Properties of CMAS glass from desert sand

Abstract

X-ray diffraction analysis of as-received desert sand from a Middle East country showed the presence of quartz (SiO2), calcite (CaCO3), gypsum (CaSO4.2H2O), NaAlSi3O8, Mg2(Al3.9Si5.1O18) and Mg3Al2(SiO4)3 phases. A batch of as-received desert sand was melted into calcium magnesium aluminosilicate (CMAS) glass at ~1500°C. From inductively coupled plasma-atomic emission spectrometry, chemical composition of the CMAS glass was analyzed to be 27.8CaO-4MgO-5Al2O3-61.6SiO2-0.6Fe2O3-1K2O (mole %). Various physical, thermal, and mechanical properties of the glass have been evaluated. Bulk density of CMAS glass was 2.69g/cm3, Young׳s modulus 92GPa, Shear modulus 36GPa, Poisson׳s ratio 0.28, dilatometric glass transition temperature (Tg) 706°C, softening point (Td) 764°C, Vickers microhardness 6.3±0.4GPa, indentation fracture toughness 0.75±0.15MPa.m1/2, and coefficient of thermal expansion (CTE) 9.8×10−6/°C in the temperature range 25 to 700°C. Temperature dependence of viscosity has also been estimated from various reference points of the CMAS glass using the Vogel-Fulcher-Tamman (VFT) equation as well as from the glass composition. The glass remained amorphous after heat treating at 850°C for 10h but crystallized into CaSiO3 and Ca2Mg0.5AlSi1.5O7 phases at 900°C or higher temperatures. Crystallization kinetics of the CMAS glass has also been investigated by differential thermal analysis (DTA).