Synthesis, characterization, and densification of Al2-xScx(WO4)3 ceramics for low-expansion infrared-transparent windows

摘要

Materials and Systems Research, Inc. is developing a material with a low coefficient of thermal expansion (CTE) that could be used in an infrared-transparent window. The material is derived from a solid solution of Al2(WO4)3, which has positive thermal expansion, and Sc2(WO4)3 with a negative thermal expansion. An optimum composition of Al 0.5 Sc1.5(WO4)3 was identified by synthesizing solid solutions, Al2-xScx(WO4)3, by a solid-state route with compositions ranging from x = 0 to 2.0. A single orthorhombic phase was obtained at all compositions. A composition corresponding to x = 1.5 had a low CTE value of -0.15 x 10-6/oC in the temperature range, 25-700C. A low temperature solution combustion process was developed for this optimum composition resulting in a single phase powder with a surface area of ~ 14 m2/g and average particle size (as determined from surface area) of 91 nm. Preliminary densification experiments via dry uniaxial pressing and pressureless sintering at 1100°C for 2 hours resulted in a sintered compact 97.5% in density and submicron grain size.