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The importance of ammonium zinc chloride in acid galvanising
Ammonium zinc chloride is not only used as the main salt to provide zinc ions, but is also a conductive salt itself, improving the electrical conductivity of the plating solution. With its high content and low resistance, the tank voltage is low, thus saving electricity. Learn more about the importance of ammonium zinc chloride in acid galvanizing together below!
Similarly, if the ammonium zinc chloride content is increased, the upper limit of the permissible current density rises, allowing for high current densities, higher build-up rates and productivity, shorter plating times without changing the thickness of the galvanised layer, and a reduction in the effect of metallic impurities; however, too high a content can lead to coarse crystallisation of the layer, roughness of the plating and poor deep plating ability. Insufficient levels of ammonium zinc chloride can cause a concentration split on the cathode, which is beneficial in certain amounts; however, if the concentration split is too large, excess electrons will concentrate on the plated parts due to the unavailability of zinc ions, and the plating will scorch, especially in the corners where the current density is high. In order to prevent scorching, the current density can only be reduced, but this will inevitably lower the productivity, reduce the uniform plating capacity of the plating solution and make it difficult to obtain a qualified plating layer for complex plated materials. Therefore, the concentration of zinc chloride during roll plating is generally lower than that of zinc chloride during suspension plating, and the low content of ammonium zinc chloride is conducive to improving the dispersion and coating capacity of the plating solution. Ammonium zinc chloride is usually controlled at 40-60 g/L for roll plating and 60-80 g/L for suspension plating; high zinc chloride concentrations are also used in the case of zinc plating on cast iron.
Within the permissible concentration range of ammonium zinc chloride, this is sometimes combined with the temperature of the plating solution in order to obtain a good coating. In general, the upper limit should be taken for zinc chloride in winter; the lower limit for zinc chloride in summer. The solubility of the anode plate is related to the pH and temperature of the plating solution, usually low pH and high bath temperature result in faster dissolution of the zinc plate; in general, it is important to maintain sufficient anode area to maintain the concentration of zinc ions in the plating solution, with minimal or no addition of zinc chloride.
There are still many problems with the quality of zinc chloride as a raw material for electroplating, mainly because manufacturers do not remove impurities of copper and lead. Therefore, when buying zinc chloride, it is important to buy something with a brand name and to go through the experiments of the Hal tank before placing it in the tank. Generally good zinc chloride is white crystalline tissue, also apply the phenomenon of dampness, otherwise do not use grey or grey zinc chloride. Anode zinc plates should be checked frequently to maintain sufficient anode area to provide zinc ions and minimise zinc chloride replenishment.
When adding ammonium zinc chloride, zinc chloride should be added to dissolve and then add the appropriate amount of zinc powder to stir and filter thoroughly before adding. Generally, half of the tap water is added to the reserve tank, then half of the pure hydrochloric acid is added and dissolved by putting in the head of a zinc plate that normally has insufficient anode area. Theoretically, 1 mol of zinc metal requires 2 mol of hydrochloric acid. This means that 65.4 g of zinc metal requires 209 g of 35% concentrated hydrochloric acid, or about 1 kg of zinc metal requires 3.2 kg of 35% hydrochloric acid. By adding zinc chloride in this way, not only can zinc chloride be added, but also the pH can be adjusted, which is usually useless for the rest of the galvanised sheet head.
The above describes the importance of ammonium zinc chloride in acid galvanising. For more information, feel free to contact us!
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