الفهرس 
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Abstract
The capability to fabricate ultra-low and customizable coefficient of thermal expansion (CTE) materials with good mechanical properties using a simple method was demonstrated in this work. For this purpose, first, nano beta-eucryptite and alumina powders were synthesized and used in the composite’s fabrication. Four composites of alumina and a second-phase beta-eucryptite were prepared, containing 10, 20, 30, and 40 wt.% beta-eucryptite. The temperature effect on prepared composites is investigated. The results of XRD analysis and the microstructures of prepared composites are discussed with results of mechanical strength and thermal expansion at temperature ranges of 1400, 1500, and 1550 °C. The CTE of alumina-beta-eucryptite composites decrease as the beta-eucryptite content increases, reaching -1.036 x 10-6 oC-1. The findings show that a composite with a very low thermal expansion coefficient and good mechanical properties can be designed and used in different applications.
The second part of this research is to design an alumina/β-eucryptite composite with a low coefficient of thermal expansion (CTE) and then test its sinterability using alum sludge from water treatment plants as an alumina source. A suitable chemical method is used to extract alumina from alum sludge waste. In addition to extracted alumina, silica fume waste and lithium carbonate were used to prepare β-eucryptite. In order to prepare β-eucryptite, the phase formation is first to be adjusted. The prepared samples were fired at 800, 1000, and 1200 ºC, respectively. XRD, SEM, physical properties, and thermal expansion are used to characterize these samples. The results indicate that 1000ºC is the optimum temperature for eucryptite formation. The samples of alumina/β-eucryptite containing 10, 20, 30, and 40% eucryptite are then prepared, and the influence of the heat treatment on the prepared composites is studied at temperature ranges of 1300, 1400, and 1500ºC. XRD analysis, microstructure, physical, and mechanical properties of alumina/β-eucryptite composites are investigated. The coefficient of thermal expansion (CTE) for various alumina/β-eucryptite samples at 1500ºC reduces with increasing β-eucryptite content, reaching 0.8098 x 10-6 oC-1. The results demonstrate that a composite with good mechanical properties and a low thermal expansion coefficient can be formed and utilized in a variety of different applications.