Effects of Sintering Aids on Properties of Silica-Based Dry Ramming Mixes

This study systematically investigated how sintering aid type and amount, silica properties, and temperature affect the characteristics of silica-based dry ramming mixes. We selected boric anhydride and sodium polyphosphate as the sintering aids. Phase evolution results and properties evaluated via X-ray diffraction analysis and property testing indicate that fine-grained, high-purity quartz from Hubei presented the fastest phase formation after firing at 1550 °C. Both sintering aids accelerated phase transformation; however, additional boric anhydride did not modify the process further. Sodium polyphosphate caused pronounced volumetric expansion of up to 20% at 1400 °C, but this expansion gradually decreased as sodium polyphosphate increased at 1550 °C. The sintering behavior and properties of silica-based dry ramming mixes were governed by the interplay between the extent of phase transformation (dominant at 1400 °C) and the quantity of liquid phase (dominant at 1550 °C). Overall, boric anhydride is more suitable for silica from Hubei and Hebei; however, based on the conditions assessed in the present investigation, a high content of sodium polyphosphate (3 wt%) is required for Henan-derived silica.