Uranium

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Uranium,  92U
General properties
Name, symbol Uranium, U
Allotropes α-U (orthorhombic), β-U (tetragonal), γ-U (body-centered cubic)
Appearance Metallic gray
Uranium in the periodic table
Nd

U

Uqh
Protactinium ← Uranium → Neptunium
Atomic number 92
Standard atomic weight (Ar) 238.02891(3)
Group, block , f-block
Period period 7
Electron configuration [Rn] 5f3 6d1 7s2
per shell
2, 8, 18, 32, 21, 9, 2
Physical properties
Metallic gray
Phase Solid
Melting point 1405.3 K ​(1132.2 °C, ​2070 °F)
Boiling point 4404 K ​(4131 °C, ​​7468 °F)
Density near r.t. 19.1 g/cm3
when liquid, at  17.3 g/cm3
Heat of fusion 9.14 kJ/mol
Heat of 417.1 kJ/mol
Molar heat capacity 27.665 J/(mol·K)
 pressure
Atomic properties
Oxidation states 6, 5, 4, 3, 2, 1 ​ ​(a weakly basic oxide)
Electronegativity Pauling scale: 1.38
energies 1st: 597.6 kJ/mol
2nd: 1420 kJ/mol
Atomic radius empirical: 156 pm
Covalent radius 196±7 pm
Van der Waals radius 186 pm
Miscellanea
Crystal structure ​Orthorhombic
Speed of sound thin rod 3155 m/s (at 20 °C)
Thermal expansion 13.9 µm/(m·K) (at 25 °C)
Thermal conductivity 27.5 W/(m·K)
Electrical resistivity 0.28·10-3 Ω·m (at 0 °C)
Magnetic ordering Paramagnetic
Young's modulus 208 GPa
Shear modulus 111 GPa
Bulk modulus 100 GPa
Poisson ratio 0.23
Vickers hardness 1960–2500 MPa
Brinell hardness 2350–3850 MPa
CAS Registry Number 7440-61-1
History
Naming After planet Uranus, itself named after Greek god of the sky Uranus
Discovery Martin Heinrich Klaproth (1789)
First isolation Eugène-Melchior Péligot (1841)
· references

Uranium is a radioactive chemical element, member of the actinide group. It has the symbol U and atomic number 92. Because the uranium isotope Uranium-238 has a half-life of 4.468 billion years, the great majority (99.284%) of natural uranium is composed of this isotope. The uranium with a higher concentration of U-238 than the U-235 isotope (the fissile isotope) is commonly known as depleted uranium (DU).

Properties

Chemical

Uranium reacts with almost all non-metal elements and their compounds, the reactivity increases at higher temperatures. It will quickly tarnish in air, forming a dark layer of uranium dioxide. Hydrochloric and nitric acids dissolve uranium, but other non-oxidizing acids attack the element very slowly. When finely divided, it is very pyrophoric and can react with cold water.

As an actinide that displays the "quasi-group" property, uranium acts similarly to Group 6 metals: its most characteristic oxidation state is +6.

Physical

Uranium is a silvery-white metal in the actinide series of the periodic table. Its density is 18.9-19.1 g/cm3 about 70% higher than that of lead, but slightly lower than that of gold or tungsten.

Availability

Uranium is available for sale at chemical suppliers such as United Nuclear in its depleted form. In the US it may require a license[1] above certain quantity[2]. Boeing 747 planes produced between 1968 and 1981 used triangular DU counterweights, before they were replaced with tungsten ones.[3] GoodFellow sells uranium foil and wire.

Uranium compounds, such as ammonium diuranate (aka "yellowcake") and uranium dioxide can also be purchased from United Nuclear.

Preparation

Uranium metal can be prepared by reducing its compounds with a more reactive metal, such as calcium. The reduction should be performed under inert conditions, as uranium is pyrophoric.

Projects

Handling

Safety

Natural and depleted uranium is weakly radioactive and poses little radiation risk. The metal and its compounds are toxic to the organism and should be handled with proper protection. Inhalation of powdered depleted uranium or uranium compounds is dangerous due to it's status as an alpha emitter. The main danger with uranium is not its radiation (it can safely be handled by hand), but its toxicity on ingestion.

Bulk DU is difficult to ignite, but finely divided uranium is highly pyrophoric.

Storage

As uranium will slowly react with the air, it should be stored under oil or in an inert container. Because of it's low radioactive hazard, depleted uranium does not require radiation shielding (the storage container walls will effectively absorb the weak alpha radiation).

Disposal

As uranium compounds are toxic and is a heavy metal, it is recommended to avoid dumping the compounds in the environment and should be taken to waste disposal facilities.

If the uranium was extracted from its natural ore taken from an area where the said ore can be easily collected, it's not entirely a bad idea to dispose of the ore wastes as well as uranium compounds residues in the said area, as the ore area is already naturally contaminated and the amount of ore waste is the same as the one you originally picked it up. Note that this method is not 100% sure and some research on its disposal is necessary.

References

  1. http://www.nrc.gov/reading-rm/doc-collections/cfr/part040/part040-0025.html
  2. http://www.nrc.gov/reading-rm/doc-collections/cfr/part040/part040-0013.html
  3. http://pbadupws.nrc.gov/docs/ML0321/ML032180089.pdf

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