Effect of Sodium Sulfide on Hydrogen Absorption of Ti-6% Al-4% V Alloy

The hydrogenation inhibitive effect of sodium sulfide (Na₂S) on Ti-6% Al-4% V alloy (UNS R56400) in aqueous sulfuric acid solution (H₂SO_4[aq]) was investigated qualitatively and quantitatively using optical microscopy, x-ray diffraction (XRD), and glow-discharge spectrometry (GDS). Introduction of Na₂S into the electrolyte resulted in an obvious inhibitive effect of hydrogen absorption on as-received (covered with a thin thermal oxide film < 0.5 μm) and abraded specimens (free of thermal oxide film) irrespective of applied current density and operating period. The contrary effect of Na₂S on Ti-6% Al-4% V alloy vs ferrous alloys could have resulted from the fact that molecular hydrogen sulfide (H₂S), which adsorbed on the titanium surface as on the iron surface, facilitated formation of a thin layer of Ε titanium hydride (TiH₂). TiH₂ effectively retarded ingress of hydrogen.