B. Applications

Date: 2015-10-07; view: 548.

Before radiation was discovered, uranium was primarily used in small amounts for yellow glass and pottery dyes (such as uranium glass and in Fiestaware.) There was also some use in photographic chemicals (esp. uranium nitrate.) It was used in filaments for lamps and in the leather and wood industries for stains and dyes. Uranium salts are mordants of silk or wool. Uranium was also used to improve the appearance of dentures. After the discovery of uranium radiation, additional scientific and practical values of uranium were pursued.

After the discovery in 1939 that it could undergo nuclear fission, uranium gained importance with the development of practical uses of nuclear energy. The first atomic bomb used in warfare, "Little Boy", was a uranium bomb. This bomb contained enough of the uranium-235 isotope to start a runaway chain reaction which in a fraction of a second caused a large number of the uranium atoms to undergo fission, thereby releasing a fireball of energy.

The main use of uranium in the civilian sector is to fuel commercial nuclear power plants. Generally this is in the form of enriched uranium, which has been processed to have higher-than-natural levels of ²³⁵U and can be used for a variety of purposes relating to nuclear fission. Commercial nuclear power plants use fuel typically enriched to 2–3% ²³⁵U, though some reactor designs (such as the Candu reactors) can use natural uranium (unenriched, less than 1% ²³⁵U) fuel. Fuel used for United States Navy submarine reactors is typically highly enriched in ²³⁵U (the exact values are classified information). When uranium is enriched over 85% it is known as "weapons grade". In a breeder reactor, ²³⁸U can also be converted into plutonium.

Currently the major application of uranium in the U.S. military sector is in high-density penetrators. This ammunition consists of depleted uranium alloyed with 1–2% other elements. The applications of these armor-piercing rounds range from the 20 mm Phalanx gun of the U.S. Navy for piercing attacking missiles, through the 30 mm gun in A-10 aircraft, to 105mm and larger tank barrels. At high impact speed, the density, hardness, and flammability of the projectile enable destruction of heavily armored targets. Tank armour and the removable armour on combat vehicles are also hardened with depleted uranium (DU) plates. The use of DU became a contentious political-environmental issue after US, UK and other countries' use of DU munitions in wars in the Persian Gulf and the Balkans raised questions of uranium compounds left in the soil.

Other uses include:

• The long half-life of the isotope ²³⁸U (4.51 × 10⁹ years) make it well-suited for use in estimating the age of the earliest igneous rocks and for other types of radiometric dating (including uranium-thorium dating and uranium-lead dating).
• Uranyl acetate, UO₂(CH₃COO)₂ is used in analytical chemistry. It forms an insoluble salt with sodium.
• Uranium metal is used for X-ray targets in the making of high-energy X-rays.
• Its high atomic mass makes ²³⁸U suitable for radiation shielding.
• It is alloyed with iron to make “ferrouranium” that imparts special properties to steels by increasing elastic limit and tensile strength and as a cathode in photoelectric tubes responsive to ultraviolet radiation.
• Distinctive ²³⁴U / ²³⁸U activity ratios (ARs) are a useful environmental tracer of sources of ground water to discharge springs.
• It is a more powerful deoxidiser than vanadium and will denitrogenise steel.
• It is used in high-speed steels as an alloying agent to improve strength and toughness.
• Depleted uranium (uranium with the percentage of ²³⁵U lowered to 0.2%) has found use as counterweights for aircraft control surfaces, as ballast for missile re-entry vehicles and as a shielding material. Due to its high density, this material has also found use in inertial guidance devices and in gyroscopic compasses.