Uranium dioxide

Cubic

A = 547 pm

U, O

Uranium dioxide

Brown to black crystalline powder

Fixed

10.97 g · cm -3

2865 ° C

Insoluble in water

Risk

Template: Infobox chemical / molecular formula search is not possible

Uranium ( IV) oxide (often uranium dioxide UO2) is an oxide of uranium. In nature, there is, for example, as uraninite ago, the original of uranium (IV ) oxide existing uraninite partly to uranium (VI ) oxide is further oxidized.

Production and representation

By reduction of U (VI ) oxide with hydrogen is formed uranium ( IV) oxide.

The need for the production of fuel rods in nuclear power plants uranium (IV ) oxide is produced mainly from uranium (VI ) fluoride. For the conversion, there are several methods. Wet chemical methods are the AUC and ADU method.

The AUC method ( ammonium uranyl carbonate process) is formed by means of water, ammonia and carbon dioxide, ammonium uranyl carbonate and then this is converted by heating to uranium ( VI) oxide. This is then reduced with hydrogen to uranium ( IV) oxide.

With the ADU method ( diuranate method) of UF6 hydrolysis to uranyl fluoride precipitation with ammonia solution and subsequent calcination to diuranate in a hydrogen stream uranium (IV ) oxide produced. The equations for the ADU method are:

The ADU method is also well suited for the recovery of uranium from solutions containing U (VI ) compounds.

In addition to these method, a dry method, the DC powder method is used. In this process the uranium hexafluoride directly to (IV ) oxide is converted at higher temperatures. An advantage here is that no waste solutions occur with uranium levels, which require further treatment. The equation for this process is:

A further method for the preparation of uranium ( IV) oxide is used the PUREX process for reprocessing of fuel rods. In this uranyl nitrate is formed by an extraction, which in turn is converted by heating in the uranium ( VI) oxide, and then to uranium ( IV) oxide is reduced.

Properties

Physical Properties

Uranium (IV) -oxide is a brown to black crystalline powder. It has a cubic crystal system, has the space group Fm3m with a lattice parameter a = 547 pm, and four formula units per unit cell. The structure type is the type CaF2 ( fluorite ) and the coordination numbers are U, O.

Uranium ( IV) oxide is also a semiconductor. Thus, a functioning Schottky diode could be produced in laboratory experiments of UO2. Due to problems with the doping finds this material in electronic circuit technology does not apply.

Freshly produced uranium (IV ) oxide from terrestrial natural uranium has a specific activity of 22300 Bq / g

Chemical Properties

Uranium (IV ) oxide -air mixtures (dust clouds) are explosive, as a fine powder, it reacts violently with air, releasing heat ( pyrophoric ). It burns to Triuranium octoxide U3O8.

Applications

Uranium ( IV) oxide is the most important fuel in nuclear reactors. It will be processed to so-called "pellets", to be used in fuel rods. It was formerly used as a coloring additive in various glasses and ceramics.

In the form of a URDOX - resistance with thermistor properties he served to limit the current in the heating circuits of Allstromgeräten.