A study was made Pb diffusion in synthetic (CePO4) and natural monazites under dry 1atm conditions. Powdered mixtures of pre-reacted CePO4 and PbZrO3 were used as the Pb source for in-diffusion experiments conducted within sealed Pt capsules for durations of a few hours to several weeks. Following diffusion annealing, the Pb concentration profiles were measured using Rutherford back-scattering spectroscopy and secondary ion mass spectrometry. In order to evaluate compositional effects, diffusional Pb loss, out-diffusion experiments were also carried out on Pb-bearing natural monazites. Monazite grains were surrounded with a synthetic zircon powder, to act as a sink. These monazites were analyzed using secondary ion mass spectrometry. At 1100 to 1350C, the Arrhenius relationship for in-diffusion in synthetic monazite was:

D (m2/s) = 9.4 x 10-1 exp[-592(kJ/mol)/RT]

The diffusivities for synthetic and natural monazites were similar, as were the results for a given sample; made using Rutherford back-scattering and secondary ion mass spectrometry. The activation energy for Pb diffusion was more than 3 times that previously reported for natural monazite; with Pb diffusivities below 1200C that were significantly lower than those reported earlier. However, they were similar to that in zircon.

Pb Diffusion in Monazite - a Combined RBS/SIMS Study. D.J.Cherniak, E.B.Watson, M.Grove, T.M.Harrison: Geochimica et Cosmochimica Acta, 2004, 68[4], 829-40