Confocal Micro X-Ray Fluorescence for Spatial Analysis of Mineral Inclusions, Biomineralization Composites and Building Materials

Micro X-ray Fluorescence (MXRF) spectrometers enable non-destructive and elemental analysis of a wide variety of solid samples with a lateral resolution of a few tens of micrometers using focusing optics. Confocal MXRF (CMXRF) offers additional depth-dependent measure­ment capabilities, based on a three-dimensional probing volume created by the confocal ar­rangement of a focusing lens in the excitation and detection channel. Therefore, CMXRF pro­vides micro-scalic resolved measurements of complete sample volumes by depth profiles (1D), cross section mappings (2D) and stacked element distribution images (3D). The strengths, challenges and potential of a modified (confocal) MXRF tabletop spectrometer for non-destruc­tive and depth-sensitive element analysis will be illustrated by geoanalytical and geo-related appli­cations:

The first application is the three-dimensional analysis of mineral inclusions. The sophisticated compositional studies and identification of mineral phases by CMXRF provides micro-scalic resolutions with certain limitations due to X-ray absorption, but also preserves the integrity of isolated inclusions for further analysis.

Another example is the study of biomineralization products, due to the biomimetic behavior of deep-sea sponges under extreme conditions resulting in the formation of novel three-dimen­sional composites. Several mineralization products such as atacamite, goethite and lepido­crocite have been studied by three-dimensional reconstruction of the elemental distribution of the formed composites.

The third application is the depth-sensitive analysis of the elemental composition of ce­ment stone corrosion zones simulating the acidic chemical attack on concrete samples. The interest in describing those corrosion processes is motivated by defining the occurring kinetics and deriving information about the persistence, strength and durability of concrete.