phase diagrams of KCl-KBO2-K2CO3, K2MoO4-KBO2-K2CO3, and K2WO4-KBO2-K2CO3 ternary systems were studied by a calculation-experimental method and differential thermal analysis (DTA). The coordinates of ternary eutectics were determined to be E1: 622°C, 8.5 mol % KBO2, 56.5 mol % KCl, and 35 mol % K2CO3; E2: 710°C, 23 mol % KBO2, 43 mol % K2CO3, and 34 mol % K2MoO4; E3: 710°C, 23 mol % KBO2, 43 mol % K2CO3, and 34 mol % K2WO4. The specific heats of melting of the eutectics were determined.