The mechanisms underlying the four approaches to improve the electromagnetic wave absorption performance of SiC fibers are not entirely the same. Element doping can form conductive phases, magnetic loss phases, and heterogeneous interfaces inside SiC fibers to increase their electromagnetic losses, thus improving the electromagnetic wave absorption performance. Surface coating design can increase electromagnetic wave loss mechanisms, while optimizing impedance matching to attenuate electromagnetic waves. Structural design enables more electromagnetic waves to enter the interior of SiC fibers and utilizes structural features to increase electromagnetic wave transmission distance and multiple reflections, effectively attenuating electromagnetic waves and improving absorption performance. Thermal treatment can regulate the composition and crystallite size (microstructure) of SiC fibers, causing changes in fiber electrical resistivity and electromagnetic parameters, thereby improving electromagnetic wave absorption. For SiC fiber-reinforced composites, the multidimensional design of SiC fibers, interface, matrix, and their structures can enhance absorption performance. However, despite many achievements in the research of electromagnetic wave absorption properties of SiC fibers and their composites, studies on the synergistic improvement of structure absorption and other functional properties of SiC fiber-reinforced composites are still scarce. It is thus necessary for the functional application of SiC fibers in complex environments to strengthen the synergistic design of SiC fiber structural units in different scales and the research on structure-property evolution of SiC fiber reinforced electromagnetic wave absorbing composites under service conditions.

Na-ion batteries (NIBs) have a great potential as next-generation large-scale energy storage devices. Among various cathode materials for NIBs, P2-type layered transition metal oxides have attracted much attention because of their excellent kinetics and easy processability. In P2-type layered oxides, Na ion occupies two different sites, i.e., Na_e and Na_f. The triangular prism polyhedron of Na_f site shares faces with two TmO6 octahedrons, while Na_e shares edges with six TmO6. The migration behavior of Na ions at different positions is diverse due to the distinction of distance and electrostatic force between Na⁺-Tmⁿ⁺. The migration of Na ions at Na_e site has a lower migration energy barrier, compared to that of Na_f position. Namely, more Na ions at Na_e site and increasing the occupation ratio of Na_e/Na_f can effectively improve the electrochemical performance of P2 layered oxides. Previous research indicates that the ratio of Na ions at different sites can be modulated by introducing inactive ions to transition metal layers. However, the introduction inevitably results in the capacity sacrifice. The ration of Na_e/Na_f is mainly affected by two aspects, i.e., the interaction between Tmⁿ⁺ and Na⁺, and the interaction between Na⁺ and Na⁺. In the case with the same transition metal component, the design of Na content is expected to achieve the regulation of Na_e/Na_f ratio, mainly from the following three reasons: 1) Na content affects the valence state of transition metals, and thus modulates the interaction between Tmⁿ⁺ and Na⁺; 2) Na content changes the Na interlayer distance, and then affects the distance between Na⁺ and Tmⁿ⁺ and the corresponding interaction between Na⁺ and Tmⁿ⁺; and 3) Na content regulates the distance between Na⁺ and Na⁺. In this paper, we proposed a novel strategy to optimize the Na_e/Na_f occupancy ratio with the same transition metal composition via adjusting Na content in the material. This strategy could open up new opportunities to design high-performance cathode materials for NIBs.

Na_xNi_0.1Mn_0.9O₂ (x = 0.45, 0.55, and 0.65, denoted as Na45, Na55, Na65) were prepared by a simple high-temperature solid-phase method. The precursors were Na₂CO₃, NiO and Mn₂O₃ and weighed according to a required stoichiometry ratio with a 5% excess of Na₂CO₃. After grinding, they were heatd in an alumina crucible in a muffle furnace at an elevated rate of 5 ℃/min up to 950 ℃. After heated at 950 ℃ for 15 h, the powdered materials were obtained by natural cooling and finally transferred to an argon-filled glove box. The working electrodes were prepared via spreading the slurry of active materials, acetylene black and polyvinylidene difluoride with a mass percent of 75∶15∶10 on Al foil. After drying in vacuum at 80 ℃ for 12 h, the electrodes were transferred to an argon-filled glove box and assembled into CR2032-type button cells. The counter electrode was metal sodium, the separator was a glass fiber, and the electrolyte was 1 M NaClO₄ in propylene carbonate (PC) solution with 5% fluoroethylene carbonate (FEC) additive.

The effect of Na content on the occupancy ratio of Na_e/Na_f positions and the corresponding evolution of structure and electrochemical properties was investigated. All the Nax compounds have a hexagonal P2 structure with P6₃/mmc space group. According to the XRD refinement and eletrochemical results, Na55 material has the maximum Na_e/Na_f occupancy ratio and specific discharge capacity, mainly originating from the better mobility of Na ions at Na_e sites. Na55 exhibits a prominent capacity of 174.5 mAh·g^-1 at 0.2 C, which is much higher than that of Na45 and Na65. Benefited from the optimized Na_e/Na_f ration, Na55 displays 10^-10-10^-12 cm²·s^-1 of Na⁺ diffusion coefficient, which is much higher than 10^-12-10^-14 cm²·s^-1 of the usual transition metal layered oxides cathodes. Also, Na55 exhibits an excellent rate performance with a capacity of 83.6 mAh·g^-1 at 10 C rate, and a great cycling stability with a 92.95% capacity retention after 200 cycles.

Na_e/Na_f occupancy ratio of P2-type layered oxides was modulated by an extremely simple strategy for Na content optimization. The combined results of XRD refinement, electrochemical curve, transmission electron microscopy, cyclic voltammogram, ex-situ XRD and X-ray photoelectron spectroscopy showed that a higher Na_e/Na_f ratio in Na55 materials effectively enhanced the Na⁺ diffusion rate, consequently resulting in a high specific capacity (174.5 mAh·g^-1 at 0.2 C), an outstanding kinetic performance (87 mAh·g^-1 at 10 C) with an excellent cycling performance (92.95% capacity retention after 200 cycles). Compared to conventional P2 materials with common Na content, Na55 had a smaller volume change without any phase transition during electrochemical process. The simple and effective strategy could offer an insight into the rational design of high-performance layered cathode materials and also enhance the practical application of NIBs.

Ammonia selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) is an effective technology for NO_x removal. As a catalyst, V₂O₅-WO₃ (MoO₃)/TiO₂ has a high denitrification activity, but suffers from the problems of poor low-temperature activity, high V-toxicity, and susceptibility to heavy metal toxicity at 300-400 ℃. Heavy metals such as Cd, Pb, Zn, etc. widely present in the flue gas of solid waste incineration and coal-fired power plants. The toxic effects on catalysts are manifested via covering the active sites on the catalyst surface, reducing the redox properties, acidifying the surface and chemically adsorbing oxygen, leading to severe catalyst deactivation. CeO₂ as an effective catalyst has a higher oxygen release/storage capacity, which is characterized by a higher oxygen release/storage capacity, compared to the conventional catalysts. CeO₂ is used as a main active component in the preparation of rare-earth-based denitrification catalysts due to its high oxygen release/storage capacity. Manganese oxide (i.e., MnO_x) exhibits a good low-temperature catalytic activity, which is often used as a modified component to improve the low-temperature denitrification activity of catalysts. TiO₂ interacts with the active component and has a higher thermal stability and a sulphur resistance. However, Ce-Mn/Ti catalysts are susceptible to poisoning by toxic substances in the flue gas, and there are more studies on the poisoning of Ce-Mn/Ti catalysts by SO₂, H₂O, etc.. However, a few studies on the poisoning of Ce-Mn/Ti catalysts by heavy metals are reported. Catalysts with three-dimensional ordered macroporous structures have superior redox properties, sufficient chemisorbed oxygen and suitable acid sites to promote its NH₃-SCR denitrification reaction. In this paper, Ce-Mn/Ti catalysts with three-dimensional ordered macro-porous structures were thus prepared to increase the redox properties and acidic sites and promote the denitrification activity.

17 mL of tetrabutyl titanate was added drop by drop into 30 mL of anhydrous ethanol under vigorous stirring, which was recorded as liquid A. Concentrated nitric acid (65%, in mass fraction) was added dropwise into the mixed solution of deionized water (1.5 mL) and anhydrous ethanol (10 mL) at pH values of 2-3, which was recorded as liquid B. The solution was then mixed into a mixture of deionized water (1.5 mL) and anhydrous ethanol (10 mL). Liquid B was slowly mixed into liquid A under vigorous stirring to obtain a homogeneous and transparent TiO₂ solution. A certain amount of PMMA template was added to the TiO₂ precursor solution, sealed and stayed for 12 h. The remaining precursor solution was removed by vacuum filtration and baked at 50 ℃ for 24 h. Finally, the samples were baked at 300 ℃ for 2 h, and then heated at a heating rate of 1 ℃/min at 500 ℃ for 5 h. The ordinary structure TiO₂ carriers were prepared in the same process as 3DOM TiO₂ without PMMA template. After the preparation of TiO₂ carriers, Ce(NO₃)₃-6H₂O and Mn(NO₃)₂ mixtures were prepared at different molar ratios, and impregnated with 3DOM TiO₂ and normal TiO₂, respectively, and stirred at room temperature for 4 h. Afterwards, the catalysts were transferred to an oil bath and stirred at 80 ℃ for 6 h. They were baked at 80 ℃ for 24 h, and finally, the catalysts were heated at 1 ℃/min at 500 ℃ for 5 h. The obtained samples were recorded as fresh-CMT-3DOM (i.e., fresh-CMT). The catalyst with heavy metals (i.e., Cd, Pb, Zn) were prepared by an excess impregnation method. A certain amount of cadmium nitrate, lead nitrate, and zinc acetate solution was prepared at different mass ratios of metal ions to catalyst (10% Cd, 10% Pb and 5% Zn), and fresh-CMT-3DOM and fresh-CMT catalysts were added to the heavy metal salt solutions, respectively.

The morphology structure was detected by a scanning electron microscope (SEM, TESCAN MIRALMS Co., Czech Republic). The specific surface area and pore size were determined by specific surface area intruement based on BET (Micromeritics Co., USA). The crystalline phase structure of the catalysts was analyzed by an X-ray diffracometer (XRD, Bruker Co., Germany). The elemental valence states of the catalysts were analyzed by an X-ray photoelectron spectroscope (XPS, Thermo Scientific Co., USA) using Al K_α as X-ray sources. The redox properties of the catalysts were characterized using a FINESORB-3010 adsorption apparatus (Finetec Instruments Co., China). The ammonia adsorption experiments of the catalysts were carried out by a Nicolet 6700 instrument (Thermo Fisher Scientific Co., USA) to determine the type of acid on the catalyst surface. The NH₃-SCR denitrification activity was analyzed in a fixed bed quartz reactor at 1 000 mg/L NO, 1 000 mg/L NH₃, 5% (v/v) O₂ and N₂ as ab equilibrium gas. The denitrification efficiency of the catalyst was calculated according to the results that were determined by a flue gas analyzer.

The NO conversion for 10% Cd-CMT-3DOM, 10% Pb-CMT-3DOM, and 5% Zn-CMT-3DOM exceeds 85% at 175-300 ℃. However, the denitrification activity decreases at 100-150 ℃. Compared to the activity of CMT and the three metals after poisoning, the maximum NO conversion of 10% Cd-CMT decreases to less than 85% at 100-300 ℃. The maximum NO conversion of 10% Pb-CMT is less than 100%, and fresh CMT is weakly poisoned by Zn. The three-dimensional ordered macro-porous structure enhances the CMT-3DOM catalyst's tolerance to Cd, Pb, and Zn to some extent.

The ratio of Ce³⁺ can be determined via calculating the peak area ratio of Ce³⁺/(Ce³⁺ + Ce⁴⁺). The proportion of Ce³⁺ in fresh-CMT-3DOM (19.0%) is greater than that in fresh-CMT (15.7%), accounting for the favorable denitrification activity of CMT-3DOM catalyst. After adding Cd, Pb and Zn, the content of Ce³⁺ in the fresh-CMT-3DOM catalyst shows a better resistance to heavy metals, compared to the fresh-CMT catalyst. This indicates that the fresh-CMT-3DOM catalyst is more resistant to heavy metals. Based on the calculation results of Mn⁴⁺ content, which decreases similarly to Ce³⁺ content, fresh-CMT-3DOM and fresh-CMT display the greatest reduction in Mn⁴⁺ content after Cd poisoning, followed by Pb poisoning. Zn poisoning has a smaller impact on the Mn⁴⁺ content reduction. The Mn⁴⁺ content on the surface of fresh-CMT-3DOM is relatively higher after three heavy metals poisoning rather than that on the corresponding fresh surface. Also, the relative contents are higher than those of the corresponding fresh-CMT catalysts. This indicates that the Mn⁴⁺ content of fresh-CMT-3DOM catalysts is less affected by heavy metal poisoning, which is beneficial to improving the anti-heavy metal performance of fresh-CMT-3DOM catalysts. The relative content of O_α in the catalysts is obtained via the calculation. The amount of chemisorbed oxygen in fresh-CMT-3DOM catalysts (i.e., 35.2%) is greater than that of fresh-CMT. The relative content of O_α, Ce³⁺ and Mn⁴⁺ depict a consistent pattern of variation in these catalysts, which coincide with the outcomes of the NH₃-SCR activity. This further shows the safeguarding ability of the catalysts active species through the three-dimensionally ordered macropore structure. Based on the H₂-TPR reduction peak results, the reduction peaks of fresh-CMT-3DOM move to lower temperatures, compared to those of fresh-CMT catalysts. The relative peak areas of fresh-CMT-3DOM are greater, indicating that the 3DOM structure is more favorable for the redox reaction of the catalysts. When Cd, Pb, and Zn are introduced, the reduction peaks of both catalysts shift towards at higher temperatures, indicating that the heavy metals form bonds with the active species of the catalysts. The reduction peaks of all catalysts are analyzed to determine the relative peak areas. The influence of Cd, Pb, and Zn on the catalytic redox activity aligns with SCR denitrification performance. This indicated that the catalysts ability to undergo redox reactions is a crucial factor affecting their heavy metal resistance and SCR denitrification activity. The NH₃-DRIFTS characterization results indicate that the Lewis acid is a primary acid type in both fresh-CMT-3DOM and fresh-CMT catalysts. Moreover, fresh-CMT-3DOM catalysts have a higher concentration of the Lewis acid sites rather than fresh-CMT. Fresh-CMT-3DOM after the heavy metal poisoning has the more Brønsted acid sites, compared to fresh-CMT catalysts, and the influence of heavy metals on its acid sites is reduced. Fresh-CMT-3DOM catalysts possess a larger number of acidic sites, resulting in a greater resistance to heavy metals.

TiO₂ carrier with a three-dimensional ordered macro-porous structure was prepared using PMMA template, and fresh-CMT-3DOM catalysts were obtained after loading with Ce and Mn. The activity and heavy metal resistance performance were investigated. The experimental results showed that the fresh-CMT-3DOM catalyst had the excellent activity with the NO conversion rate of more than 85% at 100-300 ℃. The low-temperature activity was higher than that of fresh-CMT, which still remained at 85% at 100-150 ℃. When Cd, Pb and Zn were introduced, NO conversion rate of fresh-CMT-3DOM at 175-300 ℃, while the fresh-CMT activity after Cd, Pb and Zn poisoning decreased, in which the maximum NO conversions of the catalysts corresponding to Cd and Pb poisoning were less than 85% and 100%, respectively. The characterization results indicated that the NO conversions of the catalysts corresponding to Cd, Pb and Zn poisoning were higher than those of fresh-CMT-3DOM and fresh-CMT-3DOM. 3DOM and fresh-CMT catalysts had the similar crystalline phases, but the diffraction peaks of fresh-CMT-3DOM were weaker in intensity and its active components were more dispersive. Compared with fresh-CMT catalysts, fresh-CMT-3DOM catalysts had excellent Mn⁴⁺/Mn³⁺/Mn²⁺ and Ce⁴⁺/Ce³⁺ redox cycling, higher redox capacity and more acidic sites, thus improving the anti-heavy metal performance of fresh-CMT-3DOM.

Chloride-induced corrosion is a primary factor contributing to the degradation of coastal concrete infrastructure. To counteract the corrosion of steel reinforcement, epoxy resin coatings are commonly used. However, ensuring their durability in alkaline environments is a challenge, and these epoxy coatings also alter the mechanical bond between steel and concrete. It is thus crucial to develop thin inorganic conversion coatings. Layered double hydroxides (LDH) have a potential application in corrosion protection. However, steel tends to passivate in alkaline environments, limiting the growth of LDH on its surface. Hong et al achieved the in-situ growth of LDH on steel and elucidated its growth mechanism. Despite its potential in corrosion prevention, the growth of LDH presents a lamellar structure, creating micropores that serve as channels for the invasion of corrosive ions. Hence, developing a dense composite film for effective steel protection remains a challenge. This paper was to investigate two methods for LDH densification and characterize their composition, density, and corrosion resistance.

Steel sheets and rebars were sequentially polished with #240, #500, #1 000 and #2 000 SiC sandpaper to remove surface oxides. After polishing, they were placed in anhydrous ethanol for 5 min under ultrasonic cleaning to eliminate surface impurities, resulting in a smooth and uniform bare steel named as B. Subsequently, steel samples were immersed in solutions containing 0.057 5 mol/L Mg(NO₃)₂·6H₂O, 0.025 mol/L Al(NO₃)₃·9H₂O, and 0.375 mol/L urea dissolved in deionized water (DI). The surface of steel materials was washed with 5% dilute nitric acid and then vertically placed in a reaction vessel. The heating procedure was to increase from room temperature to 120 ℃ for 2 h, and maintain at 120 ℃ for 24 h. The pressure was self-supplied by the reaction vessel during the heating process. After the hydrothermal reaction, the samples were removed, rinsed with deionized water and dried for 3 d, resulting in the samples with only Mg/Al-CO₃^2--LDH membrane growth, named as L₁.

Furthermore, LDH samples were placed in a 100% CO₂ for half a day, then immersed in saturated calcium hydroxide for 2 h. Afterwards, they were taken out, placed in an oven at 50 ℃, and dried for 3 d. The sample represented the first method of calcium carbonate densification after LDH growth, named as L₂. For the second method, LDH samples were immersed in saturated calcium hydroxide for 6 h, followed by exposure to CO₂ for 10 s, and then dried in an oven for 3 d, resulting in the sample denoted as L₃. This aimed to investigate the optimal method for calcium carbonate densification between LDH pores. All the samples obtained the two methods were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and specific surface area analysis (BET). The corrosion resistance of the composite films under different conditions was also determined by electrochemical impedance spectroscopy and potentiodynamic polarization analysis.

Based on the XRD patterns and FTIR spectra, a layered double hydroxide (LDH) film and calcium carbonate composite occur on the steel surface. The results show that the peak intensity of calcium carbonate of the sample L₃ is higher than that of the sample L₂, indicating a higher content of calcium carbonate in the sample L₃. Based on the SEM images, the surface pores and the compactness of calcium carbonate occur, and the thickness and cross-sectional compactness appear. The analysis of internal compactness reveals that the compacted samples maintain their thickness and achieve a compaction in internal pores. From the analysis of pore size and pore volume, the pore size and volume decrease for the samples L₁, L₂, and L₃.

The results by electrochemical impedance spectroscopy and potentiodynamic polarization curves indicate that the sample L₃ has an optimum corrosion resistance. Also, the sample L₃ has a superior corrosion resistance rather than the sample L₂. This can be since the sample L₂ is initially placed in CO₂, resulting in some carbon dioxide remaining in the pores. However, the sample L₃ is firstly immersed in Ca(OH)₂ solution. In the soaking process, Ca(OH)₂ solution effectively penetrates the pores in the film layer. This sample is able to form a large amount of calcium carbonate to compact the LDH film through carbonization, having a protective performance. This method of filling is simpler, more economical, and faster, making it more conducive to industrial applications.

The in-situ growth of MgAl-CO₃^2--LDH films on steel substrates was achieved through two methods, allowing for the compact composite of calcium carbonate within the pores of the LDH film.

1) The thickness of the LDH film hardly changed after the incorporation of calcium carbonate, remaining at approximately 17 μm. The compaction of calcium carbonate was on the surface of the LDH and permeated into the inner pores of the LDH film.

2) All the LDH film layers exhibited a superior corrosion resistance in chloride ion intrusion. The sample subjected to Ca(OH)₂ immersion followed by carbonization had a superior corrosion inhibition performance and an impressive corrosion inhibition efficiency of 95.22%.

The surface properties, pore size distribution and specific surface area of porous carbon are the main factors affecting its electrochemical performance. To further improve the electrochemical properties of porous carbon materials, two commonly used strategies are activation and doping with non-metallic heteroatoms. In this paper, a hierarchical porous carbon (HPC) was prepared by a one-step carbonation-activation method with poly(vinylpyrrolidone) as a carbon source, fibrous brucite as a template, and trispotassium phosphate as an activator to achieve the passive regulation of the pore structure and surface properties of porous carbon. The pore structure and specific surface area of hierarchical porous carbon were modulated, and the in-situ doping of nitrogen atoms were achieved. In addition, the influence of tripotassium phosphate addition on the pore size distribution, specific surface area, pore structure and electrochemical properties of the porous carbon was also investigated.

A certain amount of polyvinylpyrrolidone (PVP), tripotassium phosphate and fibrous brucite were mixed with deionised water under ultrasonication and stirring, obtaining a homogeneously dispersed mixture. The mixture as a precursor was sintered in a tube furnace via high-temperature carbonization to obtain a template/carbon composite. Afterwards, the composite was acid washed to remove the template and dried, obtaining a hierarchical porous carbon. The physical phase, pore structure, morphology and elemental composition of the hierarchical porous carbon were analysed by X-ray difffraction (XRD), scanning electron microscopy (SEM), specific surface area measurement (BET), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS). The electrochemical properties of hierarchical porous carbon were determined by galvanostatic charge-discharge (GCD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a three-electrode system using Hg/HgO, Pt sheet and the obtained hierarchical porous carbon as reference, counter and working electrodes, respectively. For the preparation process of the working electrode, the synthesised hierarchical porous carbon, conductive carbon black and PTFE emulsion were mixed in a mortar at a mass ratio of 8∶1∶1, and the mixture with an appropriate amount of ethanol solution was ground into a homogeneous slurr. The slurry was coated on the nickel foam collector, dried, and then pressed in a manual hydraulic press for 5 min to obtain the working electrode.

The results of XRD and EDS show that the characteristic diffraction peaks of potassium fluorosilicate appear in the synthesised hierarchical porous carbon in addition to the amorphous carbon, but their contrast capacitance hardly contributes. The hierarchical porous carbon has a one-dimensional hollow carbon tube stacked reticular structure, which is conducive to the rapid transfer of electrons. Meanwhile, the hierarchical porous carbon obtained after the activation of tripotassium phosphate contains abundant pores, which can provide a large number of active sites for the electrolyte ions and a convenient channel for the rapid diffusion and transport of ions. In addition, the microporosity and specific surface area of the activated hierarchical porous carbon increase significantly, compared with those of the unactivated porous carbon. The specific surface area and pore volume are 707.9 m²/g and 1.65 cm³/g, respectively. The large specific surface area and pore volume can lead to more active sites and diffusion channels. The results of XPS demonstrate that element N also appears in the hierarchical porous carbon, indicating that nitrogen in-situ doping is realised during the carbonisation process. The introduction of nitrogen improves the electrical conductivity and wettability of the carbon material, and also has active sites and pseudocapacitance. Compared with the unactivated porous carbon, the activated hierarchical porous carbon exhibits superior electrochemical properties due to its rich pore structure, suitable heteroatom doping and hierarchical porous structure.

Nitrogen-doped hierarchical porous carbon was synthesized by a one-step carbonation-activation method with fibrous brucite as a template and tripotassium phosphate as an activator. Meanwhile, the different additions of tripotassium phosphate could achieve the regulation of the morphology, specific surface area, pore structure and electrochemical properties of the hierarchical porous carbon. The hierarchical porous carbon with an appropriate addition of tripotassium phosphate exhibited high specific surface area and superior electrochemical properties. The results showed that the specific capacitance of HPC/K₃ activated by tripotassium phosphate could reach 281.94 F/g at a current density of 0.5 A/g, which was greater than that of non-activated HPC/K₀ (i.e., 200.31 F/g). The capacity retention rate after 8 000 charge-discharge cycles reached 84.7%. This study demonstrated that tripotassium phosphate activation could improve the electrochemical performance of porous carbon. In addition, this study could also provide some insights for the high value-added application of natural mineral fibrous brucite.

Using coral concrete made from coral aggregates instead of conventional coarse and fine aggregates and seawater instead of freshwater for island reef construction can reduce costs and shorten the construction period for the development of the marine economy. However, coral concrete has some challenges such as high brittleness, poor toughness, and limited durability, thus restricting its application in engineering. Previous studies confirm that incorporating fibers can effectively enhance the mechanical properties of concrete. Therefore, in coral concrete, some microfibers with high elastic modulus are considered to reduce the microcracks, and some macro-fibers with high fracture toughness and elongation are considered to bridge the macrocracks, enhancing its mechanical performance in multiple scales. Carbon fibers (CFs) have the maximum elasticity modulus among commonly used micro-fibers. However, replacing carbon fibers with more economical and relatively high-modulus basalt fibers (BFs) is an effective approach. In this paper, CFs and BFs were selected as microfibers. High-elongation plastic steel fibers (PSFs) were also selected as macro-fibers instead of the steel fibers most commonly used in concrete. The CFs, BFs, and PSFs were incorporated into coral concrete. The mechanical properties of the hybrid fibers-reinforced coral concrete (HFRCC) under axial compression were investigated, and the corresponding constitutive model was proposed.

Cement used was ordinary Portland cement P·O 42.5, adhering to the code GB175. A coarse aggregate used was a crushed coral with a continuous gradation of 5 mm to 20 mm and a tube compressive strength of 3.1 MPa. A fine aggregate used was a coral sand with a fineness modulus of 3.0. Seawater was taken from Beibu Gulf, Guangxi, China. The admixtures include a polycarboxylate superplasticizer, a hydroxypropyl methyl cellulose (HPMC), and an antifoaming agent. The study involved sixteen mix proportions for HFRCCs with different dosages of CFs, BFs and PSFs.

A uniaxial compression test was conducted on prismatic specimens with the dimensions of 100 mm×100 mm×300 mm by a model RMT-201 electro-hydraulic servo testing machine (1 500 kN). To measure the axial deformation of specimens, two LVDTs were placed in the middle of the specimen. Simultaneously, during the loading, a digital image correlation (DIC) system was arranged at the front and rear positions of the specimen to record complete deformations throughout the specimen failure. The failure process, failure modes, and stress-strain curves of the specimens were determined via uniaxial compression tests. Key parameters such as peak stress, peak strain, residual stress, and ultimate strain were extracted from the stress-strain curves. The strain field and failure process were analyzed by digital image correlation (DIC) system. In addition, a modified constitutive model suitable for HFRCC was also established based on the experimental data.

The uniaxial compression process of HFRCC can be divided into four stages, i.e., linear elasticity, stable crack development, unstable crack propagation, and post-peak failure. Microfibers predominantly affect the crack development before the peak stage, while macro-fibers play a crucial role in the post-peak stage. In the post-peak failure stage, a combination of DIC system obtained horizontal strain distribution cloud maps reveals that HFRCC with micro-fibers exhibits a more uniform strain distribution, compared to HFRCC without fibers or with only macro-fibers. However, in HFRCC with macro-fibers, the main through crack has a width of approximately 1 mm, which is smaller than that of HFRCC without fibers or with only micro-fibers (approximately 1.5 mm). The incorporation of high-modulus microfibers and high-fracture toughness macro-fibers into coral concrete enhances its mechanical properties in multiple scales. This is attributed to a ability of micro-fibers at low dosages to form a randomly oriented fiber network in the concrete matrix. This network bridges the micro-cracks, suppresses the extension of initial cracks, and transfers stress across micro-cracks to reduce stress concentration as well as enhances the performance of the interface transition zone. However, most of them break or pull out after macro-crack formation due to the high modulus and low fracture toughness of micro-fibers. Also, macro-fibers with a higher fracture toughness can continue to bridge macro-cracks and transfer stress between them even after the formation of macro-cracks. For the both strength and toughness, HFRCC exhibits a superior performance when the volume fractions of CFs and BFs are 0.15% each, and PSFs dosage is 7 kg/m³. Compared to the coral concrete without fibers, the peak stress, peak strain, and post-peak compressive toughness of HFRCC are increased by 6.22%, 38.54% and 116.44%, respectively.

A modified constitutive model suitable for HFRCC is proposed based on the CEB-FIP model and the Guo Zhenhai model, and the calculated data of the model fit well with the measured results. The damage evolution process of HFRCC investigated by the modified constitutive model reveals that the incorporation of CFs, BFs, and PSFs can synergistically delay the damage progression of coral concrete.

The uniaxial compression process of HFRCCs could be divided into four stages, i.e., linear elasticity, stable crack development, unstable crack propagation, and post-peak failure. Microfibers played a crucial role in expanding microcracks during the first three stages, showing beneficial effects on the peak stress, peak strain, and pre-peak compressive toughness. Macro-fibers acted as bridging elements for macro-cracks in the peak failure stage, demonstrating a more significant impact on the residual stress, ultimate strain, and post-peak compressive toughness. Each type of fiber had an optimal dosage level, and the reasonable dosage of fibers could generate positive synergistic effects. When only micro-fibers were added, BFs contributed more to the increase in peak stress rather than CFs, but their improvement in peak strain and compressive toughness was slightly lower than that of CFs. This indicated that for engineering applications with lower toughness requirements, it could be feasible to replace CFs entirely with more cost-effective BFs. The calculated data of the modified constitutive model aligned well with the experimental results. This work investigated the damage evolution process of HFRCC, revealing that the incorporation of CFs, BFs, and PSFs could collaboratively delay the damage progression of coral concrete.

In general, the electrolyte preparation methods discussed can be categorized into two aspects. The first aspect refers to methods for high performance. The as-fabricated films exhibit a high quality (i.e., thin, dense, and uniform), and their microstructures can be highly adjustable. Typical methods include magnetron sputtering, pulsed laser deposition, and chemical vapor deposition. However, these methods are often featured by high cost and difficulty in large area preparation. The second aspect refers to methods for large scale industrial production, which features simple process, high robustness, low cost, and suitability for large area preparation. Representative approaches are tape casting, screen printing, spraying, etc.. However, the electrochemical performance of the as-fabricated electrolyte still needs to be improved.

It is important to further elucidate the structure-property relationships for SOFC electrolytes through fine processing and characterizing methods. The structure factors that should be considered include compositions, phase structures, microstructures, mesostructures, and interfaces. Also, it is essential to develop large-scale, low-cost, and robust preparation methods, and explore the influencing factors of performance in actual service conditions. Synergistic collaboration between these aspects is conducive to further enhancement of electrochemical performance while holding cost. In addition, the development of SOFC electrolyte preparing methods is a systematic engineering, necessitating consideration of adaptability to other components and practical application scenarios. The pursuit of these development directions will contribute to the commercialization of SOFC, thereby facilitating the realization of 'carbon neutrality' target.

Li₆Gd(BO₃)₃ (LGBO) crystal is an effective scintillator for neutron detection as well as a laser host and phosphor material. However, it is difficulty to grow large-size and high-quality crystals because of high viscosity of the melt and crystal cracking. Although LGBO crystals are grown by the Czochralski and other methods, the crystal size is small and the quality is poor for its practical application. The vertical Bridgman method is suitable for growing borate crystals due to its slow growth rate and small temperature gradient. This paper was to investigate the crystallization behavior of deep supercooling melt and grow LGBO crystals prepared by a modified vertical Bridgman method. In addition, the thermal properties of crystals were also analyzed to provide a reference for practical application.

LGBO polycrystalline materials were synthesized with high-purity chemicals (i.e., Li₂CO₃, 99.99%; H₃BO₃, 99.99% and Gd₂O₃, 99.99%) by a high-temperature solid-state method. LGBO crystal was grown by a modified vertical Bridgman method. The crystals were characterized by X-ray diffraction, ultraviolet excitation and emission spectroscopy, and differential scanning calorimetry. The thermal expansion coefficient of the crystals was measured by a model TMA 402 F1 thermomechanical analyzer. The thermal diffusivity coefficient of the crystals was measured by a model LFA 457 laser thermal conductivity meter, and the thermal conductivity of the crystals was calculated accordingly.

LGBO crystal was grown in a Platinum crucible with a seed well. Seed crystal was obtained via spontaneous nucleation in advance. The DSC curves of LGBO show that the melting point is 845 ℃, and the crystallization temperature is 731 ℃. Thus, the seeding and slow growth rates are the key issues for the growth of LGBO crystal because of the deep supercooling melt. The growth parameters are optimized with a <001>-oriented seed, a slope of 30 degrees at shoulder, a small temperature gradient of 30 ℃/cm at solid-liquid interface and a very slow descent rate of 2.4 mm/d. The transparent LGBO crystal with the sizes of 20 mm in diameter and 30 mm in length is obtained and the transmittance is close to 85% in a range of 320-800 nm. The excitation-emission spectra of the crystals are tested and the mechanism of luminescence is discussed.

The thermophysical properties of the crystal are investigated via measuring the specific heat capacity, thermal expansion, thermal conductivity and diffusion coefficient. Since the specific heat capacity of the crystal is large and changes significantly with temperature, the temperature change is relatively small when the crystal absorbs heat, and the ability to withstand thermal shock is high. The thermal expansion coefficient is an important parameter in the thermal properties of crystals, which has an important reference value for the selection of seed orientation and crystal processing in crystal growth. The gap between the thermal expansion coefficients of the two directions becomes larger with the increase of temperature. The thermal diffusivity and thermal conductivity are both physical quantities that characterize the heat transfer of materials. The thermal diffusivity of crystal phases (020) and (100) decreases with increasing temperature at 25-300 ℃. The thermal conductivity curve of LGBO crystal at 25-300 ℃ obtained by the thermal conductivity calculation formula indicates that the thermal conductivity of LGBO crystal is larger in the similar crystals.

Large-size LGBO crystals were grown by a modified vertical Bridgman method. The high viscosity of the melt and the extra-large supercooling determined the extremely slow growth rate of LGBO crystals. The specific heat capacity of the crystal at room temperature was 0.898 J/(g·K). The thermal expansion coefficients for the crystal phases (100) and (020) were 12.768×10^-6 K^-1 and 21.146×10^-6 K^-1, respectively. The thermal conductivities for crystal phases (100) and (020) at room temperature were 2.72 W/(m·K) and 2.60 W/(m·K), respectively. The thermal expansion had a great anisotropy as the temperature increased, and the thermal diffusivity decreased with the increase of temperature. The results indicated LGBO crystal under a high power could have a potential application due to its large specific heat.

With the rapid development of assembled buildings, the low-carbon and high-efficient production of precast concrete components becomes a hotspot for the industry. Portland cement (PC), as one of the most important cementitious materials for the preparation of precast components, has the disadvantages of insufficient early strength development and late volumetric shrinkage. To realize the volume stability of non-steam-cured precast components, expansion agents are often introduced into Portland cement. Sulphoaluminate cement (CSA) with a large amount of Ye'elimite and gypsum is often used to improve the early strength and volumetric stability of PC. Different types of CSA have different expansion capacities due to the different contents of Ye'elimite and gypsum, affecting the composition of the hydration products with the saturation of ettringite. In this paper, the mechanical properties and volumetric stability of the specimens were investigated via varying the relative contents of and in Portland cement (i.e., molar ratio and content). The hydration process, phases composition, and the microstructure of system were characterized to analyze the effect of on the hydration of Portland cement.

Portland cement clinker (Tangshan Jidong Cement Sanyou Co., Ltd., China), and anhydrite (Tangshan Polar Bear Building Materials Co., China) were used as raw materials. CaCO₃, Al₂O₃, and CaSO₄-2H₂O mixed in a molar ratio of 3∶3∶1 were heat-treated in a high-temperature muffle furnace for 2 h to obtain the mineral. Four different molar ratios of M, 2, 5, 8 and 11 were designed, while five content levels of 5%, 10%, 15%, 20% and 25% were set up in a total of 20 sets of crossover experiments. The 10%-M2 represents the content of this sample of in Portland cement clinker is 10% at the molar ratio M of 2.

The water-cement ratio was 0.35, and the paste was molded as a net paste test block with the sizes of 20 mm×20 mm×20 mm. The compressive strength at the corresponding age was determined. The phase compositions of the hydration products were analyzed by a model D/Max-RB X-ray diffractometer and a model STA 449F3 thermal analyzer. The pore structure of the specimens was characterized by a model AutoPore IV 9500 V1.09 instrument.

has an effect on the free expansion rate of Portland cement, and it can significantly increase the early compressive strength of Portland cement clinker. When the content of ≤15% in the sample, the free expansion rate is small, the volumetric stability is better. When hydration time is 14 d, the free expansion rate remains stabilized, and the expansion rate of the specimen does not change at 28 d. The free expansion rate of the sample is lower than that of the sample with . The effect of on the expansion properties of Portland cement belongs to the ettringite-type expansion. The key reason of the volume stability and early strength development of the system is affected by the amount of ettringte. Ettringite growth in the molding paste is limited as the crystal grows, the pressure of ettringite on the surrounding paste environment gradually increases, reaching a certain threshold that makes the specimen gradually collapse. As a result, the amount of ettringite generation is strictly controlled. At ettringite content of less than 8.51%, the compressive strength increases with the increase of ettringite content. Ettringite plays a role of dense pore. However, at the ettringite content of more than 8.51%, the expansion increases with increasing ettringite content, and the mechanical properties of the cement begin to decrease.

The most available pore sizes of the specimens 10%-M11 were smaller than those of the specimens 5%-M11, while the specimens 10%-M11 have a narrower distribution of pore sizes and smaller total porosity, which can account for the maximum mechanical properties. The location and the crystallization situation of hydration products both have an influence on the expansion properties of Portland cement. Ettringite fills the pores of the paste, and the C-S-H gel can adhere other hydration products such as ettringite to enhance the performance of the cement, and avoid the ettringite abnormal growth.

The 10% content of appropriately increased the expansion deformation of Portland cement, limited its late volumetric deformation and stablized the expansion rate. The content of also improved the early mechanical properties of Portland cement, having a positive effect on the development of mechanical properties. Under the condition of 10% and the molar ratio of of 11, the compressive strength of Portland cement at 12 h was increased by 102%, and the free expansion rate at 28 d was 0.279%. There were three main reasons of high early strength in the system, i.e., hydration of , hydration of C₃A with , and rapid hydration of C₃S. The increased content of facilitated the formation of ettringite, and hydration consumed Ca(OH)₂ in the hydration product to generate ettringite to cause the expansion, accelerating the hydration rate of the silicate phase and improving the cement hydration degree. The ettringite generated by the hydration of could compensate for the self-shrinkage of Portland cement, and the short and fine needle-like ettringite grew on the surface of the hardened cement paste and in the pores, and the staggered lapping filled the pores, reducing the total porosity of the cement and the most available pores. An appropriate amount of could optimize the distribution of ettringite in the system, and avoid the expansion caused by the abnormal growth of ettringite crystal size.

The corrosion of nuclear waste glass over long-time is undoubtedly the most complex problem in glass science to date. Because its components include dozens of oxides, there are cracks formed during the cooling stage, the geometry of the glass block is complex, the thermal, chemical and water boundary conditions are time-varying, involving many coupling phenomena. In addition, the time scale of deep geological disposal security assessment goes beyond direct verification. There is therefore a need to develop one or more rigorous, multi-scale theories to integrate basic understandings into models, which can be verified through dedicated experiments and compared with corrosion in natural or archaeological glass. Future models predicting a long-term corrosion of silicate glasses in aqueous environments should consider the spatial and temporal coupling of glass dissolution and silica precipitation and growth, controlling the transport of chemicals through the growing corrosion zone. Some specific issues include the evolution of porosity and structure over time in SAL, and how to control the transfer of materials between the aqueous solution and the glass; in the actual process, the nuclear fission products and actinides in the nuclear waste glass are what is the reaction during the glass corrosion process. Radioactive elements generate a large amount of heat during the placement process, and the ion irradiation they generate cause damage to the glass structure and SAL. The nucleation and growth of silicon dioxide at the reaction interface affect the glass dissolution rates and the use of ceramics and glass-ceramics for deep geological disposal of radioactive nuclear waste.