Copper corrosion in molten sodium polyphosphate and sodium borates

Corrosion rates for Cu in melts of NaPO3 containing 0-80 mole% NaBO2, Na2B4O7, or NaB5O8 at 800-10000 decreased significantly with increasing concentration of the B compounds. Corrosion decreased in the series NaB5O8>Na2B4O7>NaBO2 at comparable concentrations. Average activation energies for corrosion were NaPO3-NaBO2 8.3, NaPO3-Na2B4O7 15.2, and NaPO3-NaB5O8 17.2 kcal/mole. Anodic polarization curves for Cu were determined at 8500 in melts containing 0, 20, and 100 mole % Na2B4O7, and the solubilities of CuO were determined for all melts at 8500. Addition of B salts reduced both anodic potentials and oxide solubility