以黃銅及鑄鐵於氯化鈉水溶液探討浸泡試驗與電化學試驗評估腐蝕動力學之差異

The Difference of the Estimated Corrosion Kinetics between Immersion and Electrochemical Tests of Brass and Cast Iron in NaCl Aqueous Solutions

本研究選用黃銅（C27000）、鑄鐵（F32800）兩種輸水系統常用材料，於20℃~ 60℃之3.5 wt.% NaCl水溶液進行浸泡與電化學試驗，探討兩種原材是否發生選擇性侵蝕，並探討浸泡試驗與電化學試驗的腐蝕速率差異。實驗結果顯示，鑄鐵在浸泡試驗有氧化物生成與石墨化，電化學試驗則造成石墨化。黃銅在浸泡試驗與電化學試驗均發生脫鋅，反應速率與選擇性侵蝕隨溫度之昇高而愈增加。鑄鐵之腐蝕速率高於黃銅，反應活化能則低於黃銅。浸泡試驗與電化學試驗因試驗時間與表面生成物之不同，使黃銅電化學試驗的反應速率與反應活化能均高於浸泡試驗；但鑄鐵於浸泡試驗的反應速率卻高於電化學試驗，且兩種試驗所評估活化能幾乎相同。

The water supply system materials, bass (C27000) and cast iron (F32800) were selected in this study to investigate the selective leaching of materials and the difference in evaluated corrosion kinetics between electrochemical measurement and immersion tests. The corrosion tests were carried out in 3.5 wt.% NaCl aqueous solution at 20 ~ 60 ℃. The results show that there are some oxides formed, and graphitization occurred in the cast iron after immersion test. The graphitization occurs in the cast iron after electrochemical tests, but without corrosion products remained on specimen surface. The dezincification occurs in the brass after both immersion and electrochemical tests. The corrosion rate and selective leaching are increasing with increasing temperature for both materials. The corrosion rate of cast iron is higher than that of brass at all tested temperatures; however, brass behaved the higher activation energy. Due to the testing duration and corrosion products formed, the corrosion rate and activation of brass evaluated form electrochemical tests are higher than that of immersion tests. For cast iron, the corrosion rate estimated form immersion tests are higher than that of electrochemical tests, and the activation energies are near the same in the both kind of tests.