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Nitric Acid Purity for Titanium Passivation

Hi,

We currently clean CP-2 Titanium metal parts in a mild soap solution, followed by 30% Nitric Acid. Then rinse in Hot DI water. We use bottles of 60% Nitric acid that cost ~$127/Liter (EM Science p/n 441-2). The specs on the EM Science acid lists ~40 impurities with values less than 0.005ppm. We have found a less expensive supplier (CCI) that will supply 55 gal drums for $300-$400. CCI only specs the 29.5-30.5%(v/V). Has anyone had a bad experience with Nitric acids with too many impurities?

Mark Curtis
- Northridge, California, USA
2003

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First of two simultaneous responses --

No bad experience with titanium, but some poor results on stainless steel using "Technical Grade" You should be able to find bottles of semiconductor grade nitric and the 2.2 liter (9 Lb ?) should only run about $10.00 a bottle in case quantities. Easier to handle than a drum, triple rinse and brake em up.

Jon Quirt
- Minneapolis, Minnesota
2003

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Second of two simultaneous responses --

I do not remember seeing a spec for impurities for nitric on titanium. You would like chlorides to be under 10 ppm if my failing memory is correct. Why just nitric? A half pound per gallon of ammonium bi fluoride will give a mild etch to the Ti that will make it look like a new dime on machined surfaces and clean up mill surfaces significantly. Some people call out for using Hydrofluoric acid instead of the bifluoride, but that is terribly nasty and not recommended unless mandatory.

James Watts
- Navarre, Florida
2003