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

[silva]

Want some help?

https://www.sciencedirect.com/science/article/pii/B9780080999258000259

Abstract

When two dissimilar metals are in direct contact in a conducting liquid, experience shows that one of the two may corrode. This is called galvanic corrosion. Galvanic corrosion works like a cell composed of two electrodes: the cathode, where reduction takes place; and the anode, where oxidation takes place. It works like a battery cell and is based on the same principle, and therefore the following three conditions must be met simultaneously: different types of metals, presence of an electrolyte and electrical continuity between the two metals.

13.7.4 Distance from the contact zone

Galvanic corrosion is a local form of corrosion. It is limited to the contact zone. The intensity of corrosion decreases rapidly with increasing distance, even by a few centimetres, from the point of contact between the two metals. This decrease is greater when the electrolyte is a poor conductor.

This type of corrosion is so localized because of electrical reasons. Electrical current flows according to a path as linear as possible. Since galvanic corrosion often tends to develop at depth, it is not uncommon that galvanic corrosion perforates parts several millimetres thick.

... so your denial:

The rim example doesn't work because the valve is free to vibrate and the oxide falls off allowing the hole to grow.

... was wrong.
It is like I said:

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]

No galvanic corrosion, but this:

Galling.

https://en.wikipedia.org/wiki/Galling

Galling is most commonly found in metal surfaces that are in sliding contact with each other. It is especially common where there is inadequate lubrication between the surfaces. However, certain metals will generally be more prone to galling, due to the atomic structure of their crystals. For example, aluminium is a metal that will gall very easily, whereas annealed (softened) steel is slightly more resistant to galling. Steel that is fully hardened is very resistant to galling.

Galling is a common problem in most applications where metals slide while in contact with other metals. This can happen regardless of whether the metals are the same or of different kinds. Alloys such as brass and bronze are often chosen for bearings, bushings, and other sliding applications because of their resistance to galling, as well as other forms of mechanical abrasion.

 

[raleighnut]

No galvanic corrosion, but this:

https://en.wikipedia.org/wiki/Galling

A stem does not rotate in the fork neither does a seatpost in a frame yet both can become stuck