Abstract
In this paper are investigated microstructural, phase, physical and mechanical properties of mullite ceramics obtained from clay and Bayer electrofilter fines. Clay and alumina were mixed in such ratio that provides the amount of Al2O3 and SiO2 corresponding composition of mullite. One mixture was manually mixed and other was milled three hours in ceramic mill. After isostatic molding and heat treating at 1580°C and 1635°C XRD analysis revealed approximately 60% of mullite and 40% of corundum in first mixture and in second mixture 70% of mullite and 30% of corundum. Two types of mullite were observed in SEM micrographs beside corundum grains and glassy phase. The results of investigation indicate that preparation of mullite ceramics from these raw materials is possible, if clay and alumina are well homogenized and milled before molding.
Highlights
Mullite is an aluminosilicate compound that is used for conventional and advanced ceramic applications due to low density, low thermal conductivity, low thermal expansion, low dielectric constant, excellent mechanical properties at high temperature, low creep rate and good chemical stability [1,2,3]
Mullite synthesis process occurs at high temperatures by diffusion of particles [1], i.e. below 1300°C the major reaction is the kaolinite series reaction which converts into primary mullite and the cristobalite phase, amorphous silica and the reactive alumina remains unreacted
Specimens which are in this paper marked as A contain 39 % of clay sieved through mesh openings 0.5 mm and 61 % of Bayer electrofilter fines, mixed manually
Summary
Mullite is an aluminosilicate compound that is used for conventional and advanced ceramic applications due to low density, low thermal conductivity, low thermal expansion, low dielectric constant, excellent mechanical properties at high temperature, low creep rate and good chemical stability [1,2,3]. Mullite synthesis process occurs at high temperatures by diffusion of particles [1], i.e. below 1300°C the major reaction is the kaolinite series reaction which converts into primary mullite and the cristobalite phase, amorphous silica and the reactive alumina remains unreacted. It acts as an inert material below 1300°C [8].
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