Sciencemadness Discussion Board

Best acid combination to erode steel.

Tacho - 27-10-2004 at 04:25

I was considering the possibility of doing some "chemical machining" on steel. Common steel, not ss.

Could anyone come up with a better etching mix than HCl + H2O2? Is that a good mix at all?

And, please, I have easy acess to industrial chemicals, but not to research chemicals (Aldrich kind) so zoobydoobyisocyanate is out of question.

I have already done CM quite well on copper and brass using ferric chloride.

Hermes_Trismegistus - 27-10-2004 at 06:23

Alternative to HCl + H2O2

rikkitikkitavi - 27-10-2004 at 08:51

try hot diluted sulfuric acid, about 15-50 %. preferably boiling , it will not give off gases like HCL and heat increases corrosion rate dramatically. Cold conc HCl compared to warm conc HCl is also a big difference


Hermes_Trismegistus - 27-10-2004 at 09:45

Originally posted by rikkitikkitavi
try hot diluted sulfuric acid, about 15-50 %./rickard

Pretty loose def'n of dilute you got there Partner!

(p.s. Maybe 9/11 wasn't a terrorist attack, perhaps they were just landing "near" JFK's runway #4)

JustMe - 27-10-2004 at 18:49

This may turn out to be REALLY dumb, but I thought I'd throw it out, because he said it wasn't stainless steel.

A LOOOOONG time ago I was show a quick and easy way to corrode steel wool, it works immediately, but I've never tried it on bulk steel. Simply mix equal quantities of Vinegar (5% acetic acid) and commercial bleach (~5% sodium hypochlorite). It generates Hypochlorous acid continously... resulting in instant rust. YMMV

Oh uh, I just re-read the post, he want's etching, not corroding. Well, never mind.

atombum - 27-10-2004 at 22:05

Aqua Regia perhaps? ....and then there's also the chlorine fluorides, not acid in their anhydrous state, but said to be able to even cut steel, and just about anything else.

Mr. Wizard - 28-10-2004 at 06:47

Tacho, if you just want to etch steel, as in an engraving or writing your name on a tool or knife blade, try using a NaCl solution on a sponge hooked to the - NEG side of a battery charger (3 -12 volt DC) and the thing to be etched hooked to the + PLUS side, where the nascent Cl is liberated. Protect the surface of the blade with wax by melting on a thin layer, scratch the pattern through the wax and on the first pass with the electrolytic sponge it will darken any exposed metal. Even fine lines scratched through the wax will be sharply defined. The etching is quite permanent, as I found out after trying to redo some mistakes. With a good photo resist as used in circuit board production, and a computer generated negative or mask, you could even transfer simple images.

I've been told that Chlorine gas. used in many facilities in my area, will quickly eat through a steel pipe if the chlorine becomes contaminated with water.

Dodoman - 28-10-2004 at 14:09

I didn't know that about Cl and water. Anyway i gave it a go and it works very fast. Nice tip ;)

Ferric Chloride

chloric1 - 28-10-2004 at 14:10

You know I would add a small amount of HCl to your Ferric Chloride and use and electrolytic method simular to Mr. Wizard's. May cut quicker or deeper.

Tacho - 30-10-2004 at 17:28

Thanks all,

H2SO4 75% and H2SO4(75%)+H2O2(200vol, 35%?) are worse than HCl (37%)+H2O2(200vol, 35%?). The best etching I got is 0,17mm for a 6 hours bath (using HCl). I’m looking for 1mm/hour etching. I’ll try Mr. Wizard’s suggestion tomorrow.

Tacho - 31-10-2004 at 02:43

Using NaCl and electricity was, so far, the best method. More than a mm of steel disappeared in less than ½ hour under 15V and strong current. Thanks Mr.Wizard.

Now I have that feeling: “how come I didn’t think of that before…”

Mr. Wizard - 31-10-2004 at 10:24

Tacho, Thanks for the feedback. I've never used it for anything but engraving knife blades, or tools, so 0.5 mm in 30 minutes is surprising. Are you using a mask (resist or wax) and how much surface area are you cutting?

I've also been told by professionals that Chlorine will ignite and burn steel if heated over either 86C or 186C, I don't remember which. It is supposed to evolve brown clouds of FeCl3 smoke.

[Edited on 31-10-2004 by Mr. Wizard]

Tacho - 31-10-2004 at 11:56

I am willing to cut steel plates and steel pipes. More immediately, I am considering the possibility of making a screw for an oil extracting screw press out of a steel pipe and some epoxy resin, or from a solid steel rod.

I have been doing my tests on a 1.6mm diameter steel wire. It took about 6 hours for the acids to reduce the diameter to 1.25mm. I was surprised because I was expecting faster results. Using the electrolytic way, the submerged wire had a sharp needle shape in about 30 minutes. So I assume a 0.8mm in ½ hour. Results could be different for a plate (sheet?) but , comparatively, electrolytic is clearly faster.

Hermes_Trismegistus - 31-10-2004 at 12:48

Peroxymonosulphuric acid

Sorry tacho, I didn't mention that conversion to Caro's acid requires both high-test sulphuric and peroxide.

but considering the price of salt and electricity I'd say that you cannot beat that other method with a stick.

Tacho - 31-10-2004 at 17:15

I have never seen Caro's acid in action, but I have a feeling that it's too dangerous for my taste. That's why I used only 75% H2SO4 in my mix.
After all...
"...pirahna bath spatter + eyeballs = ray charles. "

[Edited on 1-11-2004 by Tacho]

tokat - 6-11-2004 at 22:37

in enginering they use nitric acid, and phospric acid in 50%/50% MIX. AS A EICHING MIX.

tom haggen - 6-11-2004 at 23:48

What do you think would happen if you mixed HCl with caros acid?