Open main menu
Home
Random
Recent changes
Special pages
Community portal
Preferences
About Wikipedia
Disclaimers
Incubator escapee wiki
Search
User menu
Talk
Dark mode
Contributions
Create account
Log in
Editing
Zirconium tungstate
Warning:
You are not logged in. Your IP address will be publicly visible if you make any edits. If you
log in
or
create an account
, your edits will be attributed to your username, along with other benefits.
Anti-spam check. Do
not
fill this in!
{{More citations needed|date=August 2024}} {{chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 470637657 | Name = Zirconium(IV) tungstate | ImageFile = ZrW2O8 opaque polyhedra.svg | ImageName = Zirconium(IV) tungstate | OtherNames = zirconium tungsten oxide |Section1={{Chembox Identifiers | CASNo_Ref = {{cascite|changed|??}} | CASNo = 16853-74-0 | ChemSpiderID = 10710102 | EINECS = 240-876-3 | PubChem = 21954342 | StdInChI=1S/8O.2W.Zr/q;;;;4*-1;;;+4 | StdInChIKey = OJLGWNFZMTVNCX-UHFFFAOYSA-N | SMILES = [O-][W](=O)(=O)[O-].[O-][W](=O)(=O)[O-].[Zr+4] }} |Section2={{Chembox Properties | Formula = Zr(WO<sub>4</sub>)<sub>2</sub> | MolarMass = 586.92 g/mol | Appearance = white powder | Density = 5.09 g/cm<sup>3</sup>, solid | Solubility = negligible | MeltingPt = | BoilingPt = }} |Section7={{Chembox Hazards | ExternalSDS = [https://web.archive.org/web/20100201192127/http://www.espi-metals.com/msds's/zirconiumtungstate.pdf MSDS] | GHS_ref=<ref>{{cite web |title=C&L Inventory |url=https://echa.europa.eu/information-on-chemicals/cl-inventory-database/-/discli/details/111452 |website=echa.europa.eu |access-date=8 December 2021}}</ref> | GHSPictograms = {{GHS07}} | GHSSignalWord = Warning | HPhrases = {{H-phrases|315|319|335}} | PPhrases = {{P-phrases|}} | NFPA-H = 2 | NFPA-R = 0 | NFPA-F = 0 }} }} '''Zirconium tungstate''' is the [[zirconium]] [[ionic salt|salt]] of [[tungstic acid]] with the formula {{chem2|Zr(WO4)2}}. The phase formed at ambient pressure by reaction of [[zirconia|ZrO<sub>2</sub>]] and [[tungsten oxide|WO<sub>3</sub>]] is a [[metastable]] [[cubic phase]], which has [[negative thermal expansion]] characteristics, namely it shrinks over a wide range of temperatures when heated.<ref>{{cite journal|title=Negative Thermal Expansion from 0.3 to 1050 Kelvin in ZrW<sub>2</sub>O<sub>8</sub>|journal=Science|date=1996-04-05|first=T. A.|last=Mary|author2=J. S. O. Evans |author3=T. Vogt |author4=A. W. Sleight |volume=272|issue=5258|pages=90β92|doi= 10.1126/science.272.5258.90|url=http://www.sciencemag.org/cgi/content/abstract/272/5258/90|access-date=2008-02-20|bibcode=1996Sci...272...90M|s2cid=54599739|url-access=subscription}}</ref> In contrast to most other ceramics exhibiting negative CTE (coefficient of thermal expansion), the CTE of ZrW<sub>2</sub>O<sub>8</sub> is isotropic and has a large negative magnitude (average CTE of β7.2 Γ 10<sup>β6</sup>K<sup>β1</sup>) over a wide range of temperature (β273 Β°C to 777 Β°C).<ref>{{cite journal|title=Isotropic Negative Thermal Expansion|journal=Annu. Rev. Mater. Sci.|year=1998|first=A.W.|last=Sleight|volume=28|pages=29β43|doi=10.1146/annurev.matsci.28.1.29|bibcode = 1998AnRMS..28...29S }}</ref> A number of other [[phase (matter)|phases]] are formed at high pressures. ==Cubic phase== [[Cubic (crystal system)|Cubic]] zirconium tungstate (alpha-ZrW<sub>2</sub>O<sub>8</sub>), one of the several known [[phase (matter)|phases]] of zirconium tungstate (ZrW<sub>2</sub>O<sub>8</sub>) 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.{{cn|date=September 2023}} This phase is [[thermodynamics|thermodynamically]] [[unstable]] at [[room temperature]] with respect to the binary [[oxides]] [[zirconia|ZrO<sub>2</sub>]] and [[tungsten oxide|WO<sub>3</sub>]], but may be [[Chemical synthesis|synthesised]] by heating [[stoichiometric]] quantities of these oxides together and then quenching the material by rapidly cooling it from approximately 900 Β°C to room temperature. The structure of cubic zirconium tungstate consists of corner-sharing ZrO<sub>6</sub> [[octahedral]] and WO<sub>4</sub> [[tetrahedral]] structural units. Its unusual expansion properties are thought to be due to vibrational modes known as [[Rigid Unit Modes]] (RUMs), which involve the coupled rotation of the polyhedral units that make up the structure, and lead to contraction. ===Detailed crystal structure=== [[Image:ZrW2O8 W2O8 diagonal.JPG|thumb|left|304x304px|An image of the crystal structure of cubic ZrW<sub>2</sub>O<sub>8</sub>, showing the corner-sharing octahedral (ZrO<sub>6</sub>, in green) and tetrahedral (WO<sub>4</sub>, in red) structural units. An incomplete unit cell is shown so that the positioning of the W<sub>2</sub>O<sub>8</sub> unit along the body diagonal of the unit cell may be seen.]] The arrangement of the groups in the structure of cubic ZrW<sub>2</sub>O<sub>8</sub> is analogous to the simple [[NaCl structure]], with ZrO<sub>6</sub> octahedra at the Na sites, and W<sub>2</sub>O<sub>8</sub> groups at the Cl sites. The unit cell consists of 44 atoms aligned in a primitive cubic [[Bravais lattice]], with unit cell length 9.15462 [[Angstrom]]s. The ZrO<sub>6</sub> [[octahedra]] are only slightly distorted from a regular conformation, and all oxygen sites in a given octahedron are related by symmetry. The W<sub>2</sub>O<sub>8</sub> unit is made up of two crystallographically distinct WO<sub>4</sub> tetrahedra, which are not formally [[chemical bond|bonded]] to each other. These two types of tetrahedra differ with respect to the W-O bond lengths and angles. The WO<sub>4</sub> tetrahedra are distorted from a regular shape since one oxygen is unconstrained (an atom that is bonded only to the central [[tungsten]] (W) atom), and the three other oxygens are each bonded to a zirconium atom (''i.e.'' the ''corner-sharing'' of polyhedra). The structure has ''P2<sub>1</sub>3'' [[Space group|space group symmetry]] at low temperatures. At higher temperatures, a centre of inversion is introduced by the disordering of the orientation of tungstate groups, and the space group above the [[phase transition]] temperature (~180C) is ''Pa<math>\bar3</math>''. Octahedra and tetrahedra are linked together by sharing an oxygen atom. In the image, note the corner-touching between octahedra and tetrahedra; these are the location of the shared [[oxygen]]. The vertices of the tetrahedra and octahedra represent the oxygen, which are spread about the central [[zirconium]] and [[tungsten]]. Geometrically, the two shapes can "pivot" around these corner-sharing oxygens, without a distortion of the polyhedra themselves. This pivoting is what is thought to lead to the [[negative thermal expansion]], as in certain low frequency [[normal modes]] this leads to the contracting 'RUMs' mentioned above. ==High pressure forms== At [[high pressure]], zirconium tungstate undergoes a series of [[phase transitions]], first to an [[amorphous]] phase, and then to a [[Triuranium octaoxide|U<sub>3</sub>O<sub>8</sub>]]-type phase, in which the zirconium and tungsten atoms are disordered. ==Zirconium tungstate-copper system== [[File:XRD Spectra.jpg|left|thumb|416x416px|XRD Spectra from Verdon & Dunand (1997).]] [[File:Reaction Mechanism.jpg|thumb|373x373px|Proposed reaction mechanism in the HIP process of zirconium tungstate-copper system from Verdon & Dunand (1997).]] Through hot-isostatically pressing (HIP) a ZrW<sub>2</sub>O<sub>8</sub>-Cu composite (system) can be realized. Work done by C. Verdon and D.C. Dunand in 1997 used similarly sized zirconium tungstate and copper powder in a low carbon steel can coated with Cu, and they were HIPed under 103MPa pressure for 3 hours at 600 Β°C. A control experiment was also conducted, with only a heat treatment (i.e., no pressing) for the same powder mixture also under 600 Β°C for 3 hours in a quartz tube gettered with titanium. The results from X-ray diffraction (XRD) in the graph in Verdon & Dunand's paper shows expected products. (a) is from the as received zirconium tungstate powder, (b) is the result from the control experiment , and (c) is the ceramic product from the HIP process. Apparently there are new phases formed according to Spectrum (c) with no ZrW<sub>2</sub>O<sub>8</sub> left. While for the control experiment only partial amount of ZrW<sub>2</sub>O<sub>8</sub> was decomposed. While complex oxides containing Cu, Zr, and W were believed to be created, selected area diffraction (SAD) of the ceramic product has proven the existence of Cu<sub>2</sub>O as precipitates after reaction. A model consisted of two concurrent processes were surmised (as presented): (b) the decomposition of the ceramic and loss of oxygen under low oxygen partial pressure at high temperature leads to Cu<sub>2</sub>O formation; (c) copper diffuses into the ceramic and forms new oxides that absorb some oxygen upon cooling. Since only very few oxides, those of noble metals which are very expensive, are less stable than Cu<sub>2</sub>O and Cu<sub>2</sub>O was believed to be more stable than ZrW<sub>2</sub>O<sub>8</sub>, kinetic control of the reaction must be taken into account. For example, reducing reaction time and temperature helps alleviate the residual stress caused by different phases of the ceramic during reaction, which could lead to a delamination of the ceramic particles from the matrix and an increase in the CTE.<ref>C. Verdon and D.C. Dunand, High-Temperature Reactivity in the ZrW<sub>2</sub>O<sub>8</sub>-Cu System. ''Scripta Materialia'', 36, No. 9, pp. 1075-1080 (1997).</ref> ==References== {{reflist}} ==External links== * [http://www.livescience.com/technology/041215_unusual_material.html Strange Shrinking Material] {{commons category|Zirconium tungstate}} {{Zirconium compounds}} {{Tungstates}} [[Category:Zirconium(IV) compounds]] [[Category:Tungstates]]
Edit summary
(Briefly describe your changes)
By publishing changes, you agree to the
Terms of Use
, and you irrevocably agree to release your contribution under the
CC BY-SA 4.0 License
and the
GFDL
. You agree that a hyperlink or URL is sufficient attribution under the Creative Commons license.
Cancel
Editing help
(opens in new window)
Pages transcluded onto the current version of this page
(
help
)
:
Template:Chem2
(
edit
)
Template:Chembox
(
edit
)
Template:Cite journal
(
edit
)
Template:Cn
(
edit
)
Template:Commons category
(
edit
)
Template:More citations needed
(
edit
)
Template:Reflist
(
edit
)
Template:Sister project
(
edit
)
Template:Tungstates
(
edit
)
Template:Zirconium compounds
(
edit
)