Impact of recently discovered sodium calcium silicate solutions on the phase diagrams of relevance for glass-ceramics in the Na2O-CaO-SiO2 system

Although phase relations in the Na ₂O-CaO-SiO ₂ system are vital to melting and thermal treatments in glass and glass-ceramics industries, the available data for thermodynamic modeling are mostly based on reports published in 1920s and 1950s. The present investigation verifies the formation of solid solutions of Na ₂CaSiO ₄ and Na ₂Ca ₂Si ₂O ₇ which have previously assumed to be stoichiometric compounds. The impact of these solid solutions on the features of the phase diagram were investigated using the equilibration-quenching-EDS/EPMA technique. The data were reported as liquidus projections and in isothermal sections within the temperature range of 1000 and 1400 °C. Ten primary phase fields were identified, namely SiO ₂, Na ₂Ca ₃Si ₆O ₁₆, combeite, Na ₄CaSi ₃O ₉ss, CaSiO ₃, Na ₂CaSiO ₄ss, Na ₂Ca ₂Si ₂O ₇ss, Na ₂Ca ₆Si ₄O ₁₅, Ca ₃Si ₂O ₇ and Ca ₂SiO ₄. In addition, some novel liquidus data and invariants points were examined in more detail. The fundamental data obtained can be employed for the thermodynamic reassessment of the Na ₂O-CaO-SiO ₂ system. The present study also discusses the findings and their impact on melting and annealing processes during the manufacture of glass and glass-ceramics.