Characterization of the Thermally Contracting Tungstates Ta ₂₂ W ₄ O ₆₇ , Ta ₂ WO ₈ , and Ta ₁₆ W ₁₈ O ₉₄

An investigation of the properties of high‐purity (>99 wt%) tantalum tungstates (Ta 22 W 4 O 67 , Ta, WO 8 , and Ta 16 W 18 O 94 ) included determination of density (bulk and theoretical), refined lattice constants, maximum use temperatures, micro‐hardness, heat capacity, thermal expansion (contraction) and diffusivity, calculated thermal conductivity, and electrical resistivity. Usable to ∼ 1700 K in air or inert atmospheres, these tantalum tungstates have theoretical densities of 7.3 to 8.5 g/cm 3 , are relatively soft (120 to 655 kg/mm 2 hardnesses), and are electrical insulators (6× 10 3 to 2× 10 8 Ω . cm resistivities). The distinguishing properties of the materials are their thermal expansion (average CTE values from + 0.6×10 −8 /K to −5.1× 10 −6 /K at 293 to 1273 K), thermal expansion hysteresis with minimal observable microcracking, and thermal diffusivity