Alkali Tungstates: Stability Relations in the Systems A 2 O WO 3 ‐WO 3

Phase relations in the systems alkali monotungstate‐tungsten trioxide were investigated in the range 600° to 1100°C.In the Li system, compounds with an A 2 O/WO 3 ratio of 1:2 and 1:4 are stable and melt incongruently at 745° and 805°C, respectively. In the Na system, the 1:2 compound melts congruently at 746°C, whereas the other 2 sodium tungstates (1:4 and 1:6) melt incongruently at 835° and 913°C, respectively. The K system includes compounds of 1:2, 1:3, 1:4, and 1:6 which melt incongruently at 684°, 842°, 912°, and 964°C, respectively. Eutectic points between the 1:l and 1:2 compounds in these respective systems are at 692°C and 56 mol%WO 3 , 622°C and 56.3 mol% WO 3 , and 633°C and 63 mol%WO 3 . In the Rb and Cs systems, the 1:2 and 1:3 compounds form complete solid‐solution series, and their melting temperatures increase with increasing WO 3 content, respectively, from 690° to 868°C and from 732° to 902°C. The 1:6 compounds are also stable in these systems and melt incongruently at 1040° and 1046°C, respectively.