The System SiO ₂ –P ₂ O ₅

Abstract

Phase relations in the binary system between SiO 2 ‐P 2 O 5 and SiO 2 were investigated by the quenching method using sealed platinum tubes to prevent the loss of P 2 O 5 . The compound Si0 2 ‐P 2 O 5 exists in two forms, the low‐temperature β form inverting sluggishly but reversibly to the high‐temperature β form at 1030°C. The β form melts congruently at 1290°C. The compound 2SiO 2 ‐P 2 O 5 melts incongruently at 1120°C to a silica‐rich liquid and SiO a ‐P 2 O 5 . In the region between 5 and 25 mole % PO 2 , reactions were so sluggish that no data could be obtained by quenching.