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I have been looking for a preferably electrolytic method of rust removal
and have subsequently been experimenting with steel-anode
[object-to-be-cleaned]-cathode in lye or sodium carbonate solution
electrolysis. This method however has not been quite as successful as some
have made it out to be! I have found that at the initial application of
current from a battery charger much of the surface rust (red Fe2O3) is
removed, whilst leaving small clumps of black material, which I assume to be
Fe(II) oxides and hydroxides. Letting the cell run in the solution for a
further, say 1/2 hour, an amorphous, matte black coating forms on the
cathode. I had initially thought the layer might have been Iron aluminate,
however the effect has been observed in Na2Co3; NaOH; & acidified NaCl
solutions. Consequently I am at a loss as to what it might be, and as to how
I might remove it! It seems that the coating forms more rapidly in hot &
I would greatly appreciate it if someone could explain this effect, how
I might be able to prevent it (or suggest an entirely different method of
electrolytic rust removal) and how I could possibly clean the items that
have already been tarnished! I would also be interested in any literature
someone might be able to suggest on the subject of electrolytic metal
cleaning. Ultimately what I would like to be able to achieve is a completely
bare, shiny metal surface on steel through chemical means only.
"George" <[Only registered users see links. ]> wrote in message news:<3f47fa31$1$14564$[Only registered users see links. ]. au>...
Some time ago I was messing around with electrocleaning, mainly out of
curiosity, but I also wanted to clean some old steel tools for
painting. I suspected the black film on the cathode was the
redeposition of trace quantities of iron ions from solution. The
normal way around the problem is to initially make the job the cathode
then after the bulk of the cleaning is done, you reverse polarity and
the deposits will strip clean in a few seconds.
I doubt you will ever get smooth shiny steel with this bath. I've
always ended up with a rough and dark looking pitted surface.
Electropolishing may be required as an additional step. Try searching
[Only registered users see links. ] for steel electropolishing bath formulaitons.
A quick google search gave me this one;
[Only registered users see links. ]
Adam Seychell wrote:
I checked in Electropolishing, Anodizing and
Electrolytic Pickling of Metals by Fedot'ev & Grilikhes,
and their cathodic baths for electrolytic pickling
of steel use also deposit lead on the workpiece.
I figured the original poster wouldn't want to
mess around with lead.
>From: "George" [Only registered users see links. ]
I have electrocleaned the battery clips on my grandfather's old Sears 6/12
volt battery charger with success. They don't come out shiny. See below.
This was an old copper-oxide semiconductor laminated rectifier and was
marvellously resitant to abuse for that reason. It had a nice meter.
I threw it away when my first lover died and I did some house cleaning. I'd
been holding onto the memory of my grandfather since he died in 1976, while I
was away at high school in Germany. I didn't get to attend his funeral. Linda
died in 2000. I held onto that piece of crap for 14 years. I still have his
ruler, a nice steel engraved 6 inch ruler. Real quality, that. Will last
Sorry, I think what you meant was chemical and electrical means only. That's
the whole point, right?
Well, George, you're in for a bit of a fight, and here's why.
When you electroclean steel, the work is negative. When you electropolish it,
the work is positive, and much more power is required.
When the work is negative, electrons available at the surface attract hydrogen
(H), which is slightly postively charged by it's "bent" configuration in the
water molecules. When hydrogen is an ion, it is H+. It cannot get any more
positively charged than that, because it consists only of a proton nucleus, no
neutrons, and a single electron orbiting the proton, or according to quantum
mechanics, likely to be found near the proton according to a certain probablity
density function which is surprisingly, quite easy to find.
So these hydrogen atoms leave their existing oxygen partners, and it is those
oxygen atoms you see bubbling to the surface. Oxygen is negatively charged,
usually. When the H combines with the O in Fe2O3, it forms H2O and "recycles"
into solution, where it can be stripped again, forming another bubble nucleus
of oxygen. And on and on. So the H shuttles back and forth, while the O in the
rust goes to bound O in H2O, then is released as O2 when the H is pulled, yet
again, to the negative electrode. Ambient heat "stirs" the water near the
Now, this leaves fine particles of iron, in fact one or two iron atoms at a
time, "more or less" attached to the workpiece, but again, ambient heat can
stir them into "solution", where they form a toxic powdered iron hazardous
waste. On drying and mixing with an oxidizer like salt peter, this sludge may
be ignited yielding the bright orange spark characteristic of a steel mill
pouring hot iron into molds for milling. This can be dangerous. Do not mix
metal powders with the hypochlorites, chlorites, chlorates, or perchlorates.
It's quite dangerous.
So ambient heat rips the "cleaned" steel atoms from the work. The best you can
expect at room temperature is to remove all the rust, create sludge, and end up
with the steel, wherever it is sound, bared for your inspection.
Now when you look at it, it looks pretty ratty, but with electropolishing comes
some hope of redemption. You have to understand surface roughness some. At
least it helps. At this point the work is chemically clean, cleaner than
anything else in the room, and will rust immediately.
Now, when you electropolish, the work is positive, just like for anodizing
aluminum, which forms a protective coat of aluminum oxide on the metal, thicker
and smoother than that formed by exposure to air. Only when you electropolish,
you are ripping metal atoms from the surface, a mechanical process that takes
large amounts of energy. The metal atoms like to go positive, for example Fe+
or Fe++, and to combine with them you have to get the oxygen atoms to separate
from the water and combine with the iron, forming finely powdered rust, which
can be recycled in a thermite reaction if mixed with the right oxidizer.
Hydrogen bubbles to the surface. Rust falls to the bottom.
I am not going to disclose in this article the chemistry of a thermite
reaction, because one can easily melt through a steel laboratory desk top, set
a house on fire (they were used as incendiary weapons in WWI, destroy an engine
block, or weld steel rail, which is what they are used for, mostly. I do not
want anyone to get hurt just from reading what I write.
Anyway, for a reason I do not understand, this tends to happen on "asperities",
which are the pointiest bits exposed by the electrocleaning. Electropolishing
rounds off asperities by turning them to rust.
Now, to walk to the bottom of a valley is easy. You just head off downhill,
stroll along easily, and in a few minutes or hours, you are there. But if you
are an oxygen atom looking an iron atom, you are effectively coming vertically
downward at a mountainous landscape and your job is to level the entire
landscape one pebble at a time, until it's all valley.
Now what if you were a spoonful of dirt, and your job was to fill the valley?
While not as easy as walking downhill, this is also not as hard as rounding off
the mountains. So what we need to do is PLATE iron back onto the steel in a way
that fills the valleys first, and we can worry about the little mountain tops
Well, to PLATE a metal, it must be an ION in SOLUTION, and we haven't got any.
The removed rust fell as iron to the bottom of the tank, and the removed iron
fell as rust. Neither is an ion. So if the solution is neutral in pH, that is,
tap water with salt added, not acid or base, the above will happen and we won't
be able to fill in the valleys, and rounding off the mountains will take a
lifetime and the entire output of the Northestern grid, which went down
recently, by the way.
So which way do we tweak the pH? Acid or base?
Surprisingly, I think either would do. All I know is that metal likes to be
positive, so you either add an acid and hope it reacts with and dissolves the
fine iron particles that fall off during electrocleaning, or you add a base,
hoping that some of the iron atoms ripped from the solution will mate with the
HO- instead of the O+, go into solution as what is called a "solution
inventory" meaning there are essential no molecules of iron hydroxide left,
they are all broken up.
Anyway, if you leave the solution neutral and then try to alternate stripping
the rust and depositing fresh iron to plate over the valleys, what you end up
with is iron over rust, not clean metal, which is why shit made in China is
cheap, because they pour all their sludge into the river they drink from, and
why it doesn't last, because it's iron plated rust. Now if you machine freshly
cast or milled metal and dip it in Cosmoline, you can keep the surface clean
essentially forever, and some of the good stuff I have got from China like my
drill press follows this regimen closely.
So very little care (some oil or grease) is needed to PROTECT iron, but great
effort and energy is required to REPAIR it, which is all the folks in the
rec.crafts.metalworking newsgroup I love so much like to refinish old machine
tools: it's fascinating.
At the very least, you will need a specification of electrolyte and sludge
disposal regimen for two separate processes, the first of which must be taken
to completion, that is, chemically clean metal, and the second of which can be
taken as far as you like, be it filling up the valleys with plated iron, or
another plating, or polishing down the mountains with the appropriate
electrolyte and sludge disposal regimen for electropolishing. You really can't
do both in the same can.
One of the problems with filling up the valleys is that the little dirt clods
(iron ions in solution) are first attracted to the mountains. There is no such
thing as electrical gravity. They don't just fall toward the surface, they are
pulled, and if the first thing they encounter is a mountain peak, an asperity,
they stick to it, making the surface even rougher.
Moral of the story: Try to keep the blood from your cut finger off the drill
you stuck through it. It doesn't just rust the tool, it can dull the cutting
Replikon Research (via aol.com)
Nuclear weapons are just Pu's way of ensuring that plenty of Pu will be
available for The Next Big Experiment, outlined in a post to
sci.physics.research at Google Groups under "supercritical"
I have done a fair amount of work in this area, however, I have
generally looked at stainless surfaces, typically 304L and with the
slant of decontamination from plutonium environments. For that, I can
give you a fairly simple recipe for a fairly uniform electro-etch at low
current densities in a mild alkaline solution. For carbon steel,
several recipes for electropolishing are given in John Jumer's article
"Electropolishing" in Metal Finishing vol 93, no 1A, (1994) pp 420-427
that might be of use -Doug W
[Only registered users see links. ]
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|cleaning , electrolytic|
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