Papers by Keyword: Porosity

Abstract: This paper discussed various types of pore formers that have previously been applied as porosity enhancers in the NiO YSZ-based planar SOFC anode since porosity plays an important role to easily diffuse the fuel, thus increasing the triple-phase boundary area and electrochemical performance. Therefore, this study emphasized reviewing recent experiments to find out more effective pore formers by making a comparison between natural (rice starch), polymer-based (PMMA), and carbon-based materials such as graphite. It has been found that rice starch at 7 vol.% gives 10.05% porosity at 1000 °C while activated carbon graphite gives only 4.25%. PMMA shows the highest porosity of 41% at 30 vol.% at 250 °C with almost no residue left behind as proven via TGA analysis which showed only about 0.7%. These findings highlight not only the benefits but also the compromises of each approach, whether in terms of residue formation, mechanical stability, or processing cost. The review further suggests that hybrid strategies, which combine different poreformers, could offer a more balanced route toward improved microstructures. Finally, future directions are outlined, with emphasis on nanostructured agents, scalable fabrication methods, and techno-economic considerations to support the commercial adoption of SOFC technology.

Abstract: The demand for refractory materials continues to increase, particularly in the copper smelting industry. Flash Smelting Funaces (FSF) require refractories that can withstand high temperatures and aggressive chemical interactions. This study evaluates the performance of Magnesia – Chromite as refractory materials in FSF through tests such as Thermal Expansion, Porosity, Cold Crushing Strength, Bulk Density and Thermal Conductivity. Initial test results show that the brick has high resistance to thermal shock, with a thermal expansion value of -0.3% cold crushing strength of 63.4 Mpa, bulk density of 3.22 g/cm3, porosity of 12.76% and thermal conductivity ranging from 2.8 to 2.9 W/m.K.

Abstract: Epoxy-based composites used in the aerospace industry are highly sensitive to moisture absorption, which can lead to porosity formation during the curing process and compromise structural integrity. Therefore, accurate prediction of temperature fields, degree of cure, and moisture concentration is essential for process optimization and defect mitigation. However, classical numerical approaches for solving the coupled governing equations are computationally expensive, limiting their applicability in real-time analyses and optimization strategies. In this work, Physics-Informed Neural Networks (PINNs) are investigated for predicting the transient thermal behavior, cure kinetics, and moisture concentration in an epoxy composite laminate during autoclave curing. Two PINNs are developed: the first solves the coupled transient heat transfer and cure kinetics equations in a compositetooling system, while the second predicts the moisture concentration field in the laminate using the temperature information provided by the first network. Different network architectures are evaluated, and their performance is compared with numerical solutions obtained via the Finite Volume and Finite Element Methods. The results demonstrate that PINNs accurately reproduce temperature profiles, degree of cure, and moisture concentration, achieving high coefficients of determination, while also providing significant computational efficiency advantages during the prediction stage. These findings highlight the potential of PINNs as a robust and efficient tool for modeling complex coupled phenomena in composite manufacturing processes.

Abstract: Carbon Fiber Reinforced Polymers (CFRPs) are essential to the aerospace industry, offering superior strength-to-weight ratios. Currently, the manufacturing of primary structures via standard autoclave curing is a robust, mastered process that successfully minimizes defects, keeping porosity levels below critical thresholds (typically < 1 %). Consequently, porosity is generally not considered as an issue in standard, optimized production lines.However, this stability may be affected by emerging industrial paradigms aimed at increasing production rates and reducing costs. The shift toward accelerated manufacturing – characterized by rapid heating rates, shortened cure cycles and by new manufacturing processes – and the introduction of complex material architectures risk re-introducing significant porosity. In parallel, there is currently no numerical model capable of accurately predicting porosity formation and evolution under these complex conditions. Existing simulation approaches are typically macroscopic and rely on homogenized porous media assumptions, failing to capture the essential micro-scale interactions between bubbles and fibres.To address this gap, this study presents an extended, custom multi-physics Computational Fluid Dynamics (CFD) solver built upon an existing OpenFOAM framework. The goal is to provide the first predictive tool for void evolution within realistic microstructures. The numerical framework couples a two-phase compressible flow model with the complete thermo-chemo-rheological physics of thermoset curing.The solver is applied to 2D Representative Volume Elements (RVEs) of a prepreg ply. Simulations of a standard autoclave cycle demonstrated the solver's ability to capture micro-scale dynamics, showing how voids are compressed and transported during the resin viscosity drop before being frozen at gelation. A parametric study comparing 3-bars and 7-bars pressures confirmed the model's physical ability in predicting void volume reduction.While currently focused on mechanical compression, the tool is designed to support the development of future manufacturing cycles. Future work will incorporate moisture diffusion physics and includes experimental validation via X-ray micro-tomography and in-situ synchrotron monitoring.

Abstract: Laser powder bed fusion (LPBF) parts are commonly fabricated using nominally uniform process parameters; however, local variations in thermal boundary conditions can significantly influence part quality. In this study, the spatial distribution of build-plate temperature during LPBF of Inconel 718 was experimentally characterized using a thermocouple grid, and its influence on porosity, microstructure and hardness was investigated. Despite a nominal build-plate set temperature of 180 °C, measured temperatures ranged from approximately 101 °C to 120 °C and exhibited a pronounced radial gradient from the center toward the edges of the build-plate. Cubic samples fabricated at locations corresponding to the highest and lowest local temperatures showed distinct microstructural differences, with higher temperatures promoting slightly coarser cellular–dendritic morphologies and lower hardness values. Although bulk volumetric porosity showed identical values for both locations (≈0.01 vol.%), the pore populations differed: the hotter location contained fewer but locally larger voids while the cooler location exhibited a higher number density of smaller pores, as shown by equivalent-diameter histograms and cumulative distributions. Samples produced at cooler locations exhibited finer microstructures and higher hardness. These results demonstrate that spatial non-uniformity in build-plate temperature can lead to local variations in microstructure and mechanical properties within a single LPBF build, highlighting the importance of characterizing local thermal conditions when establishing reliable process-structure property relationships.

Abstract: In cold bulk metal forming, coatings based on zinc phosphate are commonly used for lubrication. This has a negative impact on the environment, negatively affects human health, and requires significant pre-and post-surface treatments. Powder metallurgical (PM) components are a promising alternative to zinc phosphate coatings due to the process related porosity of the workpiece which acts as lubricant reservoir. During the forming process, the lubricant stored in the pores is released and lubricates the tool and workpiece surfaces. For an efficient process design of such components, finite element method (FEM) is an effective tool to analyse forming and friction behaviour. To this end, a realistic material model is essential for accurate simulation results. Hence, in this work, the flow behaviour of PM semi-finished products is characterised by means of compression and tensile tests. The results indicate that the material exhibits different behaviour under compression and tension. In compression, the material demonstrates higher yield strength and flow stresses compared to tension. Additionally, inhomogeneity of the material distribution can be observed, characterised by a denser core and more porous outer regions. The porous outer regions make it suitable for storing lubricant for application in forming processes.

Abstract: This study presents the preliminary characterization of commercial calcium oxide (CaO) and aluminum oxide (Al₂O₃) catalysts intended for application in the catalytic upgrading of biomass-derived bio-oil. The catalysts were characterized using Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area analysis, Thermo gravimetric Analysis (TGA), and X-ray Diffraction (XRD). SEM images revealed that both catalysts exhibit irregular, rough-surfaced particles with visible fractures and mesostructured textures conducive to catalytic activity. BET results indicated a specific surface area of 50.301 m²/g for CaO and 129.442 m²/g for Al₂O₃, with corresponding pore diameters of 2.64 nm and 2.647 nm, respectively, confirming their mesoporosity. TGA of CaO showed substantial weight loss associated with moisture, hydroxide, and carbonate decomposition, indicating the need for pre-calcination to restore active oxide phases. In contrast, Al₂O₃ exhibited minor mass loss mainly due to dehydration and dehydroxylation of surface-bound species. XRD analysis confirmed the presence of crystalline γ-Al₂O₃ and highly crystalline CaO with characteristic diffraction planes for their respective phases. These findings demonstrate that both commercial catalysts possess favorable physicochemical properties particularly high surface area, thermal stability, and mesoporous structure that make them promising candidates for vapor-phase upgrading in biomass pyrolysis systems.

Abstract: Wire-net stainless steel (WS) is an alternative material used to enhance heat transfer in solar air heater (SAH) by inducing swirling or rotating airflow as air passes through its pores. In this study, WS with varying porosity—corresponding to pore per inch (PPI) of 16, 20, and 25—and a constant pitch distance (P) of 0.06 m was installed within the flow channel of the SAH, and air was used as the working fluid under turbulent flow. The results showed that WS significantly improved heat transfer performance, though accompanied by increased pressure drop. An increase in PPI resulted in a maximum of Nusselt number and friction factor by factors of 13.81 and 238.61, respectively, compared to SAH without WS. The highest thermal enhancement factor of 2.48 was observed at PPI=20.

Abstract: The paper presents a new concept of a thermally sprayed composite coating obtained by mixing NiCrAl powder with chromium carbide Cr₃C₂ in an amount of approximately 30 wt.%. The aim of the research was to obtain a material combining the advantages of a metallic matrix and a ceramic phase, with increased resistance to wear and erosion. The plasma spraying (APS) process was carried out on a carbon steel substrate with variable technological parameters: arc current intensity (300/500/700 A) and hydrogen flow (4/8/12 NLPM), while maintaining the other conditions constant.The thickness, porosity, microstructure, chemical composition (using the EDS method), hardness, erosion resistance, and tribological wear of the coatings were evaluated. The results showed that the greatest thickness (approx. 150 µm) and lowest porosity (below 3 vol. %) were obtained at the maximum process parameters – 700 A and 12 NLPM. In turn, the thinnest and most irregular coating (approx. 70 µm) was obtained at the lowest hydrogen flow (4 NLPM), which was due to insufficient melting of the powder particles.Increasing the current intensity and hydrogen flow had a beneficial effect on all analyzed coating properties – especially hardness (up to 273.7 HV0.2), erosion resistance (the smallest mass loss of 0.007 g), and tribological wear resistance (the smallest volume loss of 2.925 mm³). A decrease in any of the parameters resulted in a deterioration of the layer properties. The optimal mechanical and structural properties of the NiCrAl + Cr₃C₂ composite coating were achieved at the maximum plasma spraying parameters: a power current of 700 A and a hydrogen flow rate of 12 NLPM.

Abstract: The microstructural characteristics of externally solidified crystals (ESCs) and porosities in a non-heat-treated high-pressure die-cast AlSi9MnVZr alloy are investigated under two distinct process conditions: one with the application of lower intensification pressure and the other with higher intensification pressure. Optical microscopy (OM), scanning electron microscopy (SEM), and computed tomography (CT) are employed to analyze the ESCs and porosity distribution. The alloy's microstructure primarily consists of primary α-Al, ESCs, Al-Si eutectic, and iron-rich phases. ESCs nucleate in the shot sleeve, while α-Al forms within the die cavity. When the lower intensification pressure is applied, larger dendritic ESCs are observed, along with significant gas porosity, shrinkage pores, and numerous smaller dispersed pores, resulting in a high porosity fraction. Conversely, the application of higher intensification pressure results in a notable refinement in ESCs morphology, with a significant reduction in their diameter and area fraction. Additionally, the size and fraction of porosity decrease substantially, indicating a marked improvement in casting quality.