Thermodynamic evaluation of the copper-rich part of the CuHOSP system at low temperatures

A thermodynamic evaluation for CuHOSP has been made, with special focus on the phase stabilities and solubilities for OFP-copper (phosphorus-doped copper). All binary systems including copper have been reviewed. Gaseous species and stoichiometric crystalline phases have been included for higher systems. Calculations for OFP-copper give copper sulphide and copper phosphate as stable phases. No stable hydrogen-rich compound is found stable at atmospheric pressures. Calculations for oxygen-free copper (OF-copper) gives copper oxide instead of copper phosphate. This copper oxide has a lower stability than the copper phosphate, and the copper oxide is more easily reduced by hydrogen forming water vapour. This makes phosphorus an important alloying element for copper alloys in order to minimise the risk of hydrogen embrittlement in copper.