Stress Corrosion Cracking and Corrosion Behavior of Titanium in Methanol Solutions: Effect of Metal Ions in Solution

Abstract

Abstract A study has been made of the effect of additions of various metal ions to the environment on the intergranular stress corrosion cracking (SCC) and corrosion of unalloyed titanium in a methanol-hydrochloric acid solution. Separate additions to the solution of Pd, Au, Fe (ferric), and Cu (cupric) ions, in quantities ranging from 0.01 to 1000 ppm, caused substantial increases in both susceptibility to SCC and intergranular corrosion, without the resulting passivity reported for aqueous hydrochloric acid solutions. Electrochemical studies established that these increases resulted from the enhancement of the over-all cathodic process. In the absence of metal ions, the major cathodic reaction appears to be the reduction of dissolved oxygen, although another reaction, tentatively identified as the recombination of hydrogen ions, also contributes to the over-all cathodic process. Pd or Au ions deposited as metal films, detectable by X-ray techniques, and these films, once present, facilitated the recombination of hydrogen ions. No metal films were detected with ferric or cupric ions in solution, the additional cathodic reaction in these cases probably being the reduction of these ions to their lower oxidation states. The observations are discussed in terms of the mechanism of SCC.