PHASE-EQUILIBRIA IN THE LI4SIO4-LI2SIO3 REGION OF THE PSEUDOBINARY LI2O-SIO2 SYSTEM

The constitution of the Li4SiO4-Li2SiO3 region of the pseudobinary Li2 O-SiO2 system was investigated between 1000 and 1300 degrees C by isot hermal heat treatment, differential thermal analysis, ceramography and X-ray diffraction. The two boundary phases of the sub-system, Li4SiO4 and Li2SiO3, melt congruently at 1258 degrees C and 1209 degrees C, r esp. An intermediate high-temperature phase, Li6Si2O7, forms peritecti cally at 1030 degrees C and decomposes eutectoidally at 1020 degrees C . A eutectic sub-system exists between Li4SiO4 and Li6Si2O7 with the e utectic temperature and composition of 1025 degrees C and 38.3 mol% Si O2, resp. Li6Si2O7 can be quenched to room temperature in a metastable stale and crystallizes in a tetragonal system with the lattice parame ters a = 770.9 pm and c = 486.0 pm.