The Corrosion and Electrochemical Behaviour of Ductile Chromium Alloys BENEFICIAL EFFECTS OF PLATINUM GROUP METAL ADDITIONS

Until recently the brittleness of chromium and its alloys has limited their use in applications which require a high resistance to corrosion in oxidising environments. Now, minor additions of selected metals can produce alloys with satisfactory low temperature ductility and work-ability, but even these alloys are susceptible to corrosion in non-oxidising environments. Passivation and corrosion resistance in such conditions can be increased by cathodic additions of noble metals; this paper reports a study of the efects of such additions on the corrosion and electrochemical behaviour of ductile chromium alloys in non-oxidising environments. The high corrosion resistance of chromium and its alloys in oxidising environments makes them promising construction materials for use in chemical, oil refining and other industries. Formerly their employment has been limited by their brittleness but in recent years minor additions of several metals have been made to chromium to produce alloys with adequate low temperature ductility and workability ( I, 2). However, the extra opportunities created by these new alloys are still limited by the fact that chromium alloys are generally susceptible to corrosion in non-oxidising media such as hydrochloric and sulphuric acid solutions. I t has already been shown (3, 4, 5) that the tendency to passivation, and the corrosion resistance of chromium in a non-oxidising acid environment, can be increased by alloying with certain noble metals. A more detailed study of the electrochemical be-haviour of these alloys and its effect on their corrosion has now been made. Ductile alloys with 0.1 to 0.4 weight per cent of ruthenium, osmium, or iridium or up to I per cent of rhenium were prepared at th