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Journal ArticleDOI

Sintering of Mullite Precursor Powder Prepared by Semi-Colloidal Technique

01 Apr 2003-Transactions of The Indian Ceramic Society (Taylor & Francis)-Vol. 62, Iss: 2, pp 112-116
TL;DR: In this paper, the powder was compacted with TiO2 as additive in various proportions and the sintering of the compacted masses was studied by measuring the firing shrinkage, apparent porosity, bulk density and specific gravity.
Abstract: Precursor powder for the preparation of mullite was synthesized through a non-conventional semi-colloidal technique. The precursor powder was characterized by chemical analysis, DTA, measurement of surface area, bulk density and X-ray analysis. The powder was compacted with TiO2 as additive in various proportions and the sintering of the compacted masses was studied by measuring the firing shrinkage, apparent porosity, bulk density and specific gravity. The phase development and phase distribution in the sintered masses were studied by XRD and SEM. It was observed that TiO2 exhibited a positive influence on the formation of mullite from the said precursor powder at elevated temperatures. The grain size of the mullite crystals increased with the increase in TiO2 content.
Citations
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Journal ArticleDOI
TL;DR: Mullite ceramics were synthesized using boehmite (-AlOOH) as alumina source and polymethysilsesquioxanes (PMS) as silica source.
Abstract: Mullite ceramics was synthesized using boehmite (-AlOOH) as alumina source and polymethysilsesquioxanes (PMS), a novel class of preceramic polymer, as silica source Quantitative mullitization was

1 citations

References
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Journal ArticleDOI
TL;DR: The transient viscous sintering (TVS) was used to fabricate mullite/zirconia/alumina composites as mentioned in this paper, which achieved densification at higher temperatures by reaction between the alumina and silica.
Abstract: Mullite was fabricated by a process referred to as transient viscous sintering (TVS). Composite particles which consisted of inner cores of α-alumina and outer coatings of amorphous silica were used. Powder compacts prepared with these particles were viscously sintered to almost full density at relatively low temperatures (∼1300°C). Compacts were subsequently converted to dense, fine-grained mullite at higher temperatures (∼1500°C) by reaction between the alumina and silica. The TVS process was also used to fabricate mullite/zirconia/alumina, mullite/silicon carbide particle, and mullite/silicon carbide whisker composites. Densification was enhanced compared with other recent studies of sintering of mullite-based composites. This was attributed to three factors: viscous flow of the amorphous silica coating on the particles, avoidance of mullite formation until higher temperatures, and increased threshold concentration for the development of percolation networks.

238 citations

Journal ArticleDOI
TL;DR: In this article, a mixture of boehmite sol and silica dispersion was used for the preparation of 3Al2O3·2SiO2 powder, which was then sintered to 98% (theoretical density) at 1650°C for 1.5 h.
Abstract: Mullite (3Al2O3·2SiO2) of stoichiometric composition was prepared by mixing boehmite sol and silica dispersion and gelling at a pH of 3. Complete mullitization takes place at or above 1300°C. Ultrafine mullite powder prepared by calcining gel at 1400°C and attrition milling could be sintered to >98% (theoretical density) at 1650°C for 1.5 h. The flexural strength of the sintered body at room temperature was 405 MPa and 350 MPa at 1300°C. Only traces of a secondary phase were observed along the grain boundary.

112 citations

Journal ArticleDOI
TL;DR: In this article, a linear relationship was obtained between the percent of theoretical density and the logarithm of time for compositions in the range 73-75 wt% Al{sub 2}O{sub 3}/SiO{ sub 2} ratio.
Abstract: Sintering behavior of mullite-containing powders was studied over a range of chemical compositions (Al{sub 2}O{sub 3}/SiO{sub 2} ratio). Densification measurements were made for both liquid phase-containing and solid state systems. Small amounts of liquid phase were observed to have a significant effect on densification rate. A linear relationship was obtained between the percent of theoretical density and the logarithm of time for compositions in the range 73-75 wt% Al{sub 2}O{sub 3}. Currently available models for intermediate stage sintering kinetics were considered to be inadequate for these systems. Grain boundary transport 0r diffusion appeared to be the primary mechanism of densification.

86 citations

Journal ArticleDOI
TL;DR: In this article, the sintering behavior of mullite powder compacts which contained soft and hard agglomerates was studied, the maximum density achieved depended on the size and packing of the agglomers.
Abstract: The sintering behavior of mullite powder compacts which contained soft and hard agglomerates was studied, The maximum density achieved depended on the size and packing of the agglomerates. Although the initial % total pore volume was kept constant, the presence of larger pores in the green compact, due to larger agglomerates, resulted in lower final densities after sintering. Densification rates were enhanced by the breakdown of agglomerates by grinding. The particle and agglomerate packing arrangements caused densification substages to occur. A schematic model is presented which agrees well with the observed experimental behavior.

64 citations

Journal ArticleDOI
TL;DR: Mullite of stoichiometric composition 3Al2O3·2SiO2 was synthesized using γ-aluminium oxide and colloidal silicon dioxide in this paper, which can be sintered in 3 h at 1650°C to 98·1% of its theoretical density, and shows high flexural strength of 385 MPa at room temperature.

41 citations