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topic 11260

Ammonium Bifluoride


 

Q. What is ammonia bifluoride? What is its context in cleaning steel-substrate?

Jack Lim
- Penang, Malaysia


 

A. Ammonium bifluoride is a white crystal salt that when put in water forms HF. It is used to brighten aluminum and other metals. This chemical does an excellent job in brightening.

NL [last name deleted for privacy by Editor]
- Atlanta, Georgia


Ammonium Bifluoride

March 1, 2013

A. Hi Jack. Fluoride ions are the only thing that I am aware of that can dissolve silicon. Stainless steel castings, aluminum alloys, and some other metals may contain silicon which often must be dissolved or removed from the surface as part of the finishing process. For example, you can't anodize aluminum if it has excess silicon at the surface. But, as far as I can think of, it wouldn't be used in cleaning steel.

If properly managed, ammonium bifluoride can be somewhat less biohazardous than hydrofluoric acid (see letter 9462, "Hydrofluoric acid vs. ammonium bifluoride").

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



(2006)

Q. Can we use Ammonium bifluoride for crystal shining process? We use HF currently.

Asim Emir
ab-ka - Turkey


March 1, 2013

Hi Asim. This site focuses on metal finishing, and I don't know a lot about glass or crystal finishing . . . but hopefully a reader who can help you will wander onto this page.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



(2001)

Q. I have a concern. We are currently using Patclin 975 to brighten the aluminum in our plating line. I have to switch it to Ammonium bifluoride, but I am not sure the make up. Should we add Nitric acid or make it up with just water. I have a 6.2 gallon tank, so I don't know the appropriate amount of Ammonium bifluoride needed to makeup the solution. Any Ideas? Ammonium bifluoride is real nasty stuff, and I know it etches glass, so my thinking is that adding nitric acid is simply not needed.

Tim Shea
- South Deerfield, Massachusetts


(2001)

A. Please don't mix proprietaries like Patclin with non-proprietaries like nitric acid or ammonium bifluoride. Either take Patclin's advice, or switch to one of their competitors and take their advise, or start from raw chemistry. There is danger in adding things like ammonium bifluoride or nitric acid to a proprietary, because you don't know what's in the proprietary!

Nitric acid is one of the few oxidizing acids and its oxidation power is required for some applications. For example, copper does not dissolve in simple acids, but excesses of it must be removed from the surface of copper-bearing aluminum alloys before they can be anodized.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2001)

A. I'm not familiar with the Patclin product, but we've used scratch-built etchants here for years, including those with ammonium bifluoride.

We use nitric acid solutions ranging around 50% with anywhere from 1% to 10% ammonium bifluoride as a de-oxidizer/etchant. I would not use it as a brightener, it leaves more of a matte finish, but that resultant finish is dependent upon the aluminum alloy.

If you're looking for a bright dip, there are far better and safer solutions than bifluorides.

Bob Denney
avionics Tampa, Florida



(2005)

RFQ: Dear Sir ,

Please advise if you can provide us with ammonium bifluoride that we are seeking to import 2 FCL ,please quote us your best quotation , CIF Alexandria Port , Egypt.

Regards,

Ahmed Sadek
IMPORT EXPORT - Cairo, Egypt
^- Sorry, this RFQ is outdated
     View Current RFQs




(2000)

Q. I am looking for a pickle bath make up to strip some cast parts. I heard of a nitric ammonium bifluoride solution. What ratios? Are there other more suitable baths?

C Culp
- Tualatin, Oregon, USA


(2000)

A. The usual solutions for the removal of scale and rust from iron and steel products are hydrochloric or sulphuric acids. These are used in concentration ranges from a few ounces per gallon to very concentrated, depending on the type of work being processed. Cold rolled can be processed in weak hydrochloric acid, whereas heavily scaled construction plate is best pickled in sulphuric. Also the use of an inhibitor are common and are optionally used to prevent over-etching and to avoid pitting.

Best regards,

Rob Wells
- Pickering, Ontario


March 1, 2013

A. Hello, C. We are probably misunderstanding you. What material are the castings made of (aluminum, stainless steel, bronze, cast iron)? And what coating do you want to strip off of them (paint, powder coating, a metal plating of some sort)?

We don't know what coating you are trying to remove, nor what substrate you are trying to not harm, so the general implication of Rob's reply would be that you don't use ammonium bifluoride except when it is required (because it is a severe biohazard). Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



July 17, 2015

Q. We are presently making up a nitric acid/ammonium bifluoride
etch solution for aluminium. We are decorative anodising Jig Plate but are having problems with the finish, white spotting and stains. We believe as Ted has stated to have silicon in the aluminium.

The nitric acid in the solution is 50%. What addition of ammonium bifluoride should we add to the bath.

Nigel Bell
- Northern Ireland


simultaneous July 17, 2015

A. One pound per gallon.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como


July 21, 2015

Good day Nigel.

I am not familiar with aluminum Jig Plate material.
I have used this make-up prior to zincate/electroplate.
Nitric (for copper) - 50%. Sulfuric (for magnesium) - 25%. Water -25% Ammonium bifluoride (for silicon) - 8-16 oz/gal.
As you well know, there is a tremendous amount of heat generated during make-up. Extreme caution must be exercised, additions must be made EXTREMELY slowly, as I am sure you are aware.
I used a stainless tank lined with PVC, with sufficient space between to allow for a flowing cold water jacket.
During lab testing, I found conventional addition of acid to water generated extreme heat. I added the sulfuric to nitric, then water.
I am not by any means recommending this, but it worked for me.
This is a very nasty beast.
Hope this helps, and good luck.

Regards,

Eric Bogner
Lab Tech. - Whitby, On., Canada.


July 23, 2015

Q. Robert / Eric.

Thanks for your feedback on this. Our tank size is 400 litres. We have already added 25 Kg which equates to approximately 9 ounces per gallon. This seems to work well but if need be can move towards the 16 ounces. Our immersion time is 25 seconds.

Just a note. We are going into the nitric/ammonium post anodise for 25 seconds. We are aware that the anodic coating may strip so we are being very cautious. We did trials pre and post anodise, and post anodise is giving us a better finish. No white spotting or stains after dying and seal.

Regards
Nigel.

Nigel Bell [returning]
- Northern Ireland


July 23, 2015

A. Hi Nigel,
Interesting that you can apply nitric/ammonia bifluoride etch post anodize before seal. At 25s dip time, understandable it may remove some of the anodize coating but, as a point of interest, does it make the anodize whiter in appearance ? Thanks.

cheah

SK Cheah
- Penang Malaysia


July 27, 2015

info Hi SK,

We actually dye the parts red. The nitric / ammonium dip pre dye and seal brightens the anodising leaving the finish with a real sheen.

Regards
Nigel.

Nigel Bell
- Northern Ireland

----
Closely Related Threads:
Letter 9462, "Hydrofluoric acid vs. ammonium bifluoride -- are they interchangeable? Is one safer?"
Letter 34536, "How to Do Ammonium Bifluoride Analysis"




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