The thermal expansion curves are reported for ''as-quenched'' and ''heat-treated'' glasses obtained by adding MgO (8-16%) and TiO2, (4%) to porphyric sands of composition: SiO2=72.40%; Al2O3=13.85%; K2O=4.60%; Na2O=3.00%; Fe2O3=2.15%; CaO= 1.30%; MgO=0.84%; TiO2=0.20%; loss on calcination = 2.06%. The variations in the glass transition temperature T-g, the thermal expansion coefficient alpha, and the dialatometric softening temperature M(g), are discussed. The experimental results can be explained by assuming that Na2O, K2O and CaO (all or a part of them) segregate preferentially with respect to MgO into the titania-rich phase. Diffusion appears to fall as the MgO content is increased.

Thermal-expansion Behavior of Glass-ceramics Derived From Prophyric Sands

BRANDA, FRANCESCO;COSTANTINI, ANIELLO;
1993

Abstract

The thermal expansion curves are reported for ''as-quenched'' and ''heat-treated'' glasses obtained by adding MgO (8-16%) and TiO2, (4%) to porphyric sands of composition: SiO2=72.40%; Al2O3=13.85%; K2O=4.60%; Na2O=3.00%; Fe2O3=2.15%; CaO= 1.30%; MgO=0.84%; TiO2=0.20%; loss on calcination = 2.06%. The variations in the glass transition temperature T-g, the thermal expansion coefficient alpha, and the dialatometric softening temperature M(g), are discussed. The experimental results can be explained by assuming that Na2O, K2O and CaO (all or a part of them) segregate preferentially with respect to MgO into the titania-rich phase. Diffusion appears to fall as the MgO content is increased.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/467447
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