Effect of Ca Hardness on the Pitting Corrosion of Copper in a Phosphonic Acid Solution and the Monitoring of Pitting Corrosion.

The effect of Ca hardness on the pitting corrosion of copper in open cooling systems that contain an inhibitor in the cooling water such as nitrilotris methylene triphosphonic acid(ATMP),benzotriazole(BTA),or sulfate of zinc (ZnSO4)has been investigated by immersion tests and electrochemical measurement.It was found that pitting corrosion occurred with difficulty when Ca hardness increased from 10 to 100.There was a close relationship between the electrochemical properties of corrosion potential after immersion for 420h ECORR/breakdown potential Eb and the occurrence of pitting corrosion in copper,such that occurred with difficulty when Eb• †ECORR.