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topic 2183

42 degree baume Nitric acid for steel mandrel


(1998)

1. Where can I get information relating Baume (specific gravity) to percent concentration for various acids?

2. I have recently seen the expression "42% absolute nitric acid". What does this mean and how does it relate to "percent concentration" and "Baume"?

3. The problem is that we are etching a carbon steel mandrel (12L14) out of a 6061 aluminum part and severely attacking the aluminum surface. The etchant currently being used is a "concentrated" nitric acid marked "50%". All former experienced personnel retired several years ago and are not available to answer the obvious question.

Richard Basil
- Redondo Beach, California


(1998)

Baume is another method of measuring specific gravity. There are conversion tables for it.

42 degree nitric is 67.18% nitric. This is a common commercial strength as it gives of a lot of NOx (a poisonous red cloud) at progressively higher strengths.

50% nitric would have a Baume around 35.

Most people use 50 % as half and half water and 42 baume nitric.

42 Be nitric will severely etch some aluminum alloys, such as those with high copper content.

Some companies will sell a 69 -71% nitric acid which will have a Be around 43 to 43.5 .

If you can get 44 Be nitric, and keep all water out, parts can not even be slightly damp, it will slowly eat the steel and not touch the aluminum.

You might have to add a little ferric chloride or a touch of hydrochloric to speed up the process. There is an extremely fine line of where it will eat the iron and not affect the aluminum alloy. Lab trials will be required.

Can you switch to 1100 aluminum? This is very nearly pure aluminum and it will not be affected by the nitric. A 50 -50 mixture will be able to eat the iron much faster than a 42 or higher Be nitric.

James Watts
- Navarre, Florida


(2003)

Where I can learn more about etching magnesium since I would like to incorporate such process to what I currently do (small moulds and dyes).

Arturo Zapien
- Leon, Gto. Mexico


Perry's ChemE Handbook

April 14, 2008

I was recently given a CAR by an aerospace prime contractor regarding the use of 42 degree Baume nitric acid in a solution and told that it did not comply with their specification requiring the use of 68% concentrate nitric acid. I responded that our chemist told me it was the same thing. Certifications from our nitric acid supplier confirmed this to be the case although the material certs did not indicate the degrees Baume. Thank you for clearing this up for me too.

Scott Putnam
metal finishing - Fountain Valley, California


September 23, 2008

You also asked for a source for converting % concentration of Nitric acid to sp gravity. Perry's ChemE Handbook =>
contains a table of the specific Gravity of Nitric Acid at various temperatures and % concentration. (note: Baume measurements are made at 60°F.)

Frank Rawolle
- Chula Vista, California



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