| Popis: |
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 Al 2 (WO 4 ) 3 , which has positive thermal expansion, and Sc2(WO4)3 with a negative thermal expansion. An optimum composition of Al 0.5 Sc1.5(WO 4 ) 3 was identified by synthesizing solid solutions, Al 2-x Scx(WO 4 ) 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, 25-700oC. A low temperature solution combustion process was developed for this optimum composition resulting in a single phase powder with a surface area of ~ 14 m 2 /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. |
