Application of synchrotron through-the-substrate microdiffraction to crystals in polished thin sections

Co–Mn Mineralisations in the Ni Laterite Deposits of Loma Caribe (Dominican Republic) and Loma de Hierro (Venezuela)

Cobalt demand is increasing due to its key role in the transition to clean energies. Although the main Co ores are the sediment-hosted stratiform copper deposits of the Democratic Republic of the Congo, Co is also a by-product of Ni–Co laterite deposits, where Co extraction efficiency depends, among other factors, on the correct identification of Co-bearing minerals. In this paper, we reported a detailed study of the Co mineralisation in the Ni­–Co laterite profiles of Loma Caribe (Dominican Republic) and Loma de Hierro (Venezuela). Cobalt is mainly associated with Mn-oxyhydroxide minerals, with a composition between Ni asbolane and lithiophorite, although a Co association with phyllosilicates has also been recorded in a Loma de Hierro deposit. In Loma Caribe, Co-bearing Mn-oxyhydroxide minerals mainly developed colloform aggregates, and globular to spherulitic grains, while in Loma de Hierro, they displayed banded colloform, fibrous or tabular textures. Most of the compositional analyses of Mn-oxyhydroxides yielded 20 and 40 wt.% Mn, with Ni and Co up to 16 and 10 wt.%, respectively. In both profiles, Mn-bearing minerals were mainly found in the transition from the oxide horizon to the saprolite, as observed in other laterite profiles in the world, where the precipitation of Mn-bearing minerals is enhanced because of the pore solution saturation and pH increase.

Discriminating the origin of calcium oxalate monohydrate formation in kidney stones via synchrotron microdiffraction

Nephrolithiasis is a multifactor disease that produces nephrolites in the kidneys. Calcium oxalate hydrate (dihydrated, COD, or monohydrated, COM) stones are the most common ones with more than sixty percent incidence worldwide. They are related to different pathologies, COD with hypercalciuria and COM with hyperoxaluria. COD is an unstable species and transforms into COM (herein named TRA to distinguish the origin of the monohydrated species). TRA and COM are chemically and crystallographically identical leading to misdiagnosis and recurrence increase. In the current study, the composition and crystalline structures of several calcium oxalate stones, classified by morpho-constitutional analysis, were examined by IR and synchrotron through-the-substrate micro-X-ray diffraction (tts-μXRD). Both IR and linear diffractogram studies were able to distinguish between the monohydrated and dihydrated phases but not between COM and TRA, as expected. The analysis of 2D diffraction patterns revealed that TRA showed a lower degree of crystallinity and less texture with respect to COM which can be used as a signature to distinguish between the two. This study confirms that despite the subtle differences between COM and TRA, the origin of the monohydrate oxalates can be unraveled using tts-μXRD. This valuable information should be taken into account in order to improve patients' diagnosis and reduce recurrence by considering and treating the origin of the formed stones.

Ammonium monoethyloxalate (AmEtOx): a new agent for the conservation of carbonate stone substrates

Ammonium monoethyloxalate (AmEtOx) is proposed as a consolidanting agent for carbonate stones such as biomicritic limestone and marble, resulting in the formation of a microcrystalline passivating phase of calcium oxalate (whewellite and weddellite).

d2Dplot: 2D X-ray diffraction data processing and analysis for through-the-substrate microdiffraction

The d2Dplot computer program provides a set of tools for the visualization, processing and analysis of 2D X-ray diffraction (2DXRD) data. Among the operations available there are the sum/subtraction of 2DXRD images, conversion to 1D data (powder pattern), azimuthal plotting, calibration of instrumental parameters, background subtraction and a command-line mode to run operations inside data processing pipelines. The graphical user interface allows easy use of the program. It also includes two main features: (i) the possibility of creating a user compound database to help in the fast phase identification of similar samples, and (ii) a detailed peak analysis routine for the application of the through-the-substrate microdiffraction methodology.

Breaking Preconceptions: Thin Section Petrography For Ceramic Glaze Microstructures

During the last thirty years, microstructural and technological studies on ceramic glazes have been essentially carried out through the use of Scanning Electron Microscopy (SEM) combined with energy dispersive X-ray analysis (EDX). On the contrary, optical microscopy (OM) has been considered of limited use in solving the very complex and fine-scale microstructures associated with ceramic glazes. As the crystallites formed inside glazes are sub- and micrometric, a common misconception is that it is not possible to study them by OM. This is probably one of the reasons why there are no available articles and textbooks and even no visual resources for describing and characterizing the micro-crystallites formed in glaze matrices. A thin section petrography (TSP) for ceramic glaze microstructures does not exist yet, neither as a field of study nor conceptually. In the present contribution, we intend to show new developments in the field of ceramic glaze petrography, highlighting the potential of OM in the microstructural studies of ceramic glazes using petrographic thin sections. The outcomes not only stress the pivotal role of thin section petrography for the study of glaze microstructures but also show that this step should not be bypassed to achieve reliable readings of the glaze microstructures and sound interpretations of the technological procedures. We suggest the adoption by the scientific community of an alternative vision on glaze microstructures to turn thin section petrography for glaze microstructures into a new specialized petrographic discipline. Such an approach, if intensively developed, has the potential to reduce the time and costs of scientific investigations in this specific domain. In fact, it can provide key reference data for the identification of the crystallites in ceramic glazes, avoiding the repetition of exhaustive protocols of expensive integrated analyses.

Serial electron crystallography for structure determination and phase analysis of nanocrystalline materials

Serial electron crystallography has been developed as a fully automated method to collect diffraction data on polycrystalline materials using a transmission electron microscope. This enables useful data to be collected on materials that are sensitive to the electron beam and thus difficult to measure using the conventional methods that require long exposure of the same crystal. The data collection strategy combines goniometer translation with electron beam shift, which allows the entire sample stage to be probed. At each position of the goniometer, the locations of the crystals are identified using image recognition techniques. Diffraction data are then collected on each crystal using a quasi-parallel focused beam with a predefined size (usually 300-500 nm). It is shown that with a fast and sensitive Timepix hybrid pixel area detector it is possible to collect diffraction data of up to 3500 crystals per hour. These data can be indexed using a brute-force forward-projection algorithm. Results from several test samples show that 100-200 frames are enough for structure determination using direct methods or dual-space methods. The large number of crystals examined enables quantitative phase analysis and automatic screening of materials for known and unknown phases.

Increasing data completeness in synchrotron tts-microdiffraction experiments for δ-recycling phasing of low-symmetry compounds

Successful phasing of synchrotron through-the-substrate microdiffraction data by

Challenges in the structural science of materials

Articles published recently in IUCrJ continue to exemplify the developments and challenges in the structural science of materials.