Derived thermodynamic properties and phase diagrams of the rare earth-tungsten systems

The thermodynamic properties and binary phase diagrams of all the 16 naturally occurring rare earth (RE) elements with tungsten have been calculated using a regular solution approximation. The regular solution parameters were calculated from the published experimental solubility data of tungsten in the liquid RE metals and the thermodynamic properties of pure RE metals and tungsten. The liquidus for each of the systems was then calculated over the entire composition range using the appropriate regular solution parameter. All the RE-W phase diagrams are characterized by low liquid solubilities, negligible solid solubilities, absence of any intermetallic compounds and eutectics very close to the melting point of the RE metal. All the systems, with the exception of Sc-W system, exhibit monotectic reactions. The eutectic and monotectic points have been calculated in all the systems where they occur. The regular solution parameters, α and the atomic sizes of RE metals (for CN = 12) show a very good linear correlation. (orig.)