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

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