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

Hydration behaviour and antioxidising effect of aluminium (ai) powder has beeninvestigated. bayerite ai(oh)3 product layers form ed on ai in pure water at 25-45 °c wereporous, so the hydration rate, although very slow at 25°c, increased rapidly with increasingtemperature from 25 to 45°c. on furth er increasing temperature from 45 to 95°c, initialhydration rate increased, but changed little over long hydration p eriods due to formation ofdenser and more continuous product layers. at loo°c, due to rapid water evaporation, hydrationproduct layers (composed ofai(oh)3 and a small amount ofboehmite aio(oh) became detachedfrom the ai surf aces, so offering less protection, so that the hydration rate of ai increasedmarkedly. the presence ofmgo or calcium aluminat e cement (cac) in water did not change thehydration 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 si02coatings on ai were useful in improving the hydration resistance ofai, and did not have a negativeeffect on the behaviour ofai as an antioxidant.