Surface Treatment of Titanium with Palladium an ECONOMICAL CORROSION PREVENTION PROCESS

Surface Treatment of Titanium with Palladium AN ECONOMICAL CORROSION PREVENTION PROCESS

Titanium, which has excellent resistance to metal is then passive. On the other hand corrosion, thus making it suitable for corro- palladium-plated titanium attains a potential sive conditions in chemical engineering, has well above the passivation potential irnrned- rather poor resistance to non-oxidising acids, iately on being introduced into the acid, and equipment for handling chlorides, for which indicates that it is superior to the alloy. example, is often fabricated from palladium- (Examination of this curve shows that after 22 titanium alloy, which resists crevice corrosion hours the potential of the palladium-coated in particular. titanium falls rapidly to a value more negative A low-cost process for the surface treatment than the passivation potential, but the authors of titanium with a very thin coating of make no comment on this aspect of the palladium has now been developed by Reiji potential-time curve.) Kawashima and Kineo Yamaguchi of Nippon The corrosion rates of titanium, 0.15 per Mining Co (Chem. Econ. Engng Rev., 1969, cent palladium-titanium and palladium- (Dec.), 20) to enhance the corrosion re- plated titanium (heat treated at low and high sistance of titanium. This process is claimed temperatures to form the alloy layer) to give results comparable to those obtained in hydrochloric, sulphuric, phosphoric, and with palladium-titanium alloys. acetic plus sulphuric acids have been studied The palladium is deposited on the surface and the results demonstrate the effectiveness of the titanium by electroless immersion of palladium plating in enhancing the plating (details of the plating process are not corrosion resistance of titanium. The authors provided), and the coated metal is then heat have also studied the crevice corrosion of treated to give a thin surface layer of a titanium and palladium-coated titanium in palladium-rich titanium alloy. The amount boiling 42 per cent magnesium chloride plus of palladium deposited is so small that it o.oo~Mhydrochloric and again demonstrate can be detected only by use of the isotope the effectiveness of palladium in controlling Pd109, but electron microprobe analysis of this form of localised attack. the alloy formed after heat treatment The authors claim that palladium-coated revealed a palladium-titanium alloy of titanium provides an economic method of -10-2op thickness, which the authors claim enhancing the corrosion resistance of titanium, is similar to that formed by a palladium- and that the corrosion resistance of the coated titanium alloy. metal is equal, or superior, to the palladium- Potential-time curves are presented that titanium alloy. The palladium-coating pro- compare the behaviour of titanium, I per cent cess, which has the advantage that it can be palladium-titanium and palladium-plated applied to selected areas of the titanium titanium in 5 per cent and 80 per cent structure, should have important applications sulphuric acid at the boiling point and at in the petrochemical and other industries, 25"C, respectively. In 80 per cent H,SO, the and should be particularly useful for titanium I per cent palladium-titanium alloy shows an structures immersed in seawater, where initial rapid decrease in potential followed by crevice corrosion is known to occur with a rapid increase to a potential that is more uncoated titanium. positive than the Flade potential, i.e., the L. L. s.

Platinum Metals Rev., 1970, 14, (2), 4747 47