In Situ SAXS/WAXS Studies of the Precipitation, Crystallization and High Temperature Phase Transitions of Minerals

S. Shaw,¹ L. G. Benning,² N. J. Terrill,³ C. M. B. Henderson,⁴ and J. A. Warner⁵

¹Department of Earth Sciences, University of Oxford, Oxford, UK OX1 3PR
²Department of Earth Sciences, University of Leeds, Leeds, UK LS2 9JT
³Diamond Light Source Ltd, Rutherford Appleton Laboratory, UK OX11 0QX
⁴Department of Earth Sciences, University of Manchester, Manchester, UK M13 9PL
⁵Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA

Specialized sample cells used in conjunction with a high-flux synchrotron X-ray source allow the in situ characterization of mineralogical reactions using time-resolved Small Angle X-ray Scattering (SAXS). Cells have been developed to allow samples to be analysed under a wide variety of chemical (pH, ionic strength) and physical (temperature) conditions with data collection on timescales down to 100's milliseconds. Three studies will be present to show the range and diversity of the reaction processes that can be studied using time-resolved SAXS:
    (1) High temperature (up to 1100ºC) studies of the breakdown and recrystallization of cement minerals/phases e.g. tobermorite (Ca₅Si₆O₁₆(OH)_2.4H₂O), hillebrandite (Ca₂Si₆O₃(OH)₂) and thaumasite (Ca₃Si(CO₃)(SO₄)(OH)_6.12H₂O), have provided information on the mechanisms and kinetics of their dehydration processes and phases transitions which occur at high temperatures.
    (2) The growth and crystallisation of environmentally important nanoparticles in aqueous solution (e.g. iron/aluminium oxyhydroxides) to characterise the transition of poorly-ordered particles to stable crystalline phases. Particle size and density information obtained from SAXS combined with crystallographic information from Wide Angle X-ray Scattering (WAXS) provide a detailed description of the kinetics and mechanism of the reactions.
    (3) Stopped-flow mixing apparatus used in conjunction with a high flux undulator insertion device allow high-speed, accurate and reproducible mixing of reactant along with high speed SAXS data collection (<1 sec). This system has been used to characterise the nucleation and growth of nanoparticles from solution during base and oxidative hydrolysis reactions.