铜管在羧酸环境下的腐蚀行为和腐蚀机理研究

铜管是空调及制冷行业用热交换器的核心部件，在服役过程中常由于蚁穴腐蚀导致设备提前失效。本文采用蒸气腐蚀、电化学腐蚀方法研究了铜管在羧酸环境下的腐蚀行为，通过金相显微镜（OM）、扫描电镜（SEM）、 X射线粉末衍射仪（XRD）观察和分析了表面腐蚀形貌和腐蚀产物的结构，通过接触角测量仪研究了羧酸与铜管的界面行为。结果表明，与CH3COOH蒸气腐蚀相比，铜管在HCOOH蒸气环境下的腐蚀速度慢，腐蚀产物更致密。在HCOOH蒸气环境下，铜管容易出现蚁穴腐蚀。铜管表面的腐蚀产物主要由羧酸铜和氧化亚铜组成。蚁穴腐蚀属于电化学腐蚀，腐蚀机理复杂。腐蚀初期，表面氧化膜被聚集在铜管表面的羧酸溶解，暴露的铜基体作为微观阳极，之后，腐蚀坑内产生的微裂纹的尖端作为微观阳极，使腐蚀加速，直至贯穿管壁。

Corrosion Behavior and Mechanisms of Copper Tube in Carboxylic Acid Environment

Copper tube is the key component of the heat exchangers used in air conditioning and refrigeration industry. However, the equipment is often failed in advance because of the ant-nest corrosion (ANC) of the copper tube during the service. In this paper, corrosion behavior and corrosion mechanisms of copper tubes in carboxylic acids were analyzed by vapor corrosion tests and electrochemical tests. The surface morphology and the structure of corrosion products were observed and analyzed by metallographic microscope (OM), scanning electron microscope (SEM) and X-ray powder diffractometer (XRD). The interface behavior between carboxylic acid and copper tube was studied by contact angle measurement. The results showed that the corrosion rate of copper tube in formic acid (HCOOH) vapor was slower and the corrosion product is denser than that in acetic acid (CH3COOH) vapor. HCOOH is more easily to cause ANC of copper tube than CH3COOH. ANC is a special electrochemical corrosion, and the corrosion mechanism is complex. The wettability of HCOOH on copper tube surface was worse than CH3COOH. In the early stages of corrosion, the surface oxide film was dissolved by the small droplets of carboxylic acid on the copper tube surface firstly. The exposed copper matrix acted as the micro-anode, and then the tip of the micro-crack generated in the corrosion pit acted as the micro-anode, and the corrosion rate was accelerated until it penetrated the tube wall.