Solubility of Hydrogen in Molybdenum and Its Alloys

Solubility of hydrogen in molybdenum and its binary solid solution alloys containing titanium, zirconium, vanadium and niobium, respectively was measured in the temperature range between 600 and 1200°C under one atmosphere pressure of hydrogen gas.The following results were obtained.(1) Relative partial molar entropy Δ\barSXS and enthalpy Δ\barH for hydrogen solubility in molybdenum were obtained as Δ\barSXS=−15.8 cal/g-atom·deg and Δ\barH=9.51 kcal/g-atom respectively.(2) The solubility increased with increase in the amount of each alloying element.(3) The entropy of the alloys first decreased with increase in the alloying elements and became almost constant with a value of approximately −17.5 cal/g-atom·deg. Vibrational frequency of hydrogen atom calculated from Δ\barSXS values was 3.0×1013 sec−1 for molybdenum and 4.0×1013 sec−1 for the alloys.(4) In Mo-Ti alloys, and Mo-V and Mo-Nb alloys containing more than about 10 at% of each alloying element, the enthalpy decreased monotonically with increase in electron/atom ratio.(5) Values of Δ\barSXS and ΔH in Mo-V and Mo-Nb alloys were minimum at the composition of about 3 at% of these alloying elements. Variation of these values seemed to be related to the electronic specific heat coefficient of alloys.(6) In Mo-Zr alloys, the lattice strain induced by alloying also affected the solubility.