The following "discussion stimulating" question was posed by Dr. Kane on several newsgroups:

"Corrosion is normally referred to as having a negative effect on materials of construction in various systems. I am looking for examples where the phenomenon of corrosion either directly or indirectly produces a positive end result. For example, these might be situations where corrosion improves performance or results in a means of achievement of a desired result in some seemingly non-corrosion application. Responses will be posted to InterCorr/96, Session 11."

Ken Collins writes:

One benefit of corrosion is that its existence allows us to witness what's described by the 2nd Law of Thermodynamics (WDB2T) ... and that its existence provides a "route"... the "raw material" for WDB2T (2 benefits). Another benefit is that, in returning stuff to ionic "states", corrosion enters into the sustenance of life on Earth.

Yes more advantages of corrosion..... One that comes to mind is in the area of refractories. Mild steel casings are used to support furnace refractory bricks, the subsequent oxidation of these casings leads to the formation of "gap sealers" between the bricks reducing slag penetration.

and what about that lovely green patina that you get on copper roofing?

This brings to mind the fact that fluorine can be contained in copper vessels and tubes, because of the protective oxidized layer of copper fluoride that forms. Since it's formed by oxidation, I guess it's corrosion.

One more example comes to mind.......in boilers a protective corrosive layer is formed in their steam generating tubes, a "magnetite layer", which when developed helps to prevent further thinning and weakening of the metal. ........... "A wise man can learn from everyone, a fool can learn from no-one."

A couple of examples comes to my mind: (1): When building the Crystal palace they used joints of rust. They had a hole in one member and stuck the next in the hole, filled with iron filings and added water: the rust swells and cemented the parts together. (2): When I was young I was told that fresh reinforcement bars very bad for reinforced concrete, they did not stick that well. It was no big problem because usually they had a week or two of rust on them. If they were fresh from the steel works (which sometimes happened since we had one in town) and the surface still was slick from the rolling mill the strength of the reinforced concrete was lower, also any bars used for attachment of things easier got ripped out. Disclaimer: I have all this second hand, I have not done the experiments myself.

It is my understanding that gun blueing, the finish on most dark colored firearms, is actually a controlled corrosion of the metal.

Controlling corrosion employs a lot of people and keeps food on the table for their families. When corrosion reduces a component to a non-functional condition, it can be recycled and used in new products. This employs a lot more people. I see a lot of benefits of corrosion. It is a natural process that taxes man's ingenuity in making products that will last sufficiently long enough to pay for the cost of recycling it into a newer and improved product.

Russ (and all the rest of you!) I have been looking over this growing list with interest. I am surprised that no-one has indicated the importance of oxidation in soaking steel ingots to remove surface defects. I guess that with the increasing use of continuous casting, soaking pits are becoming a thing of the past. I still believe that to ensure improved surface quality, significant oxidation of steel -- even in the form of slabs -- is necessary for good subsequent strip. This is one of the "good" aspects of corrosion I usually discuss in my classes. It also reminds us that high temperature oxidation is a form of corrosion!

"With tongue in cheek, or finger in keyboard, I may also add as a caver that I am most grateful for the geological occurance of karst - the corrosion of limestone, dolomite, etc by slightly acidic waters & gases to make the beautiful caverns & formations... ;)."

In some applications, corrosion is used as a timing mechanism. For example, one might want a land-mine to become disabled after a few months of deployment, saving the lives of civilians.

Some medical devides dissolve inside the body after their purpose is achieved. This is a form of corrosion , so far as I can see"

Dom (dominicf@jhunix.hcf.jhu.edu) responds:
"Well, I can think of a couple off the cuff. The controlled formation of oxide layers in fabricating microships, for example. Or, etching in various applications. of course, those are very tightly controlled in practice, so that the depth and pattern of the oxide layer, or the etching is well known."

Further, another use for corrosion is with aluminum. Aluminum and its common alloys do not "rust", that is, oxidize greatly, because aluminum forms a natural crust of oxide on its surface. Aluminum is a very reactive metal, and without this "crust" it would disintigrate in air very quickly."

Annyone who has suffered MRE rations appreciates hypercorrosive alloys as heat sources. There is the prosaic application of sand, iron filings, salt, and some interts to form a handwarmer, and a slight modification as an oxygen getter for sealed containers.

Animal radio-locating collars are fastened with links which corrode and putatively release the collar after its batteries have died.

Bronze and copper patina is decorative."

Another example: tin plating of steel cans containing fruit juice. Although the position in the electrochemical series would seem to suggest that the iron should corrode first if the tin gets a scratch, tin actually forms complex anions with fruit acids, depressing its potential so that the acid in the juice attacks the tin rather than the exposed steel. Benefits being (a) the acid doesn't eat a hole through the can wall, and (b) tin salts aren't particularly toxic."

Actually looks quite nice, though.

Also, back in WWII, the cloak-and-dagger boys once made a silent timer using a piece of wire that got slowly dissolved in acid. (This was at a stage of technology when an electronic timer would have been bigger than the thing it was detonating.)