Abstract
The wettability and the reaction between molten Al and Al2O3-SiO2 substrates were measured by the sessile drop method in a vacuum of 2×10−3 Pa at temperatures from 973 to 1173 K. The contact angles of molten Al to Al2O3 and Al2O3-SiO2 substrates decreased from about 110° to 90° as the temperature rose from 973 to 1173 K. The reaction between molten Al and NC mullite, which consisted of mullite and vitreous SiO2, produced a mixed layer of Al2O3 and mullite. The reaction layer grew in proportion to the holding time at 973 K. The linear growth was also recognized until 300 s at 1073 K, and the growth rate was controlled by the chemical reactions:3SiO2+4Al=3Si+2Al2O33(3Al2O3·2SiO2)+8Al=6Si+13Al2O3On the contrary, at 1173 K or after 300 s at 1073 K, the reaction layer grew parabolically with the increase in time. The growth rate was controlled by the diffusion of Al and Si through the reaction layer.The uniform Al2O3 layer formed between molten Al and mullite substrate at 1173 K after an incubation period. The growth rate was also governed by the diffusion of Al and Si.The Si pickup by Al drop was estimated by the thickness of the reaction layer between molten Al and NC mullite or mullite substrate.
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