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Received: September 13, 2017; Revised: October 27, 2017; Accepted: October 27, 2017
Abstract: The feasibility of using hydrazine for inhibiting pitting corrosion in copper sprinkler tubes was investigated by examining microscopical and structural evolution of corrosion by-products with SEM, EDS, and XRD. Hydrazine removed dissolved oxygen and reduced CuO and Cu2O as well. The stable phase was changed from CuO to Cu2O or Cu depending on hydrazine concentration. Hydrazine concentration of 500 ppm could convert all CuO corrosion by-products to Cu2O. In a tightly sealed acryl tube filled with aqueous solution of 500 ppm hydrazine, octahedral Cu2O particles were formed while plate-like structures with high concentration of Cu, O, N and C were formed near a corrosion pit. The inside structure of a corrosion pit was not altered by hydrazine aqueous solution. Uniform corrosion of copper was almost completely stopped in aqueous solution of 500 ppm hydrazine. Corrosion potential of a copper plate was linearly dependent on log (hydrazine concentration). The concept of stopping pitting corrosion reaction by suppressing oxygen reduction reaction could be verified by applying this method to a reasonable number of real sprinkler systems before full-scale application.