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Offline MarkPawelek

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Practical forum?
« on: June 09, 2021, 02:34:51 AM »
Chemical forums seems dedicated to chemistry careerism and academia. Is there a practical forum here?

I have a small plastic part with an old bronze screw and nut in it. I want to dissolve away to old metal so I can reuse the plastic item by replacing to old corroded metal and new screw and nut. Is there any easy way to do this? I don't have access to nitric acid. I have access to hardware store chemicals.

Can I add some sodium nitrate to hydrochloric acid to make HNO3? If so, is 10%, or 30% HCl-acid best?

Offline Borek

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Re: Practical forum?
« Reply #1 on: June 09, 2021, 03:03:42 AM »
Is there any easy way to do this?

None that I am aware of.

Nitric acid happily oxidizes organic matter (that's why it is used in some rocket engines as an oxidizer), so it can attack the plastic as well. You would need to do some tests to make sure they don't react.

Mixing hydrochloric acid with nitrates produces equivalent of a nitric acid solution, but a relatively diluted one (exact concentration depends on the solubility of the salt used), much weaker than the standard 68% stuff that nicely eats through the copper and its alloys. Doesn't mean it won't work at all, but will be definitely slower.

You should be able to dissolve the bronze with some mild oxidizer (even air oxygen) assuming you will use a bath with a strong complexing agent that will "hide" copper from the solution. That should be safe for the plastic. Unfortunately I am not aware of any ready recipes.

Take home answer is: it is 99% possible, but definitely not the way you are thinking about it now (these are not incorrect ideas, just don't take details into account), finding the reasonable approach will take experiments and some (or plenty) of tinkering.
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Offline MarkPawelek

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Re: Practical forum?
« Reply #2 on: June 09, 2021, 03:45:29 AM »
TBH, I don't know whether the old screw/nut is brass or bronze, but the exposed metal has the same pink/salmon color of copper.

Surely this must be a common problem? Why are there no common, everyday, DIY, fixes for it? I found a Nitric acid DIY guide on youtube but it's sloppy. Add 100 ml of hydrochloric acid, does explain whether its dilute or concentrated acid!, and youtube comments are no place for clarifications. So the formula is:
1. In a small flask add 80g NaNO3, or nitrate equivalent (ammonia, potassium nitrates or even garden fertilizer are suitable alternatives).
2. Add 50ml water.
3. Dissolve in the water (use hot water?)
4. If you had to warm the above to dissolve it, let it cool.
5. Add 100ml hydrochloric acid (conc. or dilute?). Make sure you add slowly, and the temperature does not rise quickly.
PS: Never add hydrochloric acid quickly to anything hot. Adding it in 5 parts seems safe to me.

Looks like a good basic formula. Data such as solubility of NaNO3 in water is handy. Which is easy to get hold of.

I can do this. I feel so excited. I haven't done this kind of stuff since I was a kid!

I'll write it up.

Offline Borek

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Re: Practical forum?
« Reply #3 on: June 09, 2021, 05:48:16 AM »
TBH, I don't know whether the old screw/nut is brass or bronze, but the exposed metal has the same pink/salmon color of copper.

Doesn't matter much - they dissolve in a very similar way.

Quote
Surely this must be a common problem? Why are there no common, everyday, DIY, fixes for it?

Most likely because the fix is too expensive and requires too much effort to be worth it.

Quote
Add 100 ml of hydrochloric acid, does explain whether its dilute or concentrated acid!

Sure they do, you just haven't paid attention :)

Note: if you don't have fume hood do it in the open, far from things/people. NO2 is quite nasty.
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Offline billnotgatez

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Re: Practical forum?
« Reply #4 on: June 09, 2021, 01:46:40 PM »
The chemical method is interesting but

My initial thought was why not do the standard method on the "brass screw"
    drill a pilot hole in the center of the screw
    and use an easy out tool  (Screw Extractor)

https://www.grainger.com/product/2LKN9?ef_id=Cj0KCQjwzYGGBhCTARIsAHdMTQwrAMcAO93FBFWcTCuSzsMqjT2k1KFNIJcMoq8WN5ODJK6SxOZ8R1waAuPiEALw_wcB:G:s&s_kwcid=AL!2966!3!496359972469!!!g!470847567000!&gucid=N:N:PS:Paid:GGL:CSM-2295:4P7A1P:20501231&gclid=Cj0KCQjwzYGGBhCTARIsAHdMTQwrAMcAO93FBFWcTCuSzsMqjT2k1KFNIJcMoq8WN5ODJK6SxOZ8R1waAuPiEALw_wcB&gclsrc=aw.ds


But then I thought  maybe they are concerned they might somehow damage the plastic part

OK

So then I thought maybe drilling out as much of the metal from the screw before doing the chemicals would speed up the process
again making sure not to damage or come in contact with the plastic.

Just a thought

When using chemicals think of safety
no breathing of fumes
eye protection
protective gloves and clothes
ability to rinse a lot if some spills on you


Offline vmelkon

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Re: Practical forum?
« Reply #5 on: July 19, 2021, 07:40:30 PM »
TBH, I don't know whether the old screw/nut is brass or bronze, but the exposed metal has the same pink/salmon color of copper.

Surely this must be a common problem? Why are there no common, everyday, DIY, fixes for it? I found a Nitric acid DIY guide on youtube but it's sloppy. Add 100 ml of hydrochloric acid, does explain whether its dilute or concentrated acid!, and youtube comments are no place for clarifications. So the formula is:
1. In a small flask add 80g NaNO3, or nitrate equivalent (ammonia, potassium nitrates or even garden fertilizer are suitable alternatives).
2. Add 50ml water.
3. Dissolve in the water (use hot water?)
4. If you had to warm the above to dissolve it, let it cool.
5. Add 100ml hydrochloric acid (conc. or dilute?). Make sure you add slowly, and the temperature does not rise quickly.
PS: Never add hydrochloric acid quickly to anything hot. Adding it in 5 parts seems safe to me.

Looks like a good basic formula. Data such as solubility of NaNO3 in water is handy. Which is easy to get hold of.

I can do this. I feel so excited. I haven't done this kind of stuff since I was a kid!

I'll write it up.

1. Using hot water accelerates the rate at which the NaNO3 dissolves. Are you in a hurry? NaNO3 is very soluble and quickly dissolves at 20 °C. Relax. Take it easy. Slow down.
2. Hardware store HCl tends to be at maximum concentration. 10 M. If you open the bottle, it emits white fumes. Keep the fumes away from your face. When done, keep it in a closed polyethylene bag.
3. Adding water might be a good idea to reduce the concentration of the HCl.
4. That recommendation for adding an acid to water seems to be mostly for conc H2SO4. It is a very exothermic reaction. I haven’t noticed heating when adding HCl to water.
5. I recommend that you try 1 M concentration for your HNO3.
6. I’ve tried KNO3 + HCl and also a wire of copper. It’s fun. It slowly attacks the copper. The presence of H+ and NO3- is needed to oxidize copper.
Some people use HCl and H2O2 (I think store bought 3% which is mighty weak).

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