Densification and crystalization kinetics of mullite diphasic gels from non_isothermal dilatometry experiments
[EN] 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...
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| Tipo de recurso: | artículo |
| Fecha de publicación: | 2008 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/9572 |
| Acceso en línea: | http://hdl.handle.net/10261/9572 |
| Access Level: | acceso abierto |
| Palabra clave: | Mullite Colloidal Sol-gel Kinetics Dilatometry Mullita Coloidal Cinética Dilatometría |
| Sumario: | [EN] 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. |
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