A solid state nuclear magnetic resonance study of industrial inorganic pigments
Nuclear magnetic resonance has been used to look at a number of colourful ceramic pigment systems, most of which are sold commercially in large quantities. Doped zircon (ZrSi04) pigments were examined using 19F, 23Na, 29Si, 51 Y and 91Zr NMR. In these systems, paramagnetic species are incorporated into the sample in small quantities creating the colourful pigment. The impurity dopants in the systems studied either dope directly into lattice sites in the zircon, or form an extra chemical phase. NMR was able to distinguish between these two doping mechanisms in a number of doped zircon pigments. Most spectra showed effects which were due to the magnetic influence of paramagnetic colouring species, and the strength of the interaction depended on the magnetic moment of the ion containing the unpaired electron. In the case of vanadium doped zircon, the moment was small enough that it allowed extra contact shifted peaks to be resolved in the spectra which indicated that the y4+ colouring ion probably substitutes into both the tetrahedral Si04 site, and at the dodecahedral ZrOg site. This is of current interest, and many other spectroscopic and computational experiments have also been performed to elucidate which of the two sites y4+ is located at. A 17 O-enriched zircon sample was also synthesised through a sol-gel route, and the local environment at the oxygen sites was followed through zircon formation from the TEOS and Zr-isopropoxide precursors. A multinuclear approach looking at the llB, 23N a, 27 Al and 29Si isotopes within silver containing glasses was able to provide information about the coordination of the isotopes within the glasses. 109 Ag NMR was evaluated as an experimental technique for examining silver containing compounds. 119Sn NMR was used to quantify the amount of Sn(II) and Sn(IY) in orange coloured SnO-ZnO-Ti02 (TZT) produced pigments, and the colour of the sample was found to correlate with the width of the Sn(IV) peak. The level of Na2C03-loading in yellow coloured TZT pigments also influenced the Sn(IV) linewidth, indicating that Sn(IV) is likely to be responsible for the perceived colour of the pigment. 170-enriched Sn02 was also synthesised, and the 170 and 119Sn spectra allowed a measure of the crystallinity of the sample to be determined as it was successively heated to higher temperatures.