[en] 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