What To Use To Prevent Galvannic Corrosion On New Quill Stem?

[Ajax Bay]

@silva What's the chemical mechanism which means an aluminium spoke nipple is more likely to seize on a stainless steel spoke's thread than a brass one?

 

[battered]

As I said: you don't understand the potential difference / the battery effect.
This potential difference, in the presence of a conducting medium, allows an electrical current to flow to the anodic material, which corrodes to then DISSOLVE within that conducting medium (named as "electrolyt").
You know what dissolving is? The anodic material desintegrates and mixes up with the electrolyt. As salt in water. Fine particles. Take away the water and you see fine powder.
Now explain me how such fine powder, coming from the jointed surfaces, is gonna seize the joint.
It's the very opposite: the joint get loose.

An example my bike suffered: the smart'o'guys of its production company chosed 2 A2-70 stainless steel to fix the bikes stand on the frame, through an aluminium block, in order to bring the to-mate surfaces parallel to eachother.
After some time, I noticed that those bolts had come loose.
I retensioned them.
They again came loose.
I retensioned them again.
But they kept on coming loose.
Then some day, at a flea market, with me parking my bike a couple dozens times, it became plain ridiculous. The bike fell down several times, with me retensioning the bolts all the time. With tens of minutes inbetween.
Back home, I wanted to know what was going on with that stand.
I took out completely the two bolts, removed the block. The bolts were covered with white dust. On the ground: fine white powder.
Then I started to realize what had happened. Galvanic corrosion that dissolved the aluminium, causing lotsa play.
The holes through the interface block, were enlarged. The thread in the bikes frame, was damaged.
I solved it by replacing the stainless steel bolts with longer non stainless steel bolts, with washers and nuts on the other side.
All greased to avoid corrosion. Not to avoid galvanic corrosion, but to avoid "common" corrosion: RUST.
And no problem since. The bikes stand just stays fixed. It's years ago now.
I informed the production company of the problem. They first asked me what alternative I would use, I proposed non stainless and grease/oil to avoid rust. They said they would take this in account for next productions. I don't know if they did.

So galvanic corrosion, that implies DISSOLVING of joints material, that causes seizure of the joint?
Seizing has a number of possible reasons. One is an inner material that expands more (ex due to oxidation) than the outer material. Abit like frost causes water to crystallize to a bigger volume. Abit like non stainless steel oxidizes to rust that occupies a bigger volume. That is for ex the reason for what they name "concrete rot". If water reaches reinforcement bars, the steel corrodes, expands, and pushes away more concrete, aggraveting/speeding up the process.

Chlorine can even make stainless steels rust. Especially the cheapest / most common grade 304 also named A2. That is even especially prone, more than common steel. Know why stainless doesn't rust? Or why aluminium doesn't rust? Because it DOES rust, BUT, the rust forms a protective layer against further rust. Take away that protective layer, or prevent its formation (case stainless) and it just continues to rust like common steel.
An example: take a so called salt lamp. That is a nice looking block salt, with a lamp in it. People use it as a sphere lamp.
But there is a danger most are unaware of: the salt block has a cold surface. Water from the air condenses on it, salt dissolves in it (so the salt block shrinks over time) and the water-with-salt flows to under the lamp. You get water with salt, possibly near metals, near electrical wiring.
I know someone that had such lamp (hence my example), discovered the water, and wondered where it came from. Person decided to put the lamp in a kitchen stainless steel bowl. Some weeks later, the bowl had holes with ugly brown edges in its bottom. In the end, person was forced to put a glass ashtray under the lamp.

So salty water is an own story. You're mixing up stories and you know it.

Silva, as I say don't take my word for it. Do the experiment. As for "I don't understand galvanic corrosion", trust me, I do. You may have a science degree, so do I. I understood galvanic corrosion before I was 18. I haven't forgotten it now, and the science hasn't changed. But believe what you like, and do the experiment.

 

[rogerzilla]

@silva What's the chemical mechanism which means an aluminium spoke nipple is more likely to seize on a stainless steel spoke's thread than a brass one?

The usual problem is that the alu nipples snap because someone has used spokes a few mm too short!

 

[silva]

@silva What's the chemical mechanism which means an aluminium spoke nipple is more likely to seize on a stainless steel spoke's thread than a brass one?

Galling.

 

[silva]

Another bicycle example case of galvanic corrosion: a stainless steel inner tube valve in an alu rim. Never noticed white stuff around the basis of the valve? Well, that's dissolved alu from around the hole in the rim. Of course, it doesnt continu forever - once the hole is bigger, there is no contact anymore, and so no electrical current.

 

[silva]

Silva, as I say don't take my word for it. Do the experiment. As for "I don't understand galvanic corrosion", trust me, I do. You may have a science degree, so do I. I understood galvanic corrosion before I was 18. I haven't forgotten it now, and the science hasn't changed. But believe what you like, and do the experiment.

It's the argument that proves, not who makes it. Applies to me, to you, and everybody.

Experimenting is one thing, interpreting results, another.

The key element here is that galvanic corrosion dissolves the anodic material.
Dissolving material from a joint, cannot seize it.
As I illustrated along removing the front door of the house, does that make it easier, or harder, to get in?
It's displaced material.
Bonded material, that became unbound.
One can wade through water, but not through ice.

Aside of this, problems can have multiple causes, with the effect of one, undoing or even overruling the effect of another. A bigger volume expansion due to rust can compensate and even overcompensate volume loss due to (under pressure) "leaking" powder caused by galvanic corrosion. Take for ex the situation of a small stainless bolt screwed into a big aluminium block. Then the effect of galvanic corrosion on the joint is minimal. But imagine now that the stainless bolt undergoes a treatment that prevents the formation of the protecting oxidation layer on stainless. For ex, if you saw in common steel, then with the same saw, uncleaned, saw in stainless, you "contaminate" the stainless with common steel particles, that serve as gateways for rust, of the stainless. So then that small stainless bolt will rust, and expand, into the aluminium. That could result in a seized joint.

But stating that galvanic corrosion, on its own, causes mechanical connections to seize, I cannot see how. Please give me a scenario where fine powder, dissolved from the materials of the joint itself, so not like putting sand on thread to then screw in hard, can render the joint seized.

It's likely that you interpreted experiment results not "fully". If one doesn't take into account a parameter, then it might look like a result is due to the other parameters alone.

 

[presta]

galvanic corrosion dissolves the anodic material.

And deposits material on the cathode, so you end up with protrusions on the cathode keyed into holes in the anode.

 

[C R]

And whenever there's nowhere for the material to go, like when you have a steel screw into an aluminium thread, things get stuck. The rim example doesn't work because the valve is free to vibrate and the oxide falls off allowing the hole to grow.

 

[silva]

And deposits material on the cathode, so you end up with protrusions on the cathode keyed into holes in the anode.

That "'depositing'" is like letting sand fall on a floor. What you name "protrusions", have no structure and no mechanical strength.
While seizing, requires mechanical strength. And also lack of space, for ex if you put sand on thread then screw in, it will be harder to do so. But galvanic corossion dissolves material first, so there is no lack of space.
Not that something new is said here.

 

[FishFright]

That "'depositing'" is like letting sand fall on a floor. What you name "protrusions", have no structure and no mechanical strength.
While seizing, requires mechanical strength. And also lack of space, for ex if you put sand on thread then screw in, it will be harder to do so. But galvanic corossion dissolves material first, so there is no lack of space.
Not that something new is said here.

....... Do you work for a brexit think tank ?

 

[silva]

And whenever therWhile in reality, it's an inverse trend, the bigger the distance becomes between valve and rim hole, the less the galvanic corrosion.e's nowhere for the material to go, like when you have a steel screw into an aluminium thread, things get stuck. The rim example doesn't work because the valve is free to vibrate and the oxide falls off allowing the hole to grow.

When you connect a battery to a lamp, and you increase the length of the wiring, what happens with the light intensity?
The same happens to the intensity of the galvanic corrosion. At some distance required tresholds aren't reached anymore, and the process will cease completely.

 

[C R]

That "'depositing'" is like letting sand fall on a floor. What you name "protrusions", have no structure and no mechanical strength.
While seizing, requires mechanical strength. And also lack of space, for ex if you put sand on thread then screw in, it will be harder to do so. But galvanic corossion dissolves material first, so there is no lack of space.
Not that something new is said here.

In a threaded component the oxide has nowhere to go, and in the case of aluminium, the volume of the oxide is larger than the volume of aluminium it replaces, so things get stuck.

 

[C R]

When you connect a battery to a lamp, and you increase the length of the wiring, what happens with the light intensity?
The same happens to the intensity of the galvanic corrosion. At some distance required tresholds aren't reached anymore, and the process will cease completely.

 

[silva]

....... Do you work for a brexit think tank ?

No, I work for construction companies.
Working for a government committee? Lol , I would be ashame.

 

[silva]

In a threaded component the oxide has nowhere to go, and in the case of aluminium, the volume of the oxide is larger than the volume of aluminium it replaces, so things get stuck.

But the aluminium powder origins from the aluminium threads and without threads no mechanical connection.
Which is why my bike stand loosened. The stainless bolts threads had less and less material to engage.
They losened.
Powder fell out.
I retensioned.
Repeat.
Until no threads in the alu left, and the bike just fell aside.

Stuck things?
No, the OPPOSITE.