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Chemical Stability and Compatibility - Acid digestion for Sn-containing alloy

 
I am currently analyzing samples of Sn-containing alloys, and I could not get reliable result for the Sn concentration. I dissolved the sample in aqua regia and diluted the solution until the final concentration of HCL is around 3%. However, I've found that the signal coming from Sn slowly disappears over time, which indicates that the solution is not stable. I'm aware now that Sn can easily precipitate out of the solution, and that HF is almost always needed to stabilize it in the solution. The question is how much do i need to add HF?
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admin Total posts: 529

The amount of HF necessary to stabilize metals is typically 6-8 moles of HF for every mole of metal. For example, 120 ug/mL (ppm) of Sn in solution is equivalent to approximately 1 mmol of Sn, so 6-8 mmol of HF would be recommended, which corresponds to roughly 0.02-0.03% (v/v) of HF (assuming concentrated 49 wt.% HF is used). These calculations assume that Sn is the only metal requiring HF for stability, and if other metals are present that also complex fluoride (e.g., Al), then the amount of HF required will increase.

Posted: 07/18/18 14:38:10

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