Ammonium Bifluoride

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.

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,

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,

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.

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.

A. The usual solutions for the removal of scale and rust from iron and steel products are hydrochloric or sulfuric 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 sulfuric. Also the use of an inhibitor are common and are optionally used to prevent over-etching and to avoid pitting.

Best regards,

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,

A. Hi Nigel,
Interesting that you can apply nitric/ammonia bifluoride etch post anodize before seal. At 25 sec 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

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.

Specialty Chemicals

Comparatively Speaking: Commodity vs. Specialty Chemical

Hi Aakansha. Yes, it is used in finishing products, certain cleaning products, glass etching products, etc. Apparently, somewhere around a million pounds is produced annually.

I think you would have to be very clear on exactly what "specialty chemicals" means to you before anyone could try to answer that question because per Wikipedia and other sources, ammonium bi-fluoride sounds more to me like a commodity chemical or pseudo-commodity chemical than qualifying as a "specialty chemical" (although I don't know of a list of one vs. the other).

Regards,

A. Hi Aakansha. When questions are posted I try to spend a few minutes of googling so I can learn from them, and as a courtesy to posters to not leave there questions unaddressed ... but I'm a plating equipment engineer not a chemical market researcher. I quickly found a reference which said a half million pounds was manufactured some years ago with projections of about a million by now; don't rely on my second-hand numbers though, find the sources of the data yourself.

Ammonium bifluoride is sold in reagent grade; I'm not sure about analytical grade or possible analytical uses.

Sorry, I don't understand what you mean by "being a toxic substance, is it preferable?". Certainly if a less toxic but affordable alternative is available for some particular purpose, that alternative would be used. In some ways it's less dangerous than hydrofluoric acid and is used as an alternative to HF in some applications. Good luck.

Regards,

A. Hi Aakansha, Ted,

Ammonium bifluoride is sold in analytical grade for some uses, we use it to remove iron in chromate analysis (you make an error in excess by oxidizing iron if you don't add it).

As Ted said, it is widely used as an alternative to hydrofluoric acid, and I don't know whether there is or not some safer alternative.

I think that if you are working manufacturing this product, the best you can do to know better the market is going to your actual clients and see for yourself what do they make with your product.

Best of luck!

A. Hi M. Commercial cleaners available to consumers are dangerous and contain 2-5% ABF. But whether that is the right strength for your application and how long you would need to dip those parts with unknown amounts of silica stain is hard to say ... but in order of magnitude probably several seconds to a minute or so; certainly not hours.

Chloride and fluoride are very different things and you need to be very careful of typos that could mislead you or others. You didn't introduce yourself and your situation, so we're not confident that you can safely use such fluorides (for example, is this an industrial application in a plant which has a safety program including haz-mat training? do you have Calcium Gluconate [affil links] on hand?). People are reluctant to suggest using fluorides unless you're quite sure what your white residues are. Where did they come from, what's the process? Would avoiding them through the use of DI water be more practical?

Good luck.

Regards,

A. Hi again. Several seconds to a minute of so in 5% ABF is the best guess I can make from this distance. No guarantees that this will fix your problem though, because over-etched aluminum may have other alloying ingredients left on its surface besides silicon. It's hard to say what corrosion protection you need, but aluminum is frequently chromate conversion coated. You might consider sending the parts to an aluminum processing shop who can etch, desmut, and conversion coat them for you. Good luck.

Regards,