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"Analytical technique for confirmation of 49% HF solution"

May 6, 2010


I thought my question seemed rather simple until I started looking on-line for a suitable answer. I am trying to set up an etchant solution for the removal of Si Oxides. My customer has requested that I confirm the initial concentration of HF to be 49% and I have not been able to find any mention of a suitable analytical technique. We currently do not perform any HF analysis and I have seen posts explaining the use of Ferrous Sulfate, Thorium Nitrate and Specific Ion Electrode. What would be the most simple and least expensive method for confirming our solutions start with a 49% HF concentration?

Thanks for you help!

Rich Frits
Engineer - Derby, Connecticut

Ed. note: the author of the posting surely knows it, but for the benefit of others in this one-room schoolhouse called the internet, 49% HF is one of the most dangerous materials you'll ever work with, diffusing through your skin to dissolve your bones, sometimes anesthesizing the area so you don't know it's happening.

May 10, 2010

Ted's note at the bottom of your post is very important. Hopefully, you are starting out with 49% HF rather than diluting 70% with water. You can use small containers of 70% to top up with proper PPE.
An acid base titration is all you need as long as there are no other acids involved. Cheap, accurate, quick and reasonably safe.

James Watts
- Navarre, Florida

May 11, 2010

And I would go even simpler - buy it at 49% certified off the shelf and don't even test it. Just use it.

Terry Tomt
- Auburn, Washington

May 12, 2010

That is great for the initial start up, but as it is used it must be analyzed to maintain it within some preset limits.

James Watts
- Navarre, Florida

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