Abstract
Pure Zircon and Zircon: Alumina (ZrSiO4: ?-Al2O3) composite powders were subjected to densification studies employing spark plasma sintering (SPS). Physico chemical and microstructural properties of the samples were evaluated and compared with that of conventionally sintered (CRH-Constant Ramp and Hold) compacts. Density measurements and microstructural evaluation revealed a low temperature densification of Zircon: Alumina at temperatures as low as 1300?C by SPS. Increase of temperature to 1350?C had shown negligible changes in density and on further heating the sample melts at 1400?C as a result of excessive formation of liquid phase. However, pure zircon could not be densified in the absence of alumina under SPS conditions. It is evident that addition of alumina enhances partial low temperature decomposition of zircon under the influence of plasma generated during SPS. Mullite formed as a result of this insitu reaction between alumina and silica acts as a bonding phase as revealed by the X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Electron disperse scanning (EDS) analysis.
Highlights
Zircon ceramic is an excellent refractory material with high chemical inertness and low thermal expansion coefficient
Sintering of zircon has been a subject of several studies [1,2,3,4,5] and generally reaction sintering of alumina and zircon mixture in stoichiometric proportions lead to the decomposition reaction of zircon (ZrSiO4→ZrO2 + SiO2) followed by the reaction between alumina and silica forming mullite and zirconia composites (Al2O3 + ZrO2 + SiO2 →ZrO2 + Al6 Si2 O13) [6,7,8,9,10]
The objective of the present study is to explore the densification behaviour of pure zircon and zircon with alumina as a sintering aid by the spark plasma sintering technique (SPS) and to provide a comparative evaluation with the conventional sintering
Summary
Zircon ceramic is an excellent refractory material with high chemical inertness and low thermal expansion coefficient. Sintering of zircon has been a subject of several studies [1,2,3,4,5] and generally reaction sintering of alumina and zircon mixture in stoichiometric proportions lead to the decomposition reaction of zircon (ZrSiO4→ZrO2 + SiO2) followed by the reaction between alumina and silica forming mullite and zirconia composites (Al2O3 + ZrO2 + SiO2 →ZrO2 + Al6 Si2 O13) [6,7,8,9,10]. In addition to this, according to the stoichiometric reaction 3Al2O3 + 2ZrSiO4 Al6Si2O13 +ZrO2, the reaction mixture should have 45.54% by weight of Al2O3 and 54.35% by weight of ZrSiO4 and corresponding reactions results in volume changes that competes with the densification shrinkage necessitating very critical processing conditions. Further the zirconia produced as a result of the reaction imparts volume changes while transformation to monoclinic zirconia during cooling leading to
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