Thermodynamic properties of Ti in Ag–Cu–Ti alloys

The titanium activities at dilution in Ag–Cu brazing alloys have been measured at 1273 K by an oxygen sensor. The equilibrium oxide phase formed by the reaction of Ti in the eutectic Ag–Cu melts with Al2O3 crucible was TiO (solid). It was found that the Ti activity and activity coefficient in the eutectic Ag–Cu melts increase with the increment of Ti concentration and show a negative deviation from the ideal solution behavior at 1273 K. The Ti activity coefficient at infinite dilution is about 0.076 relative to pure solid Ti. Besides, the activity coefficient of Ti decreases with the increment of Cu concentration and increases with the increment of Ag concentration in Ag–Cu melts containing 1 wt.% Ti at 1273 K. Experimental results demonstrate that Sn decreases the activity coefficient of Ti in the Ag–Cu melts, probably due to its higher Ti solubility than Ag at the same temperature.