Abstract
Abstract Refractory ceramics were produced from clays and alumina waste. Specimens were shaped by uniaxial pressing, subjected to thermal analysis by dilatometry and heat-treated in a conventional furnace at 1300 and 1400oC, applying a heating rate of 5oC/min and a dwell time of 2 and 3 hours at the maximum temperature. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and physicomechanical properties. The dilatometric analysis before heat treatment indicated that the formulation containing the largest amount of fluxing oxides presented the highest linear shrinkage. The XRD analysis revealed that mullite was the major phase and needle shaped crystals typical of mullite obtained from clay minerals were observed by SEM. The increase in firing temperature and dwell time at the maximum temperature improved the physicomechanical properties of the specimens. The thermal expansion coefficient (TEC) in the range of 25 to 1000oC varied from 6.2 to 6.9 x 10-6°C-1.
Highlights
Refractory ceramics are materials that do not undergo any physical or chemical change when used in high temperature applications
Based on the data obtained in this study, the following conclusions can be drawn about the chemical, thermal, mineralogical, microstructural and physicomechanical properties of these refractory ceramics
The scanning electron microscopy (SEM) micrographs revealed the formation of needle shaped crystals typical of mullite derived from clay minerals
Summary
Refractory ceramics are materials that do not undergo any physical or chemical change when used in high temperature applications. The main thermomechanical and thermophysical properties of refractories are related to their ability to withstand different degrees of thermal and mechanical stresses, and to resist corrosion by liquids and gases[1,2]. These properties depend on the characteristics of raw materials and formulations (chemical and mineralogical composition, particle size and shape distribution) the forming process and sintering temperature[3,4,5]. Compositions containing silica and alumina are extensively studied After heat treatment, these compositions generate mullite and corundum (α-Al2O3), which applications include furnace linings, refractory supports and thermal insulation[2]
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