Organic acid vapours and their effect on corrosion of copper: a review

Abstract

Carboxylic acids of low molecular weight, such as formic, acetic, propionic and butyric acids, as well as other acids (n-pentanoic, hexanoic, heptanoic, etc.), are present in rain, snow, clouds and particulate matter. They contribute about 16–36% of rain acidity. It is estimated that ∼64% of formic acid and ∼88% of acetic acid are in the vapour phase. Carboxylic acids are produced by the combustion of biomass, and analyses of the smoke from fire events reveal concentrations of about 300–500 ppb for formic acid and 3000–5000 ppb for acetic acid. Industrial emissions of carboxylic acid are produced by plants processing biological materials, such as food, paper, wood, etc. Acetic acid vapours are found in several industrial atmospheres. Vinegar is one important source of acetic acid vapours in food processing plants. The present review shows that for copper specimens exposed to organic vapours for 21 days at 100% relative humidity (RH) and a contaminant level in the range of 10–300 ppm, the relative aggressiveness of these acids is (from high to low): acetic>formic>butyric>propionic.