• H S Tripathi

      Articles written in Bulletin of Materials Science

    • Effect of sillimanite beach sand composition on mullitization and properties of Al2O3–SiO2 system

      H S Tripathi B Mukherjee S K Das A Ghosh G Banerjee

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      Mullite was developed by reaction sintering of sillimanite beach sand and calcined alumina. Two varieties of sillimanite beach sand viz. S and Z having different compositions were selected. Synthesis and properties of mullite were very much dependent on the sillimanite beach sand composition. Presence of higher amount of impurities in the Z-variety of sillimanite sand favours the densification by liquid phase formation. Presence of zircon in Z-variety increases the hardness and fracture toughness. Alumina addition improves the mechanical/thermomechanical properties of the samples. Mullite retains the usual orthorhombic habit of sillimanite. Rounded to sub rounded zirconia dispersed within the mullite matrix of the sample ZA is noticed.

    • Solid state sintering of lime in presence of La2O3 and CeO2

      T K Bhattacharya A Ghosh H S Tripathi S K Das

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      The sintering of lime by double calcination process from natural limestone has been conducted with La2O3 and CeO2 additive up to 4 wt.% in the temperature range 1500–1650°C. The results show that the additives enhanced the densification and hydration resistance of sintered lime. Densification is achieved up to 98.5% of the theoretical value with La2O3 and CeO2 addition in lime. Grain growth is substantial when additives are incorporated in lime. The grain size of sintered CaO (1600°C) with 4 wt.% La2O3 addition is 82 𝜇m and that for CeO2 addition is 50 𝜇m. The grains of sintered CaO in presence of additive are angular with pores distributed throughout the matrix. EDX analysis shows that the solid solubility of La2O3 and CeO2 in CaO grain is 2.9 and 1.7 weight %, respectively. The cell dimension of CaO lattice is 4.803 Å. This value decreases with incorporation of La2O3 and CeO2. The better hydration resistance of La2O3 added sintered lime compared to that of CeO2 added one, is related to the bigger grain size of the lime in former case.

    • Microstructure and properties of sintered mullite developed from Indian bauxite

      H S Tripathi A Ghosh M K Halder B Mukherjee H S Maiti

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      Dense mullite aggregates with 72% Al2O3 have been synthesized by reaction sintering of two varieties of Indian bauxite and silica sol. The bauxites used are of inferior grade with different levels of accessory impurities such as Fe2O3, TiO2, CaO. The phase and microstructure development of sintered samples were investigated by XRD and SEM. It was found that morphology of the sintered grain is very much dependent on the impurity level. Mullite formed from bauxite-1 with low impurity is mostly equiaxed, whereas mullite developed from bauxite 2 with higher impurity particularly CaO is needle shaped. Presence of CaO in bauxite was found to be more detrimental than TiO2 and Fe2O3.

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

      P Kumar M Nath A Ghosh H S Tripathi

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      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 ZrO2 up to 20 wt% significantly improves flexural strength and fracture toughness. The transformation of t $\rightarrow$ m zirconia was found to be the dominant mechanism for enhancement in mechanical properties. ZrO2 occupies both the intergranular as well as intragranular positions. However, intragranular zirconias are much smaller compared to intergranular zirconias.

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