Influences Of Matrix Microstructure Parameters On Thermal Properties Of Corundum Based Castables

In this paper, the thermal properties of corundum based castables bonded by calcium aluminate cement (Secar 71 cement) andρ-Al₂O₃ were studied. This paper includes three parts: Influence of pore structure parameters on thermal conductivity of corundum based castables; Influence of several typical microstructure parameters on thermal expansion properties and the thermal shock resistance of corundum based castables.Firstly, the influence of pore structure parameters of the corundum based castables bonded by calcium aluminate cement (Secar 71) andρ-Al₂O₃ on thermal conductivity was studied through adjusting particle size distribution, heating treatment temperature and the content of dextrin additive contents. Research results indicate that, the apparent porosity and median pore diameter were both increased as the increase of heating treatment temperature and dextrin content; as the critical particle size increased, the packing density of the castable sample become higher and the sintering became more significant, thus, the apparent porosity was decreased, and the median pore diameter was increased. It was found that the thermal conductivity of the castable samples in room temperature was decreased as the apparent porosity and the median pore diameter increased, and the variation of the critical particle size does not affects the changing tendency of the thermal conductivity, but it affects the numerical value of the thermal conductivity. In contrast to the median pore diameter, the apparent porosity affects the thermal conductivity significantly. Besides, the grey interrelation degree between the pore size of 3⁹μm and the thermal conductivity of corundum based castables bonded byρ-Al₂O₃ is high.Because under the same temperature gradient, all aluminum oxygen octahedron in the coru- ndum based castable samples has the same cumulative expansion ratio, the linear expansion ratio of all samples is quite similar. As the increase of reactiveα-Al₂O₃ micro powders'content and t- he increase of critical particle size, the average expansion coefficient of samples was increased. When the content of large particle within castable samples increases, the average expansion coe- fficient of samples was decreased firstly, and then will be tended to accordance. The average ex- pansion coefficient of corundum based castables bonded by Secar 71 cement andρ-Al₂O₃ are all decreases with the increase of the apparent porosity.Sintering densification of samples byρ-Al₂O₃ decreases internal micro-pore and increases the amount of large pore, which improves the thermal shock resistance due to enhanced passiva- tion of thermal shock crack tip and enhanced ability of releasing thermal stress, thus, with the hi- gher heating treatment temperature, the residual modulus of rupture of samples after water cooli- ng test can keep higher. The original cracks and cracks caused by test expand aggressively under continued thermal stress caused by increased number of air cooling cycles. Some cracks are even transcrystalline. All of these effects reduce thermal shock resistance of samples. The introduction of polystyrene hollow balls can adjust the apparent porosity of samples, which can improve the thermal shock stability performance of .For theρ-Al₂O₃ bonded castable samples, with the incre- asing of polypropylene hollow balls additive content, the residual modulus of rupture of the sam- ples decreases at first and then increases. The additive of polystyrene hollow balls results in hig- her apparent porosity of castable samples. For the Secar 71 cement bonded castable samples, the residual modulus of rupture of samples increases at first and then decreases later, and finally will be kept on a stable level.