Sulfur corrodes many metals through tarnishing. Electrons flow from the anodic areas into the electrolyte as the metal corrodes. Runoff from a copper roof corrodes aluminum and steel guttering. It also corrodes iron slowly, although copper, brass, or stainless metals are not affected. The slag both protects and corrodes MHD materials. However, it reacts with water and corrodes readily and also burns in air when heated. A protective surface layer of oxide and carbonate ( forms as the zinc corrodes. As long as there is moisture, the zinc corrodes and eventually disappears. The venom causes blood clotting and corrodes muscle tissue and can kill people. The sacrificial metal then corrodes instead of the protected metal. LiH normally contains some metallic lithium, which corrodes steel or silica containers at elevated temperatures. The sacrificial metal instead of the protected metal, then, corrodes. In presence of moisture it corrodes steel, including stainless steel. Mild steel corrodes more readily than wrought iron, but is cheaper and more widely available. Copper roofing in rural atmospheres corrodes at rates of less than in 200 years.