Black Oxide

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GlennW
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Black Oxide

Post by GlennW » Mon Oct 05, 2009 12:30 pm

So this is sort of a continuation of this thread for those who did not follow it:

http://www.chaski.org/homemachinist/vie ... hp?t=82893

I had to make a dozen of these from 6.5” OD Tubing and they needed coating of some sort so I decided it was time to try Black Oxide.

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This is the finish on the parts as machined.

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The recipe can be found on the internet and it contains Water, Potassium Nitrate, and Sodium Hydroxide. The parts are boiled in the solution. I used 100% Potassium Nitrate and 99% Technical Grade Sodium Hydroxide as common drain cleaners are only 30% to 60% pure and contain other ingredients.

Here is what I used: A gas burner from a turkey fryer with huge BTU’s and a three gallon enameled stock pot.

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The burner worked great as it had instant control of the solution. Turn it up and it instantly boiled, turn it down and it stops boiling. Easy to manage.

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I wired four collars together in a stack and looped the wire to form feet to keep them off of the bottom of the pot and boiled them for 15 minutes and the result was a nice black coationg. It forms a little smut on the parts that wiped right off to expose the black finish which I then wiped with an oily rag. Here is a before after.

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Viola…..Twelve shiny black collars!

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Just as an experiment I cleaned off the socket/wrench I had tried and failed earlier (on the right) and boiled it with another one I had recently made. The one on the left coated just fine as did the two dowel pins in it so hardness does not seem to be the issue with the lack of plating. As with the part on the right. Thinking back, I believe that the one on the right was most likely 1144 so I’m guessing that the Sulfer content is the possibly problem as I tried coating that one three times with no luck..

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I wore a full face shield and made sure I stayed upwind from the pot as this stuff will wake you right up breathing the fumes READ THE MSDS I POSTED a little farther down in this thread. I used long tongs to place and remove the parts from the pot also. Obviously all done outside! I also had a couple of five gallon buckets of clean water handy to dive into in case I splashed some solution on myself.
Last edited by GlennW on Mon Oct 05, 2009 4:07 pm, edited 1 time in total.
Glenn

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GlennW
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Post by GlennW » Mon Oct 05, 2009 1:08 pm

Well, it took the enamel off of the interior of the pot and turned the solution dark, so the next experiment will be to try a stainless steel pot. The instructions I had said to use an enameled pot since he had not tried a SS pot so that's what I tried!

Stay tuned!
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

websterz
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Re: Black Oxide

Post by websterz » Mon Oct 05, 2009 1:39 pm

Glenn Wegman wrote:
...made sure I stayed downwind from the pot...
I hope you meant to stay UPwind of it. :wink:

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GlennW
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Post by GlennW » Mon Oct 05, 2009 1:40 pm

I'm left handed too!
Glenn

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BadDog
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Post by BadDog » Mon Oct 05, 2009 2:17 pm

Nice results, I would love to try that.

How do you plan to store the solution, or do you?
Russ
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GlennW
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Post by GlennW » Mon Oct 05, 2009 2:31 pm

I just poured it back in the plastic water jug. I am going to get a heavier jug such as a one gallon diesel fuel jug and mark it appropriately.

The really nice thing is that all I need to do now is dump it in the pot and light the burner. I can have coated parts within 20 minutes of making them :D
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

Jose Rivera
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Post by Jose Rivera » Mon Oct 05, 2009 2:34 pm

Where can one buy those chemicals now days without being the CIA watch list ?

I would love to try that instead of using Blue-Wonder.

It does OK but it will not reach sharp corners or small grooves, threads, etc. very well.
There are no problems, only solutions.
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GlennW
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Post by GlennW » Mon Oct 05, 2009 3:05 pm

http://www.essentialdepot.com/servlet/t ... Categories

http://www.spectracide.com/ProductCateg ... efault.htm

I used Distilled Water and measured the chemicals out carefully on a postage scale. If something did not work, I did not have to wonder if the solution was incorrect by doing it that that way.

I'll add this too so READ IT before you play with this stuff!

http://www.seas.upenn.edu/~nanofab/chem ... e_NaOH.pdf
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

J. Randall
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Post by J. Randall » Mon Oct 05, 2009 11:33 pm

Glenn, seems like I have read sometime in the past that stainless will kill the solution(with the commercial salts anyway). I know that a gunsmith friend of mine made his tanks from mild steel sheet, and they work fine.
James

Jose Rivera
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Post by Jose Rivera » Mon Oct 05, 2009 11:54 pm

A internet friend from Australia had caustic substances in his garage.
Apparently bottled in glass. His dog accidentally broke that bottle and got his four paws almost dissolved.
Also part of his mouth as he tried to lick his paws.

Definitely no glass containers should be used and if plastic, heavy thick stuff is a most.

This is a very interesting thread because metal blacking give one of the best finishes to steel.
There are no problems, only solutions.
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Harold_V
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Post by Harold_V » Tue Oct 06, 2009 3:42 am

Jose Rivera wrote:This is a very interesting thread because metal blacking give one of the best finishes to steel.
Most importantly, it doesn't change size.

Like you, I'm keenly interested in the process. Can't thank Glenn enough for his invaluable contribution.

I'd also like to research Parkerization, a phosphoric acid process. It was used by the defense department for military arms. A great finish.

Harold

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GlennW
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Post by GlennW » Tue Oct 06, 2009 4:47 am

J Randall,

Thanks for the tip!

I'll do a little more resesrch on that and report back.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

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