Masao Kimura

Quaternary granitic bodies are considered to host high-temperature geothermal reservoirs containing supercritical fluids exceeding 400 °C. However, both the micro- and reservoir-scale geometry and connectivity of pore networks within granite under such extreme conditions remain poorly understood. In this study, we performed micro X-ray computed tomography (µCT) analyses on drill core samples from well WD-1a, which penetrates the Kakkonda granite in northeast Japan. To characterize the geometry and spacing of micropores, we conducted topological data analysis (TDA) using persistent homology. Using 0th-dimensional persistent homology (PH0), we quantified the geometry and spacing of pores as sets of birth and death values {( b _i , d _i )}. Their statistical characteristics were further analyzed using principal component analysis (PCA). Three types of pores were identified: (1) alteration-type pores formed at feldspar replacement fronts, (2) relatively large facet-type pores bounded by crystal faces, and (3) cracks occurring along grain boundaries. Integrated PH0 and PCA results revealed variations in micropore topology among samples collected across the hydrological boundary and deeper thermal conduction zone. In the weakly metamorphosed granodiorite sample from the hydrothermal convection zone, abundant alteration-type pores exhibited fine-grained textures and close spacing. The sample from near the hydrological boundary showed both alteration and facet-type pores, but had low µCT-derived connected porosity. In the deeper sample, located within the thermal conduction zone, large facet-type pores were interconnected by grain-boundary cracks, forming extensive networks. The observed differences in pore topology are broadly consistent with the permeability variations measured among samples in the laboratory, highlighting the importance of pore generation mechanisms in evaluating geothermal reservoir potential.

We report the development and initial applications of the multi-functional research and development beamlines BL-11A and BL-11B at the Photon Factory, which are designed to enable simultaneous use of hard and soft x-rays. The two beamlines share a common bending-magnet source and deliver independently monochromatized hard- and soft-x-ray beams that can be focused onto the same sample position in a downstream experimental hutch, providing a versatile platform for two-beam experiments in which hard and soft x-rays can serve as pump and/or probe beams in various combinations. As proof-of-concept demonstrations, we performed probe–probe measurements of water electrolysis on a cobalt electrocatalyst and pump–probe measurements of x-ray-induced dissociation of a caged compound. In the probe–probe scheme, hard- and soft-x-ray absorption spectroscopy was carried out simultaneously to track correlated changes in the catalyst oxidation state and oxygen-related intermediates during the oxygen evolution reaction. In the pump–probe scheme, chemical changes in 2-iodosobenzoic acid induced by hard-x-ray excitation at the iodine L3 edge were monitored using soft-x-ray absorption spectroscopy at the oxygen K edge.

Acidic oxygen reduction is often discussed as if catalytic activation and mass transport were inseparable. Here, biomass‐derived carbon was used to examine these contributions through oxidation, ammonia annealing, and KOH activation. The onset potential is associated primarily with defect‐derived p _z / π electronic states, whereas the maximum slope in the transport‐influenced region is associated with hierarchical pore accessibility and connectivity. Apparent electrochemically accessible surface area does not correlate significantly with onset potential in the six‐sample series, although it covaries with maximum slope; this covariance is attributed to pore accessibility rather than surface area itself. Multiscale X‐ray tomography of the optimized catalyst visualizes connected pore pathways from macro‐ to submicrometer scales, while the connected framework may be partly inherited from the rice‐husk precursor. The combined results support preferentially separate consideration of electronic activation and pore‐network accessibility for the acidic oxygen reduction reaction.

The redox mechanisms of silica-supported Ni particles were investigated using their in situ X-ray absorption fine structure, providing mechanistic insights into partially reduced NiO and partially oxidized metallic Ni. The results of surface oxidation of partially reduced NiO particles at room temperature revealed that the surface was not fully covered with metallic Ni and that metallic Ni had also formed within the particle interior. During NiO particle reduction, the process initiates at specific surface sites, and before the metallic Ni phase fully covers the surface, O²⁻ ions are expelled from the particle. Conversely, the oxidation of metallic Ni particles progresses inward from the surface, with an accompanying increase in the thickness of the NiO layer that forms upon O₂ exposure at room temperature. This mechanism is supported by observations that the reduction of a thin NiO shell on metallic Ni particles was completed below 200 °C, while reduction temperatures shifted to higher values as the NiO layer thickness increased. The distinct oxidation and reduction mechanisms are attributed to differences in the migration direction of O²⁻ ions. During reduction, it is proposed that O²⁻ ions within the particles migrate to the surface along the interface between the NiO phase and the metallic Ni phase. This study elucidates the detailed mechanism behind the redox interconversion between NiO and metallic Ni in solid catalyst particles.

The valence state and 3D structure of vacuum-deposited Cu species on α-Al ₂ O ₃ (0001) surface have been determined using the PTRF-XAFS technique and DFT calculations.

The reducibility and mechanical properties of iron ore sinter in blast furnace is critical to effective plant operation. The reduction reaction of sinters progresses heterogeneously owing to microstructures with various mineral phases and pore networks. The reduction process was investigated by semi-microbeam synchrotron X-ray multimodal analysis. Heterogeneous chemical state evolution of Fe and trigger sites of crack formation were visualized using two-dimensional Fe K-edge X-ray absorption near-edge structure analysis and were discussed based on reduction gas transfer. The elemental composition map and X-ray diffraction microanalysis were also combined to reveal the microprocesses during the reduction, such as calcium ferrite decomposition and crystal grain growth.