Corrosivity of binary and ternary mixtures of some pure alcohols and alcohol/gasoline blends towards an aluminium alloy

The Sasol Dynamic Corrosion test apparatus has been developed further into a truly portable laboratory instrument with which the corrosivity of alcohols and alcohol/gasoline blends towards metallic fuel system components can be assessed semi-quantitatively. The size of the apparatus has been scaled down so that repeatable results can now be obtained with as little as two litres of sample being required for a 100 hour test cycle. The miniaturisation of the test apparatus has not compromised the high sensitivity of this accelerated corrosion test for alcohol-aluminium corrosion. The Miniature Dynamic Alcohol Corrosion (Mini-DAC) apparatus was used to assess the corrosivity of a range of binary and ternary blends of pure alcohols towards an aluminium alloy, LM-24, which had previously been found to be sensitive to alcohol corrosion. The same alcohol blends were also tested at concentrations of 12 vol% in a matrix of unleaded gasoline, with which lower boiling azeotropes readily form at the standard test temperature of 85 degrees C. All these tests were carried out without the addition of corrosion inhibitor additives. The results indicated that the boiling point distributions of the alcohol mixtures most probably had the biggest impact on the type and extent of corrosion caused by these blends. As in earlier work, it was found that the physical phenomenon of a boiling liquid may be a prerequisite for the onset of alcohol-aluminium corrosion. Thus the formation of azeotropes between alcohols may be of critical importance in determining the overall corrosivity of the alcohol blend at a set temperature. Temperature, however, remains the overall most critical influencing factor on the alcohol/aluminium reaction.