Cerium uranium blue
Encyclopedia
Cerium uranium blue is the name given to solid solution
s of cerium(IV) oxide
, CeO2, and uranium(IV) oxide, UO2, of variable composition from 0 to 100% uranium.
with an excess of magnesium chloride
at high temperature. The composition of the product was somewhat variable, approximating to 2CeO2.UO2. A similar product was obtained when ammonia was added to a solution containing uranyl nitrate
and cerium(III) nitrate; the precipitate, initially yellow in colour, turned blue after a while. It is more conveniently made by heating together cerium(IV) oxide, CeO2, and uranium(IV)oxide, UO2, at 1000°C for several days.
Both CeO2 and UO2 crystallize with the fluorite
crystal structure. The lattice constant
s are very similar, 5.41 Å
and 5.47 Å, respectively. Solid solutions can be made with uranium content from 0 to 100%. The lattice constant changes smoothly between the values for the two components as the composition changes. A similar series of solid solutions are formed between cerium(IV) oxide and thorium oxide.
The blue colour is due to an intense charge transfer transition when an electron is transferred from an orbital
localized on uranium(IV), a mild reducing agent
, to an orbital localized on cerium(IV), a strong oxidizing agent
. Complete transfer would result in the production of uranium(VI) and cerium(III), the reverse of the reaction observed with the precipitate from aqueous solution.
Solid solution
A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase...
s of cerium(IV) oxide
Cerium(IV) oxide
Cerium oxide, also known as ceric oxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare earth metal cerium...
, CeO2, and uranium(IV) oxide, UO2, of variable composition from 0 to 100% uranium.
Synthesis and properties
Cerium uranium blue was first obtained by heating together cerium sulfate and uranyl sulfateUranyl sulfate
Uranyl sulfate a sulfate of uranium is an odorless lemon-yellow sand-like solid in its pure crystalline form.It has found use as a negative stain in microscopy and tracer in biology...
with an excess of magnesium chloride
Magnesium chloride
Magnesium chloride is the name for the chemical compounds with the formulas MgCl2 and its various hydrates MgCl2x. These salts are typical ionic halides, being highly soluble in water. The hydrated magnesium chloride can be extracted from brine or sea water...
at high temperature. The composition of the product was somewhat variable, approximating to 2CeO2.UO2. A similar product was obtained when ammonia was added to a solution containing uranyl nitrate
Uranyl nitrate
Uranyl nitrate is a water soluble yellow uranium salt. The yellow-green crystals of uranium nitrate hexahydrate are triboluminescent.Uranyl nitrate can be prepared by reaction of uranium salts with nitric acid...
and cerium(III) nitrate; the precipitate, initially yellow in colour, turned blue after a while. It is more conveniently made by heating together cerium(IV) oxide, CeO2, and uranium(IV)oxide, UO2, at 1000°C for several days.
Both CeO2 and UO2 crystallize with the fluorite
Fluorite
Fluorite is a halide mineral composed of calcium fluoride, CaF2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon...
crystal structure. The lattice constant
Lattice constant
The lattice constant [or lattice parameter] refers to the constant distance between unit cells in a crystal lattice. Lattices in three dimensions generally have three lattice constants, referred to as a, b, and c. However, in the special case of cubic crystal structures, all of the constants are...
s are very similar, 5.41 Å
Ångström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....
and 5.47 Å, respectively. Solid solutions can be made with uranium content from 0 to 100%. The lattice constant changes smoothly between the values for the two components as the composition changes. A similar series of solid solutions are formed between cerium(IV) oxide and thorium oxide.
The blue colour is due to an intense charge transfer transition when an electron is transferred from an orbital
Atomic orbital
An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...
localized on uranium(IV), a mild reducing agent
Reducing agent
A reducing agent is the element or compound in a reduction-oxidation reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized"...
, to an orbital localized on cerium(IV), a strong oxidizing agent
Oxidizing agent
An oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...
. Complete transfer would result in the production of uranium(VI) and cerium(III), the reverse of the reaction observed with the precipitate from aqueous solution.