Search Results (88)

This study demonstrates the successful fabrication of high-performance reaction-bonded silicon carbide (RBSC) ceramics through an optimized liquid silicon infiltration (LSI) process employing multi-modal SiC particle gradation and nano-carbon black (0.6 µm) additives. By engineering porous preforms with hierarchical SiC distributions and tailored carbon sources, the resulting ceramics achieved a compressive strength of 2393 MPa and a flexural strength of 380 MPa, surpassing conventional RBSC systems. Microstructural analyses revealed homogeneous β-SiC formation and crack deflection mechanisms as key contributors to mechanical enhancement. Ultrafine SiC particles (0.5–2 µm) refined pore architectures and mediated capillary dynamics during infiltration, enabling nanoscale dispersion of residual silicon phases and minimizing interfacial defects. Compared to coarse-grained counterparts, the ultrafine SiC system exhibited a 23% increase in compressive strength, attributed to reduced sintering defects and enhanced load transfer efficiency. This work establishes a scalable strategy for designing RBSC ceramics for extreme mechanical environments, bridging material innovation with applications in high-stress structural components. Full article

This paper presents a novel, non-contact method for measuring capillary water uptake in porous materials based on the phenomenon of moisture-induced expansion. The proposed approach establishes a quantitative relationship between the amount of water absorbed by the material and the deformations measured on its surface. Digital Image Correlation (DIC) was used to track the displacements of reference points on gypsum specimens during capillary rise. The absorbed water mass was determined from the recorded displacements using a mechanical model that incorporates the moisture expansion coefficient. The method was validated by comparison with conventional continuous gravimetric measurements. The results demonstrate that the displacement-based approach accurately captures the capillary rise process, particularly in the initial phase, where the gravimetric method suffers from significant measurement errors due to surface tension effects. The proposed method eliminates these limitations, providing higher accuracy and temporal resolution. In addition, it enables the testing of larger samples and offers the potential for spatially resolved moisture analysis. The findings confirm that the method is suitable for studying moisture transport in porous materials and may serve as a valuable alternative to traditional gravimetric techniques. Full article

The dynamic non-equilibrium effect (DNE) describes the non-unique character of saturation–capillary pressure relationships observed under static, steady-state, or monotonic hydrodynamic conditions. Macroscopically, the DNE manifests as variations in soil hydraulic characteristic curves arising from varying hydrodynamic testing conditions and is fundamentally governed by soil matrix particle size distribution. Changes in the DNE across porous media with discrete particle size fractions are investigated via stepwise drying experiments. Through quantification of saturation–capillary pressure hysteresis and DNE metrics, three critical signatures are identified: (1) the temporal lag between peak capillary pressure and minimum water saturation; (2) the pressure gap between transient and equilibrium states; and (3) residual water saturation. In the four experimental sets, with the finest material (Test 1), the peak capillary pressure consistently precedes the minimum water saturation by up to 60 s. Conversely, with the coarsest material (Test 4), peak capillary pressure does not consistently precede minimum saturation, with a maximum lag of only 30 s. The pressure gap between transient and equilibrium states reached 14.04 cm H₂O in the finest sand, compared to only 2.65 cm H₂O in the coarsest sand. Simultaneously, residual water saturation was significantly higher in the finest sand (0.364) than in the coarsest sand (0.086). The results further reveal that the intensity of the DNE scales inversely with particle size and linearly with wetting phase saturation (Sw), exhibiting systematic decay as Sw decreases. Coarse media exhibit negligible hysteresis due to suppressed capillary retention; this is in stark contrast with fine sands, in which the DNE is observed to persist in advanced drying stages. These results establish pore geometry and capillary dominance as fundamental factors controlling non-equilibrium fluid dynamics, providing a mechanistic framework for the refinement of multi-phase flow models in heterogeneous porous systems. Full article

The crystallization of soluble salts is one of the most significant agents of deterioration affecting porous building materials in historical architecture. This process not only compromises the physical integrity of the materials but also results in considerable aesthetic, structural, and economic consequences. Soluble salts involved in these processes may originate from geogenic sources—including soil leachate, marine aerosols, and the natural weathering of parent rocks—or from anthropogenic factors such as air pollution, wastewater infiltration, and the use of incompatible restoration materials. This study examines the role of capillary rise as a primary mechanism responsible for the vertical migration of saline solutions from the soil profile into historic masonry structures, especially those constructed with calcareous stones. It describes how water retained or sustained within the soil matrix ascends via capillarity, carrying dissolved salts that eventually crystallize within the pore network of the stone. This phenomenon leads to a variety of damage types, ranging from superficial staining and efflorescence to more severe forms such as subflorescence, microfracturing, and progressive mass loss. By adopting a multidisciplinary approach that integrates concepts and methods from soil physics, hydrology, petrophysics, and conservation science, this paper examines the mechanisms that govern saline water movement, salt precipitation patterns, and their cumulative effects on stone durability. It highlights the influence of key variables such as soil texture and structure, matric potential, hydraulic conductivity, climatic conditions, and stone porosity on the severity and progression of deterioration. This paper also addresses regional considerations by focusing on the context of Spain, which holds one of the highest concentrations of World Heritage Sites globally and where many monuments are constructed from vulnerable calcareous materials such as fossiliferous calcarenites and marly limestones. Special attention is given to the types of salts most commonly encountered in Spanish soils—particularly chlorides and sulfates—and their thermodynamic behavior under fluctuating environmental conditions. Ultimately, this study underscores the pressing need for integrated, preventive conservation strategies. These include the implementation of drainage systems, capillary barriers, and the use of compatible materials in restoration, as well as the application of non-destructive diagnostic techniques such as electrical resistivity tomography and hyperspectral imaging. Understanding the interplay between soil moisture dynamics, salt crystallization, and material degradation is essential for safeguarding the cultural and structural value of historic buildings in the face of ongoing environmental challenges and climate variability. Full article

Herein, a novel super-hygroscopic material, steam-exploded modified corn stalk pith (SE-CSP), was developed from corn stalk pith (CSP) via the steam explosion (SE) method, and its hygroscopic properties and mechanisms were evaluated. The results confirmed that SE effectively removed lignin and hemicellulose, disrupted the thin cell walls of natural CSP, and formed an aligned porous structure with capillary channels. SE changed the bonding distribution and surface morphology, and enhanced the crystallinity and thermal stability of CSP. The equilibrium hygroscopic percentage of SE-CSP (62.50%) was higher than that of CSP (44.01%) at 25 °C and 80% relative humidity (RH), indicating significantly greater hygroscopicity. The hygroscopic process of SE-CSP followed a Type III isotherm and fitted the Guggenheim–Anderson–de Boer (GAB), Peleg, and pseudo-first-order kinetic models. This process exhibited multi-layer adsorption with enthalpy-driven, exothermic behavior, primarily through physical adsorption involving hydrogen bonds and van der Waals forces. This work offered a new approach for advancing sorption dehumidification technology. Full article

This study presents a preliminary evaluation of candidate wick material and working fluid for a flat-loop heat pipe (F-LHP) designed to operate within the temperature range of 500–700 K. The selection process considered key thermal and physical parameters, including thermal conductivity, chemical compatibility between wick and fluid, capillary pressure generation, pressure drop across the wick structure, and structural integrity at elevated temperatures. A range of metallic and ceramic wick materials, along with suitable high-temperature working fluids, were reviewed and compared based on performance metrics and practical availability. Special attention was given to oxidation and corrosion resistance, capillary performance, and thermal stability under elevated-temperature conditions. Nine different porous wicks with distinct materials and microstructures—differing in pore size, porosity, and permeability—were analyzed in combination with seven different working fluids. The analysis focused on determining which combinations generated the highest capillary pressure and which exhibited the lowest flow resistance due to external flow, thereby enhancing the LHP’s performance. Based on these results, the study identifies the most effective wick–fluid pairings for F-LHP applications, offering an optimal balance of thermal performance and long-term reliability. These findings provide a foundation for further experimental validation and the development of prototypes. Full article

Biomass residues from the agricultural industry, logging and wood processing activities have become a valuable fuel source. If processed under pyrolysis combustion, several products are generated. Bio-oil and gases are essential alternatives to fossil coal-based fuels for energy and electricity production, whose need is constantly growing. Biochar, the porous carbon-based lightweight product, often ends up as a soil fertilizer. However, it can be applied in other industrial sectors, e.g., in plastics production or in modifying cementitious materials intended for construction needs. This work dealt with the application of small amounts of softwood-based biochar up to 2.0 wt.% on hydration kinetics and a wide range of physical and mechanical properties, such as water transport characteristics and flexural and compressive strengths of modified cement pastes. In the comparison with reference specimens, the biochar incorporation into cement pastes brought benefits like the reduction of open porosity, improvement of strength properties, and decreased capillary water absorption of 7-day and 28-day-cured cement pastes. Moreover, biochar-dosed cement pastes showed an increase in heat evolution during the hydration process, accompanied by higher consumption of clinker minerals. Considering all examined characteristics, the optimal dosage of softwood-derived biochar of 1.0 wt.% of Portland cement can be recommended. Full article

The growing use of microfluidic-based devices necessitates an analysis of flow characteristics through both experimental methods and computational fluid dynamic (CFD) simulations. CFD simulations facilitate the investigation of various devices, including medical sensors, by providing detailed insights into flow behavior. In this study, we conducted experimental and CFD analysis of the microfluidic flow in three devices: a COVID-19 rapid test kit, a blood glucose kit, and a PDMS kit. Our findings revealed that the changes in wall adhesion (contact angles) during the capillary flow could cause significant deviation from theoretical flow speed predictions. A hemodynamic analysis of the blood glucose kit and PDMS kit showed that capillary filling decreased in length, and flow speed could depend on the microchannel diameter. CFD results indicated the prominent role of porosity in the simulation of porous media material such as the COVID-19 test kit, as well as surface tension coefficients and wall adhesion (contact angles) in blood glucose kits and PDMS kits. Therefore, considering adaptive dynamic contact angles in CFD simulation software such as Ansys-Fluent 2024 could result in a more accurate prediction than simplified theoretical techniques, which is useful for sensor optimization and development. Full article

The inherent porous structure of concrete enables the penetration of water and Cl⁻ ions through its pores, which eventually leads to rebar corrosion within the concrete. Consequently, the densification and impermeability of concrete protective layers play a critical role in the durability of reinforced concrete structures. This study proposes a composite anti-corrosion treatment for mortar protective layers by integrating nano-ion capillary crystalline with silane hydrophobic processing. Targeting existing mortar samples, a series of experiments were conducted, utilizing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential scanning calorimetry-thermogravimetry (DSC-TG), X-ray computed tomography (X-CT), contact angle measurements, permeability tests, and electrochemical tests. These experiments systematically evaluated the effects of composite anti-corrosion treatment on the microstructure of hydration products, pore characteristics, surface hydrophobicity, impermeability, and the overall corrosion resistance of mortar-rebar samples in a Cl⁻-contained environment. The results reveal that nano-ion capillary crystalline materials react with free calcium ions in the mortar to produce secondary hydration products, effectively filling micro-pores, densifying the pore structure and inhibiting the invasion of Cl⁻ ions. The combination of capillary crystalline and silane hydrophobic processing synergistically enhances surface hydrophobicity and impermeability, preventing the ingress of corrosive agents, such as Cl⁻ ions, and significantly improving the anti-corrosion performance of mortar in a Cl⁻-contained environment. Full article

Urbanization in hot and humid regions such as southern China has increased the demand for comfortable indoor environments. In order to design a material for efficient passive indoor humidity regulation, this study investigates a composite material that combines the hygroscopic properties of salt and the adsorption capacity of diatomaceous earth (DE). Firstly, we prepared DE and boehmite into moisture-absorbing porous materials. Then, the initial DE-based sample was innovatively doped with SiO₂ nanomaterials and loaded with LiCl to enhance the humidity regulation ability of the composite, especially in the adsorption and desorption ability of water vapour. The microstructure and phase composition of the composite samples were analysed, and we observed an increase in porosity, filling performance and capillary condensation upon the introduction of SiO₂ nanoparticles. The hygroscopic salt loaded into the pores can absorb more water when exposed to the ambient humidity. This synergic effect can effectively improve the hygroscopic performance of the composite material while maintaining the stability of the physical and chemical properties. The optimized samples showed a moisture absorption rate of 28% in high-humidity environments, meeting moisture buffer value evaluation standards. The study’s findings lay the foundation for the future integration of these materials through advanced manufacturing technologies. Full article

Ground source heat pump systems rely on soil conductivity for optimal performance, and soil conductivity is primarily influenced by soil moisture content. In this study, we investigate how biochar, a porous material derived from biomass gasification and pyrolysis, influences capillary water rise and moisture retention in soil. Mixtures of biochar with soil and sand in varying ratios, along with control mixtures, were prepared and tested on lab-scale equipment. The results showed that biochar-amended samples exhibited a significantly higher capillary water rise. At a height of 0.25 m above the water level, the minimum moisture content in the biochar-treated samples was 43.5%, much higher than the 6.5% recorded in the control group, which consisted of soil or soil and sand only. Even in the long term, mixtures with biochar maintained high moisture content, ranging from 36% to 57%, compared to the control’s 8%, at heights near 0.5 m over the free surface of the water. Moreover, the utilization of biochar as a soil improver in geothermal application is an innovative way for carbon sequestration which, in the analyzed conditions, leads to the storage of up to 0.7 tons of CO_2eq per square meter of geothermal field. Full article

Paraffin wax (PW) has significant potential for spacecraft thermal management, but low thermal conductivity and leakage issues make it no longer sufficient for the requirements of evolving spacecraft thermal control systems. Although free-state expanded graphite (EG) as a thermal conductivity enhancer can ameliorate the above problems, it remains challenging to achieve higher thermal conductivity (K) (>8 W/(m·K)) at filler contents below 10 wt.% and to mitigate the leakage problem. Two preparations of thermally conductive shape-stabilized PW/EG composites, using the pressure-induced method and prefabricated skeleton method, were designed in this paper. The expanded graphite formed a nanoscale porous structure by different methods, which enhanced the capillary action between the graphite flake layers, improved the adsorption and encapsulation of EG, and alleviated the leakage problem. The thermal conductivity and the latent heat of the phase-change materials (PCM) prepared by the two methods mentioned above are 9.99 W/(m·K), 10.70 W/(m·K) and 240.06 J/g, 231.67 J/g, respectively, at EG loading by 10 wt.%, and the residual mass fraction was greater than 99% after 50 cycles of high and low temperature. In addition, due to the excellent thermal management capability of PW/EG, the operating temperature of electronic components can be stably maintained at 68–71 °C for about 15 min and the peak temperature can be reduced by at least 23 °C when the heating power of the electronic components is 10 w. These provide novel and cost-effective methods to further improve the management capability of spacecraft thermal control systems. Full article

The moisture transfer coefficient is a key parameter for analyzing the moisture-based physical properties of materials and studying the heat–moisture coupling process within building envelopes. The liquid-water transfer coefficient, as an important aspect of this process, plays a significant role, especially under high-humidity conditions. However, the global research on liquid-water transfer coefficients is still far from complete. To further enhance the research on liquid-water transfer coefficients, this study conducted capillary water absorption experiments on seven traditional and new porous building materials, focusing on testing the moisture transfer coefficients, primarily the liquid-water transfer coefficient. A novel analysis regarding the impact of sealing materials was proposed, based on the experimental results. Based on the experimental data, the concept of a critical value related to the variation in the capillary moisture content and the liquid-water diffusion coefficient was raised, and, building upon traditional empirical models, a completely new computational model was proposed. Data processing was carried out using methods such as variability analysis, correlation analysis, and nonlinear regression for model fitting. The research findings indicate the following: (1) The capillary water absorption rate and capacity of a material are influenced by its density and porosity. (2) In terms of sealing materials, self-adhesive films performed better than non-adhesive films. (3) The concept of critical capillary moisture content was proposed, based on the rate of change in the liquid-water diffusion coefficient. For the threshold of $w$ ≤ 80%, a new calculation model with a higher correlation coefficient was proposed which can meet the calculation requirements of the diffusion coefficient under the vast majority of relative-humidity conditions. Full article

Free-standing capillary microfluidic channels were directly printed over printed electrodes using a particle/polymer mixture to fabricate microfluidic–electrochemical devices on polyethylene terephthalate (PET) films. Printed devices with no electrode modification were demonstrated to have the lowest limit of detection (LOD) of 7 μM for sensing glucose. The study shows that both a low polymer concentration in the mixture for printing the microfluidic channels and surface modification of the printed microfluidic channels using 3-aminopropyltrimethoxysilane can substantially boost the device’s performance. It also shows that both device structure and enzyme doping level of the devices play an important role in ensuring the best performance of the devices under various testing conditions. Full article

Hypercrosslinked polymers (HCPs) constructed by the Friedel–Crafts alkylation reaction of aromatic compounds have emerged as a new class of porous materials with unique merit. Herein, a HCP named HCP-TPB was coated onto a capillary column through in situ synthesis. The prepared column exhibited a nonpolar nature, and the column efficiency for n-dodecane was 3003 plates m⁻¹. Moreover, the relative standard deviations of retention time and peak area for six replicate injections of the C3–C6 were lower than 0.1% and 1.5%, respectively. The results of this study showed that it is very promising to utilize HCPs as stationary phases for the separation of C3–C6. Full article