Journal of Materials Science, Vol.52, No.11, 6767-6777, 2017
Anorthite (CaAl2Si2O8)-aluminum interface: kinetics of high-temperature interactions
The kinetics of the anorthite-Al system have been examined by exposing anorthite to pure Al at 850-1150 A degrees C for 0.5-250 h. The interfaces were investigated by electron microscopy (SEM, EDS, EPMA, and TEM). The results showed that Si4+-Al3+ interdiffusion and associated oxygen vacancies plus Ca2+-Al3+ interdiffusion and associated calcium vacancies drove the anorthite -> CA2 and the CA2 -> A (alumina) transformations, respectively, at 850 and 950 A degrees C. At 1050 and 1150 A degrees C, increased solubilities of silicon and oxygen in the liquid Al resulted in significant formation of CA2, which, when in contact with anorthite, leads to formation of gehlenite. Si4+-Al3+ interdiffusion was identified as the controlling process of the anorthite-Al interactions and so it has been quantified in terms of the activation energy of Q = 112 kJ/mol and the diffusion coefficient pre-factor of D (0) = 4 x 10(-8) m(2)/s.