Sciencemadness Discussion Board - is hydrofluoric acid good cleaner for aluminum? what metal is it compatible?

is hydrofluoric acid good cleaner for aluminum? what metal is it compatible?

felizer - 17-7-2006 at 17:05

AllanD - 17-7-2006 at 18:06

define "clean".

What exactly are you trying to do?

HF is dangerous stuff because of the biochemical changes in the body that it causes.

AllanD

woelen - 17-7-2006 at 22:47

If you don't know the chemical HF very well, and have no real ideas of the risks involved, then DO NOT USE IT! HF will kill inexperienced people. If not immediately, then at least in the long run.

Flip - 18-7-2006 at 09:14

HF is an ingredient in some commercially availiable aluminum cleaners. So the answer is yes. Probably best to just buy those, however.

BromicAcid - 18-7-2006 at 17:21

Once upon a time I was watching an episode of 'Modern Marvels' and they were talking about making soda cans. One of the key steps was a quick dip of the can in some HF. Just to give it a nice shine. So, again, yes, it is likely above average in its aluminum cleaning capacity otherwise a different acid would be used as HF is toxic to a noteable degree.

Off topic (of aluminum at least) I was reading through a book of agricultural tools (plows, pumps, mowers, etc) and they had a section on hand pump sprayers (the kind that sit on the ground and you pump them and they have a spraying wand). They happened to have an 'acid sprayer' for muratic acid / phosphoric acid / and hydrofluoric acid.... That just made me stop and go "Hummmm...."

IrC - 18-7-2006 at 19:30

"HF is an ingredient in some commercially availiable aluminum cleaners."

Indirectly for many if not most of them, as they contain ammonium bifluoride. Gotta love that ammonia smell that goes along with the shine. Somewhere I remember reading about aluminum polishes trending away from ammonium bifluoride due to the extreme hazards involved. Found the link while searching around for HF and data on it's dangers. The more I surfed the further in the back of the storage cabinet I pushed my bottle of HF.

Odyssèus - 18-7-2006 at 19:35

In a rock shop they were selling little 1/8 inch^3 pieces of flourite for like $0.40. I just thought: nooo, I'm not going to be doing anything chemical with THAT.

AllanD - 19-7-2006 at 15:44

Commonest consumer use of HF is as "rust stain remover"

Even dilute I still don't like working with it, though I used to use it to etch glass when making epoxy repairs to vacuum bells
(epoxy sticks better to the etched surface)

AllanD

futurenobellaureate - 20-7-2006 at 06:49

Hydrochloric acid is used in industry to clean aluminum.

franklyn - 20-7-2006 at 13:22

Oxalic acid is safer though it requires more elbow grease.

Note that if you ingest this, it too will damage your liver.

.

silonyl - 30-8-2006 at 06:49

First, HF is a very hazardous substance when concentrated, and must be treated with the utmost respect. Its toxicity is also pretty interesting, and this is what I remember:

The concentrated acid causes massive deep tissue injury from even minor contact because HF, being so tightly bound, diffuses deeply into tissue instead of dissociating as soon as it hits something moist. Workers frequently report only mild burning on initial contact, only later suffering from very painful damage to the underlying tissue and sometimes (see below) even death.

*sidebar: HF is actually a weak acid because it is only slightly dissociated in H2O... though weak of course does not imply safe*

**edit: fixed to reflect correction below**
A more serious health consequence is precipitation of blood calcium as the insoluble fluoride, CaF2, by free fluoride ions. This causes hypocalcemia, or decreased blood calcium, which leads to a number of systemic problems including likely cardiac arrest and death. See next post for a quote on just how much exposure this requires.

As to the Al chemistry, my guess is that it's one of only a few agents that effectively dissolve the coating of alumina, Al2O3, that so effectively passivates the surface of metallic Al. This coating renders an otherwise reactive metal pretty inert under normal circumstances, so I can imagine one might want to remove it during industrial processes that rely on an active Al surface.

[Edited on 30-8-2006 by silonyl]

Odyssèus - 30-8-2006 at 08:15

I have heard that it is hypocalcaemia: low calcium levels in the blood, probably from precipitation of calcium as the insoluble flouride.

Wikipedia

Quote:

Highly concentrated solutions may lead to acute hypocalcemia, followed by cardiac arrest and death, and will usually be fatal in as little as 2% body exposure (about the size of the sole of the foot).

[Edited on 30-8-2006 by Odyssèus]

silonyl - 30-8-2006 at 08:59

Just double-checked and you're absolutely right... severe HF exposure leads to hypocalcemia, not hypercalcemia. It does lead to hyperkalemia (excess potassium) which is probably where I got confused. As for dissolving calcium in bone, I think that's actually a myth propagated by environmental health and safety at my previous school

but yes CaF2 is insoluble in water so that wouldn't make much sense.

Still, ya don't want to touch it

Elawr - 31-8-2006 at 07:56

Why would HF work better than a dilute solution or either muriatic acid or sodium hydroxide for etching aluminum? Both lye and HCl, even dilute will eat aluminum right up in my experience. Although both are hazardous due to being caustic, neither HCl nor NaOH possess the extreme toxicity of HF. Even the highly diluted HF product Whink available OTC is dangerous if slopped around carelessly.

12AX7 - 31-8-2006 at 11:54

I would hazard a guess that, as HCl is a stronger acid, it would eat aluminum faster, but HF forms a hexafluoro- complex, too.

Guarantee you HCl + Cu(2+) eats faster than anything

Tim

not_important - 31-8-2006 at 23:09

I'd bet that the Cu(II) would end up as metallic copper plated out on the aluminium.

woelen - 1-9-2006 at 01:18

No it does not, it does not adhere to the surface and you get a mossy mess of copper around the etched area. Btw, only a small amount of copper (II) actally reacts, most of the aluminium is used up by formation of hydrogen from the acid.

This reaction of chloride + copper (II) really is remarkable. You do not even need acid, just plain table salt and copper sulfate together, when wetted make a perfect mix for etching aluminium. But you need both the copper (II) and the chloride. Take away one of them and nothing happens anymore. I think it has to do with complex formation and that this complex formation makes the reaction proceed so fast. Otherwise I do not see any role for the chloride.

stricnine - 2-10-2006 at 17:27

When I was starting, I DID associate the idea that because it is a weak acid I did not have to worry. I got one of the most PAINFUL and horrible injuries in my hand I ever had. Worse than burning with a red-hot plate. My BONES actually were in pain, and I am NOT exaggerating.

HYDROFLUORIC ACID (HF) IS A NASTY CHEMICAL AND THOSE WHO DON'T KNOW ABOUT IT SHOULD DEFINITVELY NOT FOOL WITH IT UNTIL THEY GET ENOUGH INFORMATION

Elawr - 2-10-2006 at 18:23

Amen to that - the fluoride ion is simply incompatable with all forms of animal life as we know it. Hydrochloric definitely safer choice. As For Cu++ and Al, a fun thing to do is to score a fine circumferential line around a soda pop can and then immerse in some CuCl2 solution. A vigorous replacement reaction will ensue: Cu++(aq) + Al(s) -> Cu(s) + Al+++(aq) which, if done well, will be precisely confined to the line where the protective paint was scored. The end result is can split surgically in half, held together only by the can's inner liner!

[Edited on 3-10-2006 by Elawr]

Waffles - 3-10-2006 at 11:25

Quote:

Originally posted by Elawr
Amen to that - the fluoride ion is simply incompatable with all forms of animal life as we know it.

By your reasoning, cisplatin is 'simply incompatable' with all forms of life as well. Just because large, clumsy doses can kill, doesn't mean that properly administered it can't be the key to stopping a disease or affliction in its tracks.

I'm sure you know this, and I know what you mean- I have had my own $975 emergency room visit from a casual encounter with HF. :-D But be careful not to overstate the case- the fluoride ion is the reason many middle aged people still have their teeth!

Jdurg - 5-10-2006 at 07:17

Quote:

Originally posted by iamthewaffler

Quote:

Originally posted by Elawr
Amen to that - the fluoride ion is simply incompatable with all forms of animal life as we know it.

It's actually not the fluoride ion, but the monofluorophosphate ion that builds up the strength of your teeth. (If used in moderation). When you are given fluoride treatments they aren't putting the fluoride ion into you. It just got the name "fluoride" as that is much easier and quicker to say than monofluorophosphate.

In addition to the problems with CaF2 precipitating out of your blood, if the free F- ions are in your lymphatic system or in any other fluid system in your body it can cause any free calcium ions to precipitate out of solution. This will lead to VERY painful joint and muscle conditions and is just a nasty way to go.

12AX7 - 5-10-2006 at 07:42

As I recall, the fluoride ion (obviously present in tap water and toothpaste without any phosphate) displaces the hydroxyl in hydroxyapatite, the mineral which makes up tooth enamel, changing at least the surface to fluorapatite, which is much less soluble and more resistant to the bacteria in the mouth.

Tim

Elawr - 5-10-2006 at 12:10

Your point is well taken, iamthewaffler, as a trace nutrient F- is essential for healthy bone and teeth. It is unfortunate that many municipalities no longer fluoridate the drinking water. It is within the context of concentrated haloacids that I wanted to emphasize the particular hazards of working with HF. Hydrochloric and hydrobromic acid both demand respect by virtue of Ph and volatility. In vivo, however both disassociate into anions fairly benign physiologically. HF is unique in that its relatively weak acidity allows it to breach the keratinized skin barrier with ease. The F- ion forms an extremely stable complex with Ca++, thus monkeywrenching the neuromuscular junctions at the molecular level. End result: nerves, muscle cells including cardiac muscle all stop working.

[Edited on 5-10-2006 by Elawr]

Waffles - 5-10-2006 at 13:25

http://www.rvi.net/~fluoride/000055.htm
http://www.informationliberation.com/?id=14949

:cool:

Elawr - 5-10-2006 at 22:16

There is contoversy, yes...probably should add this one to Polverone's poll of highly volatile flame-war topics thread.

Jdurg - 6-10-2006 at 09:49

Quote:

Originally posted by iamthewaffler
http://www.rvi.net/~fluoride/000055.htm
http://www.informationliberation.com/?id=14949

:cool:

WOW! It is scary what happens when someone gets a little bit of information but has a huge mouth/ego. I get the feeling that the writer(s) of those articles has very little knowledge about chemistry. Half the time he was talking about fluoride gases which simply don't exist. (I believe he meant to say fluorine gases, but if you're not bright enough to use the proper terms then I disregard everything you say).

hinz - 6-10-2006 at 13:27

The second one is really full of shit:

"...fluoridation caused slight damage to a specific part of the brain, making it more difficult for the person affected to defend his freedom and causing the individual to become more docile towards authority..."

F- will have crystallised to CaF2 long before it's in the brain

"...Fluoride is the key chemical in atomic bomb production and millions of tonnes of it were needed for the manufacture of bomb-grade uranium and plutonium..."

Millions tons of Fluoride for a critical mass of appr. 50kg of uranium? No recycling of the 238 UF6? Enrichment of plutonium over a fluorine compound?

"...the mass medication of drinking water with sodium fluoride..."

How ineffective..

[Edited on 6-10-2006 by hinz]

Waffles - 6-10-2006 at 13:31

life is good. reading things like that makes my day.

i spent 5 hours today cleaning slices of an ion trap for a mass spec in 48% HF. really clears the sinus!