DETERMINATION OF WATER IN COALS BY MEANS OF PROTON SPIN RELAXATION MEASUREMENTS

The method developed is based on the fact that the initial amplitude of the 1H n.m.r. free induction decay (FID) is proportional to the total number of protons in the sample. The number of protons can be evaluated by comparison with measurements of liquid samples with a known proton concentration. To determine the fraction of water, the total FID signal observed after a single r.f. pulse was decomposed by means of a personal computer. To enable quantitative measurements of protons the FID signal was extrapolated to zero time, which occurs in the centre of the r.f. pulse. The validity of this procedure was checked by comparison with the time evolution of the n.m.r. solid echo signal. The amount of water thus determined was compared with the results of other measurements, i.e. by near-infrared spectroscopy, thermogravimetry, and Karl-Fischer titration. The number of protons belonging to the coal was also measured by this n.m.r. technique and compared with the results from elemental analysis. © 1990.