In-situ Mullite Rodlike Crystal Reinforced BAS Composite

In-situ mullite rodlike crystal reinforced BAS composite was fabricated by solid phase reaction sintering method, using coal-gangue, alumina and barium carbonate as raw materials. DTA, XRD and SEM were employed to analyze and study the mechanism of reaction synthesis of the composite and effects of preparing method, firing temperature, composition, holding time and hot-pressing pressure on phase composition, structure and properties of the composite. Conclusions as follows:1 , Mullite whisker mostly rooted in the decomposition of coal-gangue. It began to nucleate at about 800 ℃. During the later sintering mullite grew along the C axis and grew up under the guidance of the liquid phase; The production of BAS was that firstly at about 1000℃, barium silicate was synthesized with barium carbonate and silica or barium aluminate was synthesized with barium carbonate and alumina, then hexacelsian was made at about 1200℃ by the reaction between barium silicate and alumina or between barium aluminate and silica.2, In-situ mullite rodlike crystal reinforced BAS composite was composed by the main phase BAS, the inferior phase mullite and few phase corundum. Phases combined compactly and the distribution of phases was uniform. Rod-like or needle-like mullite distributed netlike structure in space.3 , The wet mixing and pre-sintering craft was choosed for the composite prepared by pressureless sintering. The increase of firing temperature and holding time was advantageous to the densification of the samples, the growth of rod-like mullite, the formation of netlike structure in space and the uniform distribution of phases. But the firing temperature wasn't too high, which was suitable to be chosed at 1500 ～ 1550℃.4, The effect of firing temperature on densification of composite was not obvious for the composite fabricated by hot-press sintering. The flexural strength and fracture toughness were improved at the higher firing temperature. According to the composition of m(BaCO₃) : w(Al₂O₃) : m(coal-gangue)=17.2 : 25.0 : 51.8, under the condition of 1450℃×1h×20MPa, the composite possessed super mechanical properties. And the flexural strength and fracture toughness was 215.2MPa and 3.8MPa·m^1/2, which were 169% and 111% higher than that of BAS matrix respectively. The toughenig mechanism was the crack deflection and the bridging of whisker.5, The effect of pressure on properties of composite was obvious for the composite fabricated by hot-press sintering. When the pressure rised to 25MPa from 20MPa, the open porosity of composite reduced from 0.7% to 0.4%, the flexural strength increased from 176. 3MPa to 194.3MPa, and fracture toughness increased from 2.2 MPa·m^1/2 to 2.5 MPa·m^1/2.