Tungsten, a silver-gray metal, exhibits important physical properties, including a high melting point and density, as well as good thermal and electrical conductivity, a low coefficient of expansion, and exceptional strength at elevated temperatures. It is consumed predominantly as the extremely hard carbide in cutting and wear-resistant components and as the metal or alloy for lamp and lighting filaments and electrodes, electrical and electronic contact surfaces, heat and radiation shielding in high-temperature furnaces and X-ray equipment, and electrodes in certain welding methods. Some nonmetallurgical applications of tungsten are as phosphorescent chemicals in pigments, X-ray screens, television picture tubes, and fluorescent lighting. Tungsten is also used militarily as a heavy-metal alloy in armor- piercing ordnance and tank shielding.
Tungsten appears in nature combined with calcium, iron, or manganese in four major mineral forms. Although found in numerous deposits throughout the world, nearly 42% of the world's tungsten resources are in China. Other significant tungsten deposits are in Australia, Austria, Bolivia, Brazil, Burma, Canada, North Korea, Peru, Portugal, the Republic of Korea, Spain, Thailand, Turkey, the former U.S.S.R., and the United States.
The U.S. reliance on foreign sources of tungsten materials (table 1)has increased by nearly 40% since 1984 compared with the average for the previous 10 years. Much of this increase was the direct result of a steady decline in domestic mine production and an increase in the production of concentrate for the world market by the Chinese (table 4). Prices for concentrates reached record levels in the late 1970's amid strong demand for tungsten products, but then began to decline as a result of a gradual increase in supply over demand, attributed by many Western World consumers to an overproduction by the Chinese. By 1990, the estimated production of concentrate by China represented about 52% of the world market share compared with 25% in 1978. In addition to concentrate, the United States also imported a steadily increasing quantity of ammonium paratungstate (APT), most of it from China, during the period 1978 to 1987 (table 2). APT is a major intermediate material from which tungsten metal, carbides, and chemicals are produced. In 1987, the United States and China signed an Orderly Marketing Agreement limiting such imports during a period of 4 years.