A TIME-RESOLVED AL-27 NMR-STUDY OF THE COOLING PROCESS OF LIQUID ALUMINA FROM 2450-DEGREES-C TO CRYSTALLIZATION

Nuclear magnetic resonance is able to give insight into the structure and dynamics of liquids at very high temperature (T > 2000 degrees C). Al-27 NMR spectra have been recorded every 25 ms during the cooling o f an aerodynamically levitated liquid alumina droplet from 2450 degree s C to crystallisation in less than 3 s. The temperature is measured j ointly by pyrometry and NMR, and this time resolved experiment provide s a unique way of exploring the temperature dependence of both the str ucture (shift) and the dynamics (relaxation time of Al-27 Of the liqui d and the supercooled liquid alumina until the crystallisation of alph a-Al2O3. The apparent Arrhenian activation energy of 130 kJ mol(-1), d erived from T-1 measurement, is understood as the signature of the mac roscopic viscosity in this high temperature liquid.