Vacuum systems cadmium

Solder, tin-lead (vacuum technology) A solder alloy that contains tin and lead (63 37, 60 40) and does not contain any volatile constituents such as zinc or cadmium. It is thus suitable for use in a vacuum system. 

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. 

The Tygon tubing at the exit end is clamped off, and the two-way stopcock at the entrance is turned to a vacuum line. After the whole system has been evacuated, the silica tube is sealed first at the exit, and secondly beyond the rhenium(VII) oxide to give a 12-15-cm. ampul. Care must be taken not to melt the cadmium nor to resublime the rhenium(VII) oxide. The sealing operation is done with the tube in a horizontal position to prevent movement of the material. 

This shows that the reaction with zinc goes essentially to completion whilst an equilibrium mixture is observed in the cadmium system. It is therefore inadvisable to handle volatile organocadmium compounds in vacuum apparatus containing mercury, as the reverse of reaction (ii) can occur. 

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