Aluminum chlorinated solvents, corrosion

Many chlorinated hydrocarbons react readily with aluminum in the so-caHed bleeding reaction. A red aluminum chloride—chlorinated hydrocarbon complex is formed. Storage of uninhibited chlorinated solvents in aluminum vessels results in corrosion in a short period of time. Proprietary organic inhibitors permit commercial use of reactive solvents such as 1,1,1-trichloroethane and trichloroethylene for cleaning of aluminum. 

Chlorinated solvents, on the other hand, although nonflammable, are relatively toxic and contribute to pollution. In addition, they may leave chloride residues on the metal surface that can later initiate corrosive attack. They are used largely for vapor degreasing (tri- or perchlorethylene), in which the work is suspended in the vapor of the boiling solvent. Care must be exercised in the vapor degreasing of aluminum, ensuring that adequate chemical inhibitors are added and maintained in the chlorinated solvent in order to avoid catastrophic corrosion (see Section 21.1.4.1) or, in the extreme, to avoid an explosive reaction. 

Aluminum is characterized by (1) sensitivity to corrosion by alkalies and (2) pronounced attack by traces of copper ions in aqueous media. In addition, aluminum is subject to rapid attack by (3) mercury metal and mercury ions and (4) anhydrous chlorinated solvents (e.g., CCI4, ethylene dichloride, and propylene dichloride) [9,10]. 

Its use for handling chlorinated solvents requires careful consideration. Under most conditions, particularly at room temperatures, aluminum alloys resist halogenated organic compounds, but under some conditions they may react rapidly or violent with some of these chemicals. If water is present, these chemicals may hydrolyze to yield mineral acids that destroy the protective oxide film on the aluminum surface. Such corrosion by mineral acids may in turn promote reaction with the chemicals themselves, because the aluminum halides formed by this corrosion are catalysts for some such reactions. To ensure safety, service conditions should be ascertained before aluminum alloys are used with these chemicals. 

Boron nitride is one of the most outstanding corrosion-resistant materials. It is inert to gasoline, benzene, alcohol, acetone, chlorinated hydrocarbons and other organic solvents. It is not wetted by molten aluminum, copper, cadmium, iron, antimony, bismuth, silicon, germanium, nor by many molten salts and glasses. It is used extensively as crucible material, particularly for molten metals, glasses and ceramic processing. 

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