Platinum Metals Rev., 1969, 13, (2), 67
Palladium-Titanium Alloy in Chemical Plant
The natural resistance of titanium to corrosion in oxidising conditions has been extended to reducing conditions by the addition of small amounts of palladium, and the wider use of titanium in chemical plant which this permits has been the subject of comment in this journal, most recently on the work of Takamura in Japan (1).
Whereas Takamura used the 0.13 per cent palladium-titanium alloy in hot concentrated chloride solutions, W. R. Fischer, of Friedrich Krupp, Essen, has now shown that the Krupp standard alloy containing 0.2 per cent palladium is most generally useful in extended tests with a number of chloride solutions (2). Adequate protection against crevice corrosion and pitting was obtained. However, in exceptional cases an alloy with more than 0.2 per cent palladium may be necessary where particularly awkward angles occur in fabricated chemical plant.
Fischer measured weight losses and potentials of palladium-titanium alloys with 0, 0.1, 0.5, and 1.0 per cent palladium in hot sulphuric acid and hydrochloric acids and in concentrated chloride solutions. His results show that 0.1 per cent palladium is inadequate to give titanium protection in reducing conditions but that 0.5 and 1.0 per cent alloys both give sufficient protection.
He warns that pilot tests to determine the most suitable palladium content are necessary in extreme conditions, where 0.2 per cent is insufficient. However, short-term tests may be inadequate as time is needed for the formation of the palladium-rich protective film.
The weldability of the alloys is comparable to that of ordinary titanium but the usual precautions are necessary. Pure dry argon should be used to prevent access of oxygen and nitrogen to the weld and iron and other metallic impurities must be excluded.
Fischer adds that a special palladium-tantalum-titanium alloy has yet higher corrosion resistance, especially in non-oxidising acids, and is available for special purposes.
- 1Platinum Metals Rev., 1968, 12, ( 2 ), 53
- 2W. R. Fischer, Tech. Mitt. Krupp Werksber., 1969, 27, ( 1 ), 19