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HYDRATION BEHAVIOUR AND ANTIOXIDISING EFFECT OFALUMINIUM POWDER ADDED TO OXIDE- AND CARBON-BASEDCASTABLES

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Hydration behaviour and antioxidising effect of aluminium (AI) powder has been investigated. Bayerite AI(OH)3 product layers form ed on AI in pure water at 25-45 °C were porous, so the hydration rate, although very slow at 25°C, increased rapidly with increasing temperature from 25 to 45°C. On furth er increasing temperature from 45 to 95°C, initial hydration rate increased, but changed little over long hydration p eriods due to formation of denser and more continuous product layers. At lOO°C, due to rapid water evaporation, hydration product layers (composed ofAI(OH)3 and a small amount ofboehmite AIO(OH) became detached from the AI surf aces, so offering less protection, so that the hydration rate of AI increased markedly. The presence ofMgO or calcium aluminat e cement (CAC) in water did not change the hydration product, but greatly accelerate the hydration rate ofAI. Addition ofeven a small amount (e.g. 0.25wt% ofAI amount) ofMgO or CAC to water accelerated significantly the hydration ofAI, and with increasing level ofMgO or CAC, the hydration extent increased markedly. Sol-gel Si02 coatings on AI were useful in improving the hydration resistance ofAI, and did not have a negative effect on the behaviour ofAI as an antioxidant.

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