hydrofluoric acid

Here is the material safety data sheet for hydrofluoric acid. This comes from a supplier of fine chemicals. As you can see, they do not view this chemical lightly. I would be using all sorts of protection if I somehow decided to play with this stuff.

[www.mallbaker.com]

Particular emphasis should be given to the line: "Skin contact causes serious skin burns WHICH MAY NOT BE IMMEDIATELY APPARENT OR PAINFUL."

Barry was entirely right in saying that you don't feel it when it comes in contact to your skin - unless you get contaminated with a larger volume. The skin burns are the result of a necrosis of the tissue through which HF has penetrated. If you can feel it, it's too late ...

I believe this is the resume for non-chemist:

1) DON'T USE HF (hydrofluoric acid)!
2) when you use acids use only commercial type and dilute slowly IN water to obtain maximun 10% concentration;
3) use gloves;
4) work in a well ventilated area;
5) have a bucket with sodium bicarbonate solution near you;
6) after this remember that acids are always dangerous (except for 5-7% acetic acid = vinegar).

Re Paolo's No 5: I know the comment is well-meant, but without wishing to muddy the water, it is too great a generalisation, and it is simply not true that acids are always dangerous, and it doesn't really help to make people afraid of acids per se. There are many acids apart from vinegar which are considered harmless when compared to strong concentrations of the mineral acids. Several are even drunk by most of us on a regular basis: lemon juice has a pH of about 2.5 due to it's high content of citric acid, and many other fruit juices (even tomato juice) are also acidic; sparkling mineral water is carbonic acid, and of course, Coca-Cola contains both carbonic and phosphoric acid. Each acid should be considered individually, with respect to it's concentration and it's chemistry, and hence it's corrosive potential and toxicity, be it insidious or acute - compare citric, boric, hydrofluoric, and hydrocyanic acids for example.

Having said all that, I concur absolutely that the only sensible advice concerning HF is that unless you are trained in it's use and are intending to use it in a laboratory equipped for it's use, don't even think about it! It's hazards are in a league apart from most of the common acids. Just about the only other compounds I ever worked with which came anywhere close to HF in 'scare factor' were phenol di-iodo arsine and saturated solutions of organic thallium salts.

Pete N.

Sorry typo - should be item No.6, not 5

I think that non-chemist don't know existence of horganic acids, except acetic and oxalic (and perhaps citric and ascorbic).
I know that there are many horganic acids not dangerous and we eat someone very often but I've never seen someone cleaning a mineral with an apple, so is better to talk "acids are always dangerous"; trained peoples know risks and safety procedures for working with dangerous agents, but the others don't.

Re "acids are always dangerous": A very large number of collectors use HCl or other acids for cleaning minerals, so trying to frighten them with exaggerated danger warnings is unhelpful. People will use them anyway. Better to use this space to teach them the safe ways of using acids. Society these days seems to be more prejudiced against "science" dangers than it is against many other dangerous activities. When was the last time you saw any campaigns to stop people from skiing, mountain climbing or motorbike riding because these activities are dangerous?

hey... Timothy Leary used acid for fifty years and it didn't kill him! If we laid all the people who used acid since the 1960's end-to-end, we'd have... ummm... the US Congress...

I agree that people will use acids to clean their minerals, and we should teach them the safe way of using them. However, I think the thrust of the postings are that HF has too narrow a margin of safety to consider playing with. Sulfuric acid, HCl, etc can be worked with in some safety, but HF can kill you in too much of a hurry.

I must agree with most of the posts above. I have worked a summer with etching lenses with HF and HF is not for the "common user" as it is way to dangerous and could not be handle safely outside a chemical laboratory. I could only say that even the guys that I was working with regarded it as a extremely nasty chemical and did actually use all the safety precausions all the time... and that was a guy that had been etching glass for most of his life. So my advice is just to stay of HF... even though it unfortunatelly has no good substitutes for disolving quartz and other silicates.

As for the strong inorganic acids (HCl, sulphuric acid), I would say they should be handle with great precausion and in most cases acetic acid or citric acid will give even a better results wich much less "nastyness". However, they are not at all as dangerous as HF.

... well in short stay of the HF

Does anyone know if diluting HF down to below 1% makes it sgnificantly safer? We currently use it at 5% and could get it lower,to say <1%, if it made it safer to handle.

Michael, if you're going to use it that weak then you may as well use the somewhat safer ammonium bifluoride instead.

And, besides, who's doing the diluting???....You're STILL dealing w/ HF!!!!!

Yes, but diluting is a single controlled step, that we can ultimately get our suppliers to do for us. I'd like to get the % concentration down to a level where it could be handled safely, and not worry that a single splash or inhaling any stray fumes would lead to hospitalisation.

I hoped that by increasing the temperature and extending the cycle time, we could get the same result but in a safer way. I think even 0.5% might work.

I read that HF is used in car washes, and for cleaning patios. Presumably that means that at some level it becomes relatively safe - mind you - I won't stand near the spray the next time I get my car washed! Does anyone know about this?

Here's an interesting article about the use of HF in carwashes...

[www.carwash.com]

Ammonium BiFluoride will do the same job under the same conditiond as diluted HF.....with a fraction of the danger!!!

Jolyon, don't forget the article is from january 1999.
Dominik

The use of HF on cars, as described in the carwash.com article, is truly frightening. Regardless of what it does to the cars (I'm not qualified to say), having drums of HF at any concentration high enough to be useful around people who are not trained chemists or chemical workers is a dangerous situation. Please don't take this usage as proof that "you too can do this at home." I can only hope that things have improved in the car wash industry since 1999.

I do have experience with HF, having worked at a research and manufacturing facility where we used truckloads (many of them) of 70% HF. We could not get near HF above a few percent without full acid gear on -- double gloves, apron or acid suit, rubber boots, face shield, respirator. HF exposures were rare and minor, so I do believe HF can be safely and effectively used, like any other dangerous chemical. However, it takes a world-class safety program, which we had. Your typical car wash does not.

A note of clarification about painful vs. not painful burns. HF burns are reportedly extremely painful if the acid is concentrated, say 50% or more. Below 20%, the HF is still extremely dangerous but the exposure is not painful until maybe 24 hours later. So a worker may think it was just water that splashed him, and then 24 hours later when the area becomes red and painful he may not even remember what caused it, and neglect to get the proper treatment.

Lastly, about diluting to a "safe" concentration... I would venture that any concentration high enough to be useful is still dangerous.

Rick

Albert,
By this time you have probably already done some HF/Quartz experiments. If not I’ll tell you that it takes a long time to do more than just etch the surface of quartz and for the first few hours it seems to do almost nothing, even concentrated material. My experience has been that it will not leave your quartz with a lustrous 'polished' exterior like it will leave on glass. I think there is too much fear mongering on this site about the use of strong acids and not enough balanced informed discussion.
Rock