Oxide thermoelectric materials (Na 1Ày M y ) 1.4 Co 2 O 4 (M = Sr, Li; y = 0 to 0.4) were prepared by a sol-gel method. The influence of doping on the thermoelectric properties was investigated, and the phase composition was characterized by x-ray diffraction. Experimental results showed that the main crystalline phase of the undoped and Sr/Li-doped samples was c-Na 1.4 Co 2 O 4 . The thermoelectric properties of Na 1.4 Co 2 O 4 can be improved slightly by doping with Sr. Doping with Li improves the thermoelectric properties of Na 1.4 Co 2 O 4 . For a doping fraction of y = 0.1, the electrical conductivity of (Na 1Ày Li y ) 1.4 Co 2 O 4 at 288 K achieves its maximum value of 301.19 (X mm) À1 . The Seebeck coefficient and power factor of (Na 1Ày Li y ) 1.4 Co 2 O 4 at 288 K achieve their maximum values of 172.28 lV K À1 and 7.44 mW m À1 K À2 at a doping fraction of y = 0.4.

To release the environmental pressure from the massive discharge of bauxite residue (red mud), a novel recycling method of red mud in steel making process was investigated through high-temperature experiments and thermodynamic analysis. The results showed that after the reduction roasting of the carbon-bearing red mud pellets at 1100-1200 • C for 12-20 min, the metallic pellets were obtained with the metallization ratio of ≥88%. Then, the separation of slag and iron achieved from the metallic pellets at 1550 • C, after composition adjustment targeting the primary crystal region of the 12CaO•7Al 2 O 3 phase. After iron removal and composition adjustment, the smelting-separation slag had good smelting performance and desulfurization capability, which meets the demand of sulfurization flux in steel making process. The pig iron quality meets the requirements of the high-quality raw material for steel making. In virtue of the huge scale and output of steel industry, the large-scale consumption and zero-waste recycling method of red mud was proposed, which comprised of the carbon-bearing red mud pellets roasting in the rotary hearth furnace and smelting separation in the electric arc furnace after composition adjustment.

Low carbon high manganese steels with different Ce contents were melted in medium frequency vacuum induction furnace. The microstructures and mechanical properties of steels were studied by OM, SEM, EDS and mechanical property testing. The results showed that the microstructures of experimental steels were refined remarkably, inclusions distributed more finely and uniformly, the tensile strength and impact toughness of tested steels both improved greatly after the addition of Ce. Thermodynamic calculation results demonstrated that Ce contained inclusions were Ce2O3 and Ce3S4, which agreed well with the results observed by SEM and EDS. By analysis of two-dimensional lattice disregistry, it was shown that the lattice misfit parameter between δ-Fe and Ce2O3, Ce3S4 are less than 6 %, which indicated that Ce2O3 and Ce3S4 could effectively act as the heterogeneous nuclei of initial δ-Fe. Therefore, the microstructures were refined significantly and the mechanical properties were improved correspondingly in Ce-added low carbon high manganese steels.

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