Platinum Metals Rev., 1992, 36, (3), 149
Protecting Tantalum by Platinum Implantation
Tantalum is a suitable material for use in corrosive environments, due to the formation of a dense highly resistant oxide film on its surface. In hot concentrated mineral acids, however, it is attacked and although the loss of material may be acceptable in some circumstances the associated electrochemical evolution of hydrogen can cause serious problems. Tantalum readily forms hydrides, which are brittle and therefore cause loss of mechanical strength which could, perhaps, result in component failure.
It is known that palladium and platinum can protect tantalum from embrittlement, it is also known that a titanium surface modified by ion implantation with an electrocatalytically active metal can be effective in reducing corrosion. Now a communication from the University of Heidelberg, Germany, reports the results of an investigation of tantalum following platinum ion implantation, and its effect on hydrogen embrittlement (“Electrocatalytic Protection Platinum Implantation against Hydrogen Embrittlement of Tantalum in Strong Acids by Platinum Ion Implantation”, W. Ensinger and G. K. Wolf, Surf. Coat. Technol., 1992, 51, (1–3), 41–44).
Even a very small amount of platinum implanted in the surface of tantalum has a significant influence on the embrittlement by hydrogen, as determined by a mechanical bend test. Both the amount of platinum implanted, and the rate at which it was implanted had an effect on sample life; a low charging current and a high implantation dose being the most effective conditions. Implanted platinum reduces hydrogen adsorption electrochemically, it also decreases the entire corrosion process, including the cathodic hydrogen evolution reaction, and is effective for a long time in extremely corrosive environments, even though only a shallow layer of tantalum is modified. Thus tantalum implanted with platinum has greater scope as a constructional or protective material.