Cerium uranium blue is the name given to

solid solution A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word ...

s of

cerium(IV) oxide Cerium(IV) oxide, also known as ceric oxide, ceric dioxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare-earth metal cerium. It is a pale yellow-white powder with the chemical formula CeO2. It is an important commercial produc ...

, CeO₂, and

uranium(IV) oxide Uranium dioxide or uranium(IV) oxide (), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear react ...

, UO₂, of variable composition from 0 to 100% uranium.

Synthesis and properties

Cerium uranium blue was first obtained by heating together

cerium sulfate Cerium(IV) sulfate, also called ceric sulfate, is an inorganic compound. It exists as the anhydrous salt Ce( SO4)2 as well as a few hydrated forms: Ce(SO4)2(H2O)x, with x equal to 4, 8, or 12. These salts are yellow to yellow/orange solids th ...

and

uranyl sulfate Uranyl sulfate describes a family of inorganic compounds with the formula UO2SO4(H2O)n. These salts consist of sulfate, the uranyl ion, and water. They are lemon-yellow solids. Uranyl sulfates are intermediates in some extraction methods used for ...

with an excess of

magnesium chloride Magnesium chloride is the family of inorganic compounds with the formula , where x can range from 0 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which occur in natu ...

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 is a water-soluble yellow uranium salt with the formula . The hexa-, tri-, and dihydrates are known. The compound is mainly of interest because it is an intermediate in the preparation of nuclear fuels. Uranyl nitrate can be prepa ...

and

cerium(III) nitrate Cerium nitrate refers to a family of nitrates of cerium in the +3 or +4 oxidation state. Often these compounds contain water, hydroxide, or hydronium ions in addition to cerium and nitrate. Double nitrates of cerium also exist. Cerium(III) nitrat ...

; 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 (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs sca ...

crystal structure. The

lattice constant A lattice constant or lattice parameter is one of the physical dimensions and angles that determine the geometry of the unit cells in a crystal lattice, and is proportional to the distance between atoms in the crystal. A simple cubic crystal has o ...

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 Thorium dioxide (ThO2), also called thorium(IV) oxide, is a crystalline solid, often white or yellow in colour. Also known as thoria, it is produced mainly as a by-product of lanthanide and uranium production. Thorianite is the name of the minera ...

. 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 In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth meta ...

, to an orbital localized on cerium(IV), a strong

oxidizing agent An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "Electron acceptor, accepts"/"receives" an electron from a (called the , , or ). In ot ...

. 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.

References

{{reflist Uranium(IV) compounds Cerium(IV) compounds Oxides