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 Na₂O-CaO-SiO₂ 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 Na₂CaSiO₄ and Na₂Ca₂Si₂O₇ 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 SiO₂, Na₂Ca₃Si₆O₁₆, combeite, Na₄CaSi₃O₉ss, CaSiO₃, Na₂CaSiO₄ss, Na₂Ca₂Si₂O₇ss, Na₂Ca₆Si₄O₁₅, Ca₃Si₂O₇ and Ca₂SiO₄. 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 Na₂O-CaO-SiO₂ system. The present study also discusses the findings and their impact on melting and annealing processes during the manufacture of glass and glass-ceramics.