Laser-Heated High-Temperature NMR: A Time-Resolution Study

Abstract

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 27 Al in alumina nano-particles, 29 Si in silicon carbide and 23 Na 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.

Oxygen-17 nuclear magnetic resonance measurements on apatite-type lanthanum silicate (La9.33(SiO4)6O2)

“…The process of data acquisition started after the sample was heated at the desired temperature. Here, we do not describe the experimental details and the equipment used for the HT experiments [22,23]. The obtained MAS, MQ-MAS, and HT static NMR spectra were analyzed using the DMFIT program [24].…”

27Al Pulsed Field Gradient, Diffusion–NMR Spectroscopy of Solvation Dynamics and Ion Pairing in Alkaline Aluminate Solutions

“…Consequentially, nuclei with low gyromagnetic ratios necessitate the application of strong PFGs (approximately 15 times stronger for the case of 27 Al) to attenuate the resonance compared to a proton ( 1 H) resonance exhibiting identical diffusivity. Secondly and more importantly, quadrupolar nuclei exhibit fast spin–lattice ( T 1 , longitudinal) and spin–spin ( T 2 , transverse) relaxations which lead to poorly measurable signal intensity due to signal loss during the mixing time due to T 2 ( T 1 ) ≪ Δ. These relaxations tend to be enhanced in high concentrated electrolytes, and at the liquid–solid interfaces because of the host–guest interactions in physically confined systems. , These relaxations are especially enhanced because of an asymmetric solvation structure of quadrupolar nuclei such as 27 Al ( I = 5/2), 23 Na ( I = 3/2), and 25 Mg ( I = 5/2), etc.…”