Zirconium tetrafluoride

Zirconium fluoride describes members of a family inorganic compounds with the formula Zr F₄_x. All are colorless, diamagnetic solids. Anhydrous Zirconium fluoride is a component of ZBLAN fluoride glass.

Structure

Three crystalline phases of ZrF₄ have been reported, the stable β phase , α which is a high-temperature meta-stable form that can be stabilized by quenching. The γ-form is a high-pressure phase, forming at pressures between. α and γ phases are unstable and transform into the β phase at 400 and 723°C respectively. There also exists an amorphous phase.
Zirconium fluoride forms several hydrates. The trihydrate has the structure.

Preparation and reactions

Zirconium fluoride can be produced by several methods. Zirconium dioxide reacts with hydrogen fluoride and hydrofluoric acid to afford the anhydrous and monohydrates:
The reaction of Zr metal reacts at high temperatures with HF as well:
Zirconium dioxide reacts at 200 °C with solid ammonium bifluoride to give the heptafluorozirconate salt, which can be converted to the tetrafluoride at 500 °C:
Addition of hydrofluoric acid to solutions of zirconium nitrate precipitates solid monohydrate. Hydrates of zirconium tetrafluoride can be dehydrated by heating under a stream of hydrogen fluoride.
Zirconium fluoride can be purified by distillation or sublimation.
Zirconium fluoride forms double salts with other fluorides. The most prominent is potassium hexafluorozirconate, formed by fusion of potassium fluoride and zirconium tetrafluoride:

Applications

The major and perhaps only commercial application of zirconium fluoride is as a precursor to ZBLAN glasses.
Mixture of sodium fluoride, zirconium fluoride, and uranium tetrafluoride was used as a coolant in the Aircraft Reactor Experiment. A mixture of lithium fluoride, beryllium fluoride, zirconium fluoride, and uranium-233 tetrafluoride was used in the Molten-Salt Reactor Experiment.