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IUCr Congress and General Assembly

Osaka, Japan, August 2008

This is a continuation of the reports on the XXI Congress that can be found in Volume 16, No. 3 & 4

Crystallochemical Basis of Synthetic Mineral Immobilisation (KN11)

[Mineral immobilisation]
Tim White (MSE-NTU, Singapore) reviewed methods for immobilising pollutants by crystal chemical and mineralogical principles. Spent nuclear fuel, slag heaps, incinerator ash and tailing dams are major sources of inorganic waste. Key principles for immobilization in a mineral matrix are: (1) toxic metals should be incorporated in their least toxic chemical states (for example, As5+ and Cr3+ instead of As3+ and Cr6+); (2) crystal structures are preferred that have multiple cation and/or anion acceptor sites as this minimizes the number of phases required: (3) phases with large numbers of appropriate cation acceptor sites are advantageous, as they result in higher waste loadings and less ‘bulking’ of the waste product. The crystallochemical bases (e.g., framework distortion, polysomatism and incommensurate phases) of synthetic mineral immobilization have been described for several structure-types among which: perovskite, pyrochlore, zirconolite, hollandite and apatite. In particular, the flexibility of the structure of apatite in accepting a variety of ions, via different mechanisms, has been discussed in detail on the basis of several results obtained in the laboratory of the lecturer.

Giovanni Ferraris

Advances in Grazing Incidence, Reflectivity and Diffuse Scattering (MS2)

Sponsored by the IUCr Commission on Small-angle Scattering, this symposium focused on 'Advances in grazing incidence, reflectivity and diffuse scattering'. It encompassed current developments across the range of scattering in a reflection geometry, especially X-ray and neutron reflectivity (XR and NR), and grazing-incidence small-angle X-ray and neutron scattering (GISAXS and GISANS), and brought together several leading international experts.

P. Müller-Buschbaum (Germany) spoke on 'Recent developments in GISAXS and GISANS - nanobeams and in situ kinetic investigations'. He described how it is possible at the 3rd generation X-ray synchrotrons to combine microbeams and nanobeams in grazing incidence geometry to tune surface sensitivity, and thus to distinguish surface from volume structures during in situ kinetic studies of thin films. The potential of the method was illustrated by in situ GISAXS studies of nanoparticle Au sputtering on polymer fibers, a critical technology for developing next-generation photovoltaics.

T. Matsushita (Japan) spoke on 'Quick X-ray reflectometry in simultaneous multi-wavelength dispersive mode'. He described how curved crystal optics, used to provide fast time resolution in energy dispersive X-ray absorption spectroscopy, could be applied in energy-dispersive XR studies to improve the time resolution from minutes or hours in 'conventional' XR to millisecond time resolution in energy-dispersive XR. The method was illustrated with reflectivity studies of 20 ms time resolution for a rotating specimen comprising a 14.3 nm Au nanolayer film on a Si substrate.

Returning to GISAXS fundamentals, B. Lee (USA) spoke on 'Structural characterization using the multiple scattering effects in GISAXS'. Whereas the distorted wave Born approximation has been successful in describing GISAXS data, multiple scattering can complicate the picture. Its analysis can be simplified by using interference effects between scattering from the incident and from the reflected X-ray beams in incident-angle-resolved GISAXS (IAR-GISAXS). By illustration, Lee described studies of virus particles in polymer films on Si substrates.

The unique advantages provided by the neutron scattering isotope effect were highlighted by A. Takahara (Japan) in his talk, 'Neutron reflectivity study of chain conformation in polyelectrolyte brushes at the liquid interface'. His account of an NR study of polymer brushes on quartz substrates immersed in water demonstrated the power of D2O/H2O neutron contrast variation studies to tune the film density profile as a function of swelling and processing. Takahara showed how hydrophobic and hydrophilic interfaces can be distinguished, and the effects of the aqueous phase ionic strength on the conformation and surface properties of the brushes determined. The brushes can be manipulated by exploiting their mutual adhesive properties using microfluidic principles.

A combination of GISAXS and grazing-incidence X-ray diffraction (GIXD) methods to characterize, in situ, the vacuum growth and catalytic reactivity of nanoparticles on an oxide surface was described by R. Lazzari (France) who spoke on 'Following growth and catalytic reaction of oxide supported metal nanoparticles with GISAXS'. Using a high-vacuum chamber to give low background, these methods permit experimental testing of GISAXS data modeling and simulations. The growth laws and thermodynamics for Au nanoparticles on TiO2 were established, revealing a striking self-similar behavior.

The symposium retained an audience of 60 to 80 persons throughout, and clearly demonstrated the importance of such measurements in the development of advanced materials critical to emerging nanotechnologies.

Andrew Allen and Moonhor Ree