Muriatic acid and hydrogen peroxide

[edmundopt]

hello

Well, my friend is experiencing with this pcb etching, I went to take a look at it.
But I have a problem, my trousers belt has a stainless steel front. I have no idea how, but it has oxidized, same thing with my car keys.
I have cleaned it, sand it, and after some time, oxidized again, cleaned it again, some more sanding. It is oxidezed again.
Is there some chemical I can use to stop the stainless steel oxidizing??

[SeanB]

Wash in dilute alkaline solution, like regular laundry soap, along with all the clothes you wore to there. Then clean with tap water and wipe down with a cloth and polish with furniture polish. There likely is still acid vapours in your clothing and the belt itself that is coming out. The wash in soap will neutralise it and stop it stripping the protective coat off the stainless steel.

[T3sl4co1l]

Stainless steel is stainless, not stainproof.  It has to be surface treated (passivated) to maintain its corrosion protection.

Also, where are you doing the etching, and storing the muriatic acid?  Considerable amounts of acidic fumes are given off by both, in process and in storage.  The fumes will corrode everything and anything in a household.  Needless to say, they should always be used and kept either outdoors, in a fume hood, or in a sealed, acid-absorbent cabinet.

Tim

[edmundopt]

I am not doing any etching, I was watching a friend doing it yesterday.

I read in this forum that Sodium bicarbonate can help, I'll try to buy some, but have no idea how to apply it.. And let me guess, if the car keys are also oxidized, that means that the ignition lock is also going there ?

[SeanB]

Bicarb - take a cupful in 20l of  cold water and soak clothing for a half hour then wash as usual. Dip belt in there as well and soak, then rinse and let dry. If car key has no electronics then dunk as well, if there is a remote or a transponder then wipe down with a cloth and rinse.

Bicarb is a regular laundry item.

[Smokey]

I'm not sure I buy this.  I used to etch a ton of boards with HCL+H2O2 and I never had and issues like that, not even close.  And I used to get the stuff all over the place.  Was your friend using like 90% HCL or something??  Was he dispensing it with a paint sprayer??

[Psi]

HCL use in proximity to an aluminum or stainless sink/basin = Hours and hours of cleanup and polishing.

[edmundopt]

I'm not sure I buy this.  I used to etch a ton of boards with HCL+H2O2 and I never had and issues like that, not even close.  And I used to get the stuff all over the place.  Was your friend using like 90% HCL or something??  Was he dispensing it with a paint sprayer??

You are as surprised as I am...  I'am going to visit him again next weekend. It was on a wood house, I think the english word is a shed. Anyway, he allready told me that the door knob went brown!

[exapod]

" the door knob went brown! " I really hope you are doing the etching outside and not in the actual shed/house!

[janoc]

Well, that sounds like the acid was really concentrated and fuming a lot and/or kept in a poorly sealing container (a cork stopper in glass bottle or a screw-on plastic stopper on a soda bottle really is not good enough for muriatic/hydrochloric acid).

I have tried acid/peroxide combination once and never more. It is a dangerous, fuming, corrosive mess.

Guys, do your health and your surroundings a big favour and get some ferric chloride or ammonium persulfate etchant. It is more expensive than the acid to buy, but the damage you are doing to your health by breathing the fumes and the expense of replacing/restoring all the corroded bits around you is going to outweigh any savings on the etchant ...

[sleemanj]

I have tried acid/peroxide combination once and never more. It is a dangerous, fuming, corrosive mess.

You don't need the acid to be fuming at all, dilute it until it is not.

The acid does not need to be strong, it's the Chlorine and the H202 that do most the work.

NB the result of HCl, H202 and sufficient etched copper in it is essentially cupric chloride, a bright green clear liquid which is an etchant itself, you do not need to dispose of it just add a cap of (stronger=better) H202 to regenerate it every batch you etch, and a cap of HCl every few times.

[Smokey]

The HCL I was using was like 15% or something from Home Depot.  Originally marketed for swimming pools.  That worked fine, and I can still breath on my own without carrying an O2 supply.

[Nerull]

If acid vapors are etching everything around you, keep in mind that it is almost certainly dissolving into the moisture in your lungs. You don't want HCl there.

"Hydrogen chloride forms corrosive hydrochloric acid on contact with water found in body tissue. Inhalation of the fumes can cause coughing, choking, inflammation of the nose, throat, and upper respiratory tract, and in severe cases, pulmonary edema, circulatory system failure, and death."

[ahnuts72]

The h2o2 makes a huge difference as well I started out using the stuff from the store mostly water works good several min to etch a board,but then I changed to 40% h2o2 from the beauticians supply store.
Huge difference will fume like crazy if the h2o2 proportions are not right!
It works much faster like a minute or two to fully etch a board but it will undercut the toner in a heartbeat if you don't pay attention.
Lastly allways do it outside.

Sent from my CM11 Nook HD+

[T3sl4co1l]

On the upside, simple acid vapors are one of the least toxic corrosives you can come into contact with.  Standard disclaimers for those with existing conditions, asthma, etc.  If it feels bad, escape to clean air.

Although as "simple acid vapors" go, HCl is pretty much the only one.  Sulfuric acid has a high boiling point, so unless it's *really* wretched stuff, it doesn't fume.  Nitric acid has a lower boiling point, but it's not a 'simple' acid, in that it's not just acidic, it's an oxidizer as well (and its use is often accompanied by release of toxic nitrogen dioxide gas), so it's that much nastier.

Anyway, even if you can't smell the acid, or feel the fumes or aerosol emanating from its use, it's there, and will corrode, even at 15% concentration I think.  Rusty doorknobs sounds like just the sort of symptom.

Tim

[janoc]

You don't need the acid to be fuming at all, dilute it until it is not.

What I meant is that the mix releases some nasty fumes while being used, not that the acid itself is fuming - that would be really bad, but I don't think 30+% concentrated hydrochloric acid is commonly available.

[sleemanj]

What I meant is that the mix releases some nasty fumes while being used

Eh, not that I've noticed, although mine is well and truly cupric chloride by now.

I don't think 30+% concentrated hydrochloric acid is commonly available.

Depends on your country.  Here in NZ we can buy 33% HCl and 35% H202 without any trouble at all.

[T3sl4co1l]

Standard in the US is "muriatic" 31.45% HCl.  Often with a somewhat greenish color, probably dissolved iron.

It does indeed give off an ominous white fume when opened, particularly on humid days.  I believe the neutral point is around 20%, so if you dilute it by not quite half, it won't fume at any humidity.  Doesn't mean it's not still volatile and corrosive of course..

Tim