Abstract
The effect of Cu, Cr and P on the buffer capacity, β of rust has been determined by measuring the titration curve (pH 1.5-7) of the suspension consisting of demineralized water and pulverized rust. Both “artificial rust” and natural rust were used; the latter being obtained by exposing steels containing one or combinations of the interested elements to the atmosphere for one year. The presence of such elements, particularly that of Cu in the artificial or natural rusts increases β at pH's between 3 and 7. The effect is similar in the rusts of the different origin and cumulative if more than two added elements exist. The materials balance based on the chemical analysis of the supernatant shows that β depends on the adsorption of acid in the rust and the dissolution of rust in acid. In the neutral region the effect of the former predominates, while in the more acid region both factors are effective. A rust layer having a high buffer capacity is able to reduce the corrosive action of sulfuric acid derived from the industrial atmosphere by resisting the lowering of pH.
