NMR quantification in hydrothermal in situ syntheses

The considerable development of microporous materials by hydrothermal synth esis led us to develop appropriate devices to perform NMR in situ observati on of the species during the synthesis. The 'hydrothermal NMR tube' is a 10 mm outer diameter tube acting as an autoclave, withstanding temperatures a nd pressures common to these classes of syntheses and also the corrosive co nditions of hydrofluoric acid containing media. During synthesis NMR chemic al shifts and signal areas are monitored. It is therefore important to achi eve quantitative NMR measurements while synthesis proceeds. On increasing t he temperature of samples, considerable NMR signal loss occurs as a consequ ence of Curie's law. Dielectric constant and conductivity effects on signal Loss are reflected in the evolution of the quality factor of the probe. As the effects of temperature, concentration of solutes and pH on NMR respons es of aqueous samples are considerable, they were therefore carefully studi ed. The relations between acquisition conditions, transmission and receptio n and experimental NMR amplitudes were elucidated. A calibration method tha t does not make use of an internal reference and which is based on relative variations of the Q factor of the r.f. circuit leads to efficient spin cou nting. This method was successfully applied to quantifying the hydrolysis o f aluminum at variable temperature, monitoring Al-27 to follow hydrolysis a nd condensation processes. Copyright (C) 2000 John Wiley & Sons, Ltd.