影响腐蚀的结构因素

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• 2. Distance Effect
• Another important factor for galvanic corrosion is the distance effect. Galvanic corrosion rates are the largest at the interface. As the distance between the anodic reaction site and the cathode reaction site increases the transport of the ions becomes more difficult and the corrosion rate decreases. • 电偶腐蚀的另一个重要因素是距离。电偶腐蚀速 率在阴、阳极界面处最大，离阴、阳极反应界面 越远，离子的迁移越困难，腐蚀速率越小。
lgi
电偶腐蚀电池形成原理
偶接后：M2为阳极，M1为阴极，电偶电流从M1流向M2。 M2发生阳极极化，腐蚀电流从icorr2增加到icorr2’ ；M1发生阴极 极化。腐蚀电流从icorr1降到icorr1’。 阳极体金属腐蚀速度增加的效应，称为接触腐蚀效应；阴极体 金属腐蚀速度减小的效应，称为阴极保护效应。
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一、电偶腐蚀原理
• 从混合电位的角度分析电偶腐蚀电池
形成原理，可以清楚地理解电偶腐蚀
过程。
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+E
设等面积的两种金属 M1 总还原反应 和 M2，当它们分别处于含 总氧化反应 H+为去极剂的腐蚀介质中 时，由于微电池的作用， icorr2’ 将各自发生共轭电极反应 n+ 1→M1 +ne Ec 金属 M1 M icorr1 2H++2e→H2↑ n+ 金属 M M →M i 2 2 2 +ne c icorr1’ icorr2 2H++2e→H2↑
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• The anode to cathode area effect is an important characteristic. It is important in several other forms of corrosion including pitting corrosion, crevice corrosion, stress corrosion cracking and corrosion fatigue. Remember the important effects of the anode to cathode area ratios. • 阴、阳极的面积比是一个非常重要的影响 因素。在其他类型的腐蚀中，如点蚀、缝 隙腐蚀、应力腐蚀破裂和腐蚀疲劳中，阴、 阳极的面积比也十分重要。
第二章 影响腐 蚀的结构因素
第三节 异种金属组合因素
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• Dissimilar metal corrosion results from the coupling of two different metals in a corrosive electrolyte. It is also called bimetallic corrosion or galvanic corrosion. • When a galvanic couple forms, one of the metals in the couple becomes the anode and corrodes faster than it would all by itself, while the other becomes the cathode and corrodes slower than it would alone. • 异种金属彼此接触或通过其他导体连通，处于同 一个介质中，会造成接触部位的局部腐蚀。其中 电位较低的金属，溶解速度增大，电位较高的金 属，溶解速度反而减小，这种腐蚀称为电偶腐蚀， 或称接触腐蚀、双金属腐蚀。
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• Therefore, if the current flowing between the anode and the cathode is one amp and the surface areas are one cm2, then the current density in each electrode is one A/cm2. However, if the area of the anode is only 0.1 cm2, then the current density in the anode with the same one amp flowing is 10 A/cm2. The corrosion rate depends on the CURRENT DENSITY in the anode. In this case decreasing the surface area of the anode increases the corrosion rate by a factor of 10.
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二、电偶腐蚀影响因素
Factors Affecting Galvanic Corrosion
• 1. Area Effect
• When current flows between the anode and cathode, the CURRENT will be the same in the anode and cathode independent of the surface area of each electrode. It is the CURRENT rather than the CURRENT DENSITY which is equal for the anodic and cathodic reactions. • 当电流流过阴阳极时，阴阳极电流应是相等的， 而与面积无关。要注意是电流而不是电流密度与 阴、阳极的反应速率相等。
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This is one of the most common forms of corrosion as well as one of the most destructive. Here’s a classic example of galvanic corrosion; a stainless screw in contact with a cadmium plated steel washer. 电偶腐蚀是最常见的腐蚀形式之一，也是最 具破坏性的腐蚀之一。图为不锈钢螺丝与镀 镉垫片接触，发生电偶腐蚀。