Tacho
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Best rust inhibitor for vacuum station.
My vacuum station 's pump has some steel pieces that are turning the water brown with rust. What can I add to the water to prevent rust
formation?
I thought of using ethylene glycol instead of water. Any opinions?
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Mr. Wizard
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Keep the metal warm, or above ambient temperature with a small light bulb, preventing water condensation. Look around the area where it is stored, and
remove any HCl, Br2, Cl2, I2 sources, even if they are 'sealed'. It has been my experience these materials will cause rust on steel even if
the bottles seem to be tightly sealed. Rust can also be prevented or slowed by spraying with galvanizing paint, which contains powdered zinc. After
drying, it looks like a cheap gray primer paint, but it works, but won't last forever in a corrosive atmosphere.
After looking at the link it appears your corrosion was inside the pump. Maybe you could run automotive anti-freeze (ethylene glycol) with some rust
preventive additives. You also might try hooking a sacrificial anode to the frame of the motor and leaving the anode in the liquid. These anodes are
available where they sell evaporative cooler supplies and at boat repair stores, where they are available for corrosion control.
[Edited on 23-3-2005 by Mr. Wizard]
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Organikum
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Some sodium carbonate - just enough to keep the water slightly alkaline?
Shouldnt attack the pump and should prevent rust - not?
Or a dash of citric acid should work too.
[Edited on 23-3-2005 by Organikum]
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Magpie
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I concur with Organikum that keeping alkaline should do the trick.
In my previous life we protected mild steel tank walls from nuclear waste corrosion with NaOH + NaNO2. There was a pH spec and a NO2- molarity spec
but memory fails me.
If you don't change the water in your recirculation system it is likely accumulating all the salts from the nasty vapors you are evacuating - but
you already know this.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Tacho
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Thanks folks!
I did several experiments using large steel nails to test all sugestions and this is what I found:
- Making the water alkaline with sodium carbonate does improve corrosion resistance. Some rust is formed, but a lot less than pure water.
- Some nitrites in the water give the same results as the sodium carbonate.
- Some phosphoric acid prevents rust completelly, but strange things happen to the nails. A powder, I would guess powdered iron, forms on the nail.
Some bubbles evolve... no good.
- Although the nails in pure ethylene glycol did not rust, it´s a HORRIBLE bubble maker. When I added just a cup to the water, The vacuum fell
drastically and the water kept that white tint of foam (microbubbles) almost a minute after the pump ist turned off.
Finally, I used a mixture of sodium nitrite, sodium carbonate and borax. That is a commercial formula. I think the borax is used to prevent algi or
bacteria.
It´s working so far (2 days).
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mick
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Years ago I found borax worked well in neutralizing and passivating rusty car bits that had been in an acid derusting pickling bath. You could try
some of the corrosion inhibitors for car engines, I think they used to be based on stuff like dibutyl thiourea or 2-mercapto benztriazole. The
chemicals a nearly insoluble in water but enough seems to disolve to put an insoluble sulphide type layer on the iron.
A lot harder and more complicated process would be the chemical plating of nickel. I found this in chem abs as a patent proposal years ago and tried
it on the clutch/brake pedal assembly of my old car. Followed all the alkali (I seem to remember the alkali wash had to be at 50oC), acid and
distilled water washes. It was then straight into the plating solution of nickel salt (I think it was the chloride) and sodium dihydrophosphite,
phosphonite or ate, its a reducing agent anyway. After leaving over night the nickel was plated and it is still there after 25 years, paint does not
stick to it very well though.
I have probably missed a thread to this.
mick
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mick
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I have found the original notes from 1980 and above is wrong. The mixture I used was NiCl.6H2O 30 g/l, NaH2PO2.H2O, 10 g/l, NaOAc.3H20,10g/l. The rest
of the notes gives pH 6 and 60oC.
Aq solution of 0.5% mix of 3 parts NaNO2 and 1 part Borax was used to quench the plating solution.
I have found a note CA 80 73179b for a coating on steel.
3l bath +
180g CrO3
130g MgO
410ml 85% H3PO4
15 ml aq dispersion containing 13.5g poly(tetrafluoroethylene) of particle size less than 1 um.
Then heat in a furnance at 371oC for 60 min
I never tried that one but I did try the other stuff.
mick
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Tacho
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Interesting. I did some experiments with electroless nickel deposition and posted the results somewhere. I didn'k know it could plate steel. This
would be an overkill for my pump problem though.
Hipophosphite is a controlled chemical in many countries.
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mick
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In 80s it was not a problem.
mick
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