HYDRATION BEHAVIOUR AND ANTIOXIDISING EFFECT OF ALUMINIUM POWDER ADDED TO OXIDE- AND CARBON-BASED CASTABLES

Hydration behavior and antioxidising effect of aluminium (AI) powder has been investigated. Bayerite Al (OH) ۳ product layers formed on Al in pure water at ۲۵-۴۵°C were porous, so the hydration rate, although very slow at ۲۵°C, increased rapidly with increasing temperature from ۲۵ to ۴۵°C. On further increasing temperature from ۴۵ to ۹۵°C, initial hydration rate increased, but changed little over long hydration periods due to formation of denser and more continuous product layers. At ۱۰۰?C, due to rapid water-evaporation, hydration product layers (composed of Al (OH)۳ and a small amount of boehmite AlO (OH) became detached from the Al surfaces, so offering less protection, so that the hydration rate of Al increased markedly. The presence of MgO or calcium aluminate cement (CAC) in water did not change the hydration product, but greatly accelerate the hydration rate of AI. Addition of even a small amount (e.g. ۰.۲۵ wt% of Al amount) of MgO or CAC to water accelerated significantly the hydration of Al, and with increasing level of MgO or CAC, the hydration extent increased markedly. Sol-gel Si۰۲ coatings on Al were useful in improving the hydration resistance of Al, and did not have a negative effect on the behavior of Al as an antioxidant.

کلیدواژه ها:

Hydration mechanism ، Oxide carbon Refractories ، Anti ، oxidant