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Zirconium tungstate

Zirconium(IV) tungstate
Zirconium(IV) tungstate
Names
Other names
zirconium tungsten oxide
Identifiers
ECHA InfoCard 100.037.145
Properties
Zr(WO4)2
Molar mass 586.92 g/mol
Appearance white powder
Density 5.09 g/cm3, solid
negligible
Hazards
Safety data sheet MSDS
not listed
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Zirconium tungstate (Zr(WO4)2) is a metal oxide with unusual properties. The phase formed at ambient pressure by reaction of ZrO2 and WO3 is a metastable cubic phase, which has negative thermal expansion characteristics, namely it shrinks over a wide range of temperatures when heated. In contrast to most other ceramics exhibiting negative CTE (coefficient of thermal expansion), the CTE of ZrW2O8 is isotropic and has a large negative magnitude (average CTE of -7.2x10−6K−1) over a wide range of temperature (-273 °C to 777 °C). A number of other phases are formed at high pressures.

Cubic zirconium tungstate (alpha-ZrW2O8), one of the several known phases of zirconium tungstate (ZrW2O8) is perhaps one of the most studied materials to exhibit negative thermal expansion. It has been shown to contract continuously over a previously unprecedented temperature range of 0.3 to 1050 K (at higher temperatures the material decomposes). Since the structure is cubic, as described below, the thermal contraction is isotropic - equal in all directions. There is much ongoing research attempting to elucidate why the material exhibits such dramatic negative thermal expansion.

This phase is thermodynamically unstable at room temperature with respect to the binary oxides ZrO2 and WO3, but may be synthesised by heating stoichiometric quantities of these oxides together and then quenching the material by rapidly cooling it from approximately 900 °C to room temperature.


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