Letter 13860

Making up a chrome bath

I made up a hard chrome solution with the specification of CrO3 at 225 to 247 gm/l and H2SO4 at 2.15 to 2.60 gm/l. After analysis my result was CrO3 is 226.38 gm/l and H2SO4 is 2.85 gm/l.The solution ratio is 100 : 1. How am I to get the H2SO4 within the required spec.? A check was made and the high H2SO4 came from the drag out of the sulphuric acid. Is wax use in masking good for the plating tank or using of masking tape? This is my first time making-up this hard chrome solution.

Thank you for the advice in advance.

Jonathan Tessensohn
- Singapore

Sulphate can easily be removed ie precipitated, from chrome solutions by adding Barium Carbonate. 2 Kg of Barium Carbonate removes 1Kg Sulphate approx Distribute evenly over the surface with stirring so that it is all reacted out. May I suggest that it is always best to not add all the calculated ammount of BariunC at once as often the analysis for sulphate is not exactly correct and also many baths work best at not exactly 100;1 so add 50 % of recommended addition then test plate, then next25% etc Always weigh the addition so if too much is added you can calculate out how much sulphuric has been removed and go back the other way.

This particularly applies to decorative chrome plating when trying to get maximum coverage.

Geoff Whitelaw
- Port Melbourne, Vic., Australia

Jonathan:

You can use BARIUM CARBONATE to lower the sulfate (sulfuric acid) in your chrome bath. Do this in a small amount first, To find out how much you should add to the complete bath if it is a large bath. Do your analysis frequently to find the amount for the complete bath that you have to add.

Tom Haltmeyer
- Peoria, AZ, USA

Dear friend you don't need to reduce your H2SO4 level as this type of bath can tolerate a wide fluctuation in Chromic acid and sulphuric levels however you can reduce the H2SO4 level by barium carbonate qty of which can be analyzed by a chemist. it will reduce sulphate level to barium sulphate and precipitate as it is not soluble in the bath electrolyte.

All the best,

VIKRAM
- CHANDIGARH, INDIA

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