Skull Crucible

{{Crystallization The skull crucible process was developed at the Lebedev Physical Institute in

Moscow Moscow ( , US chiefly ; rus, links=no, Москва, r=Moskva, p=mɐskˈva, a=Москва.ogg) is the capital and largest city of Russia. The city stands on the Moskva River in Central Russia, with a population estimated at 13.0 million ...

to manufacture cubic zirconia. It was invented to solve the problem of cubic zirconia's melting-point being too high for even platinum crucibles. In essence, by heating only the center of a volume of cubic zirconia, the material forms its own "crucible" from its cooler outer layers. The term "skull" refers to these outer layers forming a shell enclosing the molten volume.

Zirconium oxide Zirconium dioxide (), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant sta ...

powder is heated then gradually allowed to cool. Heating is accomplished by

radio frequency induction : ''For the common use of RF induction process of heating a metal object by electromagnetic induction, see induction heating'' Radio-frequency induction or RF induction is the use of a radio frequency magnetic field to transfer energy by means of ...

using a coil wrapped around the apparatus. The outside of the device is water-cooled in order to keep the radio frequency coil from melting and also to cool the outside of the zirconium oxide and thus maintain the shape of the zirconium powder. Since zirconium oxide in its solid state does not conduct electricity, a piece of

zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...

metal is placed inside the gob of zirconium oxide. As the zirconium melts it oxidizes and blends with the now molten zirconium oxide, a

conductor Conductor or conduction may refer to: Music * Conductor (music), a person who leads a musical ensemble, such as an orchestra. * ''Conductor'' (album), an album by indie rock band The Comas * Conduction, a type of structured free improvisation ...

, and is heated by radio frequency induction. When the zirconium oxide is melted on the inside (but not completely, since the outside needs to remain solid) the amplitude of the RF induction coil is gradually reduced and

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macr ...

s form as the material cools. Normally this would form a monoclinic crystal system of zirconium oxide. In order to maintain a cubic crystal system a stabilizer is added,

magnesium oxide Magnesium oxide ( Mg O), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ...

calcium oxide Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "'' lime''" connotes calcium-containing inorganic ...

or yttrium oxide as well as any material to color the crystal. After the mixture cools the outer shell is broken off and the interior of the gob is then used to manufacture gemstones. Ceramic engineering Soviet inventions Methods of crystal growth