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What is best alternative for chromic acid as postdip after galvanizing?

Hi. I am Raffy. Before we use chromic acid for chromating stage of our galvanizing line. However, since this chemical is not good for the environment, we stopped using this. But without this chromic acid, our galvanized sheet became dull or not as shiny than when we are using the chromic acid. What would be the best alternative for chromic acid? Thanks.

Rafael Jr. Balinas
Production Head - Manila, Philippines
August 26, 2009

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September 2, 2009

You say that chromate is not good for the environment, but how does it get into the environment?
Is this an issue with disposal of waste chemical? Or spillage? Is it claimed that the galvanized steel that has been chromate treated is bad?

Surely if used in a controlled manner it does not harm the environment?

Or am I missing something important here?

Now I don't like Cr either, but what alternative is there?
If you find one, (as effective) lets all know it!

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

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In the automotive industry they have largely gone to formulations called 'trivalent passivates' or 'trivalent chromates.' These are significantly more expensive than formulations based on hexavalent chromium. They function by generating hexavalent chromium, a highly effective corrosion inhibitor, during the corrosion process (and in the ASTM B117 test). For non-chrome (i.e., no hex and no tri) passivates, the best are based on silicates of one kind or another. Silicates are significantly less effective than chromates.

Tom Rochester
CTO - Jackson, Michigan, USA
Plating Systems & Technologies, Inc.


September 14, 2009

The Citrisurf Products made by Stellar Solutions [a finishing.com supporting advertiser] are a good option.

James Dougherty
- Brownstown, Pennsylvania, USA
September 23, 2009

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James,

you mention products by Stellar, but not which ones. None of those on their website appear to be for post galvanizing passivation as an alternative to chromate. Did I miss something?

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

September 27, 2009