The O-W (oxygen-tungsten) system

This basic research deals with the microstructure evolution of a W-doped ZrB 2 ceramic, as-sintered and upon oxidation at 1650°C. Transmission electron microscopy enabled to disclose microstructural features occurred during oxidation never observed before. In the pristine material, (Zr,W)B 2 solid solutions surround the original ZrB 2 nuclei, whereas refractory W-compounds at triple junctions and clean grain boundaries are distinctive of this ceramic. After oxidation, the microstructure is typified by intragranular nanostructures, in which nanosized W inclusions remained trapped within ZrO 2 grains, or decorate their surfaces. The understanding of the oxidation reactions occurring in the system as a function of the oxygen partial pressure was fundamental to conclude that W-based compounds do not notably suppress or retard the oxidation of ZrB 2 ceramics. K E Y W O R D S ceramic, inclusions, oxidation, SEM, TEM

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“…Of the solid products, only ZrO 2 was found in the outer surface ( ZS in Figure A) since W transforms into WO 3 (l) and then volatilizes …”

Section: Resultsmentioning

confidence: 99%

Microstructure evolution of a W‐doped ZrB₂ceramic upon high‐temperature oxidation

et al. 2017

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“…Since oxygen content was not measured in this study, all phases are shown to be complete oxidized. (Under more reducing conditions, phases expressed as WO 3Àx , xo1 and as In x WO 3 , xo0.3 are known to form [20,21].) Phase relationships above 1200 C are not presented since equilibrium could not be achieved in the open-air system used in this study.…”

Section: Subsolidus Phase Relations In In 2 O 3 -Wo 3 Systemmentioning

confidence: 95%

Subsolidus phase relations and crystal structures of the mixed-oxide phases in the In2O3–WO3 system

Richard

Edwards

2004

Journal of Solid State Chemistry

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“…Tungsten trioxide (WO 3 ) is a wide band-gap (E g = 2.62 eV [1] or 2.7 eV [2]) n-type semiconductor. It shows numerous polymorphs [3] derived from the ReO 3 structure which involves a cubic array of corner-shared octahedra. At room temperature the γ-WO 3 monoclinic phase of space group P 2 1/n is observed.…”

Section: Introductionmentioning

confidence: 99%

Ab initio study of oxygen point defects on tungsten trioxide surface

et al. 2012

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The gas response of tungsten trioxide (WO 3) based sensors strongly depends on the surface properties. Reconstructed surfaces and oxygen point defects at the surface of the monoclinic WO 3 are studied using a self-consistent scheme based on first-principle. The oxygen vacancy is found to be the predominant defect independently of the oxygen partial pressure. Indeed, under rich oxygen atmosphere the formation enthalpies are found to be 1.45 eV in LDA (1.28 eV in GGA) for the oxygen vacancy instead of 2.70 eV (2.42 eV) for the oxygen adatom. When the oxygen partial pressure is lowered, the oxygen vacancy formation enthalpy decreases and becomes exothermic under very O-poor condition (-1.65 eV in LDA and-1.36 eV in GGA). On the other hand, the formation enthalpy of an oxygen adatom rises. Finally, the oxygen vacancy formation acts as a n-doping by introducing negative charge carriers at the bottom of the conduction band. All these results can be very helpful in order to explain the electrical resistivity measurements.

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The O-W (oxygen-tungsten) system

Cited by 95 publications

References 97 publications

Microstructure evolution of a W‐doped ZrB₂ceramic upon high‐temperature oxidation

Microstructure evolution of a W‐doped ZrB₂ceramic upon high‐temperature oxidation

Subsolidus phase relations and crystal structures of the mixed-oxide phases in the In2O3–WO3 system

Ab initio study of oxygen point defects on tungsten trioxide surface

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The O-W (oxygen-tungsten) system

Cited by 95 publications

References 97 publications

Microstructure evolution of a W‐doped ZrB2ceramic upon high‐temperature oxidation

Microstructure evolution of a W‐doped ZrB2ceramic upon high‐temperature oxidation

Subsolidus phase relations and crystal structures of the mixed-oxide phases in the In2O3–WO3 system

Ab initio study of oxygen point defects on tungsten trioxide surface

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Product

Resources

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Microstructure evolution of a W‐doped ZrB₂ceramic upon high‐temperature oxidation

Microstructure evolution of a W‐doped ZrB₂ceramic upon high‐temperature oxidation