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Yellow Passivation color change

2003

Hi,

We do Zinc electroplating of steel trays using an Acid Chloride Zinc bath. We use a dichromate based bath to yellow passivate our components. Our Customers recently rejected our components saying that the colour of the passivated components after 1-2 months storage have changed to a darkish mixture of red, blue, green and yellow. The storage and packing conditions are pretty normal and we are in the dark about the probable reasons. Can anyone suggest measures to prevent such recurrences?

Thanks,

T. John
Manager - Chennai, Tamilnadu, India

I have experienced a similar problem to this in the past caused by uneven distribution of heat in the drying oven producing shades of green yellow and pinkish-red. Remember passivates decompose above 140 degrees fahrenheit. Perhaps you check the temperature at which you dry your components?

Nigel D Gill, B.Sc. MIMF AIEMA MRSC
- Glasgow, South Lanarkshire, Scotland
2003