Calcium deficient hydroxyapatites were impregnated to varying degrees with fluoride in very dilute solutions of NaF at room temperature. Ca/P ratios were determined before and after fluoridation. Phosphate loss upon fluoridation was consistent with an initial mechanism of OH− vacancy filling by F−, with equivalent amounts of PO43− ions escaping to restore charge balance. Infrared measurements confirmed previous evidence of OH/F exchange and the formation of [Formula: see text] hydrogen bonds, which increased with progressive thermal activation, considerable exchange having occurred already at 120 °C and possibly below. The first signs of lattice collapse occurred near 600 °C, with the fluorided sample exhibiting somewhat better stability.

The decomposition of propan-2-01 on pure rutile and rutile doped with 0.1 mol% CrzOs, Fez03, NiO, Nb205 or W 0 3 has been studied between 438 and 5i9 K using a flow system. Rates of dehydration to propene and dehydrogenation to acetone were independent of propan-2-01 presswe between 2.9 x lo2 and 4.4 x lo3 N m-', whereas rates of partial dehydration to di-isopropyl ether exhibited a low pressure dependence. Arrhenius parameters for the formation of all three products have been determined. Poisoning experiments indicate that dehydration proceeds by an acid-base mechanism, in which the effects of doping are " geometric '' rather than " electronic ". Although doping influences dehydrogenation, the effects cannot be correlated with " geometric " or " electronic " factors.

The reduction of rutile by vacuum outgassing between 450-825"C, or by hydrogen or carbon monoxide at 350"C, yields active catalysts for low temperature parahydrogen enrichment due to the presence of surface Ti3+ ions. Since the kinetics indicate saturation of these active sites, the absolute rate of enrichment at 77 K and 1.3 x lo3 N m-2 can be taken as a direct measure of the extent of surface non-stoichiometry. Poisoning experiments with oxygen indicate Ti3+ ions are not limited to the surface layer alone, but are distributed between surface and sub-surface layers, and are effectively mobile at temperatures considerably below the Tammann temperature. The activity for parahydrogen enrichment arising from oxygen molecules physically adsorbed on fully oxidised rutile has been used to derive an equation, which is used to estimate the concentration of Ti3+ ions in reduced surfaces. This did not exceed -8.0 x 10l6 ion m-2 for the most active surface studied.

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Doping with 0.1 mol % Cr203, Fe203, NiO, NbzOs or W03 has little effect on the catalytic properties of rutile for the decomposition of nitrous oxide in the temperature range 450-590°C. For all six catalysts, first-order kinetics with respect to initial nitrous oxide pressure were obeyed. Relatively small differences in the activation energies were observed, but an apparent compensation effect resulted in the absolute rates at 550°C and 1.33 x lo4 N m-2 lying between 1.2 and 2.2 x 1OI2 molecules s-l. Parahydrogen enrichment has been investigated at 77 and 90 K over the pressure range 1.33 x lo2 to 2.66 x lo4 N m-' on the six catalysts used in nitrous oxide decomposition. The reaction proceeds