1.0wt%, the crystalline phase is mainly low cristobalite, but it also contains a little other new phase" (BSi)O_2" and "Si_(30.72)B_(1.280O_(64)".

Key words: fused silica%boric acid%sintering%crystallization