Products that may be Dangerous in Contact with Aluminium

Products that may be Dangerous in Contact with Aluminium The contact of aluminium with certain inorganic or organic products may lead to dangerous reactions, including explosion, splashes, etc. Several lists are available that include substances capable of producing such reactions with aluminium. In fact, a close analysis of such lists shows that there is very often a confusion between finely divided aluminium such as powder or granules and metal in the form of cast products or wrought semi-products: sheet, plate, profiles, bars, tubes, etc. This distinction is very important. Here are a few well-known facts:

-

-

-

The reactivity of massive metal such as that used commonly in the form of plates, sheets or profiles is in no way comparable with what can be deduced from certain thermodynamic data. The reason is simple: when aluminium is put in contact with the oxygen contained in air, it will be covered immediately by a continuous oxide film consisting of alumina, the thickness of which, between 5 and 10 nm, is sufficient to slow down and even annihilate the reactivity of aluminium with many products (see Section B.1.8), including air and oxygen, even at high temperatures. On the other hand, finely divided aluminium in the form of powder or granules has a very high reactivity with air, oxygen and numerous inorganic or organic products. During its manufacture, aluminium powder receives a passivation treatment that increases its stability at room temperature. Nevertheless, great precaution must be taken for the transportation, storage and use of finely divided aluminium. This issue is beyond the scope of the present volume. Turnings, chips, etc. resulting from machining of aluminium and aluminium alloys can, under certain circumstances (temperature, particle size), react violently with certain products such as organic solvents containing chlorine. For this reason, stabilised organic solvents have to be used in degreasing units, and any accumulation of fine turnings or machining chips at the bottom of the degreasing tank must be avoided.

Eventually, in contact with massive aluminium and aluminium alloys, only rather few inorganic or organic products are capable of provoking violent reactions that could present a hazard to workers or equipment. 603

604

Corrosion of Aluminium

Without aiming at (or being capable of) being exhaustive, the following products must be kept in mind:

-

-

concentrated inorganic hydracids, which even at room temperature react very actively with aluminium: Hydrochloride acid HC1, Sulphuric acid H2804, Hydrofluoric acid HF, concentrated inorganic bases Sodium hydroxide NaOH, Potassium hydroxide KOH, Halogens (in the presence of humidity) Chlorine C12, Fluorine F2, Bromine Br2, Iodine I, the following organic acids: Formic acid HCOOH, -

-

-

-

-

-

-

-

Chloroacetic acids (mono-, di-, and trichloroacetic acid) CHzC1COOH, CHClzCOOH, CC13COOH, and their derivatives such as sodium chloroacetates, the following halogenated derivatives: Methylchloride CH3C1, Methylbromide CH3Br, Methyliodide CH3I, Chloroform CHC13, Carbon tetrachloride CC14, Propylene chloride CH3CHC1-CHzC1, Ethyl bromide CH3CHzBr. -

-

All these products can react violently with aluminium and aluminium alloys, even at room temperature. The following chlorinated organic derivatives can react with massive aluminium and aluminium alloys around 50 ~ and this reaction can accelerate fiercely as the temperature approaches the boiling point of the product under consideration: -

Ethyl chloride CH3CH2C1, Ethylene chloride CHC1CH2C1, Ethylidene chloride CH3CHCI2, Vinyl trichloride CHClzCHzC1, Tetrachloroethane CHClzCHC12,

Products Dangerous in Contact with Aluminium

-

-

-

605

Pentachloroethane C13CHC12, Hexachloroethane CC13CC13, Propylene chloride CH3CHC1CH2C1, Dichloroethylene CHC1CHO, Trichloroethylene CC12CHC1, Tetrachloroethylene CC12CC12, Benzyl chloride C6HsCH2C1, Benzylidene chloride C6HsCHC12.

This information is given for information only, the reader is, therefore, invited to refer to official documents published by official organisations.