<VV> Derusting---Was "I was wrong..." Long

[WadeHalsey]

>also, you can use normal table salt, but water
>softening or sidewalk salt does MUCH better....and
>it's cheaper too.
>  
>
I have never heard of using table salt in any derusting solution! My 
notes on the topic gathered over the years suggest using common WASHING 
SODA instead. Following are my notes on the topic from this and other 
forums-----Wade Halsey


"Anyone restoring a rusty old car should learn about this type of rust 
removal. It uses chemistry to make work easier. You will need a large 
container to hold the solution, a battery charger such as a 10 amp, 
sacrificial piece of steel, such as a section of stainless sink because 
stainless lasts longer. Or use an old stainless pot or pot lid. You want 
a piece of steel with a lot of surface area. Then some washing soda from 
the grocery store.
Fill the container with water and add one tablespoon of washing soda per 
gallon of water, more soda is OK. Put the steel in the water and put the 
red or positive (this is important) clip from the charger on the 
stainless steel. Keep the clip out of the water since it is made of 
copper and will disintegrate fast. Take the rusty part and put it in the 
mix and attach the negative clip to it. If the clip goes in the water 
it's OK. Plug in the charger and wait. Don't let the part and the 
stainless steel touch. You will see bubbles start to come off the part 
within minutes. If you see little bubbles it's working. Give most parts 
a day and they come out with no rust. This process turns the rust into a 
black substance that you can wash off with a stainless steel wire brush 
and a scrub pad. Wear gloves while cleaning or the black stuff will 
stain you fingers. The rustier the part the longer it needs to soak. 
This process will remove paint and all the rust and will not damage the 
good metal. It is much gentler on the metal then a wire brush on a drill 
and is a lot easier. When the solution gets dirty dump it on your lawn. 
The grass likes the iron and gets real green.
The rust removal system works great. A note of caution. The bubbles 
coming off the positive and negative electrodes in the solution are 
Oxygen and Hydrogen. They aren't poisonous to breath but the Hydrogen 
gas is extremely flammable. Do this process in a well ventilated area. 
Air it out before you do any gas torch or arc welding operations.
One problem is that once you clean the part with water and a scrub brush 
you will need to dry it and be ready to paint it with a primer or it 
will flash rust. Remember, you can leave it in the solution till you're 
ready to clean it. This process will not hurt good metal only rust. I 
took a rusty rim for three days and it looks new.  Jerry Mannix White 56 -

Question: How does this solution affect other materials like rubber 
bushings or plastic parts. In other words, do steel parts to be 
de-rusted have to be completely stripped down? And one last question, 
what about embrittlement of parts like springs? Is this method safe to 
use on suspension parts etc?
It doesn't.  This is basically (really there is a lot of other stuff 
going on also, as it is a double compound replacement reaction) an 
electro-chemical process that changes the ferric oxide (Fe2O3, scaly red 
rust,) to ferrous oxide (FeO, black hard rust).  The solution sodium 
carbonate and water is a buffered basic solution with a PH of  10.  So, 
if an alkali (basic) mixture won't hurt it, it is ok.  It does not 
affect the strength or hardness of the steel or iron, beyond that 
already done by the original rust.  You are simply coating the part.  
Anodizing aluminum is a similar process although it is done through a 
chemically different process.  Aluminum or any other reactive metal in 
this bath, will pit extremely fast. Jim Davis
You can use any steel but stainless steel lasts longer. Normal steel 
like a cookie sheet will last about a month and corrode away. Get an old 
stainless kitchen pot at a yard sale.  Don't use baking soda, WASHING 
SODA makes a much better solution. Baking soda works but will slow the 
process and you need to keep adding it to the solution you have. The 
purpose of the washing soda is to create an electrolyte solution, 
washing soda is a better conductor. It also costs less then baking soda. 
You won't hurt anything by using baking soda but you may have a higher 
electric bill due to the fact it will take longer to de-rust each part. 
With either solution you use you have to change it or add more soda 
every few weeks to keep it working ant top efficiency.

I found this technique (sodium carbonate and electrolytic reduction) on 
the antique stationary engine mailing list.  I was intrigued, but also 
distrustful.  Surely it was corrosive, hazardous, or something similar. 
All the chemical derusting techniques I had seen involved acids and 
corrosion of good metal.  The stories thrown around suggested that this
was not so with the washing soda method.
I searched and found that museum conservators with irreplaceable ferrous 
artifacts prefer this method precisely BECAUSE it does not allow any 
corrosion of intact metal.  If done with Sodium Hydroxide (lye) instead 
of with Sodium carbonate, it's actually capable of converting iron oxide 
back into metallic iron.  (NOTE:  I DO NOT
RECOMMEND USING LYE FOR THIS PURPOSE.  Its advantage over washing soda 
is largely theoretical and it is vastly more DANGEROUS) For that matter, 
the process does not remove the corrosion products; they are instead
electrolytically reduced from rust to black magnetite, but they stay 
right there on the metal until you rub them off with a stiff toothbrush 
or something similar.

The solution will have no effect on rubber, but may roughen the surfaces 
of some plastics.
Remember that the reaction is done in a reducing bath with an alkaline 
electrolyte.  Hydrogen embrittlement is
from exposure to acids.  (free hydrogen radicals attacking metal) 
Admittedly, the electrochemistry alters the case somewhat, but 
emperically I'd be willing to argue against measurable ion migration out 
of the metal itself over the amount of time that derusting is performed.
The areas to be derusted need to be free of anything that would inhibit 
the solution making intimate contact with the
metal itself.  Free flow of electrolyte past the surfaces is important 
in maintaining a constant field strength and solution concentration over 
the surface being treated.  Greasy metal is a bad idea. So is a 
significant covering by anything else, although I've seen it do a fine 
job in removing paint after immersion for a week or so.
One other huge win of this process over any other rust removal procedure 
I've found is that it reverses the swelling that binds rusty parts 
together. The problem is caused by the simple fact is that rust is 
bigger than the iron from which it came.  Accordingly, a rusty bolt 
swells in the rusty hole in which it is threaded and no longer unscrews 
easily.
The electrolytic reduction process turns the rust into magnetite, which 
is both mechanically weaker and smaller than rust.  Usually you can 
unscrew parts that have rusted together if they're carefully treated in 
the bath for a while.  My test case for this was a pair of 
otherwise-good 140 HP exhaust manifolds which had bolts screwed (and 
rusted) into the drilled-out stud holes.  After cooking for about a week 
the bolts unscrewed with moderate effort. Rad Davis
Jim Davis wrote: Rad got me started with this a couple years ago.  It 
works as  advertised.  Be patient a really rusty part will take 24 to 30 
hours to  completely harden. For those young ones who have never hear of 
washing  soda; it is sodium carbonate.  It that chemical we use in 
swimming pools  to raise the PH. Jim Davis"