给外行人, the daily operation of a phosphate bath can appear daunting – perhaps even a bit convoluted. While temperature and concentration are common parameters for most chemical applications, 两种磷酸盐浴都增加了复杂的酸点, 酸比率, 溶解的铁, 油泥, 加热源, & 更多的. 在这篇文章中, we will highlight some of the key features of these processes and discuss how they can influence your finished coating.
The phosphate coating that develops in these applications is the result of several cyclical competing reactions that occur within the solution and on the surface of the part. Temperature is a key driving force in allowing this reaction to occur, 所以这些浴池的温度才会这么高. 通常, a phosphate bath is going to require a temperature over 180°F, the specific operating temp depends on the co-metal and the specific product being used. Running the bath below temp can prevent the reaction from progressing correctly, 导致了一个粗糙的, grainy coating – or no reaction at all; run the bath too hot, 你可以提高游离酸的浓度, 可能会对贱金属造成不必要的攻击.
Achieving and maintaining these temperatures relies on an adequate and reliable heat source; however, 在这个场景中，并不是所有的都是平等创建的. One peculiarity of phosphate solutions is that they are sensitive to large temperature gradients, 并逐渐加热溶液为佳. 强烈的, 局部热源, 比如燃气燃烧不足的油箱, 破坏溶液的化学平衡. This leads to the bath’s parameters deviating from the operating range, and subsequently negatively influencing the resulting coating. 一般, 这些浴池是用浸入式蒸汽盘管或蒸汽板加热的, which heat the solution over a larger surface area and disperse the heat throughout the solution. 其他 methods include tanks with an insulated jacket heating system that uniformly heats the surroundings of the tank. 大容量澳门威尼斯人网上赌场也可以利用直接, live steam to heat the bath which when combined with automatic dosing can help to compensate for the volume loss due to drag out.
Perhaps the most confusing aspect of phosphate applications would be their total and free acid values. Many chemical applications require a certain concentration for standard operating procedures, 哪一个可以通过简单的滴定快速观察到. Phosphate solutions are primarily formulated with phosphoric acid and similarly made up with some prescribed initial concentration. This value is reflected in what is referred to as the “total acid” value or points – note, that this does not necessarily directly translate into a % concentration by volume. 总酸是通过滴定到中性pH值来测定的, 与酚酞配合使用, to measure all the contributing components to the solution’s acidity. Adjustments to the total acid value are made by the addition of stock products to the bath.
What is unique with phosphate baths would be the “free acid” metric of the solution. 如前所述, 这些化学物质以磷酸为基础, 哪一种具有三protic酸的独特特性. 在本质上, it has three acidic protons (hydrogen ions) in the molecule and in solution, it exists to varying degrees in 4 separate states all at the same time. In phosphate applications, this value is the primary constituent to the overall reaction mechanism. 如果游离酸过低, the coating will fail to develop; if the free acid is too high, the solution is effectively too reactive and can attack or etch the base metal. The free acid value can be increased by heating the solution without processing work and can be decreased by adding a neutralizing agent to the bath.
Another nuanced aspect of total and free acid is the ratio between the values. This is simply determined by dividing the total acid and free acid values. When a bath is initially made up, the ratio of these components is generally 6:1 total to free acid. 如前所述, 这些浴场是波动的, dynamic systems; and as these baths are used and begin to age, 酸值开始偏离. While different products will curate specific target ranges for these values individually, the ratio between the values is also important as it suggests a relative composition of the constituents, 与总浓度无关.
Lastly, iron concentration is another key component that is monitored in phosphate applications. 正如之前简单提到的, these reactions can utilize either zinc or manganese as a co-metal in the crystal development. In addition to these co-metals, iron is also fundamental in the formation of these crystals. The recommended iron concentration is specific to the product and application but can range anywhere from 0.0-0.4%. Iron levels also have a direct correlation with the resulting coating weight as they add mass to the crystals. 初次化妆时, 溶液中不会有铁溶解, which is why the baths are often “broken in” with scrap metal or steel wool to dissolve into the solution and increase the iron level. 一些澳门威尼斯人网上赌场被设计为“无铁”运行,” and will utilize an oxidizing agent or an “accelerator” to precipitate out the excess iron to achieve low coating weights. Determining the iron level is done with a titration involving permanganate, 哪种是强还原剂.
Understanding the state of your bath and how to manipulate it is an important aspect of successfully operating these applications. Each of the aspects described has a resulting impact on the quality of the coating and serves as key indicator ahead of a successful application.
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由:Connor Callais贡献
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