无机水性金属微粉涂层工艺

1.无机水性金属微粉涂层的提出

以富锌漆和达克罗涂层等为代表的技术 直接利用非铁金属粉末参与形层，涂层防护功能强，形层过程无污染，逐渐引起人们的广泛关注。非铁金属粉末与有机或无机的粘结剂配制成涂料，刷涂或喷涂于工件表面，然后自然风干或加热烘干，形成涂层，例如有机富锌漆、无机富锌漆、达克罗涂层、交美特涂层等。 这些涂层技术的共同特点是，金属粉末在各种粘结剂和添加剂的作用下，通过物理或化学的作用，金属粉末直接参与形层，而无重熔、再结晶过程。据此，何明奕等人提出了金属微粉涂层的概念，即金属微粉涂层是采用非铁金属微粉，加入其他无机金属盐、有机或无机添加剂，以及表面活性剂和其他添加剂，采用喷涂、刷涂或其他机械力的形式，使金属微粉直接参与形成表面涂层的种表面处理技术。

2.无机水性金属微粉涂层形成原理

水性金属微粉涂层制备工艺涉及种类多，如富锌漆涂层、水性锌铝复合涂层、达克罗涂层(锌铬膜涂层)、交美特涂层等。但其形层原理有着共同的特点:采用片状(或微细颗粒状)锌粉或铝粉、无机金属盐水溶液、有机或无机还原剂混合成浆料，加人表面活性控制物质或其他添加剂，配置成水性金属微粉涂料，经过喷、涂、浸等工艺涂覆于工件表面，然后经过低温烧结或自然固化形成金属基涂层。水性金属微粉涂层的防护机理主要有三:其一是物理屏蔽作用，涂层阻止腐蚀介质渗透到基体表面;其二是涂层中部分添加剂起到缓蚀剂的作用，比如涂层中添加铬酸盐或铬酐，涂层固化或形成过程中溶出铬酸根离子，其强烈的氧化作用使金属表面钝化，从而产生优异的耐蚀性;其三就是涂层的阴极保护作用，大部分水性金属微粉涂层中的锌粉(或锌基合金粉、锌铝混合粉)的质量分数可高达80%以上，从而保证了锌粉/锌粉之间及锌粉钢基材之间良好的导电性，当水分侵人到涂层内，锌粉和钢基材之间即形成微电池，由于锌的电化学电位比铁负得多，所以就从锌粉向钢铁流过防蚀电流，从而对钢铁起到阴极保护作用。

3.无机水性金属微粉涂层的结合合机理

水性金属微粉涂层形成过程一般是在低温甚至室温下进行的，印但涂层和基体之间:一般仍使有的除层制备工艺采用后烧结固化操作，存在冶金过程或扩散过程。在除以物理结合为主，涂层/基体界面不存在冶金过程部分金属盐起到粘结剂层内部，因为涂料中添加了粘结剂或烧结过作用，致使金属微粉颗粒相互之间结合在在一起，构成涂层主体。

4.无机水性金属微粉涂层的应用

水性金属微粉涂层因具有环境友好、高强度件不产生氢脆、耐蚀性好、涂覆渗透性好等优点，被广泛应用于大型钢结构、汽车制造、家用电器小五金件等防腐领域，而且其应用已扩展到船舰等领域。

1. Preparation of Inorganic Water-borne Metal Powder Coatings
Technology such as zinc-rich paint and Dacromet coating directly uses non-ferrous metal powder to participate in the shape layer, which has strong protective function and no pollution in the shape layer process, and has gradually attracted widespread attention. Non-ferrous metal powder is coated with organic or inorganic binders, brushed or sprayed on the surface of the workpiece, then dried naturally or heated to form coatings, such as organic zinc-rich paint, inorganic zinc-rich paint, Dacromet coating [29], Jiaomeite coating [0.31]. The common feature of these coating technologies is that metal powder directly participates in the forming layer without remelting and recrystallization under the action of various binders and additives, through physical or chemical action. Accordingly, He Mingyi et al. (2.33) put forward the concept of metal micro-powder coating, that is, metal micro-powder coating is a kind of surface treatment technology that uses non-ferrous metal micro-powder, adding other inorganic metal salts, organic or inorganic additives, surfactants and other additives, and using spraying, brushing or other mechanical force to make metal micro-powder directly participate in the formation of surface coating.
2. Formation Principle of Inorganic Waterborne Metal Powder Coating
The preparation technology of water-borne metal powder coating involves many kinds, such as zinc-rich paint coating, water-borne zinc-aluminium composite coating, Dacromet coating (zinc-chromium film coating), Jiaomeite coating, etc. But the principle of its shape layer has common characteristics: using flake (or fine particle) zinc powder or aluminium powder, inorganic metal saline solution, organic or inorganic reducing agent to mix into slurry, adding surface active control substance or other additives, and configuring into water-borne metal powder coating, coating on the surface of workpiece by spraying, coating, dipping and other processes, then sintering at low temperature or solidifying naturally to form gold. Substrate coating. There are three main protective mechanisms of waterborne metal powder coatings: one is the physical shielding effect, which prevents the corrosion medium from penetrating into the surface of the substrate; the other is that some additives in the coatings act as corrosion inhibitors, such as adding chromate or chromic anhydride to the coatings, dissolving chromium ions during the curing or forming process of the coatings, and its strong oxidation effect passivates the metal surface, resulting in excellent performance. The third is the cathodic protection of the coating. The mass fraction of zinc powder (or zinc-based alloy powder, zinc-aluminum mixed powder) in most of the water-borne metal powder coatings can be as high as 80%, which ensures good conductivity between zinc powder and zinc powder and between zinc powder steel substrates. When water intrudes into the coating, micro-batteries are formed between zinc powder and steel substrates, due to the electrolysis of zinc. The potential is much more negative than that of iron, so the corrosion current flows from zinc powder to iron and steel, thus providing cathodic protection for iron and steel.
3. Bonding mechanism of inorganic water-borne metal powder coatings
The formation process of water-borne metal micro-powder coatings is generally carried out at low or even room temperature, but between the coating and the matrix: some of the delamination processes are still solidified by post-sintering, and there are metallurgical or diffusion processes. In addition to physical bonding, there is no metallurgical process in the coating/matrix interface where some metal salts play the role of binder layer. Because of the addition of binder or sintering effect in the coating, the metal powder particles combine with each other to form the main body of the coating.
4. Application of Inorganic Waterborne Metal Powder Coatings
Waterborne metal powder coatings are widely used in large steel structures, automotive manufacturing, household appliances and hardware fields because of their environmental friendliness, non-hydrogen embrittlement of high strength parts, good corrosion resistance and good coating permeability, and their applications have been extended to ship and other fields.

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