黃銅水錶於自來水中腐蝕之機制與鉛、銅、鋅釋出之評估

Abstract

腐蝕對於住戶管線系統有很大的影響，可能會造成管線滲漏、管線堵塞以及管件微量物質的釋出。此研究的目的是要了解黃銅水錶在不同的自來水水質條件下腐蝕的情形。本研究藉由感應耦合電漿質譜儀(ICP-MS)偵測鉛、銅、鋅的釋出，並結合表面分析以及電化學方法來觀察黃銅水錶在自來水中腐蝕及腐蝕產物生成的情形。結果顯示因局部電化腐蝕，大量的鉛及鋅會自黃銅水錶釋出。在實驗初期(0-5天)，根據能量色散X射線光譜分析(EDS)，黃銅水錶表面的鉛及鋅的百分比含量有明顯的下降，伴隨著腐蝕電流密度的上升以及表層電阻阻抗的下降，這些結果能夠說明實驗初期有劇烈的腐蝕現象發生；在實驗後期(>10天)，根據金屬釋出及EDS結果進行分析，可以發現含銅及鉛的腐蝕產物在黃銅表面生成，而抑制了腐蝕反應，電化學的檢測亦證實此項結果。當自來水pH值降低，會促進鉛、銅、鋅的釋出，相反的pH值的上升能抑制金屬自黃銅水錶釋出。自由餘氯能夠稍微減少鉛的釋出，然而自由餘氯會大大提升銅及鋅的釋出。

Corrosion has adverse impacts on household plumbing systems, which may lead to water leak, pipe clogging and metal release. In this study, corrosion of brass water meter was investigated using batch experiments with various tap water conditions. The release of lead, copper and zinc was monitored using inductively coupled plasma mass spectrometry (ICP-MS) and electrochemical tests. Scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) was used to investigate the change of surface morphology and elemental composition of the corrosion processes. The results showed that high levels of lead and zinc were released from brass water meter due to localized galvanic corrosion among lead, copper and zinc. During the early stage of corrosion (0-5 d), the weight percentage of lead and zinc on the brass water meter surfaces decreased substantially as evidenced by the EDS results. The corrosion current density (Icorr) increased and film resistance (RF) decreased during that period. These results illustrated that severe corrosion occurred. During the later stage (> 10 d), according to the ICP-MS and EDS results, copper and lead corrosion products formed on the brass water meter surfaces, which retarded the corrosion process. The release of lead, copper and zinc was enhanced by a lower pH. Free chlorine was found to slightly reduce the release of lead while promote the release of copper and zinc.