Cadmium Plated on Steel

Ion vapor deposition (IVD) was developed from vacuum deposition by McDonnell Douglas Corporation. They used IVD of aluminum as a substitute for cadmium plating on steel aircraft parts. Aluminum provides corrosion protection similar to cadmium, it can withstand 925°F temperatures as opposed to 450°F for cadmium, and it is cheaper on a volume basis than either cadmium or zinc (Higgins 1989). Aluminum is also far less toxic than cadmium, and its use in an IVD system offers safer working conditions and less environmental risk. 

Standard probe body from cadmium-plated mild steel (other metals available on special order)... 

The hydrogen overvoltage of cadmium is rather large and cadmium may be used, plated on steel, as an alternative to lead. Cadmium has been used as cathode material in the hydrodimerization of acrylonitrile (Chapter 31). Magnesium may be used in reductive dimerization of aliphatic esters [459]. 

Cadmium is used in a number of industrial processes, but for most of its uses there are alternatives of lower toxicity. The principal applications of cadmium fall into five categories protective plating on steel, stabilizers for polyvinyl chloride, pigments in plastics and glasses, electrode material in nickel-cadmium batteries, and as a component of various alloys. 

The reproducibility of test results between labs using the neutral salt spray tests has not been consistent, but the repeatability, within one lab, is better, and the test has value in comparing variations in coating systems. Correlation of hours of exposure in the salt spray test to actual performance of the plated part in service, even in marine atmospheres, is not consistent and usually avoided. A classic example is that cadmium deposits outlast zinc deposits on steel in salt spray tests and clean marine atmospheres, yet zinc outlasts cadmium when exposed to real, industrial atmospheres, because of the presence of sulfur-bearing corrodents in industrial environments. An important variable in salt spray testing is the position of the surface to be tested. Whereas the surface of test panels is specified to be 15—30° from the vertical (40), when salt spray testing chromated zinc-plated specimens, this range has appeared excessive (41). 

Analysis methods for hydrogen absorbed in the deposit have been described (65), and instmments are commercially available to detect hydrogen in metals. Several working tests have been devised that put plated specimens under strain and measure the time to failure. A method for cadmium-plated work has been described (66) as has a mechanical test method for evaluating treatments on AlSl 4340 Steel (67). Additional information on testing for hydrogen embrittlement is also available (68). 

D. Berman, "Effect of Baking and Stress on the Hydrogen Content of Cadmium Plated High Strength Steels," paper 192 presented at Corrosion 85 NMCE, Materials Peformance, Boston, Mass., Sept. 1985. 

Ion Vapour Deposition A variant of the process is ion vapour deposition, in which a high negative potential is applied to the workpiece during chemical vapour deposition. The process has been employed on a commercial scale chiefly for depositing aluminium on to steel and titanium in the aerospace industry as an alternative to cadmium plating, which is liable to cause hydrogen embrittlement, especially of high tensile steel components. The aluminium is evaporated from a wire-fed resistance-heated boat . 

The other method is cadmium electrodeposition on a nickel-plated steel foil (serving as current collector) using a plating bath containing acidified cadmium sulfate (type AB2C3). In this case the user is supplied with a battery in charged ( ready for use ) condition. 

Fairly stable in steel containers at 65°C. Stability improves with increasing purity. Attacks tin, magnesium, cadmium plated steel, some aluminums slight attack on copper, brass, lead practically no attack on 1,020 steel, Inconel and K-monel. 

The pure metal is used in the cadmium and Weston standard cells, invaluable for the accurate determination of E.M.F s. It is sprayed on to steel to protect against corrosion sometimes it is plated on to steel prior to chromium plating. Alloys of cadmium with 2 per cent of Ni, or of 2 25 Ag plus o-2 Cu are used in -automobiles etc, as handles, and for other purposes. 

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