Synthesis and structural transformation of zirconia aerogels

Ward, David A.; Ko, Edmond I.

doi:10.1021/cm00031a014

Cited by 184 publications

(128 citation statements)

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“…S5). The formation of tetragonal ZrO2 in chemically treated zirconia and the aerogels has been reported in the literature [24]. Although the formation of tetragonal ZrO2 has been attributed to the improved catalytic activity of zirconia in the literature [25], it is not clear whether the crystal structure determined the catalytic activity in this study.…”

Section: Ketonization Of Hexanoic Acid On Zirconiamentioning

confidence: 67%

Ketonization of hexanoic acid to diesel-blendable 6-undecanone on the stable zirconia aerogel catalyst

Lee

Choi

Suh

et al. 2015

Applied Catalysis A: General

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Section: Ketonization Of Hexanoic Acid On Zirconiamentioning

confidence: 67%

Ketonization of hexanoic acid to diesel-blendable 6-undecanone on the stable zirconia aerogel catalyst

Lee

Choi

Suh

et al. 2015

Applied Catalysis A: General

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“…Ward and Ko [54] reported that a high surface area, porous zirconia aerogel with a surface area of 130 m 2 /g was obtained after supercritical CO 2 extraction and calcination at 500°C for 2 h. A water/alkoxide mole ratio of 2 and an acid/alkoxide mole ratio of 0.761 were found to be optimal in producing zirconia with a high surface area. Davies et al [55] reported that the surface area increased with the water-alkoxide mole ratio.…”

Section: Sol-gel Synthesismentioning

confidence: 99%

“…Large crystallites contain more of such embryos and hence, will show more tetragonal to monoclinic transformation. Ward and Ko [54] observed that the tetragonal to monoclinic transformation occurred upon prolonged heating to 500°C and proposed that defects formed during the aerogel synthesis provided nucleation sites for embryos. During heating, these embryos increase in size and thus bring about the tetragonal to monoclinic transformation.…”

Section: Other Factors Affecting Crystal Phasementioning

confidence: 99%

Structural and Morphological Control in the Preparation of High Surface Area Zirconia

et al. 2008

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The methods for the formation of zirconia including precipitation from aqueous salts, sol-gel synthesis from zirconium alkoxides, and the templated synthesis using surfactants are described in this review. The surface areas obtained vary widely but invariably decrease upon prolonged calcination. Digestion of hydrous zirconia and incorporation of dopants such as lanthanum, yttrium, or sulfate ions can increase the surface area and thermal stability. However, these methods also affect the crystal phase of zirconia. The transformation from the metastable tetragonal to the monoclinic phase occurs during the cooling phase of calcination. Mechanisms for the stabilization of the tetragonal phase are discussed. Zirconia with well-ordered mesopores or in the form of hollow spheres can be prepared but lack thermal stability, unless doped with phosphates, silicates or sulfates.

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“…For the preparation of TiO 2 and ZrO 2 aerogels, the propoxides and butoxides of the metals are mainly used as precursors [50], [56][57][58][59][60]. As for the alumina gels, the amount of water added for hydrolysis is decisive for the structure of zirconia aerogel networks.…”

Section: Metal Oxide Aerogelsmentioning

confidence: 99%

Aerogels

Hüsing

Schubert

2006

Ullmann's Encyclopedia of Industrial Chemistry

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The article contains sections titled: 1. Introduction 2. Synthesis 2.1. Network Formation and Structure 2.1.1. Inorganic Aerogels 2.1.1.1. SiO 2 Aerogels 2.1.1.2. Metal Oxide Aerogels 2.1.2. Inorganic/Organic Hybrid Aerogels 2.1.3. Organic Aerogels 2.2. Drying Methods 2.2.1. Supercritical Drying 2.2.1.1. Drying in Organic Solvents 2.2.1.2. Supercritical Drying with CO 2 2.2.2. Freeze Drying 2.2.3. Ambient Pressure Drying 2.3. Modification of Aerogels after Drying 3. Properties 3.1. Structural Properties 3.2. Physical and Chemical Properties 3.2.1. Optical Properties 3.2.2. Mechanical and Acoustic Properties 3.2.3. Thermal Conductivity 3.2.4. Hydrophobicity 4. Applications 4.1. Çerenkov Detectors 4.2. Thermal Insulation 4.3. Catalysis 4.4. Application as Storage Media 4.5. Electrical and Electronic Applications 4.6. Acoustic and Mechanical Applications 4.7. Optical Applications 4.8. Other Applications 5. Future Perspectives Aerogels are unique among solid materials. They have extremely low densities (up to 95 % of their volume is air), large open pores, and a high inner surface area. This combination of properties results in interesting physical properties, e.g., for silica aerogels extremely low thermal conductivities and low sound velocities are combined with optical transparency. Aerogels are typically prepared via wet chemical processes, such as sol – gel processing, and thus their pore system is initially filled with liquid. Only special drying techniques allow for exchange of the pore liquid against air while maintaining the filigrane solid framework. The most common drying technique is supercritical extraction, and sometimes chemical modification of the inner surface can be used to facilitate drying. The structure of the gel network, and thus the physical properties of aerogels, decisively depends on the choice of the precursors and the chemical reaction parameters for preparing the gels. Therefore, the later materials properties can be deliberately designed in the starting reaction solution.

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Synthesis and structural transformation of zirconia aerogels

Cited by 184 publications

References 1 publication

Ketonization of hexanoic acid to diesel-blendable 6-undecanone on the stable zirconia aerogel catalyst

Ketonization of hexanoic acid to diesel-blendable 6-undecanone on the stable zirconia aerogel catalyst

Structural and Morphological Control in the Preparation of High Surface Area Zirconia

Aerogels

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