High temperature 27Al NMR time resolved study. Application to the CaO-Al2O3 binary system

27Al NMR spectra have been acquired during the cooling of four liquid samples (12CaO-7Al2O3, CaO-Al2O3, CaO-2Al2O3, CaO-6Al2O3) from 2400 K to supercooled liquid and then glass or crystal. Both CaO-2Al2O3 and CaO-6Al2O3 crystallize and a crystallization rate of 105 g.s-1 can be estimated for the latter. For each compound, the chemical shift values evolve linearly with temperature. The chemical shift/temperaturc slope is minimum for CaAl2O4, the more polymerized liquid of the system. For 12CaO-7Al2O3 (the only observed compound with X(CaO)/X(Al2O3)>1), the slope increases again. The slope evolution with alumina rate is similar to that observed for viscosity at high temperature, signifying a possible relation between both phenomena. For CaO-Al2O3, the study of NMR characteristic time calculated from relaxation measurements and shear correlation time deduced from viscosity in the liquid shows that these two phenomena have the same microscopic origin.