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How to obtain light blue colour with alkali zinc plating

We apply alkaline zinc plating to our products but the colour is more dark and grey compared with acid zinc plating after blue passivation.Could you tell me how I can obtain light blue color same as the passivation after acid zinc plating.

Thank you advance.

Kaan Eroglu
metal equipment - Istanbul, Turkey
2003

PLEASE TELL US WHAT TYPE OF ALKALINE ZN PLATING . IF CYANIDE THE PROBLEM WILL BE DUE TO FAILURE OF CYANIDE OR INORGANIC CONTAMINATION SO YOU MUST MAKE ANALYSIS FOR CYANIDE CONTENT. IF IT IS OK, YOU MAY ADD SODIUM SULFIDE SOLN UNTILL YOU GET GOOD ZN COLOUR, THEN RINSE AND BRIGHT DIP IN 8 ML/L HNO3, THEN BLUE PASSIVATE.

ATIF .A BAR
- CAIRO, EGYPT
2003

In all alkaline baths you must attempt to the drag-out of the alkalis, if your HNO3 pre-dip do not have pH lower than 1,2; you don't became a good blue color and the white corrosion initialize in few hours (without salt spray). Attempt to the aspect from zinc after plating, if it is good, you have the chemicals conditions from bath else you must analyze and correct. Attempt to the aspect from zinc after the pre-dip, if you became mat, spotting or dark colors you have metal contaminants ad Natrium sulfide.

Franz Robert Wagner
- Santa Catarina, Brazil.
2004

Hi Kaan,

Alkaline zincs are susceptible to iron contamination. Make sure you use a caustic pre-dip before the zinc plating tank and try and keep dissolved iron out of the plating tank. Steel anodes and tanks are not a problem. As after-dip use 0,5 - 1% nitric acid and then blue.

Regards,

Trudy Kastner
electroplating service - Durban, KZN, South Africa
2004

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2004

Mr Kaan Eroglu,

We take it you use a zincate bath and it is composed of zinc and caustic and there is no cyanide in it.

For good blue follow this.

1) Use conditioner in the bath to precipitate Hard water salts and remove bad effects of iron , if any is present.
2) Use Purifier regularly as specified by supplier.
3) Rinse well after plating.
4) Use a 1-2 percent Nitric acid dip after rinse to neutralise the Caustic so the Blue chromate works well.
5) Do not overdose brighteners in excess over specified levels.
6) maintain caustic and zinc levels as specified.

Ensure you DO NOT USE CHEAP grade caustic soda [affil links] . Do not use Zinc Oxide unless you are extremely sure it is Copper and lead free. Use a Zinc generator to push up zinc. This is a off line tank in which Mild steel baskets hold zinc slabs to dissolve chemically and push up falling zinc levels. Use 99.995 Zinc anodes. Recast locally made anodes can produce bad chromate results. They sometimes contain lead.

If the problem persists , run 0.5 GPL zinc dust [on eBay or Amazon] for 2 hours over the FILTER. By the way I hope you DO have a regular filter. Alkaline zinc needs a filter.Continuous filtration is a must for good Blue...CONFIRM THIS ASPECT.

Regards,

Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016