STUDIES OF 29Si SPIN-LATTICE RELAXATION TIMES AND PARAMAGNETIC IMPURITIES IN CLAY MINERALS BY MAGIC-ANGLE SPINNING 29Si-NMR AND EPR

Abstract

High-resolution solid state 29Si-NMR spectra and EPR spectra have been examined on twelve natural philosilicates. It has been found that presence of paramagnetic impurities is markedly effective in shortening the 29Si spin-lattice relaxation times (10 to 1000 ms), and in broadening the linewidths and is favorable for the use of solid state high-resolution 29Si NMR as a tool for structural studies of inorganic materials.

Further Consideration of the 29Si Nuclear Magnetic Resonance Spectrum of Kaolinite

“…The difference plots (Figure 2) provided the clearest illustration of any change in 29Si spectra compared with overall signal-to-noise. No significant trend in resolution vs. crystallinity index (Hinckley, 1963) was observed, however, the overall peak width did appear to depend on the sample Fe content (Table 1), in agreement with Watanabe et al (1983). ESR spectra of the five kaolinites were very similar and consistent with a majority of the Fe being present as Fe 3+ substituting for A13 § in the octahedral sites of kaolinite.…”

“…Particular care was taken to monitor the effect of Fe content on the :9Si NMR spectra in view of the findings of Oldfield et aL (1983), Watanabe et al (1983), and Fyfe et aL (1984). Compositions were determined by atomic absorption spectrometry (AAS) analysis.…”

“…Thompson (1984a) subsequently demonstrated that this resolution was due to interlayer effects: overlap of tetrahedral sites in one layer with occupied or unoccupied octahedral sites in the adjacent layer, or hydrogen-bonding effects at the silicate surface. Barron et al (1983) also noted different levels of signal splitting for different kaolinite polymorphs, and Watanabe et al (1983) observed a correlation between the kaolinite signal width and the Fe content of the sample.…”

Structural Analysis of Mixed Alkali Silicate Melts through ²⁹Si MAS-NMR and Impedance Measurements

“…21) However, this time can be shortened by the addition of paramagnetic materials, as these materials are sources of spin diffusion. 22) Thus, in this study, 0.1 wt% of the paramagnetic Fe 2 O 3 was added to shorten this relaxation time. 29 Si MAS-NMR spectra were obtained using a JNM-ECA400 (9.4 T) spectrometer operating at the Larmor frequency of 79.4 MHz.…”

Evidence of 29Si NMR paramagnetic shifts in rare-earth zeolite LSX

“…2 The effects of magnetic impurities on the 29 Si NMR spectra of alumino-silicates are well known. They decrease the spinlattice relaxation, substantially broaden the resonance line as a function of the concentration of impurities, 3 and enhance the spinning-sideband patterns. 4 High concentrations of paramagnetic species in zeolites make the acquisition of NMR spectra difficult and, in general, the signal of nuclei in the neighbourhood of paramagnetic centers is not detected.…”