HIGH-TEMPERATURE AL-27 NMR TIME-RESOLVED STUDY - APPLICATION TO THE CAO-AL2O3 BINARY-SYSTEM

Al-27 NMR spectra have been acquired during the cooling of four liquid samples ((CaO)-Ca-12-7Al(2)O(3), CaO-Al2O3, CaO-2Al(2)O(3), CaO-6Al(2 )O(3)) from 2400 K to supercooled liquid and then gla ss or crystal. B oth CaO-2Al(2)O(3) and CaO-6Al(2)O(3) crystallize and a crystallizatio n rate of 105 g.s(-1) can be estimated for the latter. For each compou nd, the chemical shift values evolve linearly with temperature. The ch emical shift/temperature slope is minimum for CaAl2O4, the more polyme rized liquid of the system. For (CaO)-Ca-12-7Al(2)O(3) (the only obser ved compound with X(CaO)/X(Al2O3)>1), the slope increases again. The s lope evolution with alumina rate is similar to that observed for visco sity at high temperature, signifying a possible relation between both phenomena. For CaO-Al2O3, the study of NMR characteristic time calcula ted from relaxation measurements and shear correlation time deduced fr om viscosity in the liquid shows that these two phenomena have the sam e microscopic origin.