Abstract
The aging of hydrated Ca-montmorillonite clay samples doped with Mn 2+ impurity ions has been investigated using 9 GHz CW EPR. It is shown that these clay samples are unstable in time when characterised by their EPR g-values and linewidth ΔB pp parameters and are extremely sensitive to the storage and measurement pressure. The EPR linewidth temperature dependence was investigated in the 20°C to 180°C interval. Up to the 120°C, random tumbling of Mn (H 2O) 6 2+ complexes narrows the EPR spectral lines. Rotational modulation relaxation is responsible for significant further line narrowing above 120°C where the dehydration process decreases the interlamellar spacing to below 1.2 nm. Storage and measurement of samples below atmospheric pressure shifts this process to lower temperatures.
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