Properties of CMAS glass from desert sand.

X-ray diffraction analysis of as-received desert sand from a Middle East country showed the presence of quartz (SiO 2 ), calcite (CaCO 3 ), gypsum (CaSO 4 .2H 2 O), NaAlSi 3 O 8, Mg 2 (Al 3.9 Si 5.1 O 18 ) and Mg 3 Al 2 (SiO 4 ) 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-5Al 2 O 3 -61.6SiO 2 -0.6Fe 2 O 3 -1K 2 O (mole %). Various physical, thermal, and mechanical properties of the glass have been evaluated. Bulk density of CMAS glass was 2.69 g/cm 3 , Young׳s modulus 92 GPa, Shear modulus 36 GPa, Poisson׳s ratio 0.28, dilatometric glass transition temperature (T g ) 706 °C, softening point (T d ) 764 °C, Vickers microhardness 6.3±0.4 GPa, indentation fracture toughness 0.75±0.15 MPa.m 1/2 , 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 10 h but crystallized into CaSiO 3 and Ca 2 Mg 0.5 AlSi 1.5 O 7 phases at 900 °C or higher temperatures. Crystallization kinetics of the CMAS glass has also been investigated by differential thermal analysis (DTA). [ABSTRACT FROM AUTHOR]