Biochar performance in applications like soil amendment depends on properties including porosity, surface area, and pore structure, which are influenced by both process conditions and feedstock characteristics such as wood anatomy. However, their effects across micro- and nanometre length scales remain poorly understood. This study therefore investigates how feedstock and process conditions affect properties of pine wood biochar produced in industrially relevant pilot-scale continuous reactor for torrefaction (291–315°C, 6–12 min) and pyrolysis (350–400°C, 25 min). High-resolution X-ray microtomography combined with AI-assisted image analysis was used to quantify earlywood–latewood distribution, porosity, pore size, cell wall thickness, and micrometre-scale surface area, while N2 and CO2 sorption probed nanometre-scale structure. The wood microstructure was largely preserved across treatments, resulting in highly anisotropic pore networks. Porosity remained high (33–77%), primarily influenced by earlywood–latewood variability rather than temperature. From torrefaction to pyrolysis, cell wall thickness and pore diameter decreased, while microporosity (<∼0.7 nm) and accessible surface area increased significantly above 350°C. Discrepancies between N2 and CO2 measurements indicate differences in pore accessibility, likely associated with ultramicroporosity, pore constrictions and/or partially inaccessible pores. Water holding capacity ranged from 1.7 to 5.3 times dry weight, with highest average at 350°C, although differences were not significant. Combined use of microtomography and gas sorption provides a multiscale framework for linking biochar structure across micro- and nanometre scales to performance-relevant properties. These findings demonstrate that wood anatomy dominates over process conditions under mild thermal treatment, highlighting new possibilities for tailoring process design through consideration of wood anatomy.
Cenospheres are plausible intermediates in entrained flow gasification (EFG) of biogenic suspension fuels. However, their structure and reactivity remain poorly understood, limiting the accuracy of numerical simulations of entrained flow gasifiers.The present study characterizes cenospheres from two experiments in a technical entrained flow gasifier using beech wood pyrolysis oil (PO) and char suspensions (slurry; POC) under intentionally low air ratios (0.35). Structural features and CO2 gasification kinetics are investigated, and mass transport effects under technically relevant conditions (1000 – 1500 °C, 10 bar CO2) are evaluated.A broad particle size distribution of the cenospheres (100 – 800 µm) is identified. Micro computer tomography reveals internal macro-structures ranging from uniformly distributed porosity to a porous shell, with embedded char particles in POC cenospheres.Micro- and mesoporosity are analyzed via argon physisorption. Only POC cenospheres show microporosity, which is assigned to the char particles. Structural ordering determined by X-ray diffraction (XRD) is stronger for smaller cenospheres. The evolution with increasing particle diameter differs between POC and PO cenospheres, with radial expansion of the graphene layers prevailing in POC cenospheres, while both radial expansion and graphene stacking vary in the structured domains in PO cenospheres.Reaction kinetics in CO2 (5 – 20 bar, 810 – 850 °C) are determined in the differential fixed bed reactor for 200 – 400 and 600 – 800 µm fractions. The reaction rate increases with increasing temperature and CO2 partial pressure as described by the Arrhenius and the power law model (activation energy: 210 – 242 kJ/mol; reaction order: 0.2 – 0.3). Especially the mantle area-to-volume ratio of the stacked graphene layers derived from XRD and the mesopore surface area are found to impact the reaction rate.
The transition of the ore-based steel industry will increase the global volumes of electric arc furnace (EAF) slag and introduce new components inherently associated with iron ore. For example, vanadium is expected to partition to the slag, and its implications on downstream slag valorization must be considered. Therefore, the present study addressed the effect of VOx concentration on characteristics relevant to valorization as a supplementary cementitious material (SCM). A synthetic water-granulated CaO‒SiO2‒MgO‒Al2O3‒FeOx‒VOx slag system was systematically varied in VOx. By incorporating VOx, the saturation of the divalent metal oxide solid solution (RO-phase) and crystallization of spinel were promoted. Furthermore, dicalcium silicate crystallized at higher temperatures, which suggested an overall greater tendency for crystallization with increasing VOx concentrations. The effect of adding VOx on the vitrified fraction of the slag was studied by Raman spectroscopy, indicating that vanadium was incorporated into network-forming structures, but still had a net depolymerizing effect. By standardized SCM reactivity testing, VOx concentration was found to improve the inherent reactivity of the slag, which was suggested to stem from the depolymerization and the fact that vanadium is not expected to introduce internal diffusion barriers upon slag particle dissolution. Consequently, incorporating VOx into future EAF slags should be further investigated for environmental aspects as the reactivity was not negatively affected.
Natural discontinuities, such as holes and cracks in rock masses, often act as stress concentration zones, rendering them highly susceptible to spalling failure under dynamic loading conditions, a critical threat to the safety and stability of underground structures. Filling reinforcement is an effective means to control this kind of damage. Therefore, in this paper, the effects of filling material strength and filling radius on the dynamic mechanical response and spallation failure characteristics of porous sandstone are systematically studied using a φ 50 mm split Hopkinson pressure bar (SHPB) system and PFC2D numerical simulation method. The results demonstrate that increasing both the strength and radius of the filling material significantly enhances spalling resistance, delays crack initiation, and reduces the number of spalling cracks, underscoring its capacity to buffer stress waves and modulate fracture development. High-speed imaging directly captures the delayed initiation and propagation of cracks within the filling material. The numerical simulation results further reveal that the filling position is another key factor affecting the reinforcement effect. Fillings at the transmission end experience greater stress superposition, resulting in more severe spalling damage compared to those at the incident end. These insights offer practical guidance for optimizing filling strategies in practical engineering applications.
Pyrometallurgical copper extraction yields large slag volumes—typically 2.2 to 3.0 tons per ton of copper produced—underscoring the need for valorization strategies to improve resource efficiency. Utilizing these slags as supplementary cementitious materials (SCMs) offers a promising pathway. However, data on how composition influences the inherent reactivity of industrial slags remain scarce. Previous laboratory studies have shown that increasing CaO enhances slag performance as an SCM, but data on industrially CaO-modified slags remain limited. This study evaluates the inherent reactivity of industrial modified copper slags with 3.2–15.9 wt.
