metallurgy

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The science and technology of producing metals, which includes extraction, alloying, and hardening. Extractive, or process, metallurgy is concerned with the extraction of metals from their ores and refining and adapting them for use. Physical metallurgy is concerned with their properties and application. Metallography establishes the microscopic structures that contribute to hardness, ductility, and strength.

Metals can be extracted from their ores in three main ways: dry processes, such as smelting, volatilization, or amalgamation (treatment with mercury); wet processes, involving chemical reactions; and electrolytic processes, which work on the principle of electrolysis.

The foundations of metallurgical science were laid about 3500 BC in Egypt, Mesopotamia, China, and India, where the art of smelting metals from ores was discovered. Later, gold, silver, copper, lead, and tin were worked in various ways, although they had been cold-hammered as native metals for thousands of years. The smelting of iron was discovered about 1200 BC. The Romans hardened and tempered iron, using heat treatment. From then until about AD 1400, advances in metallurgy came into Europe by way of Arabian chemists. Cast iron was first made in Ancient Greece for casting statues and figures. In the 14th century it was made in a crude blast furnace and came into regular production in Europe in the 16th century. The demands of the Industrial Revolution led to an enormous increase in wrought iron production. The invention by British civil engineer Henry Bessemer of the Bessemer process in 1856 made cheap steel available for the first time, leading to its present widespread use and the industrial development of many specialized steel alloys.

The disc represents the full moon, traditionally the most auspicious time for work and celebration. The disc is set towards the hoist. Effective date: 1 January 1981. >>