The system: CaO-B2O3

Abstract

The phase equilibrium diagram for the system CaO-B 2 3 has been partially worked out by means of heating curves. Completion of the diagram was impossible because the melting point of B2O3 could not be determined, while that of CaO was beyond the range of the apparatus. The following compounds were identified and their optical properties determined with the petrographic microscope: CaO-2B 2 3 , melting at 986° ±5° C; CaO-B 2 3 , melting at 1,154° ±5° C; 2CaO-B 2 3 , melting at 1,298° ±5° C; and 3CaO-B 2 3 , melting at 1,479° =1=5° C. Mixtures containing less than 23 per cent CaO were found to separate, on fusion, into two liquid layers, one of which contained 23 per cent CaO, while the other was nearly pure B 2 3. This immiscibility region extended above 1,500° C.