Recent Results from USANS Measurements of Clays and Hydrating Cement Pastes

One aspect of materials research at ANSTO has been and still is, concerned with ascertaining the suitability of certain materials as barriers (eg. cement, clay) to contain low-level and (eg. SYNROC) high-level nuclear wastes. The technique of small-angle neutron scattering (SANS) was considered ideal to help characterise the microstructure of these materials. However it soon became apparent that multiple scattering was a major factor for these kind of materials and that results could be more easily obtained from ultra small-angle neutron scattering (USANS) measurements.

Over the years at ANSTO we have used a number of different USANS facilities around the world to study the properties of condensed materials such as clays and cement pastes. Measurements of cement pastes, clays and ANSTO-produced SYNROC have been performed on the new ultra-high resolution instruments at ORNL, NIST and ILL, whereas time resolved USANS studies of hydrating cement samples have been conducted at the double crystal diffractometers V12 at HMI in Berlin and DN2 at NPI in Prague.

Results from some of these experiments and their interpretation will be presented. In particular, some of the results from hydrating cement samples have so far defied explanation, probably owing to the chemically complicated nature of the initial stages of the hydration process.

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