Regions of phase crystallization in the ternary system Na2O-Al2O3-B2O3

The concentration and temperature regions of formation of crystals from different phases in the ternary system Na2O-Al2O3-B2O3 were determined using the results on spontaneous crystallization in various high-temperature solutions of this system. The study was limited to solutions in which the contents of the three oxides varied between 20 and 55 mol% for Na2O, 0 and 35 mol% for Al2O3 and 25 and 55 mol% for B2O3, respectively. Evaporation losses, creeping and extremely high viscosities were not observed in these solutions. In the above limits, the crystallization regions of Al2O3, NaBO2, NaAlO2 and the double oxyborate Na2Al2B2O7 (Na2Al2(BO3)2O) were determined. As Na2Al2B2O7 was found to melt incongruently at 970 ± 3 °C, this made the high-temperature solution growth most appropriate for obtaining its single crystals. Studies on the habit of Na2Al2B2O7 crystals grown in different zones of its crystallization region led to some preliminary conclusions concerning the composition of the flux growth solutions.