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镀锌件镀锌彩钢板等漆防腐原理大揭秘

返回列表 来源: 发布日期: 2020.08.07

镀锌件镀锌彩钢板等漆防腐原理大揭秘

镀锌件上的油漆容易脱落。比如镀锌水管、白色镀锌铁皮等,普通的醇酸漆容易脱落,一些工业镀锌结构,由于对油漆附着力要求很高,普通环氧漆不称职,镀锌件用什么油漆附着力好,不掉漆?这里,在重防腐涂料领域,镀锌层的防腐原理总结如下:

1) 阴极保护
镀锌件冷镀锌层主要是通过电化学保护来防止钢材腐蚀。根据电化学腐蚀理论,腐蚀电池中电极电位较低的阳极经常被腐蚀。锌的标准电极电位为-0.76v,比铁的标准电极电位高-0.44v,当涂层受到腐蚀时,先腐蚀锌粉作为阳极,钢作为阴极受到保护。冷镀锌层的锌粉在保护过程中逐渐消耗,但速度很慢。腐蚀产物的形成降低了涂层与基体之间的电位差。当涂层被破坏时,新鲜的金属锌暴露在外,电位差立即增大,产生强烈的阴极保护作用。也可称为冷镀锌的“自修复”。锌在自然环境中的化学反应方程如下:(2)锌盐的保护作用,锌的化学活性大于 镀锌件铁,更容易失去电子。作为牺牲阳极,它可以保护钢表面。同时,随着锌粉的消耗,ZnO、Zn(OH)2和碱式碳酸锌[2znco3·3zn(OH)2]粉体沉积在涂层孔隙中,增加了镀层的致密性,起到了屏蔽作用,减缓了电化学腐蚀速率,大大降低了锌粉的消耗率,提高了耐用性。另据报道,这些碱性沉积物的存在起着化学钝化作用。(3) 有机树脂冷镀锌的屏蔽效果含有特殊的有机混合树脂。漆膜形成后,能阻止或抑制水、氧和离子通过涂层,从而将腐蚀性介质与钢材隔离。涂层的屏蔽作用也减缓了钢的腐蚀速度。
镀锌漆(冷镀锌漆)在钢结构中的优异性能:在我国,热浸镀锌钢材主要用于输电线路的杆塔。但由于环境污染和全球气候恶化,近年来镀锌层的实际使用寿命远远低于设计时的预期寿命。在干燥的空气中,镀锌层具有良好的防护性能,但在沿海、潮湿、酸雨环境中,其耐腐蚀性明显降低,为了延长其使用寿命,必须在其表面涂覆。

The paint on galvanized parts is easy to fall off. For example, galvanized water pipe, white galvanized iron sheet and so on, common alkyd paint is easy to fall off, some industrial galvanized structure, because of the high demand for paint adhesion, ordinary epoxy paint is not competent, what paint used on galvanized parts has good adhesion, do not drop paint? Here, in the field of heavy-duty anti-corrosion coating, the anti-corrosion principle of zinc coating is summarized as follows :

1) Cathodic protection
The coating of cold galvanizing is mainly used to prevent steel corrosion by electrochemical protection. According to the theory of electrochemical corrosion, the anode with lower electrode potential is always corroded in the corrosion battery. The standard electrode potential of zinc is -0.76v, which is more active than that of iron-0.44v. When the coating is eroded, zinc powder is corroded first as anode, and steel as cathode is protected. The zinc powder of cold galvanized coating is gradually consumed in the process of protection, but the speed is very slow. The formation of corrosion products reduces the potential difference between the coating and the substrate. When the coating film is damaged, fresh metal zinc is exposed, and the potential difference increases immediately, resulting in strong cathodic protection. It can also be called "self repairing" of cold galvanizing. The chemical reaction equation of zinc in natural environment is as follows: (2) the protective effect of zinc salt, the chemical activity of zinc is greater than that of iron, and it is easier to lose electrons. As a sacrificial anode, it can protect the steel surface. At the same time, with the consumption of zinc powder, ZnO, Zn (OH) 2 and basic zinc carbonate [2znco3 · 3zn (OH) 2] powders were deposited in the pores of the coating, which increased the compactness of the coating, played a shielding role, slowed down the electrochemical corrosion rate, greatly reduced the consumption rate of zinc powder, and improved the durability. It is also reported that the existence of these alkaline sediments plays a chemical passivation role. (3) The shielding effect of organic resin cold galvanizing contains special organic mixed resin. After the film is formed, it can prevent or inhibit water, oxygen and ions from passing through the coating, so as to isolate the corrosive medium from the steel. The shielding effect of the coating also slows down the corrosion rate of steel.
The excellent performance of galvanized paint (cold galvanized paint) in steel structure: in China, hot-dip galvanized steel materials are mostly used in transmission poles and towers of transmission lines. However, the actual service life of zinc coating in recent years is far less than the expected life at the time of design due to environmental pollution and global climate deterioration. In dry air, zinc coating has good protection performance, but in coastal, humid, acid rain environment, its corrosion resistance is significantly reduced, in order to extend its service life, it has to be coated on its surface.

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