Recent development on low-carbon/ultra-low carbon refractories with superior properties for the rapid development of green low-carbon economy and high-quality clean steel is a research hotspot. The structure and properties of low-carbon refractories in a variety of ways are optimized to solve the problem of deterioration of high- temperature properties caused by simple reduction of graphite content. The introduction of carbon nanomaterials can significantly reduce the overall carbon content of the material. Also, the mechanical strength and thermal shock resistance of carbon-containing refractories are improved simultaneously because the nanostructures absorb and buffer the thermal stress generated by a large number of thermal shocks. In addition, reinforcement phases such as carbides, borides and nitrides are also applied to improve the organizational structure and properties of low-carbon refractories to solve the long-standing problem of carbon source oxidation. However, the poor dispersion of nanomaterials in the matrix is a significant technical problem, and the synthesis process of composite powders is complex and challenging. High production costs and the difficulty of achieving large-scale application restrict the industrial development of these materials. The structural degradation at high temperatures leads to a decline in the strength of refractories and even deterioration of comprehensive performance, which cannot guarantee the stability of long-term service of refractories

The MAX phase materials were expected to achieve the balance between low carbonization and service performance of carbon-containing refractories due to their graphite-like layered structure, high thermal conductivity, high damage tolerance and good oxidation resistance and thermal shock resistance. In this work, in-situ Ti₃Si(Al)C₂ reaction bonded low carbon Al₂O₃-C refractory was prepared by a reactive melt infiltration method based on the preparation process of ceramic matrix composite materials. The effects of the amount of TiC/graphite in the prefabricated material and the type of Si-Al alloy as the infiltration medium on the phase composition, microstructure, physical properties, mechanical properties and thermal shock resistance of the refractories were investigated.

The phase composition and performance (i.e., the apparent porosity, bulk density and flexural strength) are different at different compositions of the preforms. Corundum, Ti₃Si(Al)C₂ and TiC phases appear in all the samples, and trace amounts of SiC, TiAl_xSi_y and residual Al also occur. When the preform does not contain graphite, the content of Ti₃Si(Al)C₂ in the sample is higher, and the apparent porosity is much lower. The flexural strength of the sample increases from 9.0 MPa and 23.4 MPa to 79.4 MPa and 82.2 MPa, respectively, when the graphite removes from the raw material. Also, the bulk density of refractories is higher. This is due to the poor wettability of graphite and alloy, which prevents the infiltration of alloy melt into the preform. Graphite reacts with Si to form SiC phase and consumes Si element, which affects the growth of subsequent Ti₃Si(Al)C₂ phase. The content of titanium carbide in the raw material also affects the generation of Ti₃Si(Al)C₂, increasing the content of titanium carbide is beneficial to generating more Ti₃Si(Al)C₂, which causes a lower porosity and a higher bulk density of Al₂O₃-Ti₃Si(Al)C₂-C efractories. The overall apparent porosity of samples Al₅₀Si₅₀ and Al₉₅Si₅ is lower than that of sample Al₅Si₉₅, and the bulk density is relatively high. This is related to a fact that the presence of Al promotes the infiltration of alloy melt into the precast and is conducive to the formation of Ti₃Si(Al)C₂. The flexural strength of the sample T25@Al₅₀Si₅₀ using Al₅₀Si₅₀ alloy as a penetration medium increases from 75.5 MPa to 110.5 MPa after thermal shock. The rich toughening mechanism of Ti₃Si(Al)C₂ helps to improve the thermal shock resistance of the refractory, and the oxidation products generated after the oxidation of Ti₃Si(Al)C₂ can make the structure of the refractory more dense. The presence of whiskers in the refractory is also beneficial for better thermal shock resistance.

Low carbon Al₂O₃-Ti₃Si(Al)C₂-C refractory could be prepared after the preform was infiltrated with Al₅₀Si₅₀ alloy. The presence of graphite in the preform obstructed the penetration of Si-Al alloy and ultimately affected the mechanical properties of the sample. The flexural strength of the preform without graphite was up to 82.2 MPa after the infiltration reaction at 1550 ℃. The content of Al in the infiltration medium had an effect on the production of Ti₃Si(Al)C₂ in the refractory. The presence of Al was conducive to the reduction of twinning grain boundary energy between TiC grains, effectively promoting the formation of TiCx twins. Ti₃Si(Al)C₂ phase was also easy to nucleate from the TiCx twin and grow in the Ti-Si-Al liquid phase. The Ti₃Si(Al)C₂ phase consumed energy through various deformation mechanisms, thus increasing the flexural strength of the refractory material at room temperature. Also, Ti₃Si(Al)C₂ could form a continuous and dense oxide layer during the thermal shock process, effectively preventing the Ti₃Si(Al)C₂ inside the sample from being further oxidized. The formation of the dense layer could restore or even strengthen the mechanical properties of the refractory after thermal shock. The flexural strength of sample T25@Al₅₀Si₅₀ increased from 75.5 MPa to 110.5 MPa after thermal shock.

Silicified graphite composites, as a type of ceramic-based solid lubrication material, possess the superior properties of silicon carbide ceramics, such as high strength and high hardness, along with high-temperature strength, and self-lubricating performance of graphite materials. It has extensive application prospects in aerospace, chemical engineering, and nuclear energy. The reactive melting infiltration (RMI) method features near-net shape forming, a short processing cycle, and low cost, as an efficient approach for fabricating silicified graphite composites. Nevertheless, the infiltration reaction of liquid silicon into the porous carbon preform is extremely rapid after driven by reactive wetting and capillary forces, resulting in a sharp consumption of carbon. Hence, controlling the graphite content emerges as a crucial issue for the development of silicified graphite composites with superior lubrication properties. In this paper, a carbon source was fabricated through carbon source modification to prepare composite graphite spheres and coat on the surface of the composite graphite spheres with nano-carbon black. Subsequently, silicified graphite composites were prepared via compression molding and reaction melt infiltration. The carbon content of the composites was regulated via altering the particle size of the composite graphite spheres. The influence of the carbon content on the mechanical and tribological properties of the silicified graphite composites was discussed, and the film formation and lubrication mechanisms of the silicified graphite composites with a high carbon content under reciprocating friction conditions were analyzed.

Composite graphite spheres were prepared by mixing spherical graphite with liquid phenolic resin. First, the liquid phenolic resin and spherical graphite were weighed and mixed according to a mass ratio of 8∶10, and mechanically stirred at 45 ℃ for 20-30 min. It was cured at 80 ℃ for 2 h and 150 ℃ for 10 h to obtain the cured product in a drying oven. The cured product was carbonized in a tubular furnace with nitrogen atmosphere. The temperature increased to 1000 ℃ at 1 ℃·min^-1, and the heat kept for 2 h. Finally, the bulk materials were crushed and screened, and five kinds of composite graphite particles with different particle sizes were obtained. The average particle sizes of the selected composite graphite spheres were 203 µm, 153 µm, 135 µm, 105 µm and 75µm, respectively.

The composite graphite particles and nano carbon black were evenly dispersed in alcohol, and the mixed particles were obtained under magnetic stirring in a water bath at a constant temperature of 70 ℃ until dry. Subsequently, prefabricated 5% PVA solution was added to the dry mixed particles as a binder, and after being mixed evenly, the porous carbon preform was formed at 10 MPa for 30 s. The porous carbon preforms reacted with liquid silicon at 1550 ℃ for 30 min to obtain the silicified graphite composites. According to the size of the composite graphite spheres from large to small, the silicified graphite composites were labeled as samples GS-NCB-1, GS-NCB-2, GS-NCB-3, GS-NCB-4 and GS-NCB-5, respectively.

The introduction of nano-sized carbon black facilitates to the protection of carbon phase. The carbon content of the composites fabricated with the composite graphite particles coated by nano-sized carbon black obviously increases, compared with the composites without nano-sized carbon black. This is because that nano-sized carbon black with a higher reactivity forms a continuous and dense silicon carbide layer on the surface of the composite graphite powders, which effectively inhibits the reaction between the composite graphite powders and silicon to form β-SiC. In addition, the increase of particle size of the composite graphite particles has a positive effect on the carbon content of the silicified graphite composites. The carbon content of silicified graphite composites increases from 20.08% to 43.03%, the mechanical properties gradually decreases from 151 MPa to 96 MPa and the friction coefficient and wear rate reduce (the minimum: 0.11, 5×10^-7 mm^3·N^-1·m^-1, 15 N) as the particle size of composite graphite powders increases, indicating superior self-lubricating properties. The results show that the improvement in the lubricating properties of silicified graphite composites is achieved due to the formation of lubricating films. The dense and continuous lubrication film avoids a direct contact with the abrasive material and reduces the coefficient of friction and wear rate. The decrease of the mechanical properties of the silicified graphite composites is due to the increase of the soft carbon content.

Nano-sized carbon black layer on the surface of the composite graphite particle first contacted with liquid silicon to form a silicon carbide layer during the reactive melting process, preventing the further infiltration and reaction of liquid silicon to the composite graphite particle, playing a protective role in the composite graphite particle, and leading to the high carbon content of the silicified graphite composites.

The increase in the particle size of the composite graphite particle could improve the carbon content of the silicified graphite composites because the thickness of the silicon carbide layer after the reaction of the composite graphite particle of different particle sizes was the same, and the increase in the particle size could reduce the specific surface area of the porous carbon preform, thereby reducing the reaction contact area with liquid silicon. The silicon carbide content reduced and the carbon content increased.

The improvement of lubrication performance of silicified graphite composites was achieved due to the formation of surface lubrication film. The dense and continuous lubrication film could avoid a direct contact between grinding materials, effectively reducing the coefficient of friction and wear rate.

High piezoelectricity and optical transmittance are ordinarily difficult to simultaneously achieve in randomly oriented ceramics or textured ones, affecting their further applications in optoelectronic field. How to break this trade-off relationship becomes a challenge for realizing electrical-optical coupling. In this paper, Er³⁺-doped randomly oriented (K_0.5Na_0.5)NbO₃ (abbreviated as xEr-KNN-R) and textured (K_0.5Na_0.5)NbO₃ (abbreviated as xEr-KNN-T) ceramics were prepared via tape-casting. the results showed that the xEr-KNN-T ceramics could have a high degree of orientation and a high relative density (up to 98.8%). The piezoelectric coefficient d₃₃ of the textured ceramics substantially boosted to 121 pC/N compared to randomly-oriented ones (30 pC/N), without significant decrease of the Curie temperature. Also, refinement of grains with tiny pores and relaxor-like behavior could endow the textured ceramics with moderate optical transparency (about 30% in the visible region). Meanwhile, the xEr-KNN-T ceramics exhibited enhanced up-conversion green and red luminescence intensity. The translucent-piezoelectric ceramics could provide insight for further development of high-performance optoelectronic devices.

x% (x = 0, 0.50, 0.75, 1.00, 1.25) Er³⁺ doped KNN with a nominal composition of (K_0.5Na_0.5)_1-xEr_xNbO₃ (abbreviated as xEr-KNN) matrix powders were synthesized via conventional solid-state reaction with K₂CO₃ (99.99%), Na₂CO₃ (99.99%), Nb₂O₅ (99.99%) and Er₂O₃ (99.9%) as raw materials. Anisotropic plate-like NN templates (with about 20 µm in length and width and about 5µm in thickness) were synthesized by a two-step molten salt method. The textured ceramics (abbreviated as xEr-KNN-T) were prepared via reaction template grain growth. Meanwhile, the non-textured randomly oriented ceramics (abbreviated as xEr-KNN-R) prepared without NN templates were used for comparison purpose. The microstructures of samples were determined by scanning electron microscopy (SEM, SUPRA 55 SAPPHIRE, Carl Zeiss Co., Germany) on the surface parallel to the casting direction and the section perpendicular to the casting direction using the accelerating voltage in a range of 0.02-30 kV. To measure the electrical properties, silver paste was coated on both sides of the sintered samples, and then poled in a silicone oil under 3 kV/mm at 150 ℃ for 30 min. The temperature dependences of the relative dielectric permittivity (ε_r) and dielectric loss (tanδ) of the ceramics were recorded by an Impedance Analyzer (Agilent 4294, Agilent Technologies Inc., USA), with an oscillation voltage of 1 V, at a frequency range of 1 kHz-1 MHz and a temperature range of 25-525℃ at a heating rate of 2℃/min. The piezoelectric coefficients (d₃₃) were characterized by a quasi-static piezoelectric constant testing meter (ZJ-6A, Institute of Acoustics, Chinese Academy of Sciences, China). The polarization-electric field (P-E) loops of the ceramics were determined by a ferroelectric test system (TF Analyzer 2000, aixACCT Co., Germany) with the frequency of 200 Hz. The optical transmittance was measured by ultraviolet-visible-near infrared spectroscopy (Lambda 950, PerkinElmer Co., USA). The PL emission spectra were recorded by a spectro-fluorometer (USB4000, Ocean Optics Co., USA) equipped with a 980-nm diode laser (MDL-III, CNI Optoelectronics Tech. Co., China).

Based on the SEM image of NN template, the NN grains synthesized by the topochemical microcrystal conversion (TMC) well inherit the anisotropic morphology of the precursor BNN5, showing a typical flake morphology. The length and width of NN grains are approximately 10-20 µm and the thickness is approximately 0.5-1.0 µm, meeting the size requirement of appropriate NN template used for tape-casting. From the optical transmittance curve, the addition of large size NN template with anisotropy is unfavorable to the transmittance of higher isotropy, resulting in the reduced transmittance of xEr-KNN-T. The XRD patterns of xEr-KNN-T show sharp diffraction peaks with a good crystallinity, presenting a typical ABO₃-type perovskite structure. Er³⁺ diffuses into the KNN lattice, and the NN template has a solid solution with the KNN matrix. Based on the SEM images of all the ceramics, the conventional solid-state reaction, the tape-casting process alone cannot improve the microstructure of KNN, but leads to deterioration in density. The existence of NN template leads to relatively small-sized grains of textured KNN-T ceramics. From the up-conversion PL spectra, the introduced flake-shaped NN template can reduce the symmetry of local environment around the KNN matrix and then cause local heterogeneity and change of crystal field round Er³⁺, thus increasing the up-conversion PL intensity of the xEr-KNN-T ceramics. In electrical tests (i.e., dielectric temperature spectrum and P-E loops), compared with xEr-KNN-R, the xEr-KNN-T ceramics have an improved piezoelectric coefficient (i.e., d₃₃ = 121 pC/N), while maintaining moderate ferroelectricity and a high Curie temperature (i.e., 371℃).

Er³⁺-doped KNN ceramics with random orientation and texture were prepared by a tape-casting method. The xEr-KNN-T ceramics exhibited a high relative density (i.e., up to 98.8%) and a uniform microscopic morphology (with the grain size of 0.33 µm). The piezoelectric performance of xEr-KNN-T ceramics was optimized to a large extent (i.e., d₃₃ = 121 pC/N), which was higher than that of the xEr-KNN-R ceramics, without lowering T_C. Meanwhile, xEr-KNN-T ceramics had a moderate optical transmittance (approximately 30% in the visible region), realizing the coexistence of piezoelectricity and transparency. Enhanced up-conversion luminescence characteristics were displayed in xEr-KNN-T. The translucent-piezoelectric KNN textured ceramics could provide a possibility and an enlightenment for the research of other high-performance lead-free optoelectronic materials.

The global imperative to reduce carbon emissions has catalyzed the development of hydrogen-based metallurgical technologies, with hydrogen shaft furnaces emerging as a promising low-carbon alternative for ironmaking. These reactors demand refractory linings with an exceptional stability to withstand synergistic thermal, chemical, and mechanical stresses when operating under extreme reducing environments (i.e., H₂/CO atmospheres at 1050 ℃, 0.5-1.0 MPa). Conventional aluminosilicate refractories, while widely used, suffer from deleterious reactions in H₂-rich atmospheres, including silica volatilization, carbon deposition via the Boudouard reaction, and structural degradation induced by iron oxide (Fe₂O₃) reduction. Recent studies highlight that co-doping Fe₂O₃ with TiO₂ can mitigate these issues, yet systematic investigations into the role of TiO₂/Fe₂O₃ phase chemistry and pretreatment strategies remain scarce. This study was to elucidate the impact of TiO₂/Fe₂O₃ composite oxides on the reduction stability of mullite-based refractories under simulated hydrogen shaft furnace conditions (i.e., H₂/CO = 5∶2). We were to investigate the phase evolution and microstructural engineering influence resistance to H₂/CO induced degradation via varying the TiO₂/Fe₂O₃ molar ratio (0.5-4.0) and employing pre-sintering treatments.

High purity electromelting mullite (Al₂O₃ >70% (in mass fraction), 3-1 mm, 1-0 mm and 200 mesh), plate corundum (Al₂O₃ >99.5%, 325 μm), α-Al₂O₃ (Al₂O₃ >99.5%, 2-5 μm), Fe₂O₃, TiO₂ powder (analytically pure), silicon powder (2 μm), and high viscosity yellow dextrin (200 μm) were used as raw materials. Fe₂O₃ and TiO₂ powder were proportioned according to the mass ratio m(TiO₂):m(Fe₂O₃) of 0.5, 1.0, 1.5, 2.0, 3.0, and 4.0, respectively, and were placed into a planetray ball mill according to a mass ratio of m(zirconium ball):m(water):m(mixed powder) of 2∶1∶1, The ball mill was operated at 300 r/min for 3 h. After milling, the slurry was taken out and put it in an oven for drying at 110 ℃ for 24 h. The ground sample was screened by a sieve with 200 mesh, thus obtaining the composite oxide of titanium oxide and iron oxide without pre-burning. The sample of φ50 mm×10 mm was prepared with the sifted powder at 100 MPa, and then heated in air at 1300 ℃ for 3 h. After cooling to room temperature, pre-burned titanium-iron oxide composite oxide was obtained.

The dextrin aqueous solution was prepared according to a ratio of m(dextrin):m(warm water) of 1∶1. The mixture was trapped at 25 ℃ for 12 h, and the cylindrical sample was shaped into φ50 mm×50 mm at 150 MPa, and dried in an oven at 110 ℃ for more than 24 h. Finally, the dried sample was heated in air to 1600 ℃ for 3 h, obtaining the titanium-iron oxide composite mullite refractory. The temperature increasing rates of this experiment were 5 ℃/min at 0-1000 ℃, 3 ℃/min at 1000-1400 ℃, and 2 ℃/min at 1400-1600 ℃, respectively.

A large amount of Al₂TiO₅ and a small amount of Fe₂TiO₅ are formed in mullite refractory via the introduction of non-pre-fired titanite composite powder, which is not a dense Mosaic structure. In particular, the porosity increases during the formation of Al₂TiO₅, weakening the protective effect of iron oxide under reduction conditions, and resulting in more pores and cracks formed after the reduction atmosphere treatment. The stability cannot improve as TiO₂/Fe₂O₃ ratio increases. After reduction, the compressive strength of the sample is only 32.2-38.6MPa, showing a significant downward trend, and the attenuation rate is as high as 17.3%-26.5%.

Fe₂TiO₅ solid solution is formed in the pre-fired powder at 1300 ℃, and a large number of titanium oxide is coated iron titanate complex, forming a dense Mosaic structure in the corundum mullite matrix. Fe₂TiO₅ is formed during a progressive reduction of ferrous compound FeTiO₃, greatly inhibiting the reduction of iron oxide. Thus, the anti-reduction stability of the material is significantly improved. When the mullite refractory with m(TiO₂):m(Fe₂O₃) > 2.0 is added, the reduction stability is improved. The compressive strength remains 74.3-84.5 MPa at the reduction temperature of 1050 ℃, and the compressive strength attenuation rate at room temperature is only 2.6%-5.8%.

The results indicated that non-pre-sintered titanium-iron oxide composite samples exhibited a significant structural degradation after being treated at 950 ℃. This degradation was characterized via the formation of numerous micron-sized pores in the matrix and a weakening of the aggregate-matrix interface, leading to a peak compressive strength of only 38.6 MPa and a strength decay rate of 17.3%-26.5%. In contrast, pre-fired titanium-iron oxide composite samples maintained a good structural integrity after reduction at 1050 ℃. When a molar ratio of TiO₂/Fe₂O₃ exceeded 2, the compressive strength remained at 71.9 MPa. The microstructural analysis revealed little cracks in the samples, and the strength attenuation rate was controlled within 10%. In the non-pre-sintered titanium-iron oxide composites, the composite phase of Al₂TiO₅ and Fe₂O₃, which was introduced without pre-firing, could not effectively inhibit the reduction reaction of Fe₂O₃. This resulted in the precipitation of metallic iron and subsequent volume shrinkage. However, in the pre-fired composites, Fe₂TiO₅ was preferentially transformed into the ferrous compound FeTiO₃ during the reduction process. The resistance of the material to H₂/CO reduction erosion was enhanced via constructing a cooperative stable structure of Fe—O—Ti. This finding could provide a theoretical basis for the development of high-stability refractories for hydrogen-based shaft furnaces.

Montmorillonite (Mt) has been extensively applied in drug delivery systems owing to its high cation exchange capacity, large specific surface area, and biocompatibility. However, its strong hydrophilicity and interlayer water molecules significantly restrict the efficient loading of hydrophobic drugs (e.g., ibuprofen (IBU)). Organic modification using surfactants can enhance Mt's hydrophobicity, where cationic types dominate as mainstream modifiers due to their efficient ion-exchange characteristics, capable of expanding interlayer spacing and optimizing drug compatibility. Nevertheless, anionic surfactants rely on anion-dipole interaction adsorption, while nonionic surfactants, despite advantages in low toxicity and biodegradability, exhibit inferior binding efficiency with limited research on related drug carriers. Recently, green nonionic alkyl polyglucosides have attracted considerable attention for their environmental friendliness, superior interfacial activity, and biosafety. This study employed dodecyl glucoside (DPG) to fabricate DPG-Mt composite carriers through wet ball-milling intercalation modification. It systematically investigated the intercalation mechanisms between nonionic surfactants and Mt, along with drug-loading performance and release behaviors, aiming to overcome limitations of conventional ionic modifiers and elucidate the efficiency-enhancing principles of nonionic modification in drug delivery systems. This research not only provides novel strategies for developing safe and stable Mt-based drug delivery systems but also advances technological innovation in green pharmaceutics, demonstrating significant theoretical and practical implications.

This study employed green and safe nonionic DPG to prepare a safe and biocompatible DPG-Mt based pharmaceutical formulation through intercalation modification of natural Mt using a wet ball-milling technique. The synthesized DPG-Mt was systematically characterized for its morphology, crystal structure, functional groups, thermal stability, and colloidal properties using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), thermogravimetric analysis (TGA), BET surface area analysis, and Malvern laser particle size analysis. By investigating the effects of various DPG content on the structure and properties of DPG-Mt, the mechanistic role of DPG in modifying Mt was elucidated, and the adsorption capacity of DPG-Mt for the anti-inflammatory drug, IBU was evaluated. Finally, simulated drug release experiments were conducted to examine the IBU release behavior from drug-loaded DPG-Mt, while cytotoxicity assays were performed to assess its biocompatibility, thereby validating its potential for biomedical applications.

The characterization results of DPG-Mt revealed that the wet ball-milling process did not disrupt or exfoliate the layered structure of Mt. Instead, under the compressive, impact, and frictional forces of mechanical ball-milling, the particle size of Mt was significantly reduced. DPG overcame the weak electrostatic forces, van der Waals interactions, and hydrogen bonding between stacked Mt layers, adsorbing and intercalating into its interlayer spaces, thereby expanding the interlayer spacing of DPG-Mt. Specifically, the interlayer spacings of 1.0DPG-Mt, 2.0DPG-Mt, and 3.0DPG-Mt increased to 1.47 nm (2θ = 6.0°), 1.55 nm (2θ = 5.7°), and 1.52 nm (2θ = 5.8°), respectively. Raman spectroscopy and BET surface area analysis demonstrated that nonionic DPG did not form chemical bonds with DPG-Mt but was physically intercalated into the interlayers via hydrogen bonding and electrostatic interactions. The BET surface area of Na-Mt increased from 62.6 m²/g to 72.0 m²/g under mechanical ball-milling, likely due to the fragmentation of large Mt particles during the modification process. However, the adsorption and intercalation of DPG into DPG-Mt partially obstructed pore channels, leading to a reduction in pore volume and average pore size from 0.337 mL/g and 4.61 nm to 0.245 mL/g and 2.15 nm, respectively.

Concurrently, after organic modification, the particle size of DPG-Mt decreased from 984.0 nm (PDI = 0.34) to 605.0 nm (PDI=0.31), while its zeta potential increased from -39.7 mV to -22.5 mV. These results indicated that the adsorption and intercalation of DPG not only inhibited particle aggregation but also reduced surface charge density. Furthermore, the interfacial tension (IFT) of the DPG-Mt aqueous suspension significantly decreased from 72.75 × 10^-3 N·m^-1 to 41.12 × 10^-3 N·m^-1 after modification. This phenomenon can be attributed to the hydrophobic dodecyl chains of intercalated DPG, which weakened the hydrophilicity of DPG-Mt and enhanced its interfacial activity. Adsorption experiments to IBU demonstrated that organic modification increased the saturated adsorption capacity (Q_m) of Mt for IBU from 35.336 mg/g to 46.083 mg/g, with IBU adsorption on DPG-Mt favoring a multilayer mechanism. In vitro drug release and cytotoxicity analyses revealed that both Mt and DPG-Mt exhibited sustained release of IBU over 480 min. Notably, the biocompatible DPG-modified Mt (DPG-Mt) displayed superior biocompatibility, underscoring the synergistic benefits of organic modification in optimizing drug delivery performance while maintaining biosafety.

The wet ball-milling process exerted compressive, impact, and frictional forces on Mt, leading to reduced particle size, increased specific surface area, and enhanced colloidal interfacial activity of DPG-Mt. The organic modification of Mt by DPG occurred via physical intercalation, where DPG was physically embedded into the interlayer spaces of Mt under mechanical forces. This not only expanded the interlayer spacing and improved the thermal stability of the intercalated DPG but also effectively altered the strong polarity of Mt, thereby enhancing its affinity for the hydrophobic IBU. Consequently, the saturated adsorption capacity of Mt for IBU increased from 35.336 mg/g to 46.083 mg/g. Owing to the superior adsorption performance of DPG-Mt to IBU, DPG-Mt exhibited sustained drug release over 480 min, demonstrating favorable sustained-release performance, with the released IBU amounting to 76% of the total dosage. Cytotoxicity tests further confirmed that the organic modification of Mt with DPG conferred excellent cytocompatibility to DPG-Mt. Given its high drug adsorption capacity, excellent sustained-release properties, and outstanding cytocompatibility, DPG-Mt demonstrates significant potential as a hydrophobic anti-inflammatory drug formulation for biomedical applications.

Functional fillers, such as steel fibers, graphene, and carbon nanotubes, introduce a large number of free electrons into UHPC, becoming a conductive material "gene" of UHPC for the establishment of the intrinsic conductive path. The material "gene" simultaneously endows UHPC with excellent mechanical, durability, and sensing capabilities, facilitating in-situ monitoring of the impacts of loads and environment on infrastructure. This provides a crucial data support for infrastructure operation and maintenance, paving a way for infrastructure "digital-intelligence". SSUHPC as a high-performance/intelligent/multifunctional material with digital-intelligent characteristics is expected to transcend the boundaries between functional and structural materials, achieving structural-functional integration and functional diversification, thereby driving a paradigm shift in the field of civil engineering.

The appropriate curing methods for 3D-printed cement-based materials have not yet been clearly defined, thus restricting their durability in cold regions. This study was to investigate the effects of natural curing (NC), standard curing (SC), high-temperature curing (T₆₀), saturated Ca(OH)₂ solution curing (SCH), and internal curing withabsorbent polymer (SAP) on the performance of solid waste-based 3D printed mortar (3DFGCM). The objective was to establish quantitative relationships among curing methods, mechanical anisotropy, frost resistance, and pore structure, thereby providing a theoretical foundation for improving the service life of 3D printed structures in cold regions.

The fly ash-slag-cement based mortar (FA : GGBS : OPC=1 : 2 : 7) was prepared at a sand-to-binder ratio of 1 : 1 and a water-to-binder ratio of 0.3. After vibration casting and 3D printing of the slurry, the specimens were naturally cured for 1 day and then divided into five groups for further curing. The 28-d compressive strength and anisotropy were tested in the X, Y, and Z directions. After 28-d curing under respective conditions, the specimens were immersed in water at 15-20 ℃ for 2 d before undergoing freeze-thaw cycles. The mass loss rate, relative dynamic elastic modulus, and strength loss rate were measured. The pore structure was analyzed before and after freeze-thaw cycles to determine parameters such as air content, chord length distribution, and spacing factor. Finally, a damage evolution model based on the Weibull distribution was established to predict service life, and a neural network was used to map the relationship between pore parameters and damage.

This study systematically investigates the effect of curing method (i.e., NC, SC, T₆₀, SCH, and SAP) on the performance of 3D printed fly ash-slag-cement-based mortar (3DFGCM). The comprehensive analysis of mechanical anisotropy, frost resistance, and pore structure, combined with freeze-thaw models and service life prediction models indicates that the 28-d compressive strength and isotropy coefficient of 3D printed specimens are lower than those of cast specimens. Among the curing methods, 3D-SC demonstrates the most significant enhancement in the 28-d compressive strength, while the SAP increases the 28-d compressive strength to 36.8 MPa, which is increased by 41.17%, compared to the NC group, with the lowest anisotropy coefficient (i.e., 0.187). The frost resistance of 3D printed specimens varies significantly. The 3D-NC and 3D-T₆₀ groups both fail after 125 freeze-thaw cycles, the 3D-SAP group exhibits the optimum frost resistance, retaining 61.5% of its dynamic elastic modulus and showing a mass loss of 4.57% after 150 freeze-thaw cycles. Its closed micropores and humidity balance mechanism effectively mitigate frost heave damage. In terms of the pore structure, 3D printed specimens exhibit distinct elliptical pores. The 3D-SCH group shows a limited improvement in cavity and interlayer cold joint defects, with large pores accounting for 75% more than those in the 3D-SAP group. The incorporation of SAP improves process-induced defects and significantly inhibits pore coarsening. With the relative dynamic elastic modulus as an index, the Weibull damage and service life prediction models are applied to assess freeze-thaw damage and service life of 3DFGCM, with R² of > 0.98. The 3D-SAP group performs optimally, with a predicted service life of 15.9 years. Furthermore, based on BP neural networks, the effective correlations are established between pore structure parameters and the Weibull-predicted damage and service life, with R² of > 0.97.

In terms of mechanical anisotropy, the strength of 3D-printed specimens followed a decreasing order of Cast>X>Z>Y. The SAP curing resulted in the lowest anisotropy coefficient (i.e., 0.187), with a 41.2% increase in the strength, compared to the NC group. For the frost resistance, after 150 freeze-thaw cycles, the SAP group retained 61.7% of its dynamic elastic modulus and exhibited only 4.57% mass loss. In contrast, the NC and T₆₀ groups failed after 125 cycles due to pore coarsening. In terms of the pore structure, the initial air content of 3D-printed specimens was 1.5 times higher than that of cast specimens. After freeze-thaw cycles, the total chord length of the NC group was increased by 65.3%. The SAP effectively inhibited pore coarsening, with large pores accounting for only 36%, representing a 75% reduction, compared the NC group. Finally, a damage evolution equation was established based on the Weibull distribution model, predicting a service life of 15.9 years for 3D-SAP in cold northwestern regions. The BP neural networks were employed to predict damage and lifespan based on microscopic pore structure. This study could provide a reference for the design of methods and frost resistance optimization in 3D-printed construction materials.

The construction industry is a primary contributor to global CO₂ emissions, making the development of novel low-carbon building materials a critical scientific and engineering challenge. A promising strategy involves the valorization of waste concrete fines, which are generated in vast quantities. The thermal activation of these fines at 600-800 ℃ transforms the hydrated cement paste into a recycled cement rich in dicalcium silicate (i.e., β-C₂S), a clinker phase with a high intrinsic carbonation reactivity. This makes thermally activated recycled cement an ideal precursor for carbon-sequestering materials where CO₂ is utilized as a curing agent to enhance mechanical properties. However, its practical application is hindered by a key technical bottleneck, i.e., relatively low reaction kinetics and insufficient mechanical strength development. Therefore, identifying an effective modifier to stimulate its carbonation potential and optimize the final microstructure is of significant urgency. Metakaolin (MK) as a highly reactive pozzolan is a promising candidate due to its known ability to promote hydration and serve as a nucleation site. This study was to systematically investigate the role of MK as a synergistic component to overcome the performance limitations of carbonated recycled cement, providing a scientific basis for the development of high-performance, green building materials.

The raw materials used were a waste concrete powder (WCP) and a commercial metakaolin (MK). A thermally activated recycled cement (TARCP) was produced via first pressing a mixture of WCP and MK (0%, 10%, and 20% by mass, denoted as TARCP, MK10, and MK20, respectively) and then calcining it in a muffle furnace at 800 ℃ for 1 h. After cooling and grinding, the resulting powders were mixed with water at a water-to-binder ratio of 0.55 to prepare paste specimens. The pastes were cast and cured for 24 h before being demolded and subjected to one of two curing regimes for 7 d and 28 d, i.e., (1) water curing (25 ℃, 75% RH) and (2) accelerated carbonation curing (25 ℃, 75% RH, 20% CO₂).

The compressive strength of 20 mm cubic specimens was tested at each age. The phase evolution was comprehensively characterized by X-ray diffraction (XRD) with Rietveld quantitative analysis, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The pore structure distribution was analyzed by low-field nuclear magnetic resonance spectroscopy (NMR). The microstructure and morphology of the reaction products were determined by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX).

The experimental results demonstrate that the incorporation of an optimal amount of MK significantly enhances the performance of the carbonated recycled cement. The addition of 10% MK (MK10) yields the optimum results, with the 7-d compressive strength under carbonationof 37.7 MPa, which is increased by 119.2%, compared to the carbonated control sample (TARCP). This superior performance is attributed to a combination of physical and chemical effects induced by MK.

The phase analysis reveals that MK accelerates the consumption of the primary reactive phase like β-C₂S. After 7-d carbonation, the β-C₂S content in the sample MK10 is reduced to just 1.2%, compared to 29.8% in the TARCP control. This accelerated reaction leads to a much higher degree of carbonation. The 7-d carbonation degree for the sample MK10 is 50.79%, which is improved by 70%, compared to the sample TARCP (i.e., 29.87%). Furthermore, the MK promotes the transformation of metastable vaterite to the thermodynamically stable calcite. At 7 days, the sample MK10 is overwhelmingly composed of calcite (i.e., 72.7%), with only a negligible amount of vaterite (1.6%), whereas the sample TARCP contains a significant amount of vaterite (i.e., 8.5%). The FTIR analysis indicates the formation of a highly polymerized amorphous silica-alumina gel in the carbonated MK-modified systems, which is evidenced by the shift of the main Si—O vibration band to a higher wavenumber (~1080 cm^-1), indicating a fundamental restructuring of the silicate network.

The microstructural analysis provides the strengthening mechanism. The NMR results show that the addition of 10% MK significantly refines the pore structure. After 7-d carbonation, the proportion of large capillary pores (i.e., >50 nm) in the MK10 sample decreases from 49.88% (in the sample TARCP) to 36.56%, while the proportion of fine gel pores (i.e., <10 nm) nearly increases from 8.98% to 17.81%. This pore refinement, which is driven by the uniform deposition of carbonation products, results in a much denser matrix, which is the primary reason for the observed strength enhancement. However, the effect of MK is non-linear. An excessive dosage of 20% MK (the sample MK20), while further refining the pore structure (the capillary of pores reduces to 29.75% at 7 d), resulting in lower compressive strength than the sample MK10 at all ages. This is accompanied by a slightly lower final degree of carbonation at 28 d (51.72% for the sample MK20 vs. 52.88% for the sample MK10). This indicates that the excessive pore refinement can create a dense, impermeable microstructure that impedes the diffusion of CO₂ gas into the material core, thereby limiting the overall reaction rate and extent in the later stages. Moreover, the anomaly of lower strength despite a denser pore structure in the sample MK20 increases that the intrinsic properties of the solid phases play a critical role. It is hypothesized that the higher Al/Si ratio in the sample MK20 leads to the formation of an amorphous alumina-silica gel with a lower degree of polymerization, possessing the inferior intrinsic mechanical properties, compared to the gel formed at an optimal Al/Si ratio.

This study demonstratesd that incorporating an optimal amount of metakaolin (10% by mass) could be a highly effective strategy for enhancing the carbonation reactivity and mechanical performance of thermally activated recycled cement. The improvements could be attributed to the synergistic effects of MK, i.e., accelerating the consumption of β-C₂S, promoting the formation of stable calcite, and refining the pore structure via creating a denser, more uniform microstructure. However, an excessive dosage of MK (20%) could be detrimental. It led to a further pore densification, this could inhibit a later-stage CO₂ diffusion, limiting the final carbonation degree. Furthermore, the higher Al/Si ratio could negatively affect the intrinsic strength of the amorphous binder phase. These findings could highlight the non-linear effect of metakaolin and provide a scientific basis for optimizing the design of high-performance, carbon-sequestering building materials derived from recycled cement.

Supersulfated alkali-activated binders (SS-AABs) have emerged as a superior alternative to Portland cement due to their extensive utilization of silicon-aluminum solid waste, sulfate solid waste, and alkaline solid waste, as well as their exceptional mechanical qualities and corrosion resistance. The primary precursors of silicon-aluminum components in SS-AABs are predominantly ground granulated blast furnace slag (GGBFS), comprising 70% to 90% of the composition. Identifying alternative industrial solid waste products that serve as superior precursors for silicon and aluminum can yield significant economic and environmental advantages. Bayer red mud (BRM) is a high-alkali, challenging silicon-aluminum by-product generated in the alumina industry. Nonetheless, the crystal structure of unactivated BRM has some challenges in engaging with the alkali-activated process of the gelling system, rendering it unsuitable as a precursor for SS-AABs. The BRM, following thermal activation treatment, can yield a more active amorphous structure, facilitating enhanced dissociation and repolymerization reactions with alkaline solid waste activators, resulting in the formation of more stable hydration products and establishing a high-quality silicon-aluminum component precursor. The rationale of the detection approach for the comprehensive activity of silicon and aluminum BRMP in SS-AABs is insufficient, hence constraining engineering applications. This paper was to examine the evolution of minerals during the thermal activation of BRM, systematically analyze the characteristics of three activity testing methodologies, i.e., chemical dissolution methods (e.g., inductively coupled plasma (ICP) or chemical titration), pozzolanic activity index methods, and microstructural characterization methods (such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR)). In addition, this paper was also to investigate the changes in activity of BRM as a silicon-aluminum precursor at varying activation temperatures and propose some insights for assessing the silicon-aluminum activity of thermally activated Bayer red mud precursors (BRMP), tailored for the preparation of SS-AABs.

The activity index of thermally activated red mud was analyzed in accordance with the standard GB/T 1596—2005. A specimen with the sizes of 40 mm × 40 mm × 160 mm was fabricated with thermally activated red mud, cement, standard sand, and water in accordance with the stated proportions. It was then cured under standard conditions (i.e., (20 ± 2) ℃, 96% RH) for 7 d and 28 d, respetively. The compressive strength of the specimens was evaluated at two ages in accordance with the standard GB/T 17671—2021. The activity index was the ratio of the 7-d and 28-d compressive strength of cement mortar specimens incorporating thermally activated red mud to the compressive strength of pure cement mortar specimens at the equivalent age. A specimen SS-AABs with the sizes of 40 mm × 40 mm × 40 mm was prepared with 58% heat-activated BRMP, 25% desulfurization gypsum, and 17% carbide slag at a water-cement ratio of 0.6. The standard curing was conducted at (20 ± 1) ℃ and 96% relative humidity for 3, 7 d, and 28 d, respectively. The compressive strength of the specimens was evaluated at three ages in accordance with the standard GB/T 17671—2021. The microstructure was examined by scanning electron microscopy (SEM), its mineral composition was assessed by X-ray diffraction (XRD), and the alterations in chemical bonds were evaluated by Fourier transform infrared spectroscopy (FTIR). The solubility of Si⁴⁺ and Al³⁺ in thermally activated BRMP at various temperatures was assessed by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The leaching quantity of active Si⁴⁺ was ascertained by a potassium fluosilicate volumetric method, and the leaching quantity of active Al³⁺ was evaluated by ethylenediaminetetraacetic acid (EDTA) complexometric titration method.

The result indicates that the combined analysis of XRD-FTIR can proficiently characterize the mineral composition and alterations in chemical structure of BRMP. The pozzolanic activity index approach yields quantitative data but limits to assessing pozzolanic activity in cement systems and cannot differentiate the contributions of silicon and aluminum. The chemical titration method can quantitatively assess the dissolution rates of silicon and aluminum. However, it lacks a sensitivity to variations in ion concentration, particularly within the activation temperature range of 300-700 ℃, making it challenging to accurately represent changes in activity. Conversely, for precisely quantifying the dissolution concentrations of Si⁴⁺ and Al³⁺, the ICP-AES method can quantitatively indicate the activity changes in BRMP at different activation temperatures and differentiate the dissolution behaviors of silicon and aluminum, thereby offering a more dependable foundation for the optimization of components in SS-AABs. The thermal activation at 800 ℃ significantly enhances the breakdown of silicon and aluminum components, compared to that of unactivated BRMP.

The alteration of the mineral phase in red mud could be constrained by the activation temperature. Katoite decomposed at 400 ℃, chlorite and diaspore decomposed at 500 ℃, and grossular and nepheline decomposed at 800 ℃. The testing methodology for volcanic ash activity possessed specific constraints when examining the activity of BRMP. The conventional activity index approach was constrained by the gypsum concentration (< 5%) in Portland cement (the standard GB 175—2023), making it challenging to precisely assess the contribution of active Al₂O₃ in BRMP. The chemical titration method possessed specific advantages in indicating the mineral activity of BRMP following thermal activation. The quantity of leached active aluminum in BRMP post-thermal activation could be greater than that of active silicon. The analysis by XRD-FTIR indicated that at 800 ℃, silicon-containing minerals could fully activate, whereas aluminum-containing minerals could disintegrate more readily. The chemical titration method could partially indicate the activation impact of BRMP. However, the detected fluctuation in silicon and aluminum leaching was limited, leading to inadequate sensitivity to changes in ion concentration. The dissolution rate of active silicon and aluminum following BRMP activation by the ICP-AES method showed that the thermally activated BRMP had considerable benefits in terms of activity. The leaching quantity of Al³⁺ in BRMP post-thermal activation consistently exceeded that of Si⁴⁺, aligning with the leaching patterns of active SiO₂ and Al₂O₃ determined using chemical titration. At 800 ℃, the activation effect could be markedly intensified, with the leaching concentration of Si⁴⁺ attaining 96.4 mg/L, and the leaching concentration of Al³⁺ reaching 167.5 mg/L. Compared with the unactivated BRMP, the dissolution of silicon and aluminum elements of activated BRMP was greatly improved by thermal activation at 800 ℃.

The high-entropy strategy is an effective approach for optimizing and developing SSEs. It can not only adjust the configurational entropy to stabilize the structure, but also enhance the ionic conductivity of SSEs by regulating site energy, structural disorder, and the distribution of mobile ions. For high-entropy oxide SSEs, cation substitution is primarily employed to regulate site energy and local structure, thereby improving ion transport properties. In high-entropy sulfide and halide SSEs, the anionic sublattice offers greater flexibility in composition. Hence, beyond cationic site regulation, modifications to the anionic sublattice result in a more pronounced effect on ionic conductivity. Furthermore, such strategies can regulate micromorphology, air stability, and resistance to oxidation and reduction, laying a solid foundation for high-energy-density and high-safety solid-state batteries.

However, high-entropy solid-state electrolytes remain in their infancy, and their development faces several critical challenges and key issues. First, in the design of high-entropy solid-state electrolyte materials, the selection of elements critically governs the properties, while the compositional complexity poses significant challenges in establishing universal design principles. Besides, the development of high-entropy solid-state electrolyte materials necessitates careful trade-offs among different properties. A key scientific challenge lies in rationally choosing elements that simultaneously modulate structural configurations to enhance ionic conductivity while maintaining air stability and electrochemical stability. Current research has paid insufficient attention to elemental cost-effectiveness and safety implications, both of which substantially impact the practical application potential of these materials. Further investigations should prioritize the adoption of low-cost and high-safety raw materials to enhance the practical application. Second, current research on high-entropy SSEs mainly focused on the ionic transport properties. However, achieving practical applications requires a deeper investigation into their interfacial compatibility and stability with high-voltage cathodes and lithium metal anodes, which are critical for the performance of full battery systems. Third, future research could introduce machine learning methods to predict and screen elemental combinations and structural designs, thus accelerating the development of high-performance solid-state electrolytes. However, high-entropy solid-state electrolytes remain in the early exploratory stage, where limited experimental data and unclear structure-properties relationships constrain the accuracy of the data-driven model. To address this, researchers could combine conventional elemental doping strategies with quantitative analyses of individual element contributions to material performance. Concurrently, theoretical calculations could generate supplementary theoretical datasets. Furthermore, experimental validation should be employed to refine predictive models, establishing a "computation-data-experiment" collaborative framework. This approach will improve the model's reliability and generalizability, ultimately accelerating the rational design of high-entropy solid-state electrolytes.

Although research on high-entropy SSEs is still in its early stages, these materials are expected to provide new avenues for advancing the practical applications of solid-state batteries through ongoing fundamental studies and technological innovations.