The crack growth resistance of the bricks in MgO-C refractory bricks containing 1.5％ C （carbon black） on were investigated based on the principles of fracture mechanics. R-curves were determined and evaluated. R-curves were determined and evaluated based on notch width changes, and the critical stress intensity was calculated from the R-curves. The critical stress intensity factor in the reference sample exhibited the highest value, whereas the sample whose aggregate contents were respectively 1.6 times higher than that in the reference sample exhibited the second highest. The bridging stress, which indicates the bridging effect of the aggregate, clearly increased when the aggregate content was increased. Based on a roughness analysis, it is predicted that the bridging stress will increase when the ratio of aggregate in the refractory increases because more sites for the action of pullout force and frictional force exist on the crack surface. In conclusion, it was predicted that it will be desirable to increase the content of aggregate in the refractory with keeping the higher strength of matrix so as to provide the refractory with excellent resistance for dynamic thermal fatigue..

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Studying the dissolution mechanism of MgO in steelmaking slag is vital to reduce refractory damage in basic oxygen furnaces. In many cases, a FeO-MgO layer is formed at the interface between MgO and steelmaking slag. In this research, the dissolution rates of the FeO-MgO solid solution in molten slag were investigated by changing the composition of solid solution and slag. The following results were obtained. （1）the FeO-MgO solid solution was not stable and dissolved into slag. The dissolution rate increased with increasing FeO content in the slag, and decreased with increasing MgO content in the slag. （2）In every case, the FeO content of the solid solution near the interface of slag was higher than that in bulk. （3）A clear relation was found between FeO content in the solid solution near the interface and the dissolution rate. The FeO content in the solid solution near the interface can be considered an important factor that controls the dissolution rate. （4）A fairly good relationship was found between the FeO activity difference between the solid solution near the interface and slag bulk and the differences in FeO content between the solid solution near the interface and slag bulk．

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A porous ceramics with cylindrical pores and incorporating pores were fabricated through unidirectional solidification of aqueous ceramics powder slurry containing CO2 gas, vacuum freeze drying and sintering process. The cylindrical pores were formed during the unidirectional solidification under reduced pressure and a composite of ice and ceramics powder was obtained. Since the composite was formed by segregation of ice during the solidification, an incorporating structure of ice was obtained. The ice was removed by vacuum freeze drying method. The porous green body with cylindrical pores and incorporating pores was sintered at 1250℃ C for 5 hours. The porosity and pore size was well controlled by the pressure during the solidification and sintering temperature and time.

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