Expanded materials from quartz-porphyrite sands

Experiments on the preparation of glass from quartz-porphyrite sands showed the occurrence at about 1300° C of extensive bubble formation which cannot be easily removed on further heating at higher temperatures. This prompted us to exploit this process in the synthesis of expanded material. The research work was addressed to determining the origin of the bubble phenomenon in order to control the potential foaming at high temperature. The parameters controlling the production of cellular glass directly from quartz-porphyrite sands are presented and discussed. The results allow the preparation of polycellular vitreous material with a homogenous bulk distribution of SiO₂ microcrystals. The main features of the product are: bulk density in the range 720 to 980 kg m^–3; average bubble diameter 0.1 to 0.3 mm; thermal conductivity 0.19 to 0.28 Wm^–1 (°C)^–1; compressive strength 1.96 to 3.92 M Pa.