Abstract :
Hydration behaviour and antioxidising effect of aluminium (Al) powder has been
investigated. Bayerite Al(OH)3 product layers formed on Al 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 further increasing temperature from 45 to 95°C, initial
hydration rate increased, but changed little over long hydration periods due to formation of
denser and more continuous product layers. At 100°C, due to rapid water evaporation, hydration
product layers (composed of Al(OH)3 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 Al. Addition of even a small amount
(e.g. 0.25wt% 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 SiO2
coatings on Al were useful in improving the hydration resistance of Al, and did not have a negative
effect on the behaviour of Al as an antioxidant.
