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In this contribution the effect of In2O3 additions on the microstructure, physical, and electrical properties of the SnO2-Co3O4-Ta2O5 ceramic system was investigated. Since the effect of In2O3 has been studied typically at low levels, special attention has been paid to the effect of high levels (1 and 2 mol % In2O3) in the ceramics. Results show that up to 0.1 mol % In2O3, an increase of indium oxide content is correlated with grain size reduction and an increase of the nonlinearity coefficient (a) and breakdown voltage (EB), producing an augmentation by a factor of 2 in the nonlinearity coefficient and an increment by a factor of 8 in the breakdown voltage. However, shrinkage () and measured density are not influenced by the addition of indium oxide. For samples with 1 and 2 mol % In2O3, in non-calcined condition, In2O3 is present with cubic structure. However, in calcined specimens, In2O3 is not detected anymore and SnO2-crystal structure undergoes a change from tetragonal to cubic. These ceramic samples exhibit high resistivity, behaving like dielectric materials.

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Iron oxide (Fe 2 O 3 , 20-40 nm), aluminum oxide (Al 2 O 3 , 50 nm) and silicon oxide (SiO 2 , 20-60 nm) nanoparticles were mixed in different concentrations (1 to 5 wt %) in a magnesium oxide matrix to develop new refractory matrixes as candidates in the lining of secondary ladle metallurgy. To avoid agglomeration of nanoparticles in the magnesium oxide (MgO) matrix, it was carried out a dispersion method of nanoparticles with different dispersants. After that, the powder mixture was sintered at a temperature of 1300 and 1500 °C for 4 hours. The refractory samples obtained were studied using X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectrometer (SEM-with EDX) and also measured their density and porosity. The results showed that the samples sintered at 1500 °C with 5 wt % of Fe 2 O 3 reached the highest density and presented the MgFe 2 O 4 spinel-type phase. With the addition of Al 2 O 3 -nanoparticles in the MgO matrix, there were the formation of MgAl 2 O 4 spinel phase and in the case of SiO 2 -nanoparticles addition it was observed the formation of Mg 2 SiO 4 forsterite phase. It is well known that with the increase in spinel phase in the matrix, there is a significant help to retain quantities of ions of iron and nickel due to the dissolution of the slag into the refractory material extending their lining life.