Electrolytic Reduction Of Iron Meteorites

IRON

Iron (symbol Fe) is one of the most common of the commercial metals. It has been in use since the most remote times, but it does not occur native except in the form of meteorites — early tools of Egypt were apparently made from nickel irons from this source. The common iron ores are magnetic pyrites, magnetite, hematite, and carbonates of iron. To obtain the iron the ores are fused to drive off the oxygen, sulfur, and impurities. The melting is done in a blast furnace directly in contact with the fuel and with limestone as a flux. The latter combines with the quartz and clay, forming a slag that is readily removed. The resulting product is crude pig iron, which requires subsequent remelting and refining to obtain commercially pure iron. Sintered iron and steel are also produced without blast-furnace reduction by compressing purified iron oxide in rollers, heating to 1204°C, and hot-strip rolling. The final cold-rolled product is similar to conventional iron and steel.

Originally, all iron was made with charcoal, but because of the relative scarcity of wood and the greater expense, charcoal is now seldom in the blast furnace.

Iron is a grayish metal, which until recently was never used pure . It melts at 1525°C and boils at 2450°C. Even very small additions of carbon reduce the melting point. It has a specific gravity of 7.85. Iron containing more than 0.15% chemically combined carbon is termed steel. When the carbon is increased to above about 0.40%, the metal will harden when cooled suddenly from a red heat. Iron, when pure, is very ductile, but a small amount of sulfur, as little as 0.03%, will make it hot-short, or brittle at red heat. As little as 0.25% of phosphorus will make iron cold-short, or brittle when cold. Iron forms carbonates, chlorides, oxides, sulfides, and other compounds. It oxidizes easily and is also attacked by many acids.

Because pure iron is allotropic, it can exist as a solid in two different crystal forms. From subzero temperatures up to 910°C, it has a body-centered cubic structure and is identified as alpha (a) iron. Between 910 and 1400°C, the crystal structure is face-centered cubic. This form is known as gamma (y) iron. At 1400°C and up to its melting point of 1540°C, the structure again becomes body-centered cubic. This last form, called delta (5) iron, has no practical use. The transformation from one allotropic form to another is reversible. Thus, when iron is heated to above 910°C, the alpha body-centered cubic crystal changes into face-centered cubic crystals of gamma iron. When cooled below this temperature, the metal again reverts back to a body-centered cubic structure. These allotropic phase changes inherent in iron make possible the wide variety of properties obtainable in ferrous alloys by various heat-treating processes.

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