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Why Hydrofluoric acid is so dangerous


#1

It struck me that many people, myself included, say, “Be careful
with that” or even “Don’t even go there” with regard to HF without
really saying why. The why is very important to know - it could save
your life.

Fluorine is the most reactive element on Earth by far. It reacts with
almost everything. A stream of water will burn with a bright flame in
a fluorine atmosphere. There is a group of chemists called “The
Fluorine Martyrs” who died, were blinded or otherwise injured trying
to isolate it as an element. Henri Moissan, who also discovered
Moissanite, won the 1906 Nobel prize for finally doing it. The
chemistry of HF gets complex petty fast, but in an aqueous solution
it’s a weak acid, meaning that it doesn’t dissociate into ions very
much, more specifically it doesn’t form Hydronium ions as much as the
strong acids, Hydronium ions being what Ph paper is testing for -
acidity. This is essentially accurate, though of course it’s also a
stripped down version. Hcl dissociates at a theoretical 100%, by
contrast. Other important weak acids are phosphoric acid and boric
acid. What this means in lay terms is that it’s not dangerous so much
because of it’s acidity per se (though of course that counts, too),
it’s dangerous because of what it is - an incredibly reactive
fluorine compound.

But wait, there’s more… Osmosis is the ability of atoms and
molecules to squeeze between the spaces between other atoms and
molecules. Desalinization of sea water uses a membrane that permits
the small water molecules to pass through, but not the large salt
molecules. This is also why helium balloons deflate overnight. If you
imagine your skin as a wire mesh of, say, 1/4" grid (6mm or so), then
sulfuric acid is a marble - it will just sit on top. The tiny HF
molecule is rice, and will just pour right through your skin as
though it wasn’t there at all. This is again, essentially accurate,
though there’s more to it, also. Hydrogen bonding and stuff. So, if
you spill HF on your skin, it goes right through it, and then once it
gets inside it begins to react aggressively with everything it finds,
most importantly Calcium. Spilling some on your finger can rot the
bone underneath in minutes. More importantly it takes calcium out of
your body chemistry, creating a chemical imbalance that quickly leads
to chemical shock and death, even with agressive treatment. Medical
treatment for HF exposure is massive injections of calcium gluconate
for that very reason.

It’s (largely) not the acid, it’s the fluorine that gets you. Be
very careful if you use it - inhaling fumes is the same, but worse.

http://www.donivanandmaggiora.com


#2

Thank you John for the chemistry lesson on hydrofluoric acid. I had
always heard it’s nasty stuff, but I didn’t know why it would be any
worse than nitric acid.

I have about five pounds of “platinum divesting” crystals that I got
mixed with hydrogen peroxide, about two or three ounces H2O2 to one
teaspoonful of crystals. I tried to order some more of it for a
friend and the company informed me that they no longer carried it.
When I asked what it was so I could find a new source, they were very
evasive about it and I never got a real answer. I thought at the time
that was kind of odd, but as I have several years supply, I dropped
it. I have searched through my MDS file for info on it, but I can’t
find anything on it at all.

Any idea what it might be? Any idea how dangerous it might be? I had
always assumed it formed a weak solution of hydrofluoric acid when
mixed with peroxide as it will eat through glass, but not plastic. I
never really considered it to be any more dangerous than pickle or
rhodium solution, but I think maybe I ought to reconsider.

Thanks,
Dave


#3

I’ve told this story before.

I’m a skeptic. I don’t believe everything that I hear or read. I
require corroboration. Sometimes this gets me in trouble.

Over thirty years ago, I needed to do some enameling. In the
process, I found that I needed to remove my enamel and start over. I
acquired about a pint bottle from the local chemical supply. I did
try to take some precautions. I poured about 1/2 oz into a plastic
container. I had baking soda handy. This stuff does remove enamel
pretty quickly. When I was done I neutralized and disposed the acid
that I had used.

Sometime later, I noticed a slight burning sensation on my finger.
The first thing that I did was to touch my finger to my tongue. There
did seem to be a faint sour taste. I then tried to soak my finger in
some baking soda. The pain kept up. Having read the warnings on the
bottle, I asked my boss to see a doctor about it. the doctor looked
at me as if I was just trying to get out of work. Aside from a little
pinkening, there didn’t seem to be a problem. Had me soak my hand in
a whirlpool despite what I told him. Later, when things didn’t seem
to be getting any worse, I left. A week or so later, my fingernail
fell off.and revealed a pus like condition of the tissues underneath.
Nor further damage. A pretty cheap lesson.

My point is that this acid will pass through the skin without one’s
knowledge. Very difficult to neutralize once it gets through. In my
case, I was totally unaware when I had spilled it. It must have been
just a single drop.

This acid has some uses that can make things much easier to deal
with. I suspect that it is very easy to have a fatal error with as
well. Use this stuff with extreme caution.


#4

As many of you may know, I am a dental hygienist. In the past 2
years I have been made aware of the toxicity of fluoride (the
fluoride ion in a solution) given in the dental office, as
supplements, and added to municipal water supplies.

Since learning a little about science for the dental hygiene
curriculum, I have become skeptical of much "scientific"
Therefore I was guarded about the toxicity claimed by
researchers in Australia and Canada (this is where much of the
research is being done). However I am especially skeptical of
scientific studies whose conclusions lead to the urgency of buying
something.

So I found out that Alcoa Aluminum, who had a vast amount of toxic
fluoride to dispose of, funded research into fluoride’s effect on
dental development and decay prevention in the early sixties. This
research led to the decision to fluoridate many municipal water
supplies.

It was enlightening to read this because the effort to convince
America’s dental community of fluoride’s benefits and to mask its
dangers has been very successful! I do not let this issue become a
controversy with my peers but I thought you might appreciate this
insight into the changing role of fluoride in the mind of a few
American dental professionals.

On a side note, hydrofluoric acid has been used in the dental office
to etch porcelain on a porcelain-fused-to-metal crown in the
patient’s mouth. Rubber dams are always used when this is done.
Finally as a result of this thread I see the connection between
fluorine and its compounds in bone toxicity.

At the risk of getting too long, let me remind you all that tooth
decay is caused overwhelmingly by sugar abuse - sipping sugary
drinks, soda pop, and eating sticky sweets like fruit roll-ups and
even raisins. Starches also transform into sugars in the mouth.
Fluoride studies have not been done without educating the public of
the effect of diet and general health on dental health.

For more, see www.fluoridedebate.com.

Okay folks, see you in Tucson.

Connie Langan
www.papayani.com


#5

Connie

There is a major difference between HF and the Fluorides used to
protect teeth from acid. As a dentist who uses hydrofluoric acid as
well as fluoride rises, I know the dangers of each. Be informed,
prepared and know what to do in case of emergencies.

Charles Friedman DDS
Ventura by the Sea


#6

Bruce

You are lucky, I worked for a micro-hybrid facility and this was the
only substance we had the techs don a full ‘space suit’ to clean a
spill. It is nasty stuff. We also evacuated the building around the
spill.

Terry


#7

Hi John,

That was a very thorough and good explanation of the hazards
associated with hydrofluoric acid. However, your definition of
osmosis wasn’t strictly accurate. Osmosis isn’t the “ability of atoms
and molecules to squeeze between the spaces between other atoms and
molecules”. A) atoms and molecules can’t “squeeze” through spaces
like a squid or octopus - atoms and molecules are the size they are
and can’t make themselves smaller. B) Osmosis is actually and
specifically the diffusion of water molecules (although since I was
at Uni, it seems to have been expanded to include the diffusion of
any fluids).

The definition of diffusion being the movement of molecules from a
region of high concentration to a region of low concentration, across
a selectively permeable membrane (we used to say semipermeable but it
changed to selectively permeable as “semi” was misleading). Thus, the
definition of osmosis is the movement of water molecules from a
region of high water concentration (or low solute concentration) to a
region of low water concentration (or high solute concentration)
across a selectively permeable membrane. The process by which HF
enters the skin is more one of absorption but you’re right, it will
get in there and cause havoc with your body chemistry (something I
know a bit about, having had to be admitted to hospital two years ago
in hypovolaemic shock due to the electrolyte imbalance caused by the
primary Addison’s disease I was subsequently diagnosed with - not
something I wish to repeat in a hurry!).

Sorry to split hairs.

Helen
UK


#8
 Any idea what it might be? Any idea how dangerous it might be? I
had always assumed it formed a weak solution of hydrofluoric acid
when mixed with peroxide as it will eat through glass, but not
plastic. I never really considered it to be any more dangerous
than pickle or 

Dave - Nope, nope, nope. There are supposedly HF free platinum
devesters, which I’ve heard of, too, but a search came up empty…
There’s a post in the Orchid archives where Gesswein talks about it
(1999), but they don’t sho it on their site. There’s also this:

A small shop may wish to consider a safer devesting agent for
platinum investment as a substitute for hydrofluoric acid. Ask your
tool supplier; there are many brand names. You can also mix your own
substitute using the following formula (percent- ages are given by
weight): 25 percent sodium hydroxide, 25 percent potassium
hydroxide, and 50 percent deionized or distilled water. (The sodium
hydroxide and the potassium hydroxide should be in pearl or flake
form.) Combine all three solutions in a stainless steel container,
and heat (do not boil) for 25 to 40 minutes. Be careful mixing,
since the three ingredients will naturally heat up when combined.

I know nothing about that post personally, I’m just passing it on.
HF is a gas, and becomes hydrofluoric acid when dissolved in water
(FYI: HF + H2O -> H3O+ + F-). Meaning there’s no solid unless it’s
frozen. As Jim said lately, it could be fluoride salts, similar to
sodium bisulfate. All that stuff is proprietary, and it could be that
research could figure out some things, but I personally don’t know
the answers. Tip: The above post is alkaline, a quick test will tell
you if yours is acidic or basic - at least a start.

http://www.donivanandmaggiora.com


#9
I have about five pounds of "platinum divesting" crystals that I
got from my investment supplier. 

Dave, I already answered this today, vaguely, anyway. You just can’t
ask me questions like that - I have this intense curiousity, you
see. What I wrote earlier has one general formula that may mean
something. Otherwise if you’re interested I’d say to search Google
and Wikipedia (which doesn’t have a whole lot) for ammonium
fluoride, ammonium hydrogen fluoride, maybe potasium hydrogen
fluoride, and maybe bifluorides in general. All of those things are
still quite toxic and dangerous, but nothing approaching HF itself.
You’ll also find that they are precursors to chemical weapons, which
affects availability, these days. It’s curious that you would mix
what you have with peroxide, though, because that’s an oxidizer and
fluorine is already the baddest oxidizer on the block - maybe
there’s something going on there, though. I enjoy chemistry
(actually, I love it), but I only go so far-not a pro or anything.

http://www.donivanandmaggiora.com


#10
The definition of diffusion being the movement of molecules from a
region of high concentration to a region of low concentration, 

No, Helen, you are correct, and I appreciate the enlightenment, and
I often point out that I’m just a chemistry buff (and an element
buff, too), not a real chemist. But as you also say, the point is
that it is not just easily absorbed in the skin, but especially
easily. As for the dental discussion, that I WILL leave to the pros,
except that my own take as a consumer and human is that the proof is
in the pudding - if fluoridation were so hazardous we would know by
the people lined up in ER’s in the last 40 years. It’s well known
that fluorides are toxic at some levels, depending on what fluoride,
but the controversy about toothpaste seems a bit shrill to me, at
this stage. Again, just a consumer, not a dentist. I’ll point out,
for any who didn’t make the connection, that I started this thread
coming off of the “How to remove vitreous enamel” thread - not just
out of nowhere.

http://www.donivanandmaggiora.com


#11

Bruce

You are lucky, I worked for a micro-hybrid facility and this was the
only substance we had the techs don a full ‘space suit’

Just by way of conversation, and maybe a bit of inspiration…I’m a
civilian army brat - aerospace - so I moved every two years or less.
One time we moved, and I walked into a chemistry class in the 2nd
week of school. The teacher told me there was a test on the element
symbols the next day, but I didn’t have to take it if I didn’t want
to. So, I went home and memorized the periodic chart and got a 98 on
the test the next day. ( Not so hard - 80% or something of them are
the first letter - carbon C, oxygen O). Later on, I became a lab
assistant and had a somewhat advanced lab in my bedroom. My
fascination, as I’ve learned many others share, was the elements.
With the help of the old-school Encyclopedia Britannica, I set out
to extract as many elements as I could and start a collection. Being
poor and smart I knew that there were many that were simply
impossible - sodium requires electrolosys and it’s dangerous, not to
mention uranium and fluorine. I got pretty far, though - most of the
common metals, iodine, bromine - got a bit of a burn off that one.
My goal wasn’t to just buy graphite, it was to extract it from a
source myself. I made everything myself beyond what could be bought
at the hobby store in those little jars - acids, bases,
intermediates. It was fun and I also learned much about how those
building blocks work, and work together. Why is carbon carbon and
iron iron? Which of course leads to what steel is about, eventually.
It’s a shame that modern (American) curriculum is often strangled by
other forces - I know a few college kids who have never taken
chemistry. That means they don’t know how fire works, really. This
is all just converstion, but some knowlege of chemistry will help to
understand many things - nutrition, vitamins, which acids dissolve
which metals. Why not to pour what is almost liquid fluorine on your
hand (HF). Anyway, enough musings. A good start for any who could
use it might be Wikipedia - search for “perioodic chart”, and start
clicking on the elements. Cool stuff.

http://www.donivanandmaggiora.com


#12

Some good sources for hydrofluoric acid alternatives aRe: Precious
Metals West and United PMR (acid crystals) or Otto Frei (Super Strip
It). The latter comes with a neutralizer for safe disposal.

Jason
Casting House


#13
It struck me that many people, myself included, say, "Be careful
with that" or even "Don't even go there" with regard to HF 

I perfected a non-acid (ph 6.8) substitute for HF–Multi-Etch–which
is sold through Reactive Metals Studio. I don’t know if it would
work for platinum divesting but I do use it to clean platinum prior
to solder/welding. Of course, it also works for titanium. And it’s
ideal for bringing up detail on mokume and meteorites, etc., etc.

Chris Boothe
Exotica Jewelry
(800) 297-6707


#14

Charles,

There is a major difference between HF and the Fluorides used to
protect teeth from acid. As a dentist who uses hydrofluoric acid
as well as fluoride rises, I know the dangers of each. 

As a dental hygienist who has used fluoride rinses, and a former
dental assistant who got the hydrofluoric acid bottle out of the
fridge and assisted the dentist while he applied it, I admit I’m
certainly am more informed now than I was before this discussion
came up.

I remember when I used to have my patients rinse with fluoride in
the office. Sometimes they would get sick right afterward.

We always knew it was toxic (even though the rinse is not the same
as hydrofluoric acid, it is a weak fluoride rinse) but now I feel
more comfortable working with a dentist who wants to work without
it. We now recommend sugar discipline, general healthful habits and
good oral hygiene without fluoride. We do recommend MI paste in some
cases.

Even fluoride-hardened teeth are vulnerable to pinhole decay, which
dentists say is harder to detect when all the enamel around the
microscopic opening is so hard.

However I understand every chemical has a proper use and that
concentration (dose) makes a huge difference between toxicity and
therapeutic benefit. I anticipate more dental offices quietly moving
away from fluoride as the years go on.

I am happy to be on this forum with you. Jewelry and dentistry have
a special kinship in my opinion.

Connie


#15
if fluoridation were so hazardous we would know by the people lined
up in ER's in the last 40 years. It's well known that fluorides are
toxic at some levels, depending on what fluoride, but the
controversy about toothpaste seems a bit shrill to me, at this
stage. Again, just a consumer, not a dentist. I'll point out, for
any who didn't make the connection, that I started this thread
coming off of the "How to remove vitreous enamel" thread - not
just out of nowhere. 

Yes I agree on the toothpaste issue. If you think about it, most
things are toxic or hazardous at some level, but HF is not something
I’d not use without a proper lab set up and fume cupboard.

Helen
UK


#16
Washing soda is a brilliant neutraliser of HF, though at work we
use sodium hydroxide as it takes less volume of chemical to do the
job. we tend to clean our platinum with nitric acid rather than HF
though nitric is not very good at dissolving enamel unless the
enamel has a high borax content which is the case with some of the
enamels used in jewellery and ceramic overglaze enamels. The German
made enamels I use on silver will dissolve in nitric but the very
vitreous English and US made ones dont. 

Fluoride is added to water and toothpaste in very small quantities
in a non reactive salt. The reason is that tooth enamel is made up of
calicium phospahte in the form of hydroxyapatite. most marine
creatures like sharks and crocodiles have chlorapatite teeth, which
are stronger, but mammals cannot absorb the chlorine ion into their
teeth so the more reactive fluorine ion is used instead. get it
right and tooth decay is much reduced, too much and the tooth is
destroyed and the person poisoned.

There is an inert gas called sulphur hexafluoride that is used as an
electrical insulator in high voltage transformers instead of oil or
PCB’s (polychlorinated biphenols which destroy the ozone layer) that
is so dense you can float aluminium on it. I helped with a chemistry
department demo floating a metal boat in a fish tank of SF6 to the
amazement of the children watching and then the demonstrator did a
demo of breathing the gas in and talking which had the opposite
effect of breathing helium- he talked really slow with a very deep
voice. We then had to turn him upside down to pour the gas out of his
lungs as he couldnt breathe it out naturally so dont try that one for
yourself.

Nick


#17

Hey Chris I have a question for you, I work in glass sometimes and I
like to put an etched finish on it and I use a product that comes
from Peoria Arizona called “Etch-all” and it has 20% amonium
biflouride and 80% inert liquid, do you know anything about it? And
if you think that your stuff would work on glass could you let me
know? Or used for investment removal?

Thanks…Frankenstein


#18
I perfected a non-acid (ph 6.8) substitute for
HF--Multi-Etch--which is sold through Reactive Metals Studio. 

Does it etch glass?

Noel


#19

Before retiring, I was employed by a major aerospace contractor. One
compound a lab tech demonstrated to a group of workers one day was a
dilute mixture of hydrofluoric acid, hydrochloric acid, and nitric
acid. The final mixture was ten percent the three acids (I forgot
how much of each acid) and ninety percent distilled water. Several
years later, one “super smart” salaried type decided that I had to
keep the stuff at my work station and use it daily in my normal task.
I started asking for the MSDS for the compound and for each acid in
the compound. It seems that one of the acids should NOT be in contact
with aluminum (guess what we used the stuff on), and two of the
acids should not be in contact with each other. The next order of
business was to start asking about safety equipment and precautions.
The company said that there was a shower within 50 feet and that
should be close enough. I told them I wanted a glove box and a new
shower within fifteen feet of the work station. Less than two weeks
after the stuff was put on my table, it disappeared without comment.
I did not miss it any.

Jim


#20

Although Multi-Etch does etch glass it does it too slowly to be
practical. I have heard from a glass jeweler that Etch-all is a good
product.

Chris