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Excess fluoride consumption in cold sealing bath?

Q. I am a chemist of Al anodizing company in sri lanka. I am having a problem with chemistry of sealing process. How is fluoride involved in the sealing process; why does pH increase; and why large difference in free fluoride and total fluoride?

Alanka Wijesundara
- Sri lanaka
February 18, 2012

I guess that I have been out of the business too long. I was not aware of fluoride being used in the seal process.

The answer to your question is aluminum fluoride complex ion. If I remember correctly, 6 fluoride ions will tie up with one aluminum ion. Most of it stays in solution and does not settle out, so when you titrate you are breaking the complex thus the large total fluoride and low available fluoride.

James Watts
- Navarre, Florida
February 20, 2012

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