The a phase indicates ______. A: Sn rich phase B: Sn and Pb rich C: eutectic reaction D: Pb rich phase

During<br/>cooling of a material, when a single phase solid transforms directly<br/>to two-phase solid, this is called a ( ) reaction. A: isomorphous B: eutectic C: peritectic D: eutectoid

5-1.In the ternary system CaO-Al2O3-SiO2,<br/>there are 8 eutectic points, 7 double-peritectic<br/>points and 9 saddle point. According to phase rule, at most, it can<br/>be divided into ____sub-triangles A: 8个 B: 7个 C: 9个 D: 15个