Raman mapping routinely acquires thousands of spectra, yet fluorescence, weak signal and peak overlap can mask key phase information. We contrast two open-source workflows – an interactive, human-guided pipeline and a fully automated machine-learning routine – to reveal hidden structural differences in complex (geo)materials.

The case study is a cross-section of a prior analysed oxide-rich corrosion layer on a ferritic model alloy. Corrosion control demands separating protective from non-protective oxides e.g., magnetite, chromite and mixed spinels. In the human-guided routine, an analyst applies dimensionality reduction, chooses a clustering method, inspects cluster quality and, where warranted, performs pseudo-Voigt peak-position analysis before re-clustering. This loop resolves all the chemically distinct populations and quantifies magnetite – chromite band shifts of up to 7 cm^-1, revealing mixed spinels that standard Raman maps miss.

The automated path eliminates human decisions: a convolutional autoencoder compresses spectra to latent features and an information-criterion optimiser determines cluster numbers. While faster, the automated routine tends to merge subtle spinel variants and is more sensitive to noise. The present study dissects trade-offs in interpretability, reproducibility and library dependence, showing when expert oversight adds value.

These workflows turn phase-tagged Raman maps into quantitative micro-atlases that can be generated on notebooks using scikit-learn^[1] and TensorFlow^[2]. The presentation shows how both workflows deliver large-scale, detailed insight into chemically similar phases with differing functions.

References

[1] Pedregosa F. et al. (2011) J. Mach. Learn. Res. 12, 2825 – 2830.

[2] Abadi M. et al. (2016) Proc. 12^th USENIX Symp. (OSDI 16), 265 – 283.

Advanced characterization techniques are essential for gaining insights into the structural and chemical evolution of functional materials under reaction conditions [1]. In situ and operando methods have become increasingly important to overcome the limitations of traditional ex situ analysis conducted before and after reaction. However, there are many pitfalls one can encounter when conducting non-ambient experiments with elevated temperature, pressure, and humidity. This study highlights the necessity for interdisciplinary knowledge, such as surface and bulk chemistry, nano-size effects, fluid and gas dynamics, and flow-pressure relationships, to effectively plan and execute operando experiments through various application examples in heterogeneous catalysis. What remains non-trivial is the assessment and handling of the complexities associated with the use of corrosive or reductive/oxidative gas atmospheres.

This study presents the development of in-house operando X-ray powder diffraction (XRPD) and quasi-in situ X-ray photoelectron spectroscopy (XPS) setups for monitoring inorganic catalyst precursors under non-ambient conditions, including elevated temperatures, reaction gas environments, under pressure, or in a protective atmosphere. Operando XRPD enables real-time tracking of structural transformations, while quasi-in situ XPS provides surface-sensitive chemical state interpretation. Together, these techniques offer a comprehensive understanding of catalyst behavior under realistic reaction conditions and demonstrate the feasibility and value of in-house instrumentation for catalytic research.

[1] H. Petersen, C. Weidenthaler, A review of recent developments for the in situ/operando characterization of nanoporous materials, Inorg. Chem. Front., 9 (2022), 4244.

Photovoltaics is one of the most easily implementable renewable energy source. Highly efficient thin-film solar cells use chalcogenides such as Cu(In,Ga)Se₂ or halide perovskites like (Cs,FA,Ma)Pb(I,Br)₃ as absorbers. Since the availability of indium as well as the limited stability of halide perovskites is an object of concern regarding large scale production of solar cells, the search for novel absorber materials with long term stability is an ongoing challenge.

We studied the chalcogenides Kesterite (Cu₂ZnSnS₄) and Briartite (Cu₂ZnGeS₄) as promising candidates for photovoltaic applications. These semiconductors show a high absorption coefficient of solar radiation and long term stability. Kesterite-based thin film solar cells already reach power conversion efficiencies > 12% [1].

To understand the materials’ optoelectronic properties, deep insights into the structural properties are crucial. Both compounds crystallize in the tetragonal Kesterite structure, which is characterized by a network of corner sharing tetrahedra. Additionally Briartite shows an orthorhombic modification (Wurtz-Kesterite structure). The symmetry reduction is caused by a distortion of the coordination tetrahedra.

We investigated the structural and optoelectronic properties of Kesterite and Briartite using powder samples synthesized by solid state reaction. The formation of different Briartite modifications depends heavily on the sulfur pressure, tailored during the synthesis. The challenge in structural analysis is the differentiation of the electronic similar elements Cu, Zn and Ge. We solved this problem by applying neutron diffraction as well as multiple energy anomalous diffraction.

The presentation will give an overview of structure-property relations of these promising photovoltaic absorber materials.

[1] M.Kauk.Kuusik, J.Mater.Chem. A11 (2023) 23640

The production of ordinary portland cement releases large amounts of CO₂ by burning of fossil fuels and by decarbonation of limestone, in which CO₂ is chemically bound as CaCO₃. The burning process leads to decomposition of CaCO₃, where CO₂ is released and CaO is part of the clinker.

For this new building material, olivine is used as raw material instead. In this study, the Mg-end-member forsterite, Mg₂SiO₄, is used as model system to describe the hydration of olivine, which naturally occurs as a Mg-rich solid solution. Forsterite is able to react with water, forming serpentine, Mg₃Si₂O₅(OH)₄, and brucite, Mg(OH)₂. This reaction is known as serpentinization and lasts long time scales during geological processes, but can be accelerated by an activation process [1] for technical applications.

The activation process consists of two steps. First step is autoclavation of forsterite, which corresponds to serpentinization. Serpentine and brucite are thermally activated in second step. Annealing these hydrate phases leads to thermal decomposition, where H₂O is partially released and a reactive amorphous magnesium silicate phase is formed. The activation process is low in energy consumption and does not release chemically bound CO₂.

The activated magnesium silicate phase reacts with water forming a M-S-H phase. M-S-H has only low crystallinity [2]. Furthermore, this binder shows the possibility of CO₂ uptake by mineral carbonation, creating a CO₂-negative building material.

References:

[1] F. Bellmann, Method for producing a hydrated cement, WO2025/012209A1, 2025

[2] C. Roosz et al. (2015) Cement and Concrete Research 73, 228-237. doi: 10.1016/j.cemconres.2015.03.014

Blast oxygen furnace slag (BOF) is one major by-product of steel production by Linz-Donawitz process. It is produced in the converter during the refining from pig iron to crude steel. At HKM steel plant approximately 430.000 t of BOF slag is produced ongoing the production of 4.3 Mio. t of steel, annually. Nowadays 30.000 t of the slag is used as high-quality asphalt chippings. BOF consists in general of Ca-silicates, Ca-ferrites and Fe-oxides. The slags show further a wide variety in specific gravity due the randomized distribution of macro porosity and heavy steel particles.

One limiting factor for this application is the homogeneous specific gravity of the material, which is crucial because it controls the asphalt recipes. However, bituminous binder is one major cost factor during asphalt production.

In this study, we present a combination of analytical procedures to investigate the distribution of pores and steel pebbles in slag particles to evaluate the particle specific gravity. Based on the analytical results, a beneficiation scheme by mineral processing is presented to separate heavier from lighter particles. As an established method of gravity concentration, jigging is used as a reference. In addition, the application of sensor-based sorting using X-ray transmission technology is presented for density-based separation.

By the application of the presented processing scheme, the BOF slag´s variability in density can be reduced to a tenth of its original deviation. Thus, the presented beneficiation scheme is capable to improve BOF slag valorization due to improved value.