Nano-structural features of barite crystals observed by electron microscopy and atom probe tomography

For the first time a barite samplewas investigated by applying electronmicroscopy and atom probe tomographyin a complementary approach to characterize its inner microstructure. Pores covering the size range from a fewnanometers to a few micrometers were identified inside particles of a commercially available high purity barite.The baritematrix appeared to be a single crystal. A particular feature of the observed porous structure is a systemof layers containing a high number of homogeneously distributed nano-scale pores, alternating with layers containinga limited number of larger pores. High-resolution chemical analyses indicate that the pores contain a solutionof water and sodium chloride. The filling of these nano-scale inclusions was interpreted as residua of theinitial supersaturated solution used for particle growth by precipitation. These findings explain the high reactivityobserved in previous Ra uptake studies on the same type of barite and provide further implications for the interpretationof these results. Our results offer a new analytical approach and necessary reference data for future investigationson changes of the internal barite structure during these Ra uptake experiments