High temperature mullite dissolution in ceramic bodies derived from Al-rich sludge
authors Ribeiro, MJ; Tulyagavov, DU; Ferreira, JM; Labrincha, JA
nationality International
journal JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
author keywords sintering; microstructure-final; thermal properties; mullite; Al2O3
keywords MICROSTRUCTURAL EVOLUTION; PORCELAIN; MULLITIZATION; KAOLINITE; MIXTURES
abstract Mullite-based refractory ceramic materials were produced from an industrial Al-rich sludge derived from wastewater treatment of aluminium anodising or surface coating industrial processes, and other low cost raw materials (ball clay, kaolin and diatomite). Cylindrical samples processed by uniaxial dry pressing (32 MPa) were sintered at various temperatures (1250-1650 degrees C) to study the mullitisation process. The performance of the materials at high temperature (1650 degrees C) was evaluated through different techniques (XRD, SEM/EDS, optical microscopy, and impedance spectroscopy) to access the microstructural changes occurring under prolonged tests (dwell times up to 100 h). For dwell times < 80 h, a preferential dissolution of the smaller mullite grains in the glassy phase and its partial re-precipitation onto the coarser ones, leading to an overall coarsening of the mullite crystals. For dwell times > 80 h, coarse alpha-alumina and Cr-doped alumina developed at the surface of the specimens, being accompanied by the formation of pores in the vicinity of alumina grains. Near alumina grains, additional relevant features include the increase of surface roughness, the appearance of concentration gradients within the glassy phase, which became almost depleted in Al and enriched in alkalines. The continuity of the glassy phase and its enrichment in alkaline species enhanced the electrical conductivity of the material, enabling the use of impedance spectroscopy to access the microstructural changes occurring during prolonged heat treatment. (c) 2004 Elsevier Ltd. All rights reserved.
publisher ELSEVIER SCI LTD
issn 0955-2219
year published 2005
volume 25
issue 5
beginning page 703
ending page 710
digital object identifier (doi) 10.1016/j.jeurceramsoc.2004.03.028
web of science category Materials Science, Ceramics
subject category Materials Science
unique article identifier WOS:000227755400019
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