Influence of magnetic impurities on proton spin relaxation of water in clay |
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Authors: | K Nagashima |
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Institution: | 1. Tokyo Magnetic Resonance Inc., Tokyo and Port and Airport Research Institute, 31 Daikyo-cho, Shinjuku, 160-0015, Tokyo, Japan
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Abstract: | The1H nuclear magnetic spin relaxation of water in slurry of kaolin clay was investigated in the presence of magnetite (black
iron oxide, Fe3O4) at 0.2 T and room temperature. The water spectra at high magnetite contents showed two different resonances, presumably
from surface-associated water and free interstitial water. The difference in observed resonance frequencies increased as much
as 200 ppm with increasing magnetite content. The apparent nuclear magnetic resonance intensity decreased biexponentially
as a function of magnetite added. The observedT
2* values at low magnetite contents were in accordance with the predicted values from the resonance intensities and the estimated
magnetic susceptibilities. TheT
1 relaxation was multiexponential in character, so a uniform penalty program was used for the analysis of distribution. At
0.2 T for1H, kaolin slurry containing less than 5.5 ppm magnetite did not differ significantly from magnetite-free clay in the longitudinal
relaxation rates of water. However, higher concentrations of magnetite produced features in theT
1 distribution significantly different from those of magnetite-free clay. TheT
2 could be approximated by monoexponential relaxation, probably because the fast-decaying components relaxed before they could
be recorded. The apparent transverse relaxation ratesR
2 increased linearly as a function of magnetite content. On the basis of the comparison of spin-echo and Carr-Purcell-Meiboom-Gill
data, an empirical relation was derived to describe the signal loss due to diffusion. It can be expressed by a power function
of magnetite amount, which is multiplied by the sum of volume-dependent and volume-independent terms. |
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Keywords: | |
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