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DIY pickling of steel?

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johnf

Tue Jul 28 2015, 06:52AM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

You can jazz up the acid whatever its is by putting in hydrogen peroxide into the acid.

I do this with HCL to clean substrates before ion implantation heating the acid mix also speeds it up

Bored Chemist

Tue Jul 28 2015, 06:43PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

The trouble with adding peroxide is that it will increase the rate of etching of the metal.

klugesmith

Thu Jul 30 2015, 11:05PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

For safe mixing, do you add acid to peroxide or peroxide to acid?

I tried sulfuric acid on a small section of the same material. The acid is sold for unclogging drains, and might include inhibitors to reduce the etching of exposed iron. After 5- and 15-minute dips, I left the work overnight in a 1:1 mixture of acid and water. Outdoors, with no heating of my soft plastic containment vessel.
Behavior was consistent with most references on the Internet. H2SO4 does not dissolve scale, but needs to get underneath it (through cracks) and etch the interface to release the scale. The workpiece ended up with blistered scale, and I popped the blisters by peening with a hammer. Here's the result:

Reduction in diameter was about 0.004", which could be just from losing the scale's thickness.

I think I'll do the second 7-inch-long bar like the first, with hydrochloric acid, but pay more attention to before-and-after dimensions.

Sulfuric acid might be a way to dispose of leftover pills (prescription medication), which is not supposed to be put into the sanitary sewer system or the regular garbage stream. I don't know what they do with stuff turned in at medication drop-off sites. But right now, on my patio, one could find heavy pulverizing pestles and very strong chemical digesting agents.

klugesmith

Sun Aug 09 2015, 04:57PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

OK, time to close the book on this episode. At least until the missing steel 1x4 bars turn up.

The second pole piece is a twin of the first. Most of its scale was gone after two 1-hour sessions with occasional agitation (by squeezing the sides of the tank) and with fresh 1:4 diluted HCl for each session. Remember, there's not much acid volume compared to the workpiece surface area. It was good enough for me to proceed with neutralization and painting. The small holes are the subject of a different story.

Also I used the sulfuric acid to digest some leftover isosorbide mononitrate and prochlorperazine tablets, after pulverizing them with a thick steel roller. Some white material (inert mineral filler?) would not dissolve until I added water. Initially in very small portions, while wearing safety glasses, while stirring vigorously, and allowing to cool between portions. I'm sure there was no pharmaceutical activity left when they went down the drain.
But this was a big waste of time. The authorities here recommend that leftover medicine (with a few exceptions) be disposed of with regular garbage, in closed containers. The special considerations are to prevent diversion. Use unmarked containers, mix pills with water, put unpalatable stuff in with them, etc. I have a regular supply of turds from the cat pictured in this thread.

Conundrum

Mon Aug 17 2015, 05:27AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Apparently out of date aspirin contains a very strong acid (salicylic) and can be used to juice up PCB etching as well as enable good even plating on tin plate solution.
I noticed that some white wine and colored vinegar has an additive in it that ruins etching somehow, the fix for this is to use cheap white vinegar

Bored Chemist

Mon Aug 17 2015, 05:32PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

In the ordinary course of events, medication is almost always disposed of via the sewers- think about it; where else is it going to end up?.
Salicylic acid isn't very strong in absolute terms, but it' not bad for an organic acid.

Pulverising organic nitrates is likely to win you a Darwin award. Thankful, the ones used as drugs are normally diluted with something fairly inert.

It's more than likely that the sulphuric acid had no significant effect of the Prochlorperazine; but you probably put anyone off stealing it.

klugesmith

Tue Aug 18 2015, 01:24AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Thank you, BC, I know better now. Shouldn't've pretended to know what I was doing in that last experiment.

Of course most medicine in the sewage stream got there through ordinary toilet activity.

Re. Darwin: I knew that "ISMO" is taken for the same purpose as nitroglycerin. Never thought to see if part of a 20 mg tablet could be detonated with a hammer blow. Too late now!

MSDS for the pure material

warns: "may explode by detonation, heat, or shock." Huh? How does something explode by detonation, as opposed to by heat or by shock?

Since prochlorperazine is an oxygen-free molecule, I guess it can't be hydrolyzed or dehydrated by H2SO4. And, as you hinted, it's not unknown for druggies to abuse it.

How about if my penance is to to measure and report the specific gravity of the acidic drain opener? Good excuse to get into the glass hydrometer collection. Or a 50 ml volumetric flask and a weighing scale.

-Rich

Bored Chemist

Tue Aug 18 2015, 09:20PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

How good is your balance?
And what you really neded isn't a flask, but one of these to go with it.

Even then you won't get a reliable answer because the acid will almost certainly contain other material- apart from water and acid.

The acid is almost certainly something like 95 +/- 5% which is not a bad level of imprecision.
If you really want to know the concentration, titrate it.

hen918

Wed Aug 19 2015, 04:56PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

As far as I know, the drain unblocker I have is 92% sulphuric, 8% water. I know many people use something similar for nitration so I think it's pretty additive free.

Hazmatt_(The Underdog)

Thu Aug 20 2015, 12:25AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

No, if you dilute it, it has some kind of surfactant in it that causes frothing. Sulphuric Acid does not do that on its own. For our uses it's not a problem, but if you're doing any real lab work, it's not lab grade.

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