A radiotracer study on the reaction between zinc and chromate — II. The corrosion of zinc in dilute chromate solutions

Abstract

The reaction between zinc and chromate has been studied in solutions varying in concentration between 5 × 10 −6 and 7·5 × 10 −4 M using a radiotracer technique. The uptake of chromium from solution increases with time according to A n = kt where n varies between 1·5 and 3, depending on the concentration of chromate in solution, and log k is a linear function of n. The uptake equation is rewritten in terms of two new constants A 0 and t 0 representing a critical film thickness and the corresponding time for its formation. Experimental values of A 0 and g= 0 are found to amount to 5·690 × 10 −7g cm −2 and 465·3 h respectively. In the concentration range studied chromate accelerates the corrosion of zinc but above 7·5 ·x 10 −4 M the uptake of radioactivity follows a direct logarithmic law and inhibition of corrosion takes place.