Phase diagram investigation and thermodynamic study of Os-B system

The constitution of the Os-B system was investigated in this work. The phase regions were determined by metallographic investigations. The existence of the following borides was confirmed: OsB1.1 (hex.), Os2B3 (hex.) and OsB2 (orthorh.), while the new high temperature Os2B3 compound with a not yet identified structure was observed. OsB1.1 melts congruently at 1820 +/- 15degreesC and OsB2 at 1870 +/- 15degreesC, while the solid solubility of B in Os was found to be less than 0.5 at%B. Considering thermodynamic study of this system, the activities and activity coefficients for osmium and boron were determined in temperature interval 3300-3500 K, based on the known liquidus and solidus lines from phase diagram, according to calculation procedure given by Rao and Belton.