THE BINARY-SYSTEM PT-SI

The Pt-Si phase diagram which is still controversial on the Pt-rich side has been revised in detail (150 alloys) for specimens annealed for 4-5 months from 600 up to 950-degrees-C, by differential thermal analysis, X-ray powder diffraction analysis and microprobe analysis. The intermediate phase PtSi (melting point, 1238+/-3-degrees-C), Pt6Si5 (melting point, 1023+/-2-degrees-C; peritectic) Pt2Si (melting point, 1118+/-3-degrees-C) and Pt3Si (melting point, 876+/-2-degrees-C; peritectic) are confirmed to be stoichiometric. However, three other stoichiometric compounds have been located in the region of 20-32 at.% Si, with the composition corresponding to Pt25Si7 (found at 21.8 at.% Si), Pt5Si2 (28.6 at.% Si) and Pt17Si8 (32.0 at.% Si); both Pt17Si8 and Pt2Si undergo a polymorphic transformation. Pt7Si2 and Pt3Si are derived from the f.c.c. structure of Pt by deformation of the cubic cell.