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pig iron
Pig iron is the intermediate product of smelting iron ore. It is the molten iron from the blast furnace, which is a large and cylinder-shaped furnace charged with iron ore, coke, and limestone. Charcoal and anthracite have also been used as fuel. Pig iron has a very high carbon content, typically 3.5–4.5%, along with silica and other constituents of dross, which makes it very brittle and not useful directly as a material except for limited applications.
The traditional shape of the molds used for pig iron ingots was a branching structure formed in sand, with many individual ingots at right angles to a central channel or ''runner'', resembling a litter of piglets being suckled by a sow. When the metal had cooled and hardened, the smaller ingots (the ''pigs'') were simply broken from the runner (the ''sow''), hence the name ''pig iron''. As pig iron is intended for remelting, the uneven size of the ingots and the inclusion of small amounts of sand caused only insignificant problems considering the ease of casting and handling them.
==History==
The Chinese were making pig iron by the later Zhou Dynasty (1122–256 BC).〔Wagner, Donald. ''Iron and Steel in Ancient China''. Leiden 1996: Brill Publishers〕 To the west, smelting technology to produce pig iron and other iron products was known to the Ancient Egyptians and gradually spread around the Eastern Mediterranean as far as Ancient Greece.〔Waldbaum, Jane C. ''From Bronze to Iron''. Göteburg: Paul Astöms Förlag (1978): 56–58.〕 The Roman Empire and later the Muslim caliphates of the Middle Ages inherited and refined these technologies. Because of the collapse of the Western Roman Empire, Western Europe did not rediscover the process until the Late Middle Ages (1325–1500).〔Several papers in ''The importance of ironmaking: technical innovation and social change: papers presented at the Norberg Conference, May 1995'' ed. Gert Magnusson (Jernkontorets Berghistoriska Utskott H58, 1995), 143-179.〕 Actually, the phase transition of the iron into liquid in the furnace was an ''avoided'' phenomenon, as decarburizing the pig iron into steel was an extremely tedious process using medieval technology.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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