Laser-heated high-temperature NMR - a time-resolution study

The time resolution achievable in in-situ high-temperature nuclear magnetic resonance (NMR) experiments is investigated using laser heating of refractory materials. Three case studies using 27Al in alumina nano-particles, 29Si in silicon carbide and 23Na in a glass-forming mixture of sodium carbonate and quartz have been conducted to distinguish the cases of (a) a fast-relaxing, high natural abundance nucleus, (b) a probe nucleus with low abundance and low spin-lattice relaxation rate, and (c) a complex and changing system of industrial relevance. The most suitable nucleus for in-situ high-temperature studies is one with high abundance but slow relaxation because the differential relaxation time between hot and cold parts of the sample effectively removes the signal from the cold material. There is no ``in-situ penalty'' from the diminishing Boltzmann polarisation at high temperature since this effect is balanced by a corresponding increase of the spin-lattice relaxation rate.