Preparation of Cyanide Zinc Plating Bath
Cyanide zinc plating is an electroplating process that deposits a layer of zinc onto a metal substrate. The cyanide zinc plating process provides deposits with good coverage, uniform thickness, and strong adhesion. In particular, cyanide zinc plating is ideal for large parts, intricate parts, and components with complex geometries.
Zinc plating baths are typically composed of a range of elements, including zinc, cyanide, and acid. The acid is used to facilitate the dissolution of the zinc, while the cyanide is used to promote the uniform coverage, strong adhesion and bright finish of the zinc deposits. The composition of the bath must be carefully managed to achieve the desired results.
Step 1: Dissolve Zinc in Water
The first step in preparing a cyanide zinc plating bath is to dissolve zinc into water. In most cases, it is necessary to use an acidic medium to facilitate zinc dissolution. For example, a diluted hydrochloric acid solution can be used to dissolve the zinc. Alternatively, ammonium chloride or sodium chloride can also be used.
The amount of zinc to be dissolved should be determined by calculating the desired zinc concentration in the bath. A general guideline is to use a zinc concentration of between 1 and 3 ounces per gallon (oz/gal). Once the desired amount of zinc is determined, it should be carefully added to the water with stirring.
Step 2: Add Cyanide
The next step is to add cyanide to the bath. Potassium cyanide is the most commonly used cyanide, although sodium cyanide and calcium cyanide may also be used. The amount of cyanide to be added is determined by calculating the desired cyanide concentration in the bath. A general guideline is to use a concentration of between 1 and 5 ounces per gallon (oz/gal). Once the desired amount is determined, it should be carefully added to the bath with stirring.
It is important to note that cyanide is a hazardous chemical, and extreme caution should be taken when handling it. Special safety precautions must be taken to prevent exposure to the toxic fumes that are created when the cyanide is added to the bath.
Step 3: Adjust pH
Once the desired amounts of zinc and cyanide are added to the bath, the pH of the solution must be adjusted. The ideal pH for a cyanide zinc plating bath varies depending on the type of substrate being plated, however, for most substrates a pH of between 8 and 11 is considered ideal. To raise the pH of the bath, an alkaline solution such as sodium hydroxide can be used. To lower the pH of the bath, an acidic solution such as a diluted hydrochloric acid solution can be used.
Step 4: Check and Adjust Bath Composition
Once the desired levels of zinc, cyanide, and pH have been achieved, the bath should be checked to ensure that it meets the desired specifications. This can be accomplished by measuring the electrical conductivity of the bath, which should match the desired conductivity for a cyanide zinc plating bath. Additionally, the bath should be checked to ensure that it contains no interfering contaminants that could affect the plating process.
If necessary, the bath composition can be adjusted by adding additional compounds such as potassium chloride, potassium carbonate, and/or ammonia. Finally, the bath should be filtered and degassed before use.
Cyanide zinc plating is an important electroplating process that is used frequently to deposit a layer of zinc onto a metal substrate. The bath must be carefully prepared to ensure that it is of the correct composition to provide the desired results. The process of preparing a bath typically involves adding zinc to a dilute acid solution, adding cyanide, adjusting the pH and checking for contaminants.
