EFFECT OF INTERSTITIAL OXYGEN ON HYDROGEN SOLUBILITY IN TITANIUM, ZIRCONIUM AND HAFNIUM

Measurements of hydrogen solubility in Hf-O alloys with oxygen contents of 0.048-0.188 O/Hf were performed at temperatures of 600-850-degrees-C an H-2 pressure below 100 Pa using a constant-volume method. All the hydrogen solubility data for the Hf-O alloys closely followed Sieverts' law. The hydrogen solubility decreased with oxygen content. The enthalpy of solution for hydrogen was lower for the Hf-O alloy than for pure hafnium. These trends in solubility and enthalpy of solution for the Hf-O alloy were more similar to those for Ti-O than Zr-O alloys. Partial thermodynamic quantities for hydrogen in the Hf-O-H ternary system were estimated and compared with previous results for Ti-O-H and Zr-O-H ternary systems. The change in hydrogen solubility due to interstitial oxygen was inferred from the analysis to be attributable to a net result of the decreases in partial molar enthalpy and excess entropy of hydrogen.