The microporous refractory with low thermal conductivity shows a promising application prospect as tundish lining. In this study, the interactions between microporous magnesia aggregates and oxide inclusions in steel were explored. The experimental results and thermodynamic calculation show that the interaction process of microporous magnesia aggregates and oxide inclusions at high temperature can be divided into dissolution, reaction and post-reaction. The microporous magnesia aggregates can absorb the inclusions in steel by reaction and liquid phase penetration. The microporous magnesia aggregates have a strong adsorption for Al 2 O 3 and TiO 2 . Moreover, the microporous magnesia aggregates mainly absorb SiO 2 by penetration, but excessive SiO 2 will lead to the serious corrosion of microporous magnesia aggregates.
As a promising thermoelectric material, aluminum-doped zinc oxide (AZO) exhibits high thermal conductivity , which limits its use in high-temperature thermoelectric applications. Here, we report an effective route for forming a porous architecture and nanoinclusions by introducing nano-SiC to reduce the thermal conductivity . The simultaneous formation of a porous architecture and nanoinclusions promotes enhanced phonon scattering, resulting in fairly low thermal conductivity of approximately 3.3 W⋅ m −1 ⋅ K −1 . Meanwhile, the Seebeck coefficient shows the significant improvement due to energy filtration effect caused by porous architecture and nanoinclusions. The resultant dimensionless figure of merit of approximately 0.2 at 1050 K was 1.5 times higher than that of AZO ceramic without nano-SiC, which is attributed to the combined factors of increased Seebeck coefficient and reduced thermal conductivity .
Mold flux serves the crucial metallurgical function of absorbing inclusions, directly impacting the smoothness of the casting process as well as the cast slab quality. In this study, the dissolution behavior and mechanism of TiO 2 and TiN inclusions in molten CaO–SiO 2– B 2 O 3 -based fluorine-free mold flux were explored by in situ single hot thermocouple technology combined with X-ray photoelectron spectroscopy. The results showed that TiO 2 inclusions are effectively dissolved by the molten slag within 76 s, during which the original octahedral [TiO 6 ] 8− structures are destroyed and convert to the networker tetrahedral [TiO 4 ] 4− structures. However, the dissolution rate is much lower for TiN inclusions than for TiO 2 inclusions. This can be attributed to the fact that the TiN particles need to be oxidized and then dissolved in the molten slag to form tetrahedral [TiO 4 ] 4− and octahedral [TiO 6 ] 8− structures during the TiN inclusion dissolution process, which is accompanied by the generation of a large amount of N 2 gas. Moreover, CaTiO 3 crystals tend to nucleate and grow on bubble surfaces with sufficient octahedral [TiO 6 ] 8− structures and Ca 2+ ions, eventually resulting in the molten slag being in a solid–liquid mixed state.
The dissolution mechanism of Al 2 O 3 inclusions in molten slags was explored by in-situ single hot thermocouple technique combined with X-ray photoelectron spectroscopy. Result shows that it takes 2940 s to completely dissolve Al 2 O 3 inclusions in the molten F-bearing mold flux, which is mainly controlled by boundary layer diffusion. Because the connected [AlO 6 ] octahedra in the Al 2 O 3 inclusion is gradually destroyed by the O 2− ions in the melt. By comparison, the CaO–SiO 2 –B 2 O 3 based F-free mold flux only takes 840 s to completely dissolve Al 2 O 3 inclusions. Because the [AlO 6 ] octahedra is destroyed and further transformed to [AlO 4 ] tetrahedra and produce O 2− ions, which greatly facilitates the dissociation of the Al 2 O 3 particle. However, the formed [AlO 4 ] tetrahedra will promote the precipitation of the dense 2CaO·SiO 2 ·Al 2 O 3 crystals, which tightly encases the Al 2 O 3 particle and causes significant drop in the dissolution rate. Thus, the dissolution rate is controlled by chemical reaction and then by boundary layer diffusion.
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