CHARACTERIZATION OF FIRED SILICAS

The products produced by firing a very pure quartz and a commercial pu rity quartz, with and without a mineral additive, to temperatures betw een 1100 degrees C and 1700 degrees C have been studied by DSC. The te mperature at which the cristobalite alpha-beta inversion occurred and the degree of hysteresis observed on heating and cooling were both dep endent on the sample history. The highest inversion temperature and gr eatest degree of hysteresis on heating and cooling were obtained with pure quartz samples heated at 1600 degrees C or 1700 degrees C. Produc ts produced by firing finely ground pure quartz had a lower inversion temperature and less hysteresis than coarse grained samples. if a mine ral additive was present tridymite inversions were also observed. Firi ng of the commercial purity quartz at a given temperature led to crist obalites with lower inversion temperatures and less hysteresis. The va riations in inversion temperature and hysteresis are probably related to the degree of order in the cristobalite structure with the most hig hly ordered material having the highest inversion temperature and grea test degree of hysteresis. (C) 1998 Elsevier Science B.V.