Case Study: Nanocrystalline Yttria-Stabilized Tetragonal Zirconia Polycrystalline Ceramics

The effect of zirconium on the textural and catalytic properties of magnetite for the water gas shift reaction (WGSR) at high temperatures was studied in this chapter. The reaction is an important step in the industrial production of pure hydrogen. Samples with different amounts of zirconium (Zr/Fe (molar)= 0.1; 0.2;0.3; 0.4 and 0.5) were prepared from the decomposition of iron(III)hydroxoacetate doped with zirconium. It was found that zirconium increased the specific surface area of magnetite acting as spacer on the surface where it keeps the particles apart. Except for the zirconium-poorest solid, tetragonal zirconia was detected besides magnetite for all solids. Zirconium increased the intrinsic activity of the catalysts, stabilized the specific surface areas during reaction, and made the magnetite reduction to metallic iron more difficult. The zirconium-poorest is more active than magnetite and more resistant against deactivation by sintering and overreduction being attractive for WGSR.

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An in-situ investigation on the critical phase transformation stress of tetragonal zirconia polycrystalline ceramics

Journal of Materials Science ◽

10.1007/bf00356258 ◽

1996 ◽

Vol 31 (24) ◽

pp. 6523-6527 ◽

Cited By ~ 20

Author(s):

L. S. Pan ◽

S. Horibe

Keyword(s):

Phase Transformation ◽

Tetragonal Zirconia ◽

In Situ Investigation ◽

Polycrystalline Ceramics ◽

Critical Phase ◽

Transformation Stress

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Model analysis of boundary residual stress and its effect on toughness in thin boundary layered yttria-stabilized tetragonal zirconia polycrystalline ceramics

Journal of Materials Research ◽

10.1557/jmr.2000.0105 ◽

2000 ◽

Vol 15 (3) ◽

pp. 727-732 ◽

Cited By ~ 21

Author(s):

J. L. Shi ◽

Z. L. Lu ◽

J. K. Guo

Keyword(s):

Residual Stress ◽

Tetragonal Zirconia ◽

Ceramic Composites ◽

Boundary Phase ◽

Thin Boundary Layer ◽

Maximum Increase ◽

Proposed Model ◽

Polycrystalline Ceramics ◽

Polycrystalline Ceramic ◽

Continuous Boundary

The average thermal residual stress in a continuous boundary phase in polycrystalline ceramic composites was calculated with a simple thin boundary layer model, and a criterion for the self-cracking of the boundary phase was derived under a certain assumption. From the proposed model, the toughness of the materials can be increased by both tensile and compressive stress at boundaries when the crack propagates transgranularly. The toughness will be increased when the stress at boundary is compressive for intergranular fracture mode. The maximum increase is predicted to be achieved at boundary phase contents below 33%. The experimental results for yttria-stabilized tetragonal zirconia polycrystalline ceramics doped with different kinds of grain-boundary phase is in a qualitative agreement with the prediction by the model, but the toughness increase is largely dependent on the distribution feature of glass phases.

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