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Effects of magnesia and calcium aluminate cement on the hydration of aluminium powder in castables matrix
Hydration behaviour of Al powders after 6h at 40 deg C in water containing different amounts of MgO or CAC (0 to 4 wt% of Al amount) has been investigated, and the effect of MgO or CAC on Al hydration discussed. Al(OH)3 was identified as the main hydration product. The presence of MgO or CAC did not change the hydration product, but greatly accelerate the hydration rate of Al. Addition of even a small amount (e.g. 0.25 wt%) of MgO or CAC to water accelerated significantly the hydration of Al, and with increasing level of MgO or CAC to 4 wt%, the hydration extent increased markedly. The results were attributed to two reasons. Firstly a more basic water solution due to the presence of MgO or CAC accelerated dissolution of the natural Al2O3 film and early Al(OH)3 hydration product, decreasing the thickness of protective layers and/or exposing new Al surface. Another is that the heat released by the hydration of MgO, CAC and Al hydration increased the local temperature at the water/Al interface. Due to the accelerating effect of MgO or CAC, an optimum amount of Al with appropriate surface reactivity should be used in the castable systems containing MgO or CAC. On the other hand, this accelerating effect would make it more difficult to use Al as an antioxidant for MgO-C castables, so techniques to improve the hydration resistance of Al should be developed. The accelerated hydration of Al will also adversely affect the hydration of MgO or CAC, and thus affect e.g. the castables setting behaviour.
Effects of magnesia and calcium aluminate cement on the hydration of aluminium powder in castables matrix
Hydration behaviour of Al powders after 6h at 40 deg C in water containing different amounts of MgO or CAC (0 to 4 wt% of Al amount) has been investigated, and the effect of MgO or CAC on Al hydration discussed. Al(OH)3 was identified as the main hydration product. The presence of MgO or CAC did not change the hydration product, but greatly accelerate the hydration rate of Al. Addition of even a small amount (e.g. 0.25 wt%) of MgO or CAC to water accelerated significantly the hydration of Al, and with increasing level of MgO or CAC to 4 wt%, the hydration extent increased markedly. The results were attributed to two reasons. Firstly a more basic water solution due to the presence of MgO or CAC accelerated dissolution of the natural Al2O3 film and early Al(OH)3 hydration product, decreasing the thickness of protective layers and/or exposing new Al surface. Another is that the heat released by the hydration of MgO, CAC and Al hydration increased the local temperature at the water/Al interface. Due to the accelerating effect of MgO or CAC, an optimum amount of Al with appropriate surface reactivity should be used in the castable systems containing MgO or CAC. On the other hand, this accelerating effect would make it more difficult to use Al as an antioxidant for MgO-C castables, so techniques to improve the hydration resistance of Al should be developed. The accelerated hydration of Al will also adversely affect the hydration of MgO or CAC, and thus affect e.g. the castables setting behaviour.
Effects of magnesia and calcium aluminate cement on the hydration of aluminium powder in castables matrix
Zhang, Shaowei (author) / Hashimoto, Shinobu (author) / Lee, William E. (author)
2003
4 Seiten, 5 Bilder, 6 Quellen
Conference paper
English
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