Activation energy of mullitization from various starting materials

Okada, Kiyoshi

doi:10.1016/j.jeurceramsoc.2007.03.015

Cited by 59 publications

(33 citation statements)

References 43 publications

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“…17 There are no data available on activation energies of Zr 4+ and Si 4+ diffusion in the Al 2 O 3 -ZrO 2 -SiO 2 ternary system. Cherniak 18 studied Si diffusion in zircon (ZrSiO 4 ) and determined the activation energy to be around 720 kJ/mol for temperatures above 1350 • C. Cherniak also states that diffusion of Si in zircon is about an order of magnitude faster than diffu- sion of Hf and many orders of magnitude slower than oxygen diffusion.…”

Section: Kinetic Parameters Of Crystallizationmentioning

confidence: 99%

Crystallization kinetics of amorphous alumina–zirconia–silica ceramics

Chráska

Hostomský

Klementová

et al. 2009

Journal of the European Ceramic Society

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Section: Kinetic Parameters Of Crystallizationmentioning

confidence: 99%

Crystallization kinetics of amorphous alumina–zirconia–silica ceramics

Chráska

Hostomský

Klementová

et al. 2009

Journal of the European Ceramic Society

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“…Many elements favor the liquid formation, but the addition of Bi 3+ appears to be a promising way for mullite formation in ceramic compositions 12 and for the reduction of the formation temperature. 13 The aim of this study is to correlate the characteristics of microstructures of multilayered ceramics to their mechanical properties. Layered ceramics are obtained by the stacking of kaolinite-muscovite alternate layers and a subsequent sintering operation.…”

Section: Introductionmentioning

confidence: 99%

Mechanical properties of textured ceramics from muscovite–kaolinite alternate layers

Gridi-Bennadji

Chateigner²,

Vita³

et al. 2009

Journal of the European Ceramic Society

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“…Based on this model, the Ea for diffusion in the amorphous aluminosilicate matrix must be smaller than that of alumina released from the Y-Al 2 O 3 structure in type (1) starting materials. A summary of the Ea values found from various starting materials and a discussion of the reasons for the unusually large Ea values for mullitization has been recently published (6).…”

Section: Introductionmentioning

confidence: 99%

“…According to this phenomenological equation, the fraction ΔL/Lo of material densified after a time t is given by Z = ΔL/Lo = 1 -exp (-At m ) [6] Where m is a constant dependent on the details of densification mechanisms, A is related to the rates of the sintering and z the completed fraction of the total shrinkage.…”

Section: Introductionmentioning

confidence: 99%

Cinética de cristalización y sinterización de geles difásicos de mullita a partir experimentos no isotérmicos de dilatometría

Orgaz¹

2008

Bol. Soc. Esp. Ceram. Vidr.

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Mullite (3 AI2O3_2 SiO2) was processed by mixing silica and alumina colloids at pH below 3 in a high shear blender. The gels were sieved to ‹ 125 microns and cold isostatically pressed to form rods. The various processes involved during the sintering process such as condensation-polymerization and the competition between mullite crystallization and densification were analysed from constant heating rate equations and rate controlled sintering dilatometer experiments. Changes in the slopes permitted the identification of such processes and the activation energy for mullitization was calculated. Fast firing (20-30 K/min) in the critical mullitization temperature range of 1230-1505"C and low heating rates (2-3 K/min) in the viscous flow densification intervals of below 1230ºC and higher than 1505 gives rise to near full density and fine grain microstructures of sintered mullite. Fast firing and high (0.5 to 1 % /min) densification rate controlled processes seem to be the most suitable approaches to high density gel processed mullite. Amorphous silica is the rate controlling mechanism for the viscous flow densification process before alumina is solved and nucleation and crystallization of mullite appears. Deviations from the linear Frenkel model for viscous flow are also observed. Keywords: mullite, colloidal, sol-gel, kinetics, dilatometry. Cinética de cristalización y sinterización de geles difásicos de mullita a partir experimentos no isotérmicos de dilatometríaMullita de composición 3 Al2O3 -2 SiO2 ha sido preparada mezclando coloides de sílice y alúmina en un mezclador de alta velocidad a pH<3. Los geles formados eran secados, tamizados por debajo de 125 micras y prensados isostáticamrente para formar varillas de unos 6 mm de diámetro. Los diferentes procesos que ocurren durante el proceso de sinterización, tales como polimerización-condensación y la competición entre cristalización y densificación, han sido analizados utilizando las ecuaciones de ecuaciones de velocidad de calentamiento constantte y experimentos de dilatometría utilizando un software que permite realizar ensayos a velocidad de contracción constante. Cambios en las pendientes han permitido la identificación de tales procesos y el calculo de la energia de activación para la formación de mullita. Calentamiento rápido (20-30 K/min) en el rango critico de formación de mullita entre 1230-1505ºC y bajas velocidades de calentamiento (2-3 K/min) en las zonas de densificación por flujo viscoso daban lugar a mullitas sinterizadas con densidad cercana a la teórica y fina micro-estructura. Altas velocidades de densificación (o,5% a 1%/min) son las mas adecuadas para sinterizar mullita de alta densidad. Flujo viscoso de la sílice amorfa es el mecanismo que controla la velocidad del proceso antes de disolver la alúmina y formar mullita por un proceso de nucleación y crecimiento. Se observan también desviaciones del modelo lineal de Frenkel para el flujo viscoso.

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Activation energy of mullitization from various starting materials

Cited by 59 publications

References 43 publications

Crystallization kinetics of amorphous alumina–zirconia–silica ceramics

Crystallization kinetics of amorphous alumina–zirconia–silica ceramics

Mechanical properties of textured ceramics from muscovite–kaolinite alternate layers

Cinética de cristalización y sinterización de geles difásicos de mullita a partir experimentos no isotérmicos de dilatometría

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