Abstract
In this work, alumina-mullite composites (5-15 vol.%) were prepared using sol-gel derived alumina composite nanopowders. The results revealed the formation of intragranular and intergranular mullites inside and between the alumina grains, respectively. Accordingly, the intragranular mullites (average grain size, 0.3 ?m) were smaller than the intergranular mullites (average grain size, 0.5 ?m). Moreover, the alumina grains (average grain size, 1.0 ?m) are larger than the mullites. Meanwhile, the mullites showed positive results in the prevention of the alumina grains growth and the retardation of densification. The relative density of alumina-15 vol.% mullite that was sintered at 1650?C for 2 h, was obtained as 98.7 %. After sintering at 1750?C for 2 h, the mullite was decomposed.
Highlights
Alumina has found different applications such as insulating refractory linings of furnaces, seals, thermocouple wire protection and armors because of its physical and mechanical properties [1,2,3]
The results revealed the formation of intragranular and intergranular mullites inside and between the alumina grains, respectively
The relative density of alumina-15 vol.% mullite that was sintered at 1650 °C for 2 h, was obtained as 98.7 %
Summary
Alumina has found different applications such as insulating refractory linings of furnaces, seals, thermocouple wire protection and armors because of its physical and mechanical properties (high melting point and high strength) [1,2,3]. Mullite in the alumina matrix reduces the Young’s modulus and thermal expansion coefficient of the composite, leading to a better thermal shock resistance [4,5,6]. Small mullite additions (5–15 vol.%) allow desirable values of hardness and toughness of alumina to be maintained while reducing the Young’s modulus below that of alumina, so that it is expected that the thermal shock behaviour will be improved [8]. Schehl et al [11] presented a modified processing route which consists in the doping of a commercial high-purity alumina powder so that its microstructure is modified with such nanoparticles as zirconia and mullite, formed at the sintering stage. The grain boundaries of the high-purity alumina powder are modified by segregation of the secondary phases or by the formation of well-distributed zirconia and mullite nanoparticles.
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