What Kind of Metals Don’t Rust?
Stainless steel, gold, silver, platinum and aluminum (after forming a barrier from minimal exposure) are all rust-proof metals. Rust is the process of iron oxidization, so it specifically refers to the iron content in a metal.
Steel rusts because it contains iron. Iron decomposes over time when it comes in contact with oxygen. Gold, silver and platinum are all pure metals that don’t contain iron and, therefore, don’t rust. Stainless steel doesn’t rust because it is an alloy that contains the metals chromium and nickel. Chromium must comprise at least 10 percent of the steel alloy for stainless steel to be rust resistant. Aluminum becomes rust resistant after a short exposure to air creates a thin oxide layer.
Iron-containing objects can be made to resist rust using a process called galvanizing. Galvanizing covers the iron with molten zinc, which forms a thin protective layer of zinc oxide over the iron. Another process that protects iron uses sacrificial metal. The sacrificial metal goes physically in front of or around the iron, forming a barrier or protective shield. The sacrificial metal draws the corrosion process away from the steel, thus protecting it. Ship builders use bars of zinc as a sacrificial metal when building ship hulls.