Microstructural evolution of mullite during the sintering of kaolin powder compacts

Mullitization kinetics from silica- and alumina-rich wastes

“…In fact, aluminium silicate systems like pure clays and clay-aluminium hydroxide or clay-aluminium oxide mixtures have been extensively used to produce mullite ceramics, with special attention being paid to kaolin-based mixtures [5][6][7][8][9][10][11][12][13][14][15]. Kaolinite and kaolinite-based ceramic formulations mullitization behaviour has been studied with the purpose of producing not only mullite-rich products [6][7]10,[12][13][14][15] but also other classes of high-technology ceramics [5]. In spite of the work accomplished, it is still difficult to present a concise reaction sequence for kaolinite due to the complexities involved in its phase transformation and microstructural evolution at elevated temperature, and to its susceptibility to modifications related to structural or impurities variations [8,10].…”

“…Kaolinite and kaolinite-based ceramic formulations mullitization behaviour has been studied with the purpose of producing not only mullite-rich products [6][7]10,[12][13][14][15] but also other classes of high-technology ceramics [5]. In spite of the work accomplished, it is still difficult to present a concise reaction sequence for kaolinite due to the complexities involved in its phase transformation and microstructural evolution at elevated temperature, and to its susceptibility to modifications related to structural or impurities variations [8,10]. Pask and Tomsia [8] studied kaolinite phase evolution till 1300 8C and found that both mullite and spinel phase have the possibility to form concurrently at about 980 8C.…”

“…Pask and Tomsia [8] studied kaolinite phase evolution till 1300 8C and found that both mullite and spinel phase have the possibility to form concurrently at about 980 8C. Later work by Chen et al [10] referred that the formation either of spinel phase or of silicon-containing g-alumina at 980 8C is still under debate and reported the formation of mullite only above 1100 8C. Chen et al [13] identified the formation of mullite at 1006.5 8C and claimed that the discrepancy relative to the 980 8C reported by other authors might have been due to a different kaolin sample having somewhat different impurities or particle size distribution of the starting materials.…”

The Kaolin Residue and Its Use for Production of Mullite Bodies

“…This residue from processing of www.intechopen.com Sustainable DevelopmentEnergy, Engineering and Technologies -Manufacturing and Environment 120 kaolin consists of minerals mica, quartz and feldspar, there is also the presence of kaolinite fraction whose amount is reduced depeding chiefly on the beneficiation process. The main product after sintering of kaolinite at high temperatures is the mullite ( Lima et al, 2001;Chen et al, 2000). The ceramic products of kaolinitic have desirable properties of hardness, translucency and strength development of the mullite crystals, regardless of the effect, their number and their size and shape.…”

“…Taking into account that the reaction 2SiO 2 • Al 2 O 3 • 2H 2 O + 2Al 2 O 3  3Al 2 O 3 • 2SiO 2 + 2H 2 O occurs by a mixture of kaolinite and alumina during sintering, and assuming that the silica (SiO 2 ) in kaolinite reacts completely with the alumina (Al 2 O 3 ) to form mullite (Chen et al, 2000), the kaolin residue that showed 52.68% of SiO 2 , requires an excess of alumina for the reaction with silica, present in the residue, can result in mullite. Compositions were formulated with lower and higher levels of alumina, so that these formulations to stay within the stoichiometry of the mullite to be reached.…”