Bismuth-doped fibers (BDFs) have already proven themselves as active materials that can be used to develop optical devices with unique characteristics in previously inaccessible spectral ranges. Optical amplifiers based on these active fibers exhibit high gain and low noise across all telecommunication spectral bands (from O- to U-band), while BDF-based lasers offer the benefits of high efficiency and wide wavelength tunability. However, existing research still faces significant challenges in achieving a reliable technology for reproducing the parameters of BDFs, as well as in fabricating optical fibers with increased Bi concentrations and low unsaturable losses. Developing a high-gain, ultra-wideband amplifier that can be effectively integrated into existing communication systems remains a challenge. Future research should focus on balancing cost, energy efficiency, and device performance, which can be partially addressed by optimizing the BDF design and the device itself. All of this is necessary to meet the growing demand for high-speed data transmission over fiber-optic communication systems, which is crucial in the context of rapidly evolving artificial intelligence technologies. In this regard, the ability to utilize all available telecommunications bands appears very promising. We believe that progress in this area will undoubtedly lead to the development of optical communication systems with significantly increased bandwidth, where bismuth-doped optical amplifiers are key components. Moreover, thanks to ongoing advances in optical materials and process technology, bismuth-doped fiber technology can pave the way for efficient, reliable, and scalable solutions for next-generation fiber-optic systems.

The hydration of binder is an exothermic reaction, which results in an obvious temperature increase in concrete in the early hydration period. The shrinkage of hardened concrete due to the temperature drop is a main cracking trigger of concrete. A kind of temperature rising inhibitor is developed to decrease the hydration heat of binder in early hydration age, which can reduce the cracking risk of concrete. Cyclodextrin is a main functional composition of the temperature rising inhibitor. C₃A is an important clinker mineral influencing the early exothermal characteristics of Portland cement. In this paper, the effect of cyclodextrin on the hydration of tricalcium aluminate-gypsum (C₃A-CaSO₄·2H₂O) was investigated. This work could favor understanding the action mechanism of the temperature rising inhibitor to reduce the cracking risk of concrete structures.

Pure C₃A was calcined, the chemical pure gypsum and cyclodextrin was used. The hydration exothermal curves of C₃A-CaSO₄·2H₂O pastes containing different dosages of cyclodextrin were measured. The hydration products of C₃A-CaSO₄·2H₂O pastes containing different dosages of cyclodextrin in different ages were in-situ determined by quantitative X-ray diffraction (QXRD). The morphology of hydration products on the surface of C₃A particles immersed in different solutions was characterized by scanning electron microscopy (SEM). The etching situation on the surface of C₃A particles washed by different solutions was determined by three-dimensional white light interferometric surface profilometry.

The beginning time of second hydration of C₃A moves up and its exothermic rate decreases, but its reacting time prolongs with the increase of cyclodextrin dosage. The heat output of C₃A during its second hydration stage varies little. The consumption of C₃A and CaSO₄·2H₂O increases continuously and the exhausting time of gypsum reduces with the increase of cyclodextrin dosage. The forming quantity of ettringate in the paste containing cyclodextrin is greater than that in controlling paste. The transformation of ettringate to AFm is suppressed after the exhaust of gypsum. Cyclodextrin can expedite the dissolution of C₃A in CaSO₄ solution to form more deeper etch pits on the surface of C₃A particles, which speeds up the hydration of C₃A. Needle-like ettringite changes to stick-like one, and the transformation of ettringite to AFm restrains when cyclodextrin exists in pastes.

Cyclodextrin could promote the initial hydration of C₃A to move up the beginning of the second hydration of C₃A. The consumption of C₃A and CaSO₄·2H₂O increased continuously in the first hydration stage and the exhausting time of gypsum reduced with the increase of cyclodextrin dosage. Cyclodextrin reduced the reaction speed and prolonged reacting time of C₃A during its second hydration stage, its heat output changed little. Cyclodextrin could enhance the dissolution of C₃A in gypsum solution to form more deep etch pits on the surface of C₃A particles, speeding up the hydration of C₃A. Cyclodextrin could change needle-like ettringate to stick-like one and suppress the transformation of ettringate to AFm.

Polymer-derived ceramics are prepared via forming precursors through the polymerization of tiny molecules and cracking at high temperatures. Compared to conventional ceramics, their advantage lies in an ability to precisely control the microstructure and crystalline phase composition through the design of the molecular structure and elemental composition of the precursor and subsequent thermal treatment, thereby producing the optimal final properties. Among these, SiBCN ceramics stand out within the polymer-derived ceramics due to their flexible molecular structure designability. This enables the in-situ formation of multi-phase synergistic loss systems incorporating SiC, BN and graphitic carbon, coupled with a unique oxidation resistance mechanism, which excel particularly within polymer-derived ceramic systems. However, SiBCN ceramics primarily exist in an amorphous state at lower temperatures (i.e., < 1400 ℃), thus limiting their application in electromagnetic wave absorption. The paper was to introduce Ti nanopowder during the ceramicization process to catalyze the formation of nano-dielectric crystals such as SiC, TiC, and crystalline graphite. These crystals could enhance the dielectric imaginary part of SiBCN ceramics, thereby strengthening their electromagnetic wave attenuation capabilities.

For the synthesis of polymer precursor, tetrahydrofuran (THF)-methylvinyl dichlorosilane and borane dimethyl sulfide complex were mixed into a three-neck flask and conducted in argon for 24 h. Also, methyl dichlorosilane and hexamethyldisilazane were introduced, and the reaction was continued at the ambient temperature for 24 h. Subsequently, the mixture was then heated from room temperature to 170 ℃ for amide copolymerization reaction. After holding at this temperature for 3 h, vacuum distillation was performed, and filtrated for three cycles, thus producing a pale yellow polyborosilazane (PBSZ). For the synthesis of SiBCN ceramibs, polyborosilazane (PBSZ) was placed in a tube furnace and heated to 280 ℃ for 2 h to fully cure the precursor. The cured sample was subjected to ball grinding. The resultant ground powder was mixed with Ti nanopowder at different Ti mass contents (i.e, 0%, 5%, 10%, and 15%), and then was ground to produce different composite powders, . The composite powders were pressed into discs with the diameter of φ20 mm. The discs were heat-treated in a vertical tube furnace(i.e., firstly heating at 800 ℃ for 1 h, and thenheating at 1000 ℃ for 2 h) to allow enough molecular diffusion for TiC crystal formation, resulting in SiBCN ceramics.

The analysis of the four-component doped ceramics reveals that Ti nanoparticles doping positively affects both the phase composition and dielectric properties of SiBCN ceramics. The XRD patterns indicate that pure SiBCN ceramics remain amorphous after heat treatment at 1000 ℃, whereas the addition of Ti nano-particles promotes the formation of TiC crystals within the ceramics, thereby enhancing their crystalline properties. The SEM and TEM images demonstrate that varying the nano-Ti doping content alters the microstructure of SiBCN ceramics. Nano-Ti addition promotes the formation of a porous structure within the ceramics and facilitates the growth of crystals such as TiC and carbon nanotubes, enriching the phase composition of the ceramics. Varying Ti nanoparticles doping contents alters SiBCN's electromagnetic wave absorption and loss capabilities. Compared to pure SiBCN ceramics, Ti nanoparticles doping confers higher electromagnetic parameters and lower reflection loss, and 10% Ti nanoparticles-doped SiBCN exhibits the optimum electromagnetic wave absorption performance. The incorporation of Ti nanoparticles optimizes the ceramic structure, with synergistic interactions among various crystals and structural components, thus enhancing the overall performance.

This study demonstrated that doping Ti nano-particles into SiBCN ceramic could enhance the ceramic dielectric loss and impedance matching qualities. Ti nano-particles enhanced the low-temperature crystallization property of SiBCN. The crystallinity and microstructure of SiBCN ceramics could be adjusted by varying the nano-Ti doping content. The ceramics heat-treated at 1000 ℃ could develop porous architectures, TiC, and crystalline phases such as crystalline carbon. Ti nanoparticles improved the electromagnetic wave attenuation properties of SiBCN. The formation of TiC and carbon nanotubes, along with the heterogeneous interfaces formed with the amorphous matrix, could boost the electromagnetic wave attenuation performance of SiBCN ceramics. The crystallinity of SiBCN ceramics and the presence of abundant atomic defects resulted in a significant polarization loss, thereby enhancing the ceramic's electromagnetic wave absorption capability. At Ti nanoparticles content of 10%, the RLmin value of SiBCN ceramics at 6.24 GHz achieved -44.5 dB, with an EAB as high as 3.43 GHz, indicating that adding Ti nanoparticles could effectively enhance the electromagnetic wave absorption capacity of low-temperature heat-treated SiBCN ceramics.

The Faraday effect was discovered 180 years ago, but this phenomenon has been still utilized for practical applications as mentioned above. In particular, Tb³⁺-rich and Eu²⁺-rich oxide glasses are important for both fundamentals and applications. The Tb³⁺-rich glasses show a high transparency even in blue to ultraviolet region, so that the magneto-optical figure of merit is large enough to apply for an optical isolator. The Eu²⁺-rich glasses are ferromagnetic, so that they notably show a large Faraday effect. A new technique of glass formation such as containerless processing is effective to produce new glass compositions with further higher concentrations of rare-earth ions that are expected to exhibit a larger Verdet constant. Besides, the possible enhancement of Faraday effect based on plasmonics and Mie-tronics, i.e., the usage of localized surface plasmon resonance of metal nanoparticles and the Mie resonance of dielectric nanoparticles to increase the Verdet constant, becomes an important subject in the near future. With the development of high-power lasers, the demand for optical isolators that can operate in a wide wavelength range must increase. The oxide glasses have a promising application in such fields.

The issue of electromagnetic pollution has become increasingly severe with the development of the electronic communication technology. The excessive electromagnetic waves pose risks to the national security and the human health in daily life. Consequently, wave-absorbing materials have gradually garnered public attention. Biomass, with its inherent network structure, can be used to produce porous carbon for addressing electromagnetic pollution. Among various biomass sources, coconut shells are widely distributed in China and have long been treated as agricultural by-products or waste. Recycling and utilizing coconut shells to prepare wave-absorbing materials not only helps mitigate electromagnetic pollution but also offers a new approach for the high-value application of agricultural by-products such as coconut shells.

The experimental materials included coconut shells purchased from Hainan Wenchang Coconut Shell Co., Ltd.. Potassium hydroxide (KOH), calcium carbonate (CaCO₃), hydrochloric acid (HCl), and paraffin wax (C₂₅H₅₂) purchased from Shanghai Titan Scientific Co., Ltd. The coconut shells were processed into 1-2 cm pieces, cleaned, and dried at 80 ℃ for 24 h. The dried pieces were then ground into powder using a pulverizer and sieved through a mesh with an aperture of 250-300 μm. The coconut shell powder was mixed with CaCO₃ and KOH at mass ratios of 1.0∶1.0∶0.5, 1∶1∶1, 1∶1∶2, and 1∶1∶3, respectively. The mixtures were uniformly ground in a pulverizer to obtain alkalized coconut shell powder, which was subsequently dried. The dried alkalized powder was placed in a tube furnace, which was purged with nitrogen gas (N₂), and then carbonized at 700 ℃ for 2 h. The resulting product was neutralized with hydrochloric acid (HCl) under magnetic stirring for 12 h, washed with deionized water until neutral, and finally dried at 80 ℃ for 24 h , then the coconut shell-based porous carbon was obtained.

In this study, coconut shell was utilized as the carbon source, based on its inherent multi-level network structure and high carbon content. Using KOH and CaCO₃ as dual activators, a one-step carbonization method was employed to prepare coconut shell-based carbon wave-absorbing materials with superior microwave absorption performance. Compared to pure coconut shell carbon and coconut shell carbon activated solely with an equal mass of KOH, the sample prepared with dual activators exhibited more uniform surface pore distribution and hierarchical structure. This specific structure played a critical role in enhancing the electromagnetic wave absorption performance. Consequently, the dual-activator method offered a novel approach for preparing porous carbon materials with complex three-dimensional micro/mesoporous structures. At 700 ℃, the gradual addition of activator resulted in enlarged pores and increased defects in the porous carbon structure, ultimately causing pore collapse. Higher activator concentrations led to larger pore diameters, which reduced electromagnetic wave reflection efficiency and consequently diminished microwave absorption performance.

A coconut shell-based porous carbon material with excellent wave-absorbing performance was successfully prepared via a one-step carbonization method combined with a dual-activator (KOH and CaCO₃) activation process. By adjusting the mass ratios of KOH to CaCO₃, the pore structure of the resulting carbon material was modulated, leading to varied electromagnetic wave absorption properties. The optimal absorption performance was achieved under the conditions of a carbonization temperature of 700 ℃ and a mass ratio of coconut shell powder : CaCO₃∶KOH = 1∶1∶1. The material obtained under these conditions exhibited a minimum reflection loss (RL_min) of -45.79 dB at a sample thickness of 5.0 mm and a frequency of 5.12 GHz. This study utilized a simple one-step carbonization process to produce effective wave-absorbing materials with abundant coconut shell waste, providing valuable theoretical guidance for the development of high-performance absorbers and significantly broadening the application prospects for biomass-derived wave-absorbing materials.

With the continuous pursuit of higher efficiency and larger thrust-to-weight ratio in aero-gas-turbine engines, the turbine inlet temperature has already exceeded 1300 ℃, imposing increasingly stringent requirements on the thermal resistance and protective capability of hot-section structural materials. Environmental barrier coatings (EBCs) have become a crucial technology to ensure efficient and reliable service of ceramic matrix composite (CMC) turbine components under such extreme working conditions. However, the service environment of EBCs is exceptionally complex. Coatings are continuously exposed to corrosive gaseous species within combustion products, among which the ingression and reaction of molten calcium-magnesium-aluminum-silicate (CMAS) deposits represent one of the most detrimental degradation mechanisms.

To mitigate CMAS-induced deterioration, numerous strategies have been proposed, including compositional modification (doping, high-entropy ceramics), structural design optimization (multilayer or graded coatings), and surface engineering (laser or ion beam treatments). Although these approaches can improve corrosion resistance to some extent, most of them inevitably alter the coating chemistry or structural system, which tends to induce thermal expansion mismatch with the substrate and promotes premature failure during thermal cycling. Therefore, how to enhance CMAS-corrosion resistance while maintaining thermomechanical compatibility remains a critical challenge. Laser glazing (LG) is a surface-modification technique that locally melts and rapidly solidifies the coating surface to form a dense glaze layer. It improves surface compactness and seals microdefects without altering the coating composition, thereby presenting a promising method for improving CMAS-corrosion resistance. In this work, laser glazing is introduced to enhance the CMAS-resistance of EBCs, and the CMAS-corrosion behavior together with the underlying improvement mechanisms are systematically investigated.

SiC ceramic substrates were purchased from Fuzhou Pengkun Optoelectronics Co., Ltd. The samples were cylindrical (diameter 25.4 mm, thickness 3 mm) and mechanically grit-blasted prior to coating deposition. Yb₂Si₂O₇/Si (YbDS) EBCs were deposited on the substrates by atmospheric plasma spraying (APS). Commercial Yb₂Si₂O₇ and Si powders (Shanghai Shuitian Materials Technology Co., Ltd.) were used, and the bond coat consisted of 90% (in mass fraction) Si and 10% Yb₂Si₂O₇. A picosecond ultraviolet pulsed-laser system was subsequently applied to modify the surface microstructure of APS YbDS coatings. Four sets of parameters (L1-L4) were obtained by adjusting the laser power (6 W or 20 W) and scanning speed (100-300 mm/s). CMAS bulk material was synthesized by high-temperature melting. CMAS powder was mixed with ethanol and uniformly brushed onto the coating surface, followed by drying to achieve a coating mass of 5 mg/cm². The coated samples were exposed at 1350 ℃ for 10, 60 h, and 120 h. After corrosion, the evolution of microstructure and phase composition was analyzed to reveal the degradation behavior.

The APS-prepared YbDS coating exhibited a surface roughness of ~3.7 μm and a porosity of ~4.87%, with typical APS defects such as pores, unmelted particles, and microcracks. After laser glazing, four modified surfaces were obtained. Among them, sample L2 demonstrated the most favorable structural morphology and was selected for subsequent corrosion tests. The L2 coating showed a reduced surface roughness of ~1.824 μm and a homogeneous, dense glaze layer of ~9.6 μm thickness. Moreover, the glazed surface phase completely transformed from Yb₂Si₂O₇ to Yb₂SiO₅. During CMAS corrosion, the YbDS coating surface was continuously covered by a loose mixture of Ca₂Yb₈(SiO₄)₆O₂ and CMAS residual glass. In contrast, the laser-modified L2 coating was covered by a compact Ca₂Yb₈(SiO₄)₆O₂ reaction layer. After corrosion, both coatings displayed Ca₂Yb₈(SiO₄)₆O₂ and secondary Yb₂Si₂O₇ phases; however, their structural evolution differed significantly. After 120 h of corrosion, the YbDS coating suffered severe structural degradation, including interfacial delamination and partial spallation in cross-sectional observations. Conversely, the L2 coating maintained structural integrity, and its corrosion depth was consistently lower under the same conditions.

The improved CMAS resistance of the L2 coating can be attributed to three synergistic mechanisms: Surface densification, Laser glazing produced a dense, continuous glaze layer that sealed APS-induced pores and cracks, effectively delaying CMAS infiltration pathways; Protective reaction-layer formation, The Yb₂SiO₅ glaze reacted with CMAS to form a dense Ca₂Yb₈(SiO₄)₆O₂ layer, which further hindered molten-salt penetration ;Enhanced non-wettability, Laser glazing significantly reduced surface roughness and improved hydrophobicity. As a result, molten CMAS appeared as aggregated hemispherical droplets rather than fully spreading, making it more easily removed by high-velocity gas flow during service.

The findings of this study demonstrate that laser glazing effectively enhances the CMAS-corrosion resistance of YbDS coatings. The improvement originates from the combined effects of surface densification, pore/crack sealing, phase transformation to Yb₂SiO₅, and subsequent formation of a compact Ca₂Yb₈(SiO₄)₆O₂ reaction layer during corrosion. Additionally, the smoother and less wettable glazed surface reduces the adhesion and spreading tendency of CMAS, enabling molten deposits to be removed more easily under aerodynamic forces. As a result, the degradation rate of the coating is substantially suppressed, delaying the propagation of corrosion-induced cracks and maintaining structural integrity over prolonged exposure. Moreover, the laser-induced modifications do not alter the coating architecture or introduce thermal expansion mismatch, making the technique compatible with existing EBC design frameworks. Overall, laser glazing represents a promising strategy for improving the durability and service lifetime of EBC systems in next-generation high-temperature aero-engine applications.

Across diverse application domains, glass materials are engineered to meet increasingly stringent criteria with regard to performance, reliability, and sustainability. It is worth mentioning that the most advanced display modules and semiconductor chips are currently manufactured mostly in East Asia. This geographic imbalance provides unique opportunities and challenges for both of the glass industry and academia. New applications such as ultra-thin glass for flexible display modules and glass core substrate for semiconductor packaging will present unprecedented functionalities and benefits to glass materials.

Cement production accounts for approximately 12% of China's total CO₂ emissions, having a significant challenge to achieving the national "dual carbon goals". Carbon capture, utilization, and storage (CCUS) represent a pivotal innovative technology for mitigating these emissions. However, conventional amine-based CO₂ capture requires an energy-intensive high-temperature desorption, hindering its industrial implementation in cement plants. Also, the limited utilization pathways for captured CO₂ pose another challenge for cement CCUS. Diethanolamine (DEA) offers a promising solution as it functions both as a CO₂ absorber and a cement additive. This dual capability enables a potential carbonation utilization of CO₂ absorbed DEA solutions without requiring the desorption step within cementitious systems. This study was thus to investigate the effect of CO₂-absorbed diethanolamine (DEAC) on the early hydration behavior and strength development of cementitious systems. The findings could propose a novel approach for low-energy CO₂ capture coupled with efficient in-situ utilization within cement industry.

Cement mortars with a water-to-cement ratio (W/C) of 0.50 were prepared with P·I 42.5 Portland cement (GB 8076) and ISO standard sand. The specimens were designated as REF, D0.1%C0%, D0.1%C0.02%, D1.0%C0%, and D1.0%C0.22%, respectively. DEA and its equivalent CO₂ admixture were added as percentages of cement mass. All associated cement paste mixtures were prepared at a W/C ratio of 0.3. DEAC was prepared by continuously bubbling CO₂ gas (≥99% purity) at a flow rate of 200 mL/min through a 5 mol/L DEA solution maintained at 40 ℃ until saturation was achieved. An eight-channel microcalorimeter recorded the hydration heat of cement paste specimens at 25 ℃ for 72 h. The phase composition of hardened cement pastes was determined by X-ray diffraction (XRD). The contents of bound water, CH, and CaCO₃ were analyzed by thermogravimetric analysis (TGA). The cumulative porosity and pore size distribution of hardened paste samples at 7 d were characterized by mercury intrusion porosimetry (MIP). The compressive strength was measured on mortar specimens at 1, 3 d and 7 d of curing in accordance with the standard GB/T 17671.

The hydration calorimetry results demonstrate that D0.1%C0.02% and D0.1%C0% both accelerate the hydration rate of silicate phases, as evidenced by an increased second exothermic peak rate, while leaving the induction period duration unaffected. Conversely, D1.0%C0% and D1.0%C0.22% significantly reduce the second exothermic peak rate. D1.0%C0.22% extends the hydration induction period to 240 min, while D1.0%C0% has a negligible effect on its duration. The XRD patterns and TG analyses reveal that the impact of DEAC on the cement hydration depends critically on its specific DEA and CO₂ dosage. At a low dosage (i.e., D0.1%C0.02%), a mild carbonation promotes a concurrent hydration of silicate and aluminate phases. However, a high dosage (i.e., D1.0%C0.22%) substantially inhibits early hydration of silicates. The MIP results indicate that DEAC and DEA both refine the pore structure of hardened cement paste. The pores below 20 nm are significantly reduced in D0.1%C0% and D0.1%C0.02% systems, aligning with their enhanced early hydration kinetics. This refinement also occurres in D1.0%C0% and D1.0%C0.22% systems despite inhibited silicate hydration. The results of compressive strength tests show that D0.1%C0.02% and D0.1%C0% can enhance mortar strengths at 1, 3 d, and 7 d, respectley. The strengths of D0.1%C0.02% systems can be increased by 8.4%, 10.2%, and 16.8% at these ages, respectively, primarily due to the DEA component with the weak carbonation contributing minimal additional enhancement. The 3-day and 7-day strengths of D1.0%C0.22% and D1.0%C0% systems both are increased (more significantly in the carbonated system), indicating a synergistic hydration-carbonation effect. However, the 1-day strength of D1.0%C0.22% system drastically is reduced by 52.2%, with silicates hydration inhibition by D1.0%C0% identified as a primary factor underpinning early strength reduction. According to the analysis of bound water content, calcium hydroxide (CH) content, porosity, and compressive strength relationships, a linear correlation between CH content and mortar strength is proposed. This demonstrates that silicate phase hydration kinetics can be modulated differently by DEAC and DEA formulations-fundamentally governed compressive strength development.

The addition of 0.1%DEA with 0.02% CO₂ (D0.1%C0.02%) as DEAC enhanced the flexural and compressive strengths of cement mortar at 1, 3 d, and 7 d. In contrast, the addition of 1.0% DEA with 0.22% CO₂ (D1.0%C0.22%) significantly reduced the 1-day strength. In D0.1%C0.02% system, the CO₂ component reacted with dissolved Ca²⁺ released from cement minerals to precipitate CaCO₃. This reaction promoted cement hydration, refined the pore structure of the hardened paste by reducing the volume of harmful pores, and facilitated a synergistic enhancement of hydration and carbonation. D1.0%C0.22% addition significantly retarded cement hydration within the first 24 h, primarily by inhibiting the dissolution of silicate phases and extending the induction period, leading to the reduced early strength. Although carbonation exacerbated the retardation of silicate phase hydration via DEA interaction, the hydration process recovered normal kinetics after 7 d.

Tricalcium silicate (C₃S) is one of Portland cement clinker minerals whose proportion is over 50%. It hydrates quickly and releases lots of heat in early hydration period. The reaction rate and degree of C₃S in early hydration period are the chelloef constituent to determine the exothermal and mechanical performance of Portland cement; as well as the cracking risk of concrete. One of concrete additive, temperature rising inhibitor, was created to suppress the heat release of binder and decrease its exothermic rate. Cyclodextrin (CD) is the main functional composition of temperature rising inhibitor. It is studied that the effect of CD on the early hydration process of C₃S. This work is helpful to understand the action mechanism of temperature rising inhibitor.

Pure C₃S was calcined, chemical pure CD was used. C₃S paste with w/c= 0.5 was prepared. The CD dosage in paste is 0%, 0.05%, 0.10% and 0.20% separately. Dilute C₃S solution with the solid content of 10^-4 and containing 0, 2 mmol/L and 4 mmol/L CD solution was prepared to measure the dissolving rate of C₃S in the induction period of hydration. Pore solution of C₃S was obtained using centrifugal extraction for fresh paste or press method for hardened C₃S paste. The hydration exothermal curves of C₃S pastes containing different dosages of CD were measured using isothermal calorimetry. The time-depended concentration variation of Ca and Si in dilute C₃S solution and pore solution was measured by ICP-AES. SEM was used to investigate the formation of hydrate nucleus on the polished surface of C₃S particles etched by CD solution or pure water. The ion activity product of pore solution relative to C₃S was calculated.

There is not obvious induction period during the hydration of pure C₃S. The induction period of C₃S hydration prolongs with the increase of CD dosage in paste. The accumulate heat release of C₃S is proportional with its hydration degree. The hydration degree of C₃S paste containing CD is higher than blank one at the point of maximal exothermic rate. The accumulate heat release of C₃S paste with or without CD is almost same at the end of induction period. The addition of CD decreases the early hydration speed, but does not negatively influence the final hydration degree. CD inhibits momentarily the dissolution of C₃S in early hydration period, but does not affects the hydration of C₃S in long period. The Ca and Si concentration in pore solution increases with the increase of CD dosage in induction period of hydration. The ion activity product of pore solution relative to C₃S is changed when Cd is added into C₃S paste. CD is adsorbed at the etch pits on the surface of C₃S particles to increase the barrier ΔG_crit of the etch pit expansion model and decrease the growing speed of etch pit. There are lots of etch pit on the polished surface of C₃S particle after 1 h immersion in pure water. There are few etch pit on the polished surface of C₃S particle after 1 h immersion in 1 mmol/L CD solution.

CD prolongs the induction stage and the main reaction stage of hydration, decreases the reaction rate of C₃S. This effect is very intense when the dosage of CD increases to 0.2%. The hydration degree of C₃S paste increases in some extent at the peak reaction rate due to the prolongation of the main reaction period of C₃S paste containing CD. The ultimately hydration heat release of C₃S paste containing CD does not decrease due to the delay of hydration. CD is absorbed on the etch pit of C₃S particles in the initial hydration stage to elevate the energy barrier ΔG_crit of the etch pit expansion model. It decreases the dissolving rate of C₃S and prolongs the induction period of hydration. In the induction period the exist of CD results in an increase of Ca and Si concentration in pore solution and higher degree of supersaturation relative to Ca(OH)₂ and C-S-H. The formation of C-S-H nucleus is inhibited to hinder the acceleration of C₃S hydration

Solid oxide fuel cells (SOFCs) are high-efficient solid-state energy conversion devices. However, all-ceramic self-supported SOFCs face several challenges such as high brittleness, difficulty in mechanical processing, poor thermal shock resistance, and limited weldability, which result in high manufacturing costs and restrict the applications in mobile power systems. In contrast, metal-supported SOFCs (MS-SOFCs) with metal materials as the external structural support, exhibit remarkable mechanical strength, low cost, and rapid start-up capability, making it highly promising for mobile applications. The anode is a critical component of MS-SOFCs, serving as the site where fuel oxidation occurs to generate electrons. Its microstructure significantly influences the density and effectiveness of the triple-phase boundaries (TPB), where the gas phase, the ionic phase, and the electronic phase intersect. The TPB density largely determines the polarization resistance, with its low-frequency component being inversely related to anode gas diffusion. A common strategy to enhance gas transport is the incorporation of pore-formers, such as graphite, into the anode raw materials. Most studies focus on the type, particle size, and content of pore-formers, which directly affect the pores number, size, and distribution. In this work, atmospheric plasma spraying (APS) was employed to fabricate three types of anodes and corresponding cells. APS reduces thermal input to the metal substrate, effectively preventing oxidation, deformation, and elemental interdiffusion between the metal support and the anode at high temperatures. This study systematically investigates the influence of graphite incorporation methods on the microstructural evolution of the anode and the resulting cell performance, providing important theoretical insights into the operational mechanisms of SOFC anodes.

Porous 430L stainless steel substrates were used as supports. Three different NiO-GDC (Gd_0.2Ce_0.8O_1.9) anode powders were prepared. C1 is the baseline without a pore-former. C2 contains 40% (in volume fraction) graphite, which is mixed by spray granulation process to produce composite particles. C3 is made by mechanically mixing 40% of the same graphite with C1 powder. All powders are spherical with good fluidity. Anode layers were deposited via APS. Subsequently, the C2 and C3 anodes were heat-treated in air to remove the graphite pore-former at 750 ℃ for 2 h. A ScSZ (Sc₂O₃-ZrO₂) electrolyte and an LSCF (La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ) cathode were subsequently deposited by APS to build single cells. The microstructure and porosity of the anodes were characterized using scanning electron microscopy (SEM) and image analysis software. The surface roughness was measured by profilometer. The electrochemical performance, including the open-circuit voltage (OCV), current-voltage-power (I-V-P) and electrochemical impedance spectroscopy (EIS), were evaluated in the range of 600-750 ℃ using humidified H₂ as fuel and air as oxidant. The equivalent circuit fitting of EIS data is carried out to quantitatively analyze the contribution of charge transfer, surface adsorption/dissociation and gas diffusion in polarization impedance.

The incorporation of graphite pore-former significantly modified the pore size distribution and total porosity within the anodes. The measured porosity of C1, C2, and C3 was 26%±2%, 37%±3.1%, and 42%±2.3%, respectively. The C1 anode featured a relatively dense structure with uniformly distributed pores, which primarily consisted of submicron cracks and fine pores originating from the thermal stress inherent to the APS process. In contrast, the C2 anode showed a notable increase in both the number and size of pores, which were homogeneously dispersed without significant agglomeration. The C3 anode, however, contained a substantial amount of large pores, mostly ~5 μm in diameter, attributed to the agglomeration of graphite particles during mechanical mixing, resulting in coarse and irregular pore structures after heat treatment. Furthermore, the addition of graphite modified the thermal response characteristics of the agglomerated powder during the spraying process, promoting the formation of a more uniformly melted microstructure in the anode layer. The average surface roughness (R_a) values for C1, C2, and C3 were 6.64, 7.06 nm, and 7.66 μm, respectively, indicating that graphite addition increased anode surface roughness. This phenomenon is due to the thermal decomposition of graphite during the plasma spraying process, where high temperatures cause partial oxidation of graphite in the open atmosphere, thereby generating CO₂ gas. The release of this gas from the incompletely solidified anode surface etches irregular pits and protrusions, ultimately leading to increased surface roughness. The cell without graphite pore-former (C1) consistently demonstrated the highest OCV and maximum power density, reaching 1.0 V and 957 mW·cm^-2 at 750 ℃, respectively. EIS analysis revealed that the anodes with graphite pore-former (C2 and C3) exhibited improved charge transfer capability, thereby reducing the high-frequency polarization resistance. Despite this, the overall output performance of C2 and C3 did not show effective enhancement, which is attributed to their increased ohmic resistance (R_o) and lower OCV. The elevated surface roughness and inherent porosity in the C2 and C3 anodes adversely affected the quality of the subsequently sprayed electrolyte layer, introducing microcracks and gas permeation pathways. This resulted in increased R_o and reduced OCV, ultimately weakening the benefits gained from the reduced polarization resistance.

The method of graphite pore-former addition significantly affects the anode microstructure and overall cell performance. Compared with mechanical mixing, spray granulation produces a superior and uniform pore structure. However, contrary to conventional expectation, the introduction of graphite pore-forming agent into the APS anode reduces overall cell performance due to induced electrolyte defects, which elevated R_o and lowered OCV. Future optimization should focus on strategies to reduce anode surface roughness and refine pore structure without affecting the quality of electrolyte deposition. It is anticipated that this will further enhance the output performance of MS-SOFCs.