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| 1.
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論文
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土成, 昭弘 ; 保木井, 利之 ; 下林, 修 ; 金岡, 千嘉男
概要:
In a permeable MgO ceramic containing TiO_2 and Al_2O_3 as matrix MgO ・ Al_2O_3-2MgO・TiO_2 solid solutions were detected
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and no Al_2O_3・TiO_2 was observed. Therefore, the solid state reaction among MgO, TiO_2 and Al_2O_3 with excess MgO was studied at various firing temperatures. The formation mechanism of MgO・Al_2O_3-2MgO・TiO_2 solid solutions was studied from the results of interface reactions between MgO-TiO_2 and MgO-Al_2O_3. MgO・Al_2O_3-2MgO・TiO_2 solid solutions were detected at 1573-1673 K and increased with the firing temperature. 2MgO・TiO_2 was formed in the system MgO-TiO_2, but was not produced in the system MgO-TiO_2-Al_2O_3, because the amount of Mg diffusion at the interface of aggregate and matrix additives was not enough due to the large aggregate size of MgO. MgO・Al_2O_3 and 2MgO・TiO_2 formed at the interface between MgO-TiO_2 and MgO-Al_2O_3 decreased with the firing time at 1873 K. On the other hand, MgO・Al_2O_3-2MgO・TiO_2 solid solutions increased. Mg was recognized in the matrix without addition of MgO as a matrix. Al diffused in the layer of MgO-TiO_2, in opposition Ti diffused in the layer of MgO-Al_2O_3 by EPMA analysis. From the above results, the formation mechanism of a MgO・Al_2O_3-2MgO・TiO_2 solid solution was proposed; (1) Mg diffusion at the interface of MgO aggregate and matrix additives, (2) formation of MgO・TiO_2 and MgO・Al_2O_3, (3) formation of 2MgO・TiO_2 due to the reaction with MgO・TiO_2 and MgO, (4) reaction of the solid solution with MgO・Al_2O_3 and 2MgO・TiO_2. In the reactions between MgO・TiO2 and MgO-Al_2O_3 the product layer of MgO・Al_2O_3-2MgO・TiO_2 solid solution increased as the firing time increased. The diffusion coefficient of Mg was about 4.8×10^<-7>(cm^2/s), in a good agreement with that of Mg which was reported.
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| 2.
論文 |
論文
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土成, 昭弘 ; 保木井, 利之 ; 下林, 修 ; 金岡, 千嘉男
概要:
Changes in the structure and physical properties of porous magnesia ceramic containing TiO_2-Al_2O_3 matrix with TiO_2-Al_2O_3 molar ratio 0.96 and 15 wt% content were studied at different sizes and firing temperatures for controlling
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the pore shape. The shape of pore was complicated depending on the grain size and firing temperature, and pores were found to have a fractal nature. While the fractal dimension increased with increasing firing temperature for small grains, it decreased with increasing firing temperature for large grains. The fractal dimension of each MgO grain size tends to converge at a lower firing temperature which is close to the temperature at which the MgAl_2O_4-Mg_2 TiO_4 solid solution is formed. Specimens with small grains were found to shrink on firing, but the expansion was observed for large grained specimens. These phenomena were explained by the densification and molar volume of MgAl_2O_4-Mg_2TiO_4 solid solution and CaTiO_3 formed. From the above facts, it was possible to controll the pore shape by grain size and firing temperature.
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| 3.
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論文
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土成, 昭弘 ; 保木井, 利之 ; 下林, 修 ; 金岡, 千嘉男
概要:
Changes in the structure and permeability of porous magnesia ceramic with a TiO_2-Al_2O_3 matrix with a TiO_21Al_2O_3 molar ratio of 0.96 were studied at different matrix contents. The shape of pores became complicated and pores
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tended to have fractal nature as the matrix content increased. It was proposed that the change of pore shape was caused by the increase in the amount of the matrix and its reaction with MgO grains. Both mean pore diameter and permeability showed a maximum at a matrix content, 10 wt% and 15%, respectively. On the other hand, the fractal dimension of pore shape changed from 1.39 at 5 wt% to 1.65 at 20 wt% of matrix. The fractal dimension changed sharply between 10-15 wt%. The permeability was found to agree well with that of a nonspherical particle system by using pore size modified by the its fractal dimension.
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| 4.
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論文
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土成, 昭弘 ; 保木井, 利之 ; 平木, 外二 ; 金岡, 千嘉男
概要:
Properties of permeable magnesia refractory containing titania and alumina powder in the matrix were investigated in order to produce permeable refractory with high thermal shock resistance, corrosion resistance and low penetration of
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molten steel. By adding titania and alumina powder in the matrix, bright glossy portion and dark glossy portion were observed in the matrix and in the grain boundary of magnesia. Bright glossy portion was CaTiO_3 (Perovskite) from X-ray diffraction and EPMA analyses. Dark glossy portion was suspected to be Al_2TiO_5 (Aluminum Titanate) from EPMA analyses although Al_2TiO_5 was not detected by X-ray diffraction. The collapse of magnesia grains was caused by the generation of CaTiO_3 and Al_2TiO_5 in the magnesia grain boundary. Apparent porosity, mean; pore diameter and permeability became high and large as TiO_2/Al_2O_3 molar ratio decreased, and reached the maximum value at the equivalent molar ratio. However, above the equivalent molar ratio the values became low and small. Permeability was proportional to the product of apparent porosity and the square of average pore diameter. Thermal shock resistance increased twice compared with no addition of TiO_2/Al_2O_3. Although corrosion resistance deteriorated by adding TiO_2/Al_2O_3, it was superior to the conventional porous alumina refractory. Penetration thickness of molten steel was not dependent on TiO_2/Al_2O_3 addition, and was very small compared with conventional one. This permeable magnesia refractory will have a good possibility of being used on actual operation.
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