Stable Tetrahedron NaBO2–Na2CO3–Na2WO4–K2WO4of the Quaternary Reciprocal System Na,K∥BO2,CO3,WO4

By differential thermal analysis using the calculation-experimental method, the phase diagram of the quaternary system NaBO2–Na2CO3–Na2WO4–K2WO4 was studied, and the coordinates of ternary eutectics and two quaternary eutectics were determined: E1□ (530°C, 5.6% NaBO2, 30% Na2CO3, 55.3% Na2WO4, 9.1% K2WO4). It was shown that the calculated and experimental data on the coordinates of the quaternary eutectics agree satisfactory.