英語(yǔ)時(shí)差：不銹鋼為什么不生銹？（上）

Our modern world, with its skyscrapers, suspension bridges, and automobiles, relies heavily on steel. If you own an aging car however, you know firsthand that steel has one annoying problem: it rusts. All steel, that is, except stainless steel. What keeps this remarkable material, used commonly in kitchen sinks and cookware, from rusting? Steel’s main ingredient is iron. When steel rusts, its iron combines with oxygen and reverts to iron ore, the raw state from which it came. As this happens, the steel turns brown and begins to crumble. There are many ways to protect steel from corrosion. Steel is sometimes painted or greased, or coated with a metal that is less likely to rust. Sometimes a metal that is MORE likely to rust is attached. Known as a sacrificial metal, this works by drawing the corrosion process away from the steel. For example, bars of zinc are attached to the hulls of some ships. The zinc rusts heavily, but the steel hull stays relatively safe.