Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

Use of CeO2-based oxides in the three-way catalysis

Progress in material selection for solid oxide fuel cell technology: A review

Transport properties of solid oxide electrolyte ceramics: a brief review

A model based on Rayleigh-Gans-Debye light scattering theory has been developed to describe the light transmission properties of fine-grained, fully dense polycrystalline ceramics consisting of birefringent crystals. This model extends light transmission models based on geometrical optics, which are only valid for coarse-grained microstructures, to smaller crystal sizes. We verify our model by measuringthe light transmission properties of fully dense (>99.99%) polycrystalline alpha-alumina (PCA) with mean crystal sizes ranging from 60 mm down to 0.3 mm. The remarkable transparency exhibited by PCA samples with small crystal sizes (< 2 mm) is very well explained by thismodel.

Transparent Alumina: A Light-Scattering Model

YAG precursors were co-precipitated from a mixed solution of aluminum and yttrium nitrates using ammonia water and ammonium hydrogen carbonate as precipitants, respectively. Phase evolution of the precursors during calcination and sinterability of the resultant YAG powders were compared between the two methods. The use of ammonia water produced a hydroxide precursor with an approximate composition of Al(OH)3·0.3[Y2(OH)5(NO3)·3H2O] which transformed to pure YAG at about 1000°C via YAlO3 phase. Severe agglomeration caused poor sinterability of the resultant YAG powders. The use of ammonium hydrogen carbonate produced a carbonate precursor with an approximate composition of NH4AlY0.6(CO3)1.9(OH)2·0.8H2O. The precursor directly converted to pure YAG at about 900°C. The precursor was loosely agglomerated and the resultant YAG powders showed good dispersity and excellent sinterability. For the same calcination temperature of 1100°C, YAG powders from the hydroxide precursor and the carbonate precursor densified to ∼81.2 and ∼99.8% of the theoretical, respectively, by vacuum sintering at 1500°C for 2 h.

Co-precipitation synthesis and sintering of yttrium aluminum garnet (YAG) powders: The effect of precipitant

A new preparation method for a highly sinterable yttria powder has been developed, the resultant powder characterized, and its sinterability studied. As a precursor of the yttria powder, a fine and needle-shaped yttrium carbonate was prepared by a precipitation and aging method. A fine and low-agglomeration yttria powder was obtained by calcining the carbonate precursor at 1100°C. The primary crystallites measured ∼0.1 μm and weakly agglomerated to a size of ∼0.3 μm. The powder had a very high sinterability, so that the powder compact could be sintered to transparency by normal sintering under vacuum without additives at low temperatures, over 1600°C. The sintered transparent ceramics exhibited a homogeneous microstructure with no abnormal grain growth.

Fabrication of transparent yttria ceramics at low temperature using carbonate-derived powder

A carbonate precursor of yttrium aluminum garnet (YAG) with an approximate composition of NH4AlY0.6(CO3)1.9(OH)2z 0.9H2O was synthesized via a coprecipitation method from a mixed solution of ammonium aluminum sulfate and yttrium nitrate, using ammonium hydrogen carbonate as the precipitant. The precursor precipitate was characterized using chemical analysis, differential thermal analysis/thermogravimetry, X-ray diffractometry, and scanning electron microscopy. The sinterability of the YAG powders was evaluated by sintering at a constant rate of heating in air and vacuum sintering. The results showed that the precursor completely transforms to YAG at ;1000°C via the formation of a yttrium aluminate perovskite (YAP) phase. YAG powders obtained by calcining the precursor at temperatures of <1200°C were highly sinterable and could be densified to transparency under vacuum at 1700°C i 1 h without additives.

Low-Temperature Fabrication of Transparent Yttrium Aluminum Garnet (YAG) Ceramics without Additives

A precursor for magnesium aluminum spinel powder, composed of crystalline ammonium dawsonite hydrate (NH4Al(OH)2CO3·H2O) and hydrotalcite (Mg6Al2(CO3)(OH)16·4H2O) phases, was synthesized via precipitation, using ammonium bicarbonate as the precipitant. The precursor was characterized by differential thermal analysis/thermogravimetry, X-ray diffractometry, and scanning electron microscopy. Reactive spinel powder, which could be densified to translucency under vacuum at 1750°C in 2 h without additives, was obtained by calcining the precursor at 1100°C for 2 h.

Fabrication of Translucent Magnesium Aluminum Spinel Ceramics

A precursor for Mg‐Al spinel has been synthesized via the precipitation method, using ammonium bicarbonate as the precipitant. The precursor was composed of crystalline ammonium dawsonite hydrate [NH4Al(OH)2CO3 .H2O] and hydrotalcite [Mg6Al2 (CO3)(OH)16 .4H2O] phases. The precursor converted to pure spinel phase at900C via two steps upon calcination: (i) decomposition of hydrotalcite at lower temperatures (400‐800C) and (ii) solid-state reaction between MgO (decomposed from hydrotalcite) and g-Al2O3 (derived from NH4Al(OH)2CO3 .H2O) at higher temperatures (>800C). The eAect of calcination temperature on particle morphology and sinterability of the resultant spinel powders were investigated. # 2001 Elsevier Science Ltd. All rights reserved.

Takayasu Ikegami

Papers

Co-precipitation synthesis and sintering of yttrium aluminum garnet (YAG) powders: The effect of precipitant

Fabrication of transparent yttria ceramics at low temperature using carbonate-derived powder

Low-Temperature Fabrication of Transparent Yttrium Aluminum Garnet (YAG) Ceramics without Additives

Fabrication of Translucent Magnesium Aluminum Spinel Ceramics

Synthesis of Mg-Al spinel powder via precipitation using ammonium bicarbonate as the precipitant