Determination of the content, composition and density of the glass phase in silica refractories and its changes due to thermal cycling

The glass phase content in silica refractories before and after thermal cycling to 900–1500 °C is estimated via X-ray powder diffraction (XRD), using 20 wt.% of alumina or zinc oxide as internal standards. Four repeated XRD scans are made with CuK α and CoK α radiation and evaluated via the Rietveld method using two or three subpolymorphs of tridymite. The glass phase composition is estimated by comparison with X-ray fluorescence, and the glass phase density is estimated via the Huggins-Sun approach. The glass phase content is 6.2–8.5 wt.% in the pristine state, 8.9–11.6 wt.% after cycling to 1500 °C and exhibits a minimum after cycling to 1100 °C (4.2–6.8 wt.%). After cycling to 1100 °C the glass phase composition exhibits a minimum in the silica (SiO 2 ) content and a (local) maximum in the calcia (CaO) content. The density of the glass phase is 2.7 ± 0.1 g/cm 3 .