APPLICATION OF NEUTRON SCATTERING TECHNIQUES IN THE MINERAL SCIENCES

For over half a century neutron scattering has provided valuable information about the structure of earth materials. Important applications have been in crystallography (e.g. atomic positions of hydrogen and order/disorder), magnetic structures, phase transitions, anisotropy and residual strain in rocks and minerals [1]. With the next-generation neutron sources coming on line, mineral scientists have new opportunities to design neutron experiments that will provide insight into properties of minerals that cannot be obtained with other techniques. Inelastic and quasielastic neutron scattering, for example, are techniques ideally suited to study the structure of dynamics of hydrogen in minerals [2]. Hydration layers on the surface of nanoparticles can exert a profound influence on the properties of the oxide. In this presentation, the role of water on the surface of oxide nanoparticles will be discussed. The phases of TiO₂ (rutile and anatase) provide an excellent system to study the effect of polymorphism, particle size, and hydration on the thermodynamic properties of the phases. Inelastic neutron scattering (INS) experiments on 7 nm anatase were used determine the phonon density of states and energetics of chemisorbed water and the role this water plays in stabilizing the anatase nanoparticles. These results are compared with recent calorimetric measurements [3] and discussed in context with recent quasielastic neutron scattering (QENS) studies of the dynamics of sorbed water on rutile and cassiterite nanoparticle surfaces [4]. The combination of INS and QENS allows one to characterize the hydration layers of oxide nanoparticles and provides a powerful approach for future studies in the mineral sciences.

References: [1] Neutron Scattering in Earth Sciences (2006) Wenk, H-R., ed., MSA Reviews in Mineralogy and Geochemistry, Vol. 63, Washington, D.C. [2] Winkler, B (1999) In: Wright, K and Catlow, R (eds) microscopic Properties and Processes in Minerals. Kluwer Academic Publishers, 93-144. [3] Boerio-Goates, J. , Li, G., Li, L., Walker, T.F., Parry, T. and Woodfield, B.F. (2006) Nano Letters, 6:750-754. [4] Mamontov, E. , Vlcek, L. D. J. Wesolowski, D.J., Cummings, P.T., Wang, W., Anovitz, L.M. Rosenqvist, J., Brown, C.M., Garcia Sakai, V. (2007) J. Phys. Chem. C 2007, 111, 4328-4341