Internal Pore Structure Research Articles

Effect of pore-forming agent on degradation of phenol by iron tailings based porous ceramics

In order to realize the resource utilization of solid waste and the treatment of phenol wastewater in China, a new porous ceramic granules (PCG) with the function of degrading phenol wastewater was prepared by using titanium-containing blast furnace slag, iron tailings and fly ash as raw materials, which realized the sustainable development of "treating waste with waste". The effects of different pore forming agents on the structure, morphology, ionic state of PCG samples and the adsorption behavior of phenol in aqueous solution were investigated. The results show that the change of pore forming agent has no obvious change on the crystal structure. When carbon powder (CP) and starch (SH) are used as pore forming agents, the internal pore structure is relatively dense and less porous, and it is not easy to form liquid channels. When ammonia bicarbonate (NH) is used as pore-forming agents, the internal pore structure is very developed and has many three-dimensional pore structures. Under the conditions of PH 2, phenol concentration 10 mg/L and solid-liquid ratio 3 g/L, TOC removal rates of CP-PCG, SH-PCG and NH-PCG samples after 72 h adsorption reaction were 39.10 %, 14.00 % and 93.29 %, respectively. In addition, the surface functional groups, hydrogen bonds and π-π interactions of PCG samples may be involved in the adsorption of phenol. This work not only provides a low-cost, environmentally friendly and simple technology for phenol-containing wastewater treatment, but also provides a new idea for the effective use of solid waste resources.

Oleogel for improving the texture and flavor in rice cooking: Preparation from natural wax and rice bran oil and characterization

This study involved the preparation and characterization of oleogels from rice bran oil with different waxes and the potential application in improving the texture and flavor in rice cooking. The findings revealed a substantial improvement in rice texture with the addition of oleogel, particularly noteworthy at a 3% (w/w) incorporation of RBW (Rice Bran Wax). Under this condition, the hardness reached 15.75N, and stickiness measured 2.16N. The incorporation of 1–3% (w/w) oleogel significantly enhances the color vibrancy of rice during the cooking process, resulting in an increase in the L* value of the rice from 73.86 to 73.95-76.74. Sensory evaluation revealed higher scores for BW (Bee Wax) and RBW at 40.68 and 40.23 points, respectively. Microscopic structural analysis indicated that the incorporation of RBW oleogel led to rice samples with the smallest pores, contributing to a more refined internal pore structure in the grains. In the control rice, 7 aldehyde compounds were detected with a relative content of 43.44%. The addition of oleogel increased the number of aldehyde compounds to 9, with a relative content of 48.06%. This study expands the potential applications of oleogels in rice cooking, enriching flavor profiles and presenting opportunities for integration into the food industry.

Study of the Performance of Emulsified Asphalt Shotcrete in High-Altitude Permafrost Regions

To improve the performance of shotcrete in high-altitude and low-temperature environments, emulsified asphalt shotcrete (EASC), which can be used in negative-temperature environments, was prepared by using low-freezing-point emulsified asphalt, calcium aluminate cement, and sodium pyrophosphate as modified materials. The effect of emulsified asphalt on the performance of shotcrete was investigated through concrete spraying and indoor tests. Then, the modification mechanism of emulsified asphalt with respect to EASC was analyzed by combining scanning electron microscopy images and the pore structure characteristics of EASC. The results showed that in a negative-temperature environment, the incorporation of emulsified asphalt delayed the formation of the peak of the cement hydration exotherm, slowed the rate of the cement hydration exotherm, reduced the thermal perturbation of permafrost by EASC, increased the cohesion of the concrete, improved the bond strength between EASC and permafrost, and reduced the rate of rebound. The mechanical strength of the studied EASC decreased upon increasing the amount of emulsified asphalt in the admixture, and its resistance to cracking gradually improved. A content of less than 5% emulsified asphalt could improve the internal pore structure of EASC, thus improving its durability. Increasing the content of emulsified asphalt affected the hydration process of the cement, and the volume content of the capillary pores and macropores increased, which reduced the durability of the EASC.

Investigation of key morphological parameters of pores in different grades of asphalt mixture based on CT scanning technology

The internal pore structure of asphalt mixtures directly influences their permeability characteristics. Current research has not yet clarified the quantitative characterization of different types of meso-pore structures and their impact mechanisms on permeability characteristics. Therefore, this study, based on the acquisition of the internal pore structure of asphalt mixtures through CT non-destructive scanning technology, classifies pores according to their characteristics. It conducts a multi-dimensional and multi-scale qualitative and quantitative analysis of the meso-pore structures of asphalt mixtures in terms of pore distribution, equivalent radius of pore throats, inclination angle of pore throats, tortuosity of pore throats, and pore connectivity. The results indicate that the internal pore distributions of AC-16, SMA-16, OGFC-13, and OGFC-16 gradation asphalt mixtures are uniform, without noticeable segregation. The results of porosity obtained through non-destructive CT scanning technology demonstrate good consistency with those of macroscopic experiments. This demonstrates that analyzing CT images can accurately acquire pores and quantify pore characteristics. The number of pores in AC-16 gradation specimens is approximately 3–5 times that of other groups of gradation specimens, but the average volume of the pores is only 0.98 mm3. The average pore volume for SMA-16 gradation is 5.1 mm3, while for OGFC-13 and OGFC-16 gradation, the average pore volumes are 28.3 mm3 and 29.6 mm3, respectively. In SMA-16 grade specimens, the volume of open pores accounts for 95% of the total pore volume, despite the fact that open pores make up only 1% of the total number of pores. In the OGFC-13 and OGFC-16 graded asphalt mixtures, the volumes of interconnected pores account for 88.7% and 88.9% of the total pore volume, respectively. The number and volume proportion of pore throats decrease with the increase in pore throats angle, indicating that there are more pore throats with smaller angles, which are conducive to longitudinal drainage, and fewer pore throats with larger angles, which are conducive to lateral drainage. This suggests that the vertical permeability of samples formed by traditional Marshall compaction is usually greater than their horizontal permeability.

Multi-scale study on the mechanical properties of concrete based on crack propagation under hygrothermal coupling

During the long-term service of structures, the environmental temperature and humidity fields can lead to the evolution of the pore structure within concrete materials, thereby affecting changes in mechanical properties. However, the mechanisms of their influence still need further clarification and are challenging to correlate for prediction. Addressing this specific issue, the current study focuses on evaluating 78 cubic concrete specimens with C30 and C40 strength grades. These specimens were subjected to a 95 % humidity environment at temperatures of 40 °C, 60 °C, and 80 °C for durations of 30, 60, and 90 days. The research involved conducting both microstructural and macroscopic mechanical tests to quantify the evolution of internal hydrates, pore structures, and pore distribution, as well as to assess the changes in the macroscopic mechanical properties of the specimens. To accurately predict the process, a multiscale finite element model (FEM) based on the bilinear continuum cohesive damage model was established. This model quantifies the changes in mechanical properties of mesoscopic three-phase concrete due to microcrack evolution under hygrothermal coupling. To facilitate multiscale simulations between the Representative Volume Element (RVE) and macroscopic scale models, relevant subroutines were written using Umath, and parallel computing was employed to reduce the computational burden. For the macroscopic model in this study, a homogenized concrete cube model with dimensions identical to the experimental specimens was selected. The effectiveness of the parallel computational model was validated by comparing and analyzing the simulation results under uniaxial compression with the experimental data. The findings indicate that hygrothermal action leads to the initiation and expansion of microcracks within the concrete, thereby impacting the alteration of its mechanical properties. In addition, the parallel computing-based multiscale FEM can more accurately quantify the typical damage process of crack propagation while reducing the computational load and may provide relatively accurate predictions of the mechanical characteristics of concrete under the influence of hygrothermal coupling, ensuring effective modeling of macroscopic structural specimens in various temperature and humidity environments.

Construction of Hydrogels with Highly Salt-Resistant Honeycomb Porous Structures for Solar Desalination and Steam Generation.

Interfacial solar desalination is a method for desalinating seawater using solar energy, and the long-term use of this technology requires a stable evaporation rate and some ability to prevent salt crystallization. To address these issues, carbonized polydopamine-coated bentonite (C@PBT), poly(vinyl alcohol), and cellulose nanofibers were used to construct a three-dimensional oriented hydrogel evaporator with a multilayered honeycomb porous structure for long-term desalination. Carbon nanoparticles transferred between the layers of the bentonite, which increases the spacing of the layers and confers a more effective solar light trapping ability. The evaporation rate was 2.26 kg m-2 h-1 in 20 wt % NaCl solution, and no salt crystals were precipitated from the surface of the evaporator in 12 h of continuous operation. This phenomenon occurs due to the wide distribution of pore sizes and the large size of the pores within the evaporator, which create ample space for salt ions to move freely. Furthermore, after undergoing 300 cycles of compression, its internal pore structure remains intact, and the rate of evaporation remains stable. It ensures the evaporator stability during outdoor cycles. The research work provides an effective method to solve the salt accumulation problem and shows its great potential for application.

Fabrication of controlled porous and ultrafast dissolution porous microneedles by organic-solvent-free ice templating method

Porous Microneedles (PMNs) have been widely used in drug delivery and medical diagnosis owing to their abundant interconnected pores. However, the mechanical strength, the use of organic solvent, and drug loading capacity have long been challenging. Herein, a novel strategy of PMNs fabrication based on the Ice Templating Method is proposed that is suitable for insoluble, soluble, and nanosystem drug loading. The preparation process simplifies the traditional microneedle preparation process with a shorter preparation time. It endows the highly tunable porous morphology, enhanced mechanical strength, and rapid dissolution performance. Micro-CT three-dimensional reconstruction was used to better quantify the internal structures of PMNs, and we further established the equivalent pore network model to statistically analyze the internal pore structure parameters of PMNs. In particular, the mechanical strength is mainly negatively correlated with the surface porosity, while the dissolution velocity is mainly positively correlated with the permeability coefficient by the correlation heatmap. The poorly water-soluble Asiatic acid was encapsulated in PMNs in nanostructured lipid carriers, showing prominent hypertrophic scar healing trends. This work offers a quick and easy way of preparation that may be used to expand PMNs function and be introduced in industrial manufacturing development.

Study on the mechanical properties and microstructure of recycled concrete reinforced with basalt fibers and nano-silica in early low-temperature environments

Abstract The effects of basalt fibers (BF) and nano-silica (NS) on the mechanical properties and microstructure of recycled concrete (RC) in early low-temperature environments were investigated by placing the BF and NS modified RC specimens in the environments of −20, −10, 0, and 25°C for curing for 6 h, followed by standardized maintenance. The damage morphology and mechanical properties of modified RC were analyzed in such environments. The formulae for the compressive strength of RC, which was affected by BF and NS, were fitted using statistical product and service solutions, and a micromorphological analysis of the modified RC was conducted using scanning electron microscope. The mechanical properties of RC decreased owing to the influence of early low temperatures, among which 0°C caused the largest damage crack and the most serious effects. In the early low-temperature environments, the physical properties of RC generally increased and then decreased with the increase in BF dosage; however, increasing NS dosages improved its mechanical properties. The composite doping of BF and NS was more obvious than the single doping of BF or NS to enhance the performance of RC, and the internal pore structure was considerably improved. The preferred doping amounts were 3 kg m−3 of BF and 2% NS.

Surface-Area Enhanced Raman Spectroscopy of DNA in Porous Silica: A Quantitative and Reproducible Alternative to Plasmonic-Based SERS.

Despite the success of surface-enhanced Raman spectroscopy (SERS) for detecting DNA immobilized on plasmonic metal surfaces, its quantitative response is limited by the rapid falloff of enhancement with distance from the metal surface and variations in sensitivity that depend on orientation and proximity to plasmonic "hot spots". In this work, we assess an alternative approach for enhancing detection by immobilizing DNA on the interior surfaces of porous silica particles. These substrates provide over a 1000-fold greater surface area for detection compared to a planar support. The porous silica substrate is a purely dielectric material with randomly oriented internal surfaces, where scattering is independent of proximity and orientation of oligonucleotides relative to the silica surface. We characterize the quantitative response of Raman scattering from DNA in porous silica particles with sequences used in previous SERS investigations of DNA for comparison. The results show that Raman scattering of DNA in porous silica is independent of distance of nucleotides from the silica surface, allowing detection of longer DNA strands with constant sensitivity. The surface area enhancement within particles is reproducible (<4% particle-to-particle variation) owing to the uniform internal pore structure and surface chemistry of the silica support. DNA immobilization with a bis-thiosuccinimide linker provides a Raman-active internal standard for quantitative interpretation of Raman scattering results. Despite the high (30 mM) concentrations of immobilized DNA within porous silica particles, they can be used to measure nanomolar binding affinities of target molecules to DNA by equilibrating a very small number of particles with a sufficiently large volume of low-concentration solution of target molecules.

A discrete approach for modelling the permeability evolution of granite under triaxial and true-triaxial stress conditions

In deep underground engineering, modelling the seepage characteristics of rock masses under complex stress conditions is crucial for the safe construction and stable operation of a project. The permeability of the rock mass is not only controlled by its internal pore structure but is also closely related to the deformation and fracturing of the rock. Although discrete methods offer advantages in describing the formation and development of fractures, these methods still face challenges due to the difficulties in establishing microscopic seepage models. This paper introduces a new hydro-mechanical coupled numerical model. In this model, a simple method is proposed to couple the Rigid-Body-Spring Method (RBSM) for rock deformation and fracturing simulation and the Equivalent Matrix-Fracture Network (EMFN) for seepage simulation. Subsequently, the model is employed to simulate the permeability of granite under three-dimensional stress conditions. The simulation results show that under hydrostatic stress conditions, the model accurately captures the decrease in permeability due to pore compression and collapse. Additionally, under deviatoric stress conditions, it reveals the stage-wise increase in permeability caused by granite fracturing. Finally, the model is applied to study the permeability evolution behaviour of rocks under true triaxial stress conditions. The results unveiled the significant impact of the intermediate principal stress on permeability evolution and revealing the microscopic mechanisms underpinning these effects. This paper paves a way for enhancing the application of discrete methods in forecasting the permeability evolution behaviour of intricate rock masses.

Experimental study on the deterioration of mechanical properties of sandy mudstone under different water-gas interactions

Based on the water-rock-gas coupling test system, the work combined the scanning electron microscope and XTDIC 3D full-field strain measurement system. The Brazilian splitting test was performed on four groups of sandy mudstone specimens under contrast (CO), mash-gas soaking (MS), water-mash gas soaking (WM), and water-soaking (WS) conditions. The tensile strength, deformation failure, and microscopic characteristics of fractures were studied to reveal the deterioration mechanism of the tensile properties of sandy mudstone under water-gas coupling. The results showed that the uniaxial tensile strength of sandy mudstone specimens under the three soaking conditions was less than that of the contrast conditions. Compared with specimens in the CO group, the tensile strength of specimens in MS-WS groups was reduced; the WS group decreased the most. Specimens changed from brittle failure to plastic failure after soaking. The decrease rate in strength after the peak was consistent with the change trend in tensile strength. It led to a larger localized deformation zone of specimens and more obvious displacement. The deformation localization zone of the WS group was the broadest, with the most intense displacement. Besides, stress concentration first occurred in the submerged part of the WM group. Fractures expanded in the direction of maximum principal strain. The internal pore structure of sandy mudstone specimens in each group changed after soaking. The average porosity, maximum pore area, and probability entropy of specimens in WS-MS groups increased compared to the CO group. The WS group had the largest reduction and the MS group had the smallest. The pre-peak energy storage capacity of sandy mudstone specimens was gradually weakened. Compared with the CO group, that in the WS-MS groups was reduced. The WS group had the greatest reduction, and the MS group had the smallest. The deterioration effect of water on the interior of sandy mudstone was stronger than that of gas. The work is of great significance for understanding the stability of coal and rocks in closed-pit high-gas mines.

Understanding the drying mechanism of straw substrate culture block: Physicochemical properties, pore structure, and drying optimization

As a new type of agricultural waste block substrate utilization, the initial wet base state of the substrate culture block needs to be dried. Therefore, studying the drying mechanism of substrate culture block is critical. In this study, the substrate culture block in a dry state was taken as the research object. Based on physical and chemical properties, the internal section of the substrate culture block was characterized by scanning electron microscopy and the pore condition of the particles was quantified. The results showed that the internal pore structure was uniform and favorable for plant root growth. Based on the pore structure, pore channel modeling was constructed to investigate the distribution of the internal multiphase medium and to distinguish between channels and pore-blind channels. The applicability of the modeling was verified and discussed. By measuring the drying rate of the substrate culture block and classifying its drying stages as fast speed, constant speed, and slow speed, it is clarified that the forms of moisture existence are bound-state water and free-state water, and the moisture migration is prioritized as surface adsorption water, interparticle water, particle attached water, and capillary water. Innovate a method to quantify the change of pore space in the drying process by pore coefficient ratio to evaluate the drying quality. The results show that when the pore coefficient ratio is about 40 %, its moisture content is 20 %∼30 %, and the drying effect is best at this time. The physical drying test further confirmed the correctness of the conclusion of the drying stage division and water loss law. This study can provide a theoretical reference for the modeling study of the pore structure of the block matrix and the exploration of its drying mechanism.

Facile synthesis of MOF–808/RGO-based 3D macroscopic aerogel for enhanced photoreduction CO2

Three-dimensional (3D) macroscopic aerogels have emerged as a critical component in the realm of photocatalysis. Maximizing the integration of materials can result in enhanced efficiency and selectivity in photocatalytic processes. In this investigation, we fabricated MOF-808/reduced graphene oxide (RGO) 3D macroscopic aerogel composite materials employing the techniques of hydrothermal synthesis and freeze-drying. The results revealed that the macroscopic aerogel material exhibited the highest performance in CO2 reduction to CO, particularly when the concentration of RGO was maintained at 5 mg mL−1. In addition, we synthesized powder materials of MR-5 composite photocatalysts and conducted a comparative analysis in terms of photocatalytic CO2 reduction performance and electron transfer efficiency. The results showthat the macroscopic aerogel material boasts a high specific surface area, an abundant internal pore structure, and increased active sites. These attributes collectively enhance light energy utilization, and electron transfer rates, thereby, improving photothermal and photoelectric conversion efficiencies. Furthermore, we conducted in-situ FT-IR measurements and found that the M/R-5 aerogel exhibited the best CO2 adsorption capacity under a CO2 flow rate of 10 mL min−1. The density functional theory results demonstrate the correlation between the formation pathway of the product and the charge transfer pathway. This study provides useful ideas for realizing photocatalytic CO2 reduction of macroscopic aerogel materials in gas–solid reaction mode.

Effect of nanosilica and fiber on mechanical properties and microstructure of recycled coarse aggregates road concrete

Recycled coarse aggregate has its own characteristics of large porosity, high water absorption and high crushing index, which adversely affects the mechanical strength and durability of recycled aggregate concrete. In this study, the mechanical properties, durability and microstructure of recycled aggregate concrete (RAC) modified with nano-SiO2 (NS) and fibres were investigated to prepare road RAC, using NS polypropylene fibres (PPF) and basalt fibres (BF) as test variables. Compared with RAC only incorporating NS, NS and fibre synergism can significantly enhance the mechanical properties of recycled concrete, compressive strength increased by 27–51 %, flexural strength increased by 12 %, and abrasion resistance increased by 25–72 %. The synergistic effect of NS and PPF significantly improves the frost resistance of recycled concrete. NS has a volcanic ash effect which can react with calcium hydroxide to produce a large number of C-S-H in the secondary hydration reaction, making the internal structure of the cement matrix denser. Interfacial transition zone microstructure is more compact, thus interfacial transition zone porosity is effectively reduced. The hydration products are attached to the fibre surface, which enhances the bonding ability between the fibers and matrix. Therefore, the fibres effectively inhibit the generation and development of internal micro-cracks. NS optimises the internal pore structure of recycled aggregate concrete and enhances the interfacial transition zone, and NS synergistically with PPF can improve the strength and durability of various mechanical properties of recycled concrete. The research results provide the scientific basis for the application of road RAC.

Influence of basalt fiber and polypropylene fiber on the mechanical and durability properties of cement-based composite materials

To boost the mechanical strength and endurance quality of cement-based composites, basalt fiber and polypropylene fiber have been included cement-based composites in a single-doped and mixed manner, respectively. Through the tests of flexural strength, compressive strength, drying shrinkage and freeze-thaw cycle, the mechanics properties and endurance quality of cement-based composites with different fiber contents were analyzed. Scanning electron microscopy and a mercury intrusion test were used to compare and study the microstructure and pore structure properties of cement-based composites. The results indicate that the improvement of compressive strength for cement-based composites by single adding basalt, polypropylene fiber and mixed addition of two kinds of fibers is not obvious, but improving the flexural strength of composites by single addition of fiber and 1:1 mixing in a certain dosage range is effective. Among them, 1:1 mixed fiber shows a better advantage superposition effect, which shows better enhancement and toughening effect on composites. Fiber single doping and 1:1 mixing can reduce the Drying shrinkage and mass loss rate of the composites within a certain range, and enhance the composites' ability to resist Drying shrinkage and freezing. Based on the comprehensive mechanical properties and durability tests, it is recommended that the content range of the two fibers mixed with 1:1 is 0.4 %–0.6 %. Both basalt fiber and polypropylene fiber can be closely combined with the cement matrix, and randomly distributed in the composite material to form a network structure, which has the function of series skeleton, effectively inhibits the generation and expansion of cracks in the composite material, and improves the microstructure of the composite material. Both basalt fiber and polypropylene fiber can reduce the harmful pores and multi-harmful pores of the composite material, and transform them into harmless pores and less harmful pores, refine the internal pore structure of the composite material, and improve its compactness. The two kinds of fibers are randomly distributed to form a network structure, which refines the large pore size inside the composite material and blocks the connected pores, and the basalt fiber is refined to fill the interface between the polypropylene fiber and the cement matrix, so that the composite material is more compact, thereby significantly improving the mechanical properties and durability of the composite material.

Induced Aggregation, Solvent Regulation, and Supracluster Assembly of Aluminum Oxo Clusters.

ConspectusRecent years have witnessed the development of cluster materials as they are atomically precise molecules with uniform size and solution-processability, which are unattainable with traditional nanoparticles or framework materials. The motivation for studying Al(III) chemistry is not only to understand the aggregation process of aluminum in the environment but also to develop novel low-cost materials given its natural abundance. However, the Al-related clusters are underdeveloped compared to the coinage metals, lanthanides, and transition metals. The challenge in isolating crystalline compounds is the lack of an effective method to realize the controllable hydrolysis of Al(III) ions. Compared with the traditional hydrolysis of inorganic Al(III) salts in highly alkaline solutions and hydrolysis of aluminum trialkyl compounds conducted carefully in an inert operating environment, we herein developed an effective way to control the hydrolysis of aluminum isopropanol through an alcoxalation reaction. By solvothermal/low melting point solid melting synthesis and using "ligand aggregation, solvent regulation, and supracluster assembly" strategies, our laboratory has established an organic-inorganic hybrid system of aluminum oxo clusters (AlOCs). The employment of organic ligands promotes the aggregation and slows the hydrolysis of Al(III) ions, which in turn improves the crystallization process. The regulation of the structure types can be achieved through the selection of ligands and the supporting solvents. Compared with the traditional condensed polyoxoaluminates, we successfully isolated a broad range of porous AlOCs, including aluminum molecular rings and Archimedes aluminum oxo cages. By studying ring expansion, structural transformation, and intermolecular supramolecular assembly, we demonstrate unique and unprecedented structural controllability and assembly behavior in cluster science. The advancement of this universal synthetic method is to realize materials customization through modularly oriented supracluster assembly. In this Account, we will provide a clear-cut definition and terminology of "ligand aggregation, solvent regulation, and supracluster assembly". Then we will discuss the discovery in this area by using a strategy, such as aluminum molecular ring, ring size expansion, ring supracluster assembly, etc. Furthermore, given the internal and external pore structures, as well as the solubility and modifiability of the AlOCs, we will demonstrate their potential applications in both the solid and liquid phases, such as iodine capture, the optical limiting responses, and dopant in polymer dielectrics. The strategy herein can be applied to extensive cluster science and promote the research of main group element chemistry. The new synthetic method, fascinating clusters, and unprecedented assembly behaviors we have discovered will advance Al(III) chemistry and will also lay the foundation for functional applications.

Vat photopolymerization 3D printing of Al2O3 ceramic cores with strip‐shaped pores by using polyamide 6 fiber template

AbstractThe complex ceramic core used for hollow turbine blades requires high porosity and flexural strength. This work combined vat photopolymerization 3D printing with sacrificial template method to prepare Al2O3 ceramic cores with strip‐shaped pores using polyamide 6 (PA6) fibers as templates. When the porosity was greater than 30%, the maximum flexural strength reached up to 110.48 MPa. The sacrificial templating method improved the porosity of Al2O3 ceramic cores, forming an internal porous structure that combined strip‐shaped large pores with irregularly shaped small pores. The influences of PA6 fiber content and diameter on the shrinkage, porosity, microstructure, and comprehensive properties of alumina ceramic cores were studied, revealing the mechanism of the coexistence of high porosity and high strength.

Production of lightweight expanded aggregates from smectite clay, palygorskite-rich sediment and phosphate sludge

Abstract Lightweight expanded clay aggregates (LWAs) are porous materials with low density and high strength (EN-13055-1), and they are important in sustainable construction through their lightweight nature and ability to provide thermal or acoustic insulation. The objective of this work was therefore to evaluate the preparation of LWAs using a smectite clay (M1 formulation), whose application in common ceramic production is difficult. An alternative approach was proposed for the valorization of phosphate sludge and a palygorskite-rich sediment by mixing them with expanded clay (M2 formulation) for LWA production. This could result in economically cost-effective products with significant environmental benefits. Pellets were prepared and fired at various temperatures (1100°C, 1125°C and 1150°C), and relevant properties such as bloating index, density, water absorption and compressive strength were determined. Additionally, the microstructure, mineralogical transformations and phase compositions under various sintering temperatures were investigated. Increasing the temperature from 1000°C to 1150°C significantly improved the expansion properties of LWAs, and 1150°C seemed to be the optimal firing temperature at which the best expansion properties were achieved. In addition, the incorporation of the selected waste improved the properties of the final products, leading to lower density, greater strength and greater bloating with the development of the internal pore structure as compared to the LWAs without this addition. Because of their low density (0.6 g cm–3) and sufficient compressive strength (0.86 MPa), the manufactured LWAs can be used in construction (as insulating panels or in lightweight concrete) and in green roofs.

Multifunctional schwertmannite-loaded nano zero-valent iron for highly efficient removal of hexavalent chrome from aqueous solution

Adsorption and reduction are important ways to remediate hexavalent chrome [Cr(VI)] which is extremely hazardous to human health. Previous studies have shown that schwertmannite (Sch) and nano zero-valent iron (nZVI) are potential materials with high adsorption and strong reduction for Cr(VI), respectively. However, it has been well known that bare nZVI has limitations in remediating Cr(VI) due to its susceptibility to self-aggregation and oxidation in practical applications. Hence to address the above limitations, nZVI was added into the internal pore structure of Sch (nZVI@Sch) in this study and Cr(VI) removal capacity by nZVI@Sch in aqueous solution were systematically investigated. Results showed that under the conditions that the concentration ratio of Fe2+ and Sch is 0.25 mol/L, Cr(VI) initial concentration of 10 mmol/L, initial pH of 3, Cr(VI) remediation ability of nZVI@Sch reached up to 114.03 mg/g (with freeze-drying) and 165.69 mg/g (without freeze-drying) in 4 hours, respectively. Based on the characterization analysis of SEM-EDS, XPS and Zeta potential, the multifunctional synergistic effects of capture-reduction-adsorption-coprecipitation as a mechanism for the removal of Cr(VI) by nZVI@Sch were proposed in this study. This study provided a new remediation material and suggestions for chromium pollution remediation.

Mechanical Properties and Sulfate Freeze–Thaw Resistance of Calcium Carbonate Whisker-Reinforced Iron Ore Tailings Concrete

Iron ore tailings from iron ore mines pose environmental challenges. However, their reuse could provide significant environmental benefits. This study focused on producing clean concrete using iron ore tailings as crushed stone aggregate (IOTA) and calcium carbonate whiskers (CWs) as reinforcement. Five mixture groups were prepared: normal concrete (NAC) with natural crushed stone aggregate (NA), iron ore tailings concrete (TAC) with IOTA, and CW (10%, 20%, and 30%)-reinforced TAC (TAC-CW). Mechanical properties like the compressive strength (fcu) and splitting tensile strength (fst), as well as sulfate freeze–thaw (F-T) cycle resistance, were thoroughly investigated. Additionally, pore structure and microstructure were characterized using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) techniques. The results showed that IOTA’s complete replacement of NA decreased concrete mechanical properties and frost resistance, but incorporating CWs effectively compensated for these losses. Specifically, the fcu and fst of TAC-CW20 with 20% CWs increased by 23.26% and 49.6% compared to TAC and were higher than those of NAC. With increasing F-T cycles, concrete internal pore structure significantly deteriorated, and corrosive products increased significantly, which was further confirmed by SEM. TAC-CW20 significantly optimized pore structure. Overall, the successful application of iron ore tailings as eco-friendly materials enhanced concrete performance and reduced the environmental impact of construction activities.