Properties of Mullite-Zirconia Composites Prepared through Reaction Sintering Kaolin, α-Al2O3, and ZrO2
Mullite–zirconia composites were synthesized through reaction sintering Algerian kaolin, α-Al2O3, and ZrO2. Phases present and their transformations were characterized using x-ray diffraction. Quantitative phase analysis was performed following the Rietveld method. Hardness and fracture toughness were measured by Vickers indentation. The flexural strength was measured using a Universal Testing Machine. It was found that the microstructure of samples sintered for 2 hours at 1600°C was composed of mullite grains which have whiskers’ shape and ZrO2 particles. In the composite containing 16 wt.% ZrO2, the ratio of tetragonal zirconia transformed to monoclinic zirconia was relatively small and did not exceed 18%. However, in the composite containing 32 wt.% ZrO2 around 75% of the tetragonal structure changed to monoclinic structure. Also, it was found that the increase of ZrO2 content from 0 to 32 wt.% decreased the microhardness of the composites from 14 to 10.8 GPa. However, the increase of ZrO2 content from 0 to 24wt.% increased the flexural strength of the composites from 142 to 390 MPa then decreased it with further increase of ZrO2 content. The fracture toughness increased from 1.8 to 2.9 MPa.m1/2 with the increase of ZrO2 content from 0 to 32 wt.%; and the rate of the increase decreased at higher fractions of ZrO2 content. The average linear coefficient of thermal expansion (within the range 50 to 1450°C) for samples containing 0 and 16 wt.% ZrO2 sintered at 1600°C for 2 hours was 4.7 x10-6 K-1 and 5.2 x 10-6 K-1 respectively.
Guojun Zhang and Jessica Xu
F. Sahnoune et al., "Properties of Mullite-Zirconia Composites Prepared through Reaction Sintering Kaolin, α-Al2O3, and ZrO2", Advanced Materials Research, Vols. 160-162, pp. 1772-1778, 2011