Investigation of the sintering mechanisms of kaolin–muscovite

• Published in: Applied clay science Vol. 51; no. 4; pp. 445 - 451
• Main Authors: Lecomte-Nana, G.L., Bonnet, J.P., Blanchart, P.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01.03.2011; Elsevier
• Subjects: Activation energy; Chemical Sciences; Clay-based ceramics; CRH method; Densification; Earth sciences; Earth, ocean, space; Engineering Sciences; Exact sciences and technology; Kaolin; Material chemistry; Materials; Mica; Mineralogy; Mullite; Muscovite; Phases; Silicates; Sintering; Sintering mechanisms; Viscous flow; Asia; Bihar India; India; Clay-based ceramics; Muscovite; Kaolin; Sintering mechanisms; CRH method; Viscous flow; mullite; nesosilicates; diffusion; sintering; grain boundaries; dissolution; muscovite; mica; leucite; high temperature; activation energy; temperature; sheet silicates; silicates; framework silicates; melts; crystallites; flow
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2011.01.007

Kaolin Kga-1b and a muscovite from Bihar (India) and their mixtures were used to investigate the densifying mechanisms during the sintering. The kaolin–muscovite mixtures containing up to 25 mass% muscovite were studied by isothermal and non-isothermal methods such as the step-wise isothermal Dorn method and the constant heating rate developed by Bannister (1968) and Woolfrey and Bannister (1972). The densification of the reference proceeded through a viscous flow sintering due to the amorphous phases and diffusion at the grain boundaries at high temperatures (> 1200 °C). The activation energy was between 115 kJ/mol and 250 kJ/mol, with a peak value of 650 kJ/mol around 1250 °C due to the formation of mullite. The same trend was observed when 10 mass% muscovite were added. However, the densification started at 1000 °C and the related activation energy was 500 to 700 kJ/mol because of the formation of high-temperature phases (leucite and mullite). At muscovite contents > 10 mass%, the linear shrinkage was more sensitive to the muscovite dehydroxylaton. The densification was also controlled by grain boundary diffusion and viscous flow up to 1300 °C. Beyond this temperature, a dissolution-limited liquid sintering mechanism proceeded up to the end of sintering. The presence of crystallites, despite a larger amount of the viscous melt, led to a lower densification rate. The activation energy was below 250 kJ/mol. ► The sintering of pure kaolin is governed by viscous flow and diffusion at grain boundaries. ► Related activation energies are increased from 250 to 600 kJ/mol around 1250 °C. ► Up to 10 mass%, muscovite enables a densification at lower temperature (1000 °C). ► Above 10 mass muscovite, a dissolution-limited liquid sintering prevails from 1300 °C. ► The formation of crystallised phases tends to slow down the densification rate.