Most metals as well as other materials will have a tendency for their surface to oxidize over time. This can be considered a form of corrosion or entropy at play.
Rust I believe is typically a term used to identify a specific form of oxitation present; namely iron oxide. I believe for a material to rust, iron need be present as well as exposed to the process of oxidation.
In many cases, once an oxide layer has formed on the surface, the oxidation or corrosion of subsequent underlayers does not continue. A stable state is reached. If the oxide layer is removed through abraision or other processes. the corrosion can continue.
Aside from oxidation, there are other forms of corrosion which can eat away the material over time. There is galvanic corrosion (electro-chemical) and crevice corrosion to name a few.
Different materials are effected differently in various environments and material choice is based on the intended environment of useage.
Energy is required to initiate the corrosion process and this energy can come from various sources; heat, electrical differentials, friction and light.
Many oxide layers are very stable and can protect the underlying material from continued degridation or corrosion. Metals like aluminum, lead, silver, copper, brass and titanium oxidize rather rapidly but will stabilize to a great extent once oxidized. Unfortunately, if the oxide layer is unwanted and removed, some form of protection or coating is required to prevent further oxidation. In some cases, the oxide layer is easily removed through abrasion or erossion from the elements. In other cases, specifically titanium, the oxide surface is very hard and impervious to abrassion and errosion to a great extent. Aluminium oxide is a hard material and used extensively as an abrasive compound. Once oxidized, aluminum can hold up well in many environments where electro-chemical conditions aren't present to attack the material by other means. Oxidized aluminum can withstand the challanges of wind, rain and sun very well. Acids and oils in your skin as well as salt water can be a different story.
There are other chemicals beside oxygen that will react with materials and cause a break down in the material structure. Chlorine is a very nasty culprit here. Many metals and materials which hold up well in normal, on land, environments are prey to serious degridation and corrosion once exposed to a salt air or water environment. Ironically, the lack of oxygen and presence of free chlorine in saltwater can and has destroyed many robust stainless steel parts and pieces of hardware, often with catastrophic results. The 300 series of stainless or 18-8 which is the most common material used in consumer goods, household kitchen ware and even medical instruments has been claimed by some in the Navy, as completely inappropriate for sea going applications.
OK, sorry. Since I have no answer to the question that is likely being asked now, I will quit this ramble. The Question: "So what???"
Back to topic; no, it won't rust but yes, it can corrode or degrade if subject to the right conditions.
- Don
Disclaimer: I am not a chemist or scientist, merely a lame man so my explainations are likely oversimplified if not blatantly incorrect at some level. Although I may have completely *******ized the relationship between cause and effect, I have seen with my own eyes that there is cause and effect
I felt inclined to post this answer because at some level, I felt the question: "Do they rust?" was somewhat akin to the famous line used in a few movies; "Does your dog bite?"
A simple yes/no answer might lead to the wrong impression. (he he)
