Abstract
During the pyrolysis of cured hydridopolysilazane (HPZ) polymer to form Si–C–N ceramic fibers, large quantities of unpaired electrons are produced. For such materials dynamic nuclear polarization (DNP) provides a means of enhancing the intensity of the NMR signal, and supplies information on the localization or delocalization of unpaired electrons. 29Si, 1H, and 13C DNP gives enhancements of 250 for 13C and at least 800 for 29Si. 13C and 29Si DNP-DPMAS experiments yield the following results: (i) there are at least two distinct types of carbon, sp2 and sp3; (ii) there is a distribution of sp3 silicon environments; (iii) the unpaired electrons behave as fixed paramagnetic centers; and (iv) the unpaired electrons are distributed homogeneously throughout the sample. Proton DNP spectra can be obtained even though hydrogen is only a trace element in the finished ceramic.
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Lewis, R.H., Wind, R.A. & Maciel, G.E. Investigation of cured hydridopolysilazane-derived ceramic fibers via dynamic nuclear polarization. Journal of Materials Research 8, 649–654 (1993). https://doi.org/10.1557/JMR.1993.0649
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DOI: https://doi.org/10.1557/JMR.1993.0649