Iron impurities are very common in baths using acid zinc plating brighteners and are the most likely to cause failure.Usually, the accumulation of iron impurities is caused by the incomplete cleaning of iron parts after pickling, the workpieces falling into the galvanizing tank and not being pulled out in time to make them too corroded, and the use of some chemical raw materials that are not pure.So how should iron impurities be removed?
Bigolly Technology made an analysis based on the field experience and the characteristics of the product's acid zinc plating brightener BZ-528,A small amount of iron impurities has no effect on the zinc coating. After it is uniformly co-deposited with zinc, it will improve the corrosion resistance of the coating, but once the iron impurities exceed the limit, it will be counterproductive.Due to its small Ksp, Fe3+ exists in the form of Fe(OH)3 precipitation easily, and it only needs to be filtered out and supplemented with an appropriate amount of acid zinc plating brightener.
Since Fe2+ is similar to the standard electrode potential of Zn2+, Fe2+ has a great influence on the coating, mainly on the high area of the coating, which will form a gray or even rough coating.Since the Ksp of Fe(OH)2 is similar to that of Zn(OH)2, the concentration of Zn2+ will decrease by increasing the pH value and removing it by precipitation.
Therefore, the general method for removing iron impurities in the plating solution is:First, use hydrogen peroxide to convert oxygen Fe2+ into Fe3+, stir well, raise the pH to 6.2, and heat to 40-50 ℃, so that the generated Fe3+ precipitates well, and then raise the temperature to 70 ℃ to decompose the hydrogen peroxide in the plating solution , the plating solution is filtered and then adjusted to the process range, and an appropriate amount of acid zinc plating brightener can be added to produce.
Therefore, in the production process of using acid zinc plating brightener, we can effectively remove iron impurities in the plating solution according to the above method and reduce the occurrence of failures.