Role of corrosion in the deposition of SrCO₃ crystals

Early work depicts two distinct effects resulting from corrosion of metallic substrates on the deposition of water-formed scales: (1) Corrosion increases the microroughness of the metal substrate surface, which in turn enhances the adhesion between scale and the substrate. As a result, under similar conditions, the rate of scale deposition on a corroding surface exceeds that on a noncorroding surface. (2) In the presence of oxygen, corrosion of the metal substrate may generate OH ions at the cathodic sites (oxygen reduction), thus causing a local rise in pH of the solution. In calcium bicarbonate solution, this should cause its conversion to calcium carbonate, which may deposit on the corroding surface. Recent work has identified SrCO₃ in actual scale samples from a wet producing well. The scale was predominantly CaCO₃ EPMA analysis of the scale samples showed that in the CaCO₃ scale, there were rod-like particles that contained SrCO₃ up to 15 wt%. This stimulated us to study SrCO₃ deposition in the laboratory. The current paper presents the results of experiments designed to deposit SrCO₃ crystals on substrates of carbon steel in order to examine if the corrosion reactions influence in any way the nucleation and growth of the scaling crystals in the initial stages of deposition.