Are Trivalent Chromates really Hexavalent Chromates after Salt Spray Testing?

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The latest Plating Surface Finishing magazine has an article by Tom Rochester that states that trivalent chromates under salt spray testing result in hexavalent chrome when using the diphenyl carbizide indicator test.

We at EPi tried this on panels that had been salt sprayed at Technimet and are initial analysis supports Tom's claim. One thing we didn't do and I wonder about other testing labs and metal finishers. Do they certify that the salt spray cabinet has no hexavalent chrome in that cabinet while they are doing salt spray of trivalent chromates? I remember one time we were doing testing on a trivalent chromate and we put some panels in and my chemist Mark Kulas informed me that we had an unusual failure after 24 hours. I went over with him and in the cabinet was pressure treated wood with different fasteners lodged into the wood. The wood preservative leaches out during the test and was the root cause of the failure. Where am I going? Make sure you document what other coatings are in the salt spray cabinet when you do testing. The labs love to throw a bunch of different parts to maximize there profits. Therefore, what EPi is doing is performing tests in cabinets that have been certified not to contain hex chrome and no other parts are in the cabinet during the test. We will be doing testing in a salt spray cabinet and a humidity chamber. Hey here is another interesting fact. Technimet recently expanded to new facilities and they had to move the cabinets. During the moving process they had to take out the cooling water that helps keep the temperature constant.  The problem was that cooling water had hexavalent chrome as a corrosion inhibitor. Could cooling water some how leach into the cabinet?

 

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