Magnesia is easy to be hydrated when added to castable because it is exposed to heated steam in drying process and it leads to collapse of the structure. In addition, magnesia, as a raw material, is originally partially hydrated at start because it is exposed to moisture in the atmosphere when in storage. And this partial hydration of magnesia accelerates further hydration of magnesia in castable. Therefore, it is important to clarify mechanism and to control the hydration result from time-dependent change. In this paper, at first, influence of the time-dependent change in raw material stage on hydration rate of magnesia in castable under heated steam was investigated. As a result, castable employed magnesia whose hydration exceeded threshold level accelerated the hydration rate of magnesia in castable and collapsed under heat steam. On the other hand, castable employed preferentially carbonated magnesia didn’t collapse under heated steam. And it became possible to control hydration by application of pre-carbonated magnesia surface.

View full abstract

Silicon is generally added to the Al2O3-C system materials for slide gate plates to improve the mechanical strength and abrasion resistance under oxidation. The influence of the grain sizes of adding Si and firing temperatures on the mechanical properties of the material was studied. By adding the certain specified amount of Si to Al2O3-C system materials, the reaction of Si was enhanced more intensively with higher firing temperature and smaller grain size of Si. Consequently, the large amount of the reaction products such as β-SiC , SiO2 and Si2ON2 were formed in the materials. When the same mass ratio of Si was added to the material, the higher Si reaction ratio and the larger reaction products contributed to endow the higher mechanical strength to the materials. When the firing temperature is 1200℃ or less, much SiO2 is produced by the reaction of CO and SiO generated by the oxidation of the Si. On the other hand, at 1200℃ or more, SiO2 is decomposed to SiO react with CO, and reacts with the carbon in the matrix, and produce much SiC. The strength of the materials can be improved not by increasing the amount of Si but by adding finer Si grains being possible to enhance the Si reaction more intensively.

View full abstract