Fun with Chemistry (anti-corrosion)

[vtcnc]

I was thinking a Watts-type bath using Nickel Sulfate and Boric Acid could be something to try, perhaps with a few more ingredients. There are lots of nickel salts plating solutions, and various plating properties one can end up with. I can manage about 50A at 5V, but in our case, we can substitute time for current. The ions will plate anyway. That calculation showed me that 58.69 grams of nickel needs 2 x the number of electrons it takes to liberate 1mol worth. I figured that in 2 hours, the 7200 second worth at 0.5A would deposit 1.095grams. Getting to efficiency, and without cooking it up to 50C, we can get about 50% of that. Half a gram is not much, but is enough to fill some grooves.

Make sure you rotate your shaft in the bath periodically, or have anodes positioned around it. Plating is line of sight from the anode perspective.

A thick plating surface will pretty much follow the profile of the surface it started on. You could have a plating thickness many times the size of the imperfection, and still see the imperfection replicated on the top. I think a "filling repair" would be to plate on enough to fill the groove, then cut back to the original dimension. In my case, the oil film should be thicker than the grooves depths, so this time, the value in the plating is about corrosion protection.

You may consider reaming the bearing sleeve for this shaft rather than corrupting the nickel surface. Depending on your plating thickness and adhesion quality, you will likely flake or chip the nickel when trying to turn down the surface. Your depth of cut is going to be likely deeper than the thickness of the plating.

Yes indeed on the castings. I love that!
I wonder if one can get the plating to work through wet cotton wool swab, with solution, like you can do with gold plating? That way one could "go over" the machine surfaces exposed to rust, instead of having to dunk the whole thing in plating solution.

I would think it is possible. I would really like to figure out how to do that. I suppose painting over the nickel plating is an option as well but that is a better option for those of us with big tanks and not hobbyists.

 

[graham-xrf]

Make sure you rotate your shaft in the bath periodically, or have anodes positioned around it. Plating is line of sight from the anode perspective.

Yes - I saw that. One side was getting the coating much faster than the side away from the electrode

You may consider reaming the bearing sleeve for this shaft rather than corrupting the nickel surface. Depending on your plating thickness and adhesion quality, you will likely flake or chip the nickel when trying to turn down the surface. Your depth of cut is going to be likely deeper than the thickness of the plating.

Since starting to research nickel plating, I have discovered there is huge knowledge about the different qualities of adhesion, hardness, and built-in stresses. Non-decorative additive shimming is an established technology, and how to prevent the plating from coming away from the part when machining, using suitable low stressed plating, contrived from the bath setup. Bath control has now gone digital, with bath composition under closed-loop control.
re: Plating big heavy stuff

I would think it is possible. I would really like to figure out how to do that. I suppose painting over the nickel plating is an option as well but that is a better option for those of us with big tanks and not hobbyists.

I KNOW this can be done, because I have used this method to plate gold onto copper microstrip signal coupler tracks. It even has a special name for the technique. The search engines are now so full of bias algorithms that it does not come up anymore, but it is also called "brush plating". If it works for gold out of a cyanide solution, it must surely also work for nickel.

There is a limit to the amount of bling suitable for a machine, and gold plated machine surfaces in the cause of corrosion protection is, to my mind, a tad tacky. Is there room here for the concept "in bad taste"?

Tough nickel, inexpensive corrosion protection, repair, and making hard wearing + good looking surfaces is altogether OK.

On the "additive shimming" repair aspect, I know the plated parts are usually re-finished by grinding rather than by turning. Extremely complicated and expensive parts with damaged critical surfaces can be saved from being "big junk" and be given working high precision surfaces better than new.

 

[vtcnc]

Boy, did you send me down the rabbit hole today! I found this video on brush plating and then came back here to see your reply on "brush plating".

So, it absolutely is possible to do what you are suggesting. It appears that the rectifier control is the trick and the rest is plumbing, chemistry, tooling and setup.

This feels like it is absolutely in the wheelhouse of hobbyists from my point of view. Now to find a rectifier...

 

[graham-xrf]

Oh yes - you just know that the next thing I try with the lovely green liquid is a cotton swab on an alligator clip!

 

[graham-xrf]

@vtcnc: Hold up on the "rectifier" there. To my knowledge, "rectifier" is a simplistic thing (like a diode rectifier) that conducts only one way, and is the first component in making a DC bus from AC power. What you need is the rest of the regulator circuit. Don't take fright. They are not out of reach.

Clearly the variability of the swab connection is what we are after getting past. I am thinking that is achieved using a settable constant current supply. This trick is commonly part of the sequence in smart battery chargers, but the circuit concepts are easy, and many relatively inexpensive bench power supplies have this feature. Basically, within limits, it will raise or lower the voltage to satisfy the regulator constant current set demand. You can even profile the current/time recipe on some.

Current x Time translates directly to metal ions deposited, unless some were wasted making heat, or unwanted other products - like other gases.

All the graphs I have seen put the 80%+ baths at 40C to 60C. It may be difficult to approach that with brush plating, but at least don't do it stone cold.

 

[graham-xrf]

@vtcnc : Can you tell what you might know of what cleaning, etc. is needed for castings before plating?
Another thought.. was that a piece of Scotch-Bright pad being used in the video you linked to?

Did you spot how the shapes of the original surface gouges were still preserved on the top of the thick plated coating?

Yet another.. do you suppose one could plate in inside of a of a journal casting, so repairing scoring, then ream it out to it's original size?

I now have too many irons in the fire! I am likely going back to some circuit design for the X-Ray detection.
@homebrewed will realize how distracted I got.

 

[Aukai]

My memory from HS chemistry was that you can add acid to water, but you should not add water to acid, and it stuck with me....

 

[graham-xrf]

I took both physics and chemistry....majored in both. I enjoyed chemistry but really understood physics.

Nickel is more electro-negative than iron so any break in a nickel plate will be open to corrosion.

So suppose we went for zinc plating. I understand that even if there is a gash or cut in dip-galvanized iron that exposes the iron, it still will not rust, because the zinc makes a potential that protects it, I also know ships use sacrificial zinc bolted to a ship under the water, which rot away instead of the ship. Some even use a battery to help it.

I know that dip-galvanized steel brackets at my place do not rot, but plated zinc bolts, and so-called "zintec" corrugated iron sheets do yield to rust. I dislike that unless we fight back, everything we have that has Fe in it will try to go back into the ore from whence it came!

Hmm.. it seems one can use the vinegar method for ZINC also. Only, the solution is clear - not any colour, and no way to tell it is anything but vinegar until you start plating.

COPPER also, except you have to first plate on some nickel, because apparently, you can't plate copper onto iron directly.

So what might be the range of metals for which an acetate salt can work?
Maybe all those which can be forced (by a power supply) to deliver ions into acetic acid.

 

[RJSakowski]

So suppose we went for zinc plating. I understand that even if there is a gash or cut in dip-galvanized iron that exposes the iron, it still will not rust, because the zinc makes a potential that protects it, I also know ships use sacrificial zinc bolted to a ship under the water, which rot away instead of the ship. Some even use a battery to help it.

I know that dip-galvanized steel brackets at my place do not rot, but plated zinc bolts, and so-called "zintec" corrugated iron sheets do yield to rust. I dislike that unless we fight back, everything we have that has Fe in it will try to go back into the ore from whence it came!

Hmm.. it seems one can use the vinegar method for ZINC also. Only, the solution is clear - not any colour, and no way to tell it is anything but vinegar until you start plating.

COPPER also, except you have to first plate on some nickel, because apparently, you can't plate copper onto iron directly.

So what might be the range of metals for which an acetate salt can work?
Maybe all those which can be forced (by a power supply) to deliver ions into acetic acid.

Zinc is electropositive w/ respect to iron and will corrode instead of the iron. The zinc electroplate that is used on fasteners is too thin to be of much value. When iron is galvanized, it is hot dipped and has a fairly thick coating.

Copper can be plated on iron. In fact, when chrome plating, copper was first plated, then nickel, then the chromium. Steel MIG wire is coated with a copper electroplate. You can actually plate copper on iron by just dipping the iron into a copper sulfate or copper chloride solution.

 

[graham-xrf]

@RJSakowski : OK - I got it wrong then.
What happens without the help of a battery or power supply seems to be all about which has the greater (natural) electrode potential, (compared to hydrogen) ... I think. This stuff can get complicated. You make a solution, and already it is no longer the straightforward ingredients.
It "dissociates" splitting up into some Ni++ and (other stuff)- -
Not all mind, but only some proportion in an "equilibrium", which can get urged on by a battery.

I think, if there are other metals encountered, one will be the winner - Hmm. I did some chemistry at school, but I must have slept through this one.

I am still feeling quite stoked about the way that plating went onto the end of the shaft, and I am already dreaming of diverting whatever I can in the way of other household plastic containers to the new secret cellar purpose.

And yes - I do want to attempt some of THIS stuff! (thanks @vtcnc ).

Wow! Was that a piece of 3M Scotch Brite pad he was using to deliver the solution?