A painting is made up of complex mixtures of materials, carefully selected by an artist, usually to create a specific optical illusion or esthetic effect. Depending on its material composition and the environmental conditions that a painting is subjected to, various chemical reactions can take place which cause the paint layers to deteriorate over time. Therefore, collecting reliable chemical information from a work of art is essential to understand its composition, past and ongoing conservation issues and to develop preservation strategies. In this sense, X-ray powder diffraction is an important tool as it allows for the direct identification of crystalline phases within the complex mixtures present in a painting [1]. However, an important limitation of this method has been the amount of material that needed to be sampled [2]. In the past decade a new trend has been set towards the application of elemental and chemical imaging techniques, such as macroscopic X-ray fluorescence (MA-XRF) and reflectance imaging spectroscopy (RIS), for the study of painted artefacts as they provide valuable information on the heterogeneous composition within complete paintings [3-5].

Following this trend, the AXES research group has developed a macroscopic X-ray powder diffraction (MA-XRPD) imaging instrument that allows for the identification and visualization of the crystalline materials used in a painting in a non-invasive manner. This instrument uses a low power microfocus X-ray source (IµS, Incoatec) combined with multilayer mirrors to obtain a slightly focused and fairly monochromatic X-ray beam in combination with a large area detector (PILATUS 200K, Dectris). By moving the painting and the instrument relative to each other, a large set of diffraction images (typically >10000) is collected following a raster-scanning approach. Subsequently, this large powder diffraction dataset is azimuthally integrated after which the resulting one dimensional 2θ spectrum at each data point is individually fitted with the XRDUA software package [6] using a model comprising all identified crystalline phases. By plotting the scaling factors as grey-scale values individual images that correspond to the distribution of the crystalline materials can be created [7].

The MA-XRPD instrument can be used in a transmission geometry, suitable for underlaying and strongly absorbing paint layers, or in reflection geometry, which is more sensitive for the (thin) pictorial layers. The latter also has the added advantage that larger works of art can be investigated as the painting remains stationary while the scanning head is translated in three dimensions. Typically a (short) dwell time of 10 seconds is used with a step size of 1-2 mm over a maximum scanning range of 30 x 30 cm.

The MA-XRPD instrument has been used within several museums on well-known masterpieces, such as Van Gogh’s Sunflowers, Vermeer’s Girl with a Pearl Earring, the Ghent altarpiece by the brothers Van Eyck and The Night Watch by Rembrandt. On these works, next to the visualization of the original pigments employed by the artists and later additions or overpaint, also various chemical alteration products that have formed within/on top of the paint layers could be identified. In some cases, the data collected with the MA-XRPD instrument can be exploited to yield other types of highly-specific information, such as the buildup of the paint layer or the orientation of the crystals on the paint surface. Furthermore, the collection of large datasets allows a reliable quantification of various pigment mixtures and to track their differences within and between artworks/time periods.

[1] Artioli, G. (2013). Rendiconti Lincei-Scienze Fisiche E Naturali, 24, S55. [2] Madariaga, J. M. (2015). Anal. Methods, 7, 4848. [3] Alfeld, M., & Broekaert, J. A. C. (2013). Spectrochim. Acta, Part B, 88, 211. [4] Alfeld, M., & de Viguerie, L. (2017). Spectrochim. Acta, Part B, 136, 81. [5] Trentelman, K. (2017). Annu. Rev. Anal. Chem., 10, 247. [6] De Nolf, W., Vanmeert, F., & Janssens, K. (2014). J. Appl. Crystallogr., 47, 1107. [7] Vanmeert, F., De Nolf, W., De Meyer, S., Dik, J., & Janssens, K. (2018). Anal Chem, 90, 6436.

High-strength lightweight magnesium (Mg) alloys have substantial potential for reducing the weight of automobiles and other transportation systems and, thus, for improving fuel economy and reducing emissions. However, compared to other structural metals, the development of commercial Mg alloys and our understanding of Mg alloy physical metallurgy are less mature, and enabling the widespread use of Mg alloys requires significant improvement in strength, fatigue, and formability. The low formability of Mg alloy sheet is due to its strong basal texture in the rolling direction. The addition of Ca and rare earth elements can result in a desired weaker texture. However, despite numerous studies, the mechanisms by which this texture reduction occurs remains unknown, and it is likely that several different mechanisms occur simultaneously or sequentially. This is the topic of this research.

A Mg-3Zn-0.1Ca alloy was deformed under hot plane-strain compression and samples were subjected to annealing on ID3A on ID3A at the Cornell High Energy Syncrhotron Source (CHESS) and ID06 at the European Synchrotron Radiation Facility (ESRF). In-situ far-field and near-field high-energy diffraction microscopy (ff- and nf-HEDM) characterization was performed at CHESS, and in-situ partial intermediate-field HEDM (if-HEDM) and dark-field X-ray microscopy (DFXM) was performed on ID06 at the ESRF. By combining the different modalities, we were able to characterize the microstructure evolution during annealing on different length scales, from the subgrain morphology of individual grains (using DFXM) to the aggregate behavior of several thousands of grains (using HEDM).

The mechanical and functional properties of polycrystalline materials have significant contributions from the 3D interaction of grains that form their micro-structure. Such grain maps can be extracted from existing characterisation techniques that utilise X-rays or electrons. However, complimentary techniques using neutrons have not yet developed to maturity. Furthermore, neutrons provide distinct advantages where, due to their lower attenuation, larger materials can be analysed, such as real-world engineering materials.

Here, a novel 3D grain mapping methodology, known as Trindex, has been demonstrated to reveal the micro-structure of a prototypical cylindrical iron material. While there already exist several methods on grain mapping with neutron imaging, Trindex provides a robust and relatively straightforward approach. Trindex is a pixel-by-pixel neutron time-of-flight reconstruction method which extracts the morphology of grains throughout the sample, in addition to their pseudo-orientations.

Experiments were performed at the SENJU beamline of the Japan Proton Acceleration Research Complex (J-PARC). For the setup, an imaging detector was placed behind the sample with diffraction detectors simultaneously collecting the backscattering from the sample. Such diffraction will be used to confirm grain orientations. Details of the methodology and the resulting 3D grain maps of materials will be presented.

1. Cereser, A., et al. "Time-of-flight three dimensional neutron diffraction in transmission mode for mapping crystal grain structures." Scientific reports 7.1 (2017): 1-11.
2. Peetermans, S., et al. "Cold neutron diffraction contrast tomography of polycrystalline material." Analyst 139.22 (2014): 5765-5771.

The properties and behaviour of materials (metals, alloys, semiconductors, ceramics, polymers, drugs, biomaterials) are to a large extent determined by their phase composition, particle size, crystallinity, stress, defects and crystallographic orientation (texture). Two-dimensional (2D) X-ray diffraction is one of the most appealing techniques for users who are interested in extracting every bit of information about their samples. 2D X-ray diffraction patterns, collected using area detectors contain detailed information about all these important material characteristics. Furthermore, the high sensitivity and resolution of modern detectors (e.g. PIXcel^3D, GaliPIX^3D) make possible the collection of relevant structural information within seconds. This allows following in real time transformation processes of materials, like recrystallization, deformation or phase transitions. XRD2DScan is the Malvern Panalytical software for displaying, processing, and analyzing 2D X-ray diffraction data. The latest version of the software (version 7.0) offers new features such as orientation and crystallite size analysis, image comparison, as well as scripting for easy automation. The application of the software to the characterization of complex anisotropic materials (liquid crystals, polymers, bone, wood, ...) will be illustrated through several examples.

A material responds to its surroundings via residual changes in its structure that change its corresponding properties. The macroscopic structural evolution is instigated by the dynamics of statistical populations of defects that move, interact, and pattern – causing atomic-scale defects to create 3D networks of boundaries that comprise the heterogeneous “real-world” materials. While techniques exist to probe material defects, they are mainly limited to surface measurements or rastered scans that cannot measure the dynamics of irreversible or stochastic processes characteristic of defect dynamics. In this talk, I will introduce time-resolved dark-field X-ray microscopy (tr-DFXM) as a new tool to capture movies that visualize dislocation dynamics in single- and poly-crystals at the mesoscale. I will start by describing the infrastructure we have developed to build and align the microscope, then to interpret and quantify the information captured in our movies. With this new tool, I will then demonstrate how dislocation patterns evolve at high temperatures in aluminum (Fig. 1). Tr-DFXM holds important opportunities for future studies on mesoscale dynamics, as it can inform models that have previously been refined only by indirect measurements and multi-scale models.

This work was performed in part under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

The three-dimensional X-ray diffraction (3dxrd) technique provides a useful tool to investigate polycrystalline materials, grain-by-grain, in a non-destructive way. The approach of the scanning 3dxrd microscopy is to probe the sample by moving a pencil beam horizontally across it (y direction) with a resolution dependent on the beam size. For each step, the sample is rotated of 180° (or 360°, ω angle) in order to collect the diffraction spots of all the grains in the sample [1].

We used a combined approach of scanning 3dxrd and Phase Contrast Tomography (PCT) to investigate the hydration of a widespread hydraulic binder material, namely gypsum plaster. This material forms when the bassanite (calcium sulfate hemihydrate) reacts with water. In-situ 3dxrd measurements allowed to understand the crystallographic lattice, orientation and position of each grain in the sample during the hydration reaction (Figure 1 a,b).

The PCT reconstructions, instead, allowed the visualization of the shape of the crystals in the sample over time and a quantification of density and porosity (Figure 1 c,d).

Monitoring the evolution of the hydration reaction of gypsum plaster with both these techniques appears to be a promising tool to gain insights about the kinetics of the hydration reaction, the crystallization and growth of the hydrated phase and the shape of the final gypsum crystals that build the interlocked and porous gypsum plaster hardened mass.