Synthesis of Ba0.75Sr0.25Al2Si2O8 - ZrO2 ceramic composites by solid state reaction of mechanically activated precursor mixtures

Abstract

Precursor mixtures composed of fly ash, BaCO3, SrCO3, Al2O3 and ZrO2, were subjected to attrition milling for 0-8 h and then uniaxially pressed and sintered at 900-1500 °C/5 h, for the in situ solid state synthesis of composites with nominal Ba0.75Sr0.25Al2Si2O8 (SBAS)/ZrO2 mass ratios of: 1) 90/10, 2) 70/30, and 3) 50/50. Mechanical activation, combined with the likely generation of a considerable amount of transient liquid during sintering of the composites, notably enhanced the reactivity of the precursor mixtures. ZrO2 decreased the conversion from the hexagonal (Hexacelsian) into the monoclinic (Celsian) phases of SBAS in the composites, which became more pronounced when the content of ZrO2 was increased in the materials. Nearly full conversions could be achieved at temperatures as low as 1100 °C, by mechanically activating the precursor mixtures for times that increased with increasing content of ZrO2 in the materials. An increment in the time of mechanical activation of the precursor mixtures, as well as in their ZrO2 content and in the sintering temperature, increased the mechanical properties of the synthesized materials. Thus, the best mechanical properties were obtained for composition 3 milled for 8 h and sintered at 1500 °C.