Synthesis and characterization of mullite–zirconia composites by reaction sintering of zircon flour and sillimanite beach sand

Abstract

Mullite-zirconia composites containing 10-30 wt% zirconia were prepared by reaction sintering of zircon flour, sillimanite beach sand and calcined alumina. Raw materials were attrition milled, shaped into pellets and bars and sintered in the temperature range of 1450-1600 • C with 2 h soaking at peak temperature. Sintered products were analysed in terms of various physical, mechanical and thermo-mechanical properties. The analyses of phases developed and microstructural analyses were carried out by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. It was observed that the addition of ZrO 2 up to 20 wt% significantly improves flexural strength and fracture toughness. The transformation of t → m zirconia was found to be the dominant mechanism for enhancement in mechanical properties. ZrO 2 occupies both the intergranular as well as intragranular positions. However, intragranular zirconias are much smaller compared to intergranular zirconias.

Fabrication and characterisation of ZrO2-reinforced porous mullite ceramics

“…The detected t-ZrO 2 peaks can be mainly ascribed to the presence of impurities such as Y 2 O 3 , CaO and MgO in ZrSiO 4 powers (Table 1), which can stabilise the t-ZrO 2 phase. These are agreeing with those found by Kumar et al [28], Yuan et al [30] and Lu et al [38].

Figure 2 XRD patterns of ZrO 2 -reinforced porous mullite ceramics fabricated at 1400–1600°C (the molar ratio of Al 2 O 3 :ZrSiO 4 = 3:2).

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“…The detected t-ZrO 2 peaks can be mainly ascribed to the presence of impurities such as Y 2 O 3 , CaO and MgO in ZrSiO 4 powers (Table 1), which can stabilise the t-ZrO 2 phase. These are agreeing with those found by Kumar et al [28], Yuan et al [30] and Lu et al [38].…”

“…Their compressive strength is significantly higher than that (4.4 MPa [9] and 5.5 MPa [40]) of porous mullite samples having similar porosity fabricated using kyanite and alumina/aluminium hydroxide. Such improved mechanical properties can be attributed to (1) the presence of ZrO 2 , which acts as a reinforcement phase for porous samples [28,30]. t-ZrO 2 strengthens porous ceramics through a phase transition.…”

“…For instance, Lathabai et al [27] prepared zirconia/mullite composites using zircon and alumina powders as raw materials, and their fracture strength (330 MPa) was obviously better than that of the pure mullite sample. Kumar et al [28] fabricated nearly dense ZrO 2 -mullite ceramics with a cold bending strength of 171.7∼245.9 MPa and a fracture toughness of 4.70∼5.94 MPa•m 1/2 using ZrSiO 4 , Al 2 O 3 and sillimanite powders as main raw materials by the reactions of the sintering method. Boch et al [29] prepared ZrO 2 -toughened mullite ceramics with about 97% of theoretical density using alumina and ZrSiO 4 powders as the main materials by the reactions of the sintering method.…”

Characterization and production of slip casts mullite–zirconia composites

“…Various production methods, such as solid state sintering, thermal plasma fusion, sol-gel, spark plasma sintering, laser floating zone directional solidification method, are adopted for the synthesis of mullite-zirconia composites [15][16][17][18][19][20]. Generally, slip casting is exploited to yield zirconia-toughened mullite by improving the density and microstructure of the body so that this technique is applied in the fabrication process of many composites and refractories [10].…”