Abstract The downstream glass industry in South Korea exhibits a distinctive structure compared with that of other non-Asian countries, as its semiconductor and display sectors are tightly integrated with the glass materials supply chain. In this review, the distinct features of glass-related industrial research and development in South Korea are addressed by taking two representative applications of glasses, i.e., glass core substrate for semiconductor packaging applications and ultra-thin glass for use as cover window of flexible display modules. In the case of glass core substrate and glass interposer, the inherent brittleness of glassy materials imposes constraints across the process flow, requiring precise control over laser irradiation, chemical etching, redistribution layer formation, and singulation. Ultra-thin glass needs to be durable during repeated deformations, so that its thickness is typically on the order of several tens of micrometers. At such thickness levels, resistance to mechanical deformations becomes a primary concern, and therefore processing steps from cutting, chamfering, and healing to chemical strengthening play a decisive role in determining mechanical reliability and optical clarity of ultra-thin glass. Flexible display devices with other form factors featuring multi-foldable, slidable or rollable capability would be realized along with advancement of processing technologies associated with ultra-thin glass.
With an emphasis on the application-oriented research activities directly or indirectly related to glass materials led by South Korean universities, four different topics are introduced in this review: 1) a thermodynamic database for glass-forming systems, 2) mold flux systems used in steel casting, 3) glasses doped with quantum dots and/or perovskite nano-crystals, and 4) chalcogenide glasses for thermal imaging. For each topic, recent advances are described in conjunction with their basic concepts and future perspectives. The CALPHAD (CALculation of PHAse Diagrams) thermodynamic database for glass-forming system and glassmaking process has been actively developed to assist glass research and the manufacturing process. In addition, a multi-component diffusion model for glass systems is being actively studied for various kinetic simulations. Recent research focuses on the expansion of the database to address key issues relevant to the decarbonization of the glassmaking process such as water solubility in glass, new redox agents, refractory wear in glass melting furnace, and electrode materials for an electric melting furnace. However, the limited availability of phase diagram and thermodynamic data pose challenging issues for the database development relevant to the decarbonization process.
In order to meet the demands for advanced glass lubricants for continuous casting of steel, investigations of structural understandings and their effects on non-Newtonian rheology, thermal properties, and glass forming ability are being actively pursued. In particular, application of mixed alkali effect and Mie scattering is believed to be an effective design principle to enhance lubrication without deteriorating heat transfer controlling ability. In consideration of the necessity of increasing scrap recycling to achieve carbon neutrality during steel manufacturing, further investigations should be done on rheological behavior of supercooled silicate glass lubricant melts in order to mitigate the cracking on continuously cast steels with a greater number of accumulated impurities.
Quantum dots and perovskite nanocrystals are still widely studied for next generation color converters or phosphoric materials for high picture quality displays including micro-LED display and anti-counterfeit applications, thus offering high chances for robust quantum dot or perovskite nanocrystal embedded glasses. However, several issues such as sub-micron sized glass powders with stable PL-QY, Pb-free perovskite nanocrystals, and glass materials for direct driving LED remain as challenging issues for their future applications.
The thermal imaging market is expected to steadily expand with a conspicuously steep inflection arising in the automobile industry caused by the regulations mandating employment of the autonomous emergence braking system. It is noteworthy that the cost of LWIR image sensors based on microbolometer arrays is decreasing rapidly to meet the demands of the automotive industry, and in this regard a group of well-qualified chalcogenide glasses will be promising as molded lenses for the high-resolution thermal cameras. Specifically, those chalcogenide glasses consisting of environmentally less harmful and relatively cheaper constituents would be preferred in the civilian sectors.
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.
High-temperature vibration sensors are indispensable key components for the health detection of core equipment in fields such as aerospace and nuclear energy. The BiScO3-PbTiO3(BS-PT) system has attracted much attention due to its high Curie temperature (TC≈450 ℃) and excellent piezoelectricity (d33≈450 pC/N). However, the poor insulation properties of this material hinder its application in high-temperature vibration sensors because high electrical resistivity (ρ) and a long time constant (τ) are critical to prevent thermal runaway and ensure signal integrity. Manganese (Mn) doping is a commonly used modification method for piezoelectric ceramics. Previous studies on Mn-doped BS-PT were controversial regarding the valence state distribution and substitution positions of Mn ions, which could not be conducive to the design of high-temperature piezoelectric ceramics with the collaborative optimization of multiple electrical parameters. Therefore, this work was to clarify the defect chemical mechanism associated with manganese doping through refined structural characterization combined with electrical performance analysis, and to obtain the modified BS-PT piezoelectric ceramic components suitable for high-temperature vibration sensors.
0.365BiScO3-0.635PbTiO3-x% MnO2 (BSPT-x% MnO2, x=0.00, 0.01, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.00) ceramics were synthesized by a conventional solid-state reaction method. The powders were firstly calcined at 800 ℃ for 2 h and then sintered at 1050 ℃ for 2 h. The phase composition was analyzed by X-ray diffraction (XRD). The rietveld refinements were performed using a software named GSAS. The microstructure and elemental distribution were examined by scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). The average grain size was estimated by a software named Nano Measurer. The Mn valence states were determined by X-ray photoelectron spectroscopy (XPS). For electrical measurements, poled samples (120 ℃, 5 kV/mm, 30 min) were used. The piezoelectric coefficient (d33) was measured by a model CAS ZJ-6A quasi-static meter. The electromechanical coupling coefficient (kp) was measured by a model Agilent 4294A impedance analyzer. The temperature-dependent dielectric properties were measured by a model Agilent E4980A LCR analyzer. The high-temperature DC resistivity (ρ) was measured by a model Keithley 6517B high-resistance electrometer. The in-situ d33 was measured by a model Julang TZFD-600 variable temperature quasi-static d33 measurement system.
The Mn doping mechanism and high-temperature performance of BS-PT ceramics are systematically clarified. The XPS results confirm the coexistence of Mn2+ and Mn3+. To quantitatively verify the substitution site, the rietveld refinement reveals a non-monotonic evolution of unit cell volume. Based on the EDS evidence of Sc segregation without Ti precipitation, Mn ions preferentially substitute for B-site Sc3+. The dominant aliovalent substitution introduces defect dipoles accompanied with strong local random electric fields, significantly enhancing a relaxor behavior, while triggering a "hardening" effect that reduces tanδ and εr. The decoupling of piezoelectric and dielectric properties is achieved in specific compositions due to the grain boundary effect compensating for the hardening effect, especially obtaining the optimal piezoelectric voltage constant (g33) at the component with x of 1.00. For high-temperature capabilities, the optimal composition (x=1.00) demonstrates a superior stability, with in-situ d33 variation remaining within 20% up to 400 ℃. The thermally stable defect dipoles effectively trap oxygen vacancies, leading to a high resistivity of 109 Ω·cm and an enhanced time constant of 0.072 s at 350 ℃. Consequently, the ceramic with x of 1.00 exhibits a high g33 of 0.012 V·m/N when evaluated at a unified service temperature of 350 ℃, which is 50% higher than that of the undoped counterpart. These results indicate that the modified ceramic achieves an optimal balance of sensitivity and insulation for high-temperature vibration sensors.
This work clarified the Mn doping mechanism in BS-PT ceramics. The results of correlative XPS, Rietveld refinement, and EDS analysis confirmed that Mn ions could preferentially substitute for B-site Sc3+. The dominant aliovalent substitution induced a hardening effect, while the recovery of d33 was dominated by grain size restoration. The optimal composition (x=1.00) exhibited a robust stability with d33 variation within 20% at 400 ℃. The thermally stable defect dipoles could obtain a high resistivity (109 Ω·cm) and time constant (0.072 s) at 350 ℃. Meanwhile, a superior piezoelectric voltage coefficient (g33) of 0.012 V·m/N was achieved at 350 ℃, which was 50% higher than that of the undoped counterpart, validating its potential for high-temperature sensors.
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 (RLmin) 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 improvement of aero-engine thrust-to-weight ratio and turbine inlet temperature, the performance limitations of conventional superalloys become increasingly prominent. SiCf/SiC ceramic matrix composites (CMCs) can be core candidate materials for hot-section components due to their excellent high-temperature mechanical properties and low density. As a key technology to realize the engineering application of CMCs, compatible abradable/environmental barrier coatings (A/EBCs) that can simultaneously achieve gas path sealing, high-temperature protection and abradable performance become a research focus in the field of advanced aero-engine sealing technology. This review represents the research progress of such coatings from three dimensions, i.e., material design, microstructural regulation, and performance evaluation, while analyzing key technical challenges and development trends. In terms of material system design, conventional yttria-stabilized zirconia (YSZ) abradable coatings suffer from thermal expansion mismatch with SiCf/SiC CMCs, which are prone to failure, while conventional solid lubricants undergo oxidative degradation at > 1200 ℃. It is urgent to develop new matrix materials with a high thermal stability, a water vapor-oxygen corrosion resistance and a thermal expansion compatibility. Multi-layer structure is the main design to realize functional synergy, and the interface matching and thermal expansion adaptability between layers are a key to the service durability. The introduction of negative thermal expansion materials provides an idea to solve the mismatch problem. In addition, the construction of material system matching for multi-layer coatings and the compatibility analysis of interlayer interfaces/multiphase interfaces also become important aspects in the design of abradable/environmental barrier coating systems.
In the aspect of microstructural regulation, improving porosity is a main way to obtain excellent abradability, but there is a prominent contradiction among abradability, erosion resistance, corrosion resistance and thermal stability. Excessive or uneven porosity, as well as high-temperature sintering and closure, will lead to the performance degradation and early failure. The core challenge is to realize the precise regulation of multi-scale pore structure and the multi-performance synergy balance. In terms of performance evaluation, the existing test devices have high cost and poor universality, and it is difficult to simulate the real multi-field coupling service environment. The lack of perfect preparation and evaluation standards restricts the engineering and standardized development of CMC-compatible coatings. Finally, the development trends of A/EBCs are prospected, providing a reference for the research and development of high-temperature sealing technology and coating system for advanced aero-engines.
In summary, with the increasing service temperature of aero-engines, the abradable/environmental barrier coatings (A/EBCs) that match SiCf/SiC ceramic matrix composites (CMCs) become a key research direction. This review represents the research progress of A/EBCs in material design, microstructural regulation and performance evaluation, and points out that the current challenges mainly include thermal expansion mismatch between conventional coating materials and CMC substrate, poor high-temperature stability of lubricants, difficult balance between multi-scale pore structure and multi-performance, and lack of standardized evaluation systems and test standards suitable for multi-field coupling service environment. In the future, the research and development of A/EBCs should focus on the multi-objective synergistic design of material composition, multi-scale microstructure and performance evaluation system. It is necessary to strengthen the analysis of failure mechanism under multi-physical field coupling environment, develop new high-temperature stable matrix and lubricant materials, realize the precise regulation of multi-scale pore and interface structure, and establish a standardized preparation and performance evaluation system. Through the breakthrough of the above key technologies, the comprehensive performance and service durability of A/EBCs will be effectively improved, so as to promote the leapfrog development of high-temperature sealing technology and provide an important support for the performance improvement of next-generation aero-engines.
Continuous silicon carbide fiber reinforced silicon carbide ceramic matrix composites (referred to as SiCf/SiC composites) become the preferred high-temperature and lightweight thermal structure materials for high thrust-to-weight ratio aero engines due to their excellent high-temperature properties. However, their poor high-temperature oxidation and corrosion properties limit their long-life use. It is effective to improve the oxidation and corrosion properties of SiCf/SiC composite matrix through matrix modification, and the commonly used modified materials mainly include self-healing components, network intermediate oxides and rare-earth silicates.
The self-healing components form the liquid phase of B2O3 or borosilicate glass phase in the process of oxidative corrosion that has a certain fluidity and viscosity at a high temperature, which can fill the cracks and holes in the matrix. The volume expansion caused by oxidation makes the small defects heal when the oxidizing medium diffuses in the cracks as the oxidation phase, which can effectively block the diffusion of the oxidizing medium to the key areas that are easy to oxidize such as fibers and interfaces, thus enhancing the oxidation resistance of the material and extending its service life. The network intermediate oxide can absorb the "free oxygen" in the borosilicate glass melt and change its coordination from [MO6] to [MO4], reconstructing the silicate network damaged by water vapor erosion and maintain its integrity, and significantly improving the stability of the self-healing glass phase under high temperature water vapor conditions and the oxidation and corrosion properties of composites. Rare-earth silicate itself has excellent antioxidant corrosion properties, and the rare-earth elements migrate to the near surface of the matrix to form an antioxidant layer during the oxidative corrosion process, which inhibits the penetration of oxidative corrosion medium into the matrix and the reaction between borosilicate glass and water vapor, reduces the generation of gaseous substances, and slows down the oxidative corrosion of the matrix to a certain extent.
There are two main ways to introduce modified materials into the matrix, i.e., one refers to the direct introduction of antioxidant corrosive materials without changing their phases during use, such as directly introducing rare-earth silicates into the matrix, and another refers to the introduction of the precursor of the modified material or substances containing modified elements into the matrix, and the target modified material is obtained through chemical reactions during the oxidative corrosion process, usually in this way the introduction of self-healing components and oxidation corrosion phases into the matrix. In addition, the synthesis process of modified materials mostly adopts CVI, PIP, RMI, SI, etc., and their advantages and disadvantages of different modification processes are different. For instance, the preparation temperature of CVI process is low, but the densification cycle is long and the cost is high. The RMI process is simple, the cycle is short, and the composite material with a high density is prepared, but the melting temperature is high, which is easy to heat damage to the fiber and interface. Besides a single process, composite processes are mostly used to achieve complementary advantages, introducing modified materials into the matrix and realizing the densification of composite materials.
It is effective to introduce self-healing components, network intermediate oxides and rare-earth silicates into the SiCf/SiC composite matrix to fill the pores and cracks of the material via generating self-healing components during the oxidative corrosion process, and forming a dense oxide layer on the surface of the material to resist further erosion by the oxidizing medium, thus improving the water and oxygen corrosion resistance of the composites. However, there are still some challenges. Firstly, the research on the oxidation corrosion mechanism of composite materials is still in-depth, and there is a lack of data on oxidation kinetics, oxidative corrosion rate and oxidative corrosion depth, and the basic research on the damage evolution mechanism of materials in different environments is still relatively weak. It is thus necessary to construct a complete and reliable performance database of SiCf/SiC composites modified with different substrates, clarify the oxidative corrosion damage mechanism, and provide design parameters and theoretical support for the practical application of composites. Secondly, the effective temperature range of a single modified substance to improve the oxidative corrosion performance of composites is limited. The temperature range of B group is below
1000 ℃, and the temperature range of Al group is 1000-1300 ℃. The synergistic effect of multiple modification strategies is explored via introducing multiple modified substances into the matrix of composites at the same time. It is expected to achieve the oxidation and corrosion properties of SiCf/SiC composites in a wide temperature range and achieve a long-life cycle protection. Finally, it is also worth to develop new preparation processes, such as nano-infiltration and transient eutectic (NITE), or use hybrid processes to achieve material densification and improve the performance of SiCf/SiC composite substrates while modifying them.
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.
To achieve the 2050 carbon neutrality vision, it is necessary to promote research and development of efficient and economically beneficial green hydrogen production technologies. In the process of global transition to a low-carbon energy system, hydrogen as a key zero carbon energy carrier continues to attract much attention. This review provides a comprehensive evaluation of high-temperature solid oxide electrolysis cell technology, focusing on analyzing some related challenges and potential pathways for large-scale application.
Compared to low-temperature alternatives such as alkaline and proton exchange membrane electrolysis, SOEC has unique advantages due to its high-temperature operation, It uses ceramic materials without precious alloys and can operate at 650-1000 ℃, and it can improve the electrochemical performance, resulting in an energy conversion efficiency of > 80%, These characteristics make SOEC a promising solution for low-cost production of green hydrogen gas, The existing domestic technology is still in demonstration stage with project scales typically ranging from tens to hundreds of kilowatts. Commercial deployment needs to overcome challenges of "three highs and one low". A key is to improve power density of battery stack, increase its service life, improve system integration, and reduce costs. To solve this problem, collaborative progress is needed in fields of material innovation, structural design, and system integration.
Collaborative design approach involving electrodes, electrolytes, and sealing components is crucial in development of materials and structures. For precise microstructure control and interface optimization, battery pack can operate stably at a high current density of 2 A/cm2, while controlling attenuation rate of < 1mV/h, and significantly extending actual service life.
Optimizing multi energy data collaboration system is equally crucial, and SOEC can leverage industrial waste heat and renewable energy resources to utilize medium to low temperature thermal energy (i.e., 200-300 ℃), thereby reducing external power consumption by approximately 30% and improving overall energy utilization efficiency, It is also necessary to build a regional supply chain that covers entire process from raw material and battery preparation to integrated assembly and system integration. The integration cost should be controlled within RMB 2500 kilowatt hours, and the design life should reach 50 000 h. A key is to lay a foundation for widespread application.
The widespread promotion of SOEC still faces several constraints, i.e., loss of electrode materials under high temperature and high humidity conditions, stability challenges caused due to power input fluctuations, and relatively high initial costs. Future research should focus on developing more durable electrode materials, establishing intelligent management systems that adapt to changes in renewable energy, and promoting standardization and cost control throughout entire industry chain to achieve technological popularization.
The combination of wind and solar energy with water electrolysis can build a more adaptable clean energy resource system, Integration helps alleviate grid stability issues related to intermittent renewable energy resources and significantly reduces electricity cost of hydrogen production. Hybrid wind and solar energy system can increase hydrogen production, while reducing costs. A key is that when SOEC is matched with fluctuating power sources, oxygen electrode/electrolyte interface will degrade under frequent thermal cycles, which is an important factor affecting long-term stability of system. In global, green hydrogen production driven by renewable resources is gradually known as a key approach of reducing greenhouse gas emissions. Electrolytic hydrogen can utilize local wind and solar energy to decompose water into hydrogen and oxygen, reducing production costs. Moreover, solar and wind energy are widely distributed and naturally compatible with electrolysis equipment. Excess electricity can be chemically stored as hydrogen, efficiently regulating spatial and temporal imbalance of energy supply and demand. Therefore, generated hydrogen and oxygen can be directly applied in transportation and industrial fields without conversion, making hydrogen both a primary energy source and a data carrier.
Compared with conventional methods, the SOEC technology has a better hydrogen production efficiency and a lower unit energy consumption, and its commercialization key lies in increasing lifespan of fuel cell stack from less than 104 h to 5 × 104 h, reducing cost of hydrogen to below $1.5/kg. The current costs of photovoltaics and wind power continue to decline. In combination with growing demand for green hydrogen in industries such as chemical metallurgy, the SOEC is expected to achieve large-scale applications in "electricity hydrogen ammonia/methanol" integrated system, distributed energy network, and sustainable financing model. Its core position lies in serving as a fundamental supporting technology for carbon neutrality goals.
In transition towards a decarbonized energy system globally, hydrogen plays a crucial role as a zero carbon energy carrier. In this context, solid oxide electrolysis cell (SOEC) technology with its advantages in high-temperature operation significantly reduces material costs and improves overall system energy efficiency, compared to low-temperature solutions such as alkaline and proton exchange membrane electrolysis. SOEC system adopts a non-precious metal ceramic structure. When operating at 650-1000 ℃, electrochemical kinetics acceleration mechanism achieves a conversion efficiency of > 80%, providing a feasible approach to reduce cost of green hydrogen leveling. The existing domestic demonstration projects are limited to a scale of tens to hundreds of kilowatts, and the commercial implementation needs to break through bottleneck of "three highs and one low", thus increasing power density of fuel cell stack, extending its service life, and optimizing system integration, while reducing assets and operation and maintenance costs. Solving these obstacles requires collaborative efforts in three major fields, and innovation in materials and structures must break through conventional design framework of electrodes, electrolytes, and sealing glass. With precise microstructure design and interface stress control, system can maintain a high current density of 2 A·cm-2, while controlling degradation rate at 1 mV per thousand hours, significantly extending lifespan of battery pack. Multi-energy coupling optimization is crucial, which requires integrating the SOEC with industrial waste heat and renewable resources, thus utilizing low-grade thermal energy (i.e., 200-300 ℃), efficiently offsetting internal heating demand, reducing external electricity consumption by approximately 30%, and comprehensively improving energy utilization efficiency. For those localized supply chains, establishing a complete domestic production capacity from precursor powder to single cell manufacturing, stacking and assembly to system integration is particularly crucial. The goal is to control stacking cost at RMB 2500 per kW and achieve an operating life of 5×104 h, laying a foundation for large-scale applications. At present, although the SOEC has significant energy efficiency advantages, its promotion and application still face multiple constraints, i.e., gradual decay of oxygen electrodes under high temperature and high vapor partial pressure, mechanical and electrochemical damage caused by power fluctuations, and daunting initial capital investment. Subsequent exploration should focus on preparing new electrode materials with a higher stability, establishing flexible thermoelectric synergistic regulation mechanisms to adapt to fluctuating renewable energy, and promoting standardization and cost reduction and efficiency improvement throughout entire industry chain. The cost of photovoltaic and wind power continues to decrease, coupled with increasing demand for green hydrogen in chemical and metallurgical fields. Solid oxide electrolysis cell technology is expected to be widely applied in "electricity hydrogen ammonia/methanol" integrated system, distributed energy system, and sustainable refining scenarios. This technology will undoubtedly become a key pillar technology supporting the dual carbon goals in China.
The Faraday effect is one of the magneto-optical phenomena and refers to the conversion of linearly polarized light passing through a magnetic material into elliptically polarized light with the main axis-containing polarization plane rotated around the propagation vector. The angle by which the polarization plane is rotated, i.e., the Faraday rotation angle, is an important parameter determining the applicability of magnetic materials in devices such as electric-current and magnetic-field sensors, optical isolators, and optical circulators. Since the Faraday effect deals with a transmitted light, the transmittance of the magnetic materials is another important factor for applications. Thus, the materials are required to show a great magneto-optical figure of merit, that is defined as Faraday rotation angle or Verdet constant divided by absorbance or optical absorption coefficient. Here, the Verdet constant is defined as the Faraday rotation angle divided by external magnetic field and light path length inside the magnetic materials. It is well known that single crystals of garnet-type ferrites such as Y3Fe5O12 and (Gd,Bi)3Fe5O12 exhibit a large Faraday effect and a low optical absorption in the infrared region, especially in a wavelength range from 1.3 μm to 1.5 μm, and that they are effectively utilized as an optical isolator for optical telecommunications. However, compared to the garnet-type ferrites in the infrared region, magneto-optical materials with the superior performance, are lacking in the visible to ultraviolet region. Hence, the development of such materials is still in progress.
Oxide glasses rich in rare-earth ions exhibit a great Faraday effect, especially in the visible to ultraviolet range. Although these glasses feature magnetizations smaller than those of ferro- or ferri-magnetic oxide crystals such as abovementioned Y3Fe5O12 because the rare-earth-containing glasses are usually paramagnetic at room temperature, the transmittance of these glasses notably exceeds that of ferrite crystals in the visible to ultraviolet range. In addition, oxide glass has an advantage that it is feasible to tune continuously the composition so that optimized properties are attained and to fabricate large-sized and specific-shaped materials. In addition to the paramagnetic glasses, the Faraday effect of diamagnetic glasses is intensively investigated as well. The magnetization of diamagnetic glasses is further smaller than that of paramagnetic glasses, but the Faraday rotation angle or the Verdet constant of diamagnetic glasses is almost independent of temperature. This is an advantageous point of diamagnetic glasses, which cannot be realized in ferro-magnetic, ferri-magnetic, and para-magnetic materials. Furthermore, for wide-band gap oxide glass like SiO2 glass, which is diamagnetic, the Faraday effect can occur even in a very short wavelength range such as the deep and vacuum ultraviolet.
This review represents recent development on oxide glasses exhibiting large Faraday rotation. The macroscopic and microscopic mechanism of the Faraday effect are explained. The microscopic mechanism is very important to select magneto-optically active elements and to design glass compositions.Also, the Faraday effect of diamagnetic glasses is described. Heavy-metal oxide glasses and sulfide glasses are intensely exploited because the magnetic susceptibility of diamagnetic materials depends on the constituent atoms (ions) and the susceptibility is proportional to the squared atomic (ionic) radius and the number of electrons contained in the atom (ion). The Verdet constants of these glasses are summarized. The applications of diamagnetic glasses are briefly mentioned.
Subsequently, the Faraday effect of paramagnetic oxide glasses containing large amounts of rare-earth ions is reviewed. The pioneering work in this field has been carried out in the mid-1960s, showing that some ions like Ce3+, Pr3+, Tb3+, Dy3+, and Eu2+ give rise to larger Verdet constants in the visible range. A description is given to explain why these rare-earth ions exhibit larger Faraday effects than other ones. Recent researches seem to mainly pay attention to Tb3+-rich oxide glasses, for which higher concentrations of Tb3+ ions simply enhance the Verdet constant. In particular, Tb3+-rich oxide glasses fabricated via containerless processing, which is an emerging method and effective to expand the glass-forming region, showing the larger Verdet constant than single-crystalline Tb3Ga5O12 used as a commercially available optical isolator in the visible range. Furthermore, EuO-based amorphous oxides that have an unexpected ferromagnetism exhibit rather large Faraday effect.
In addition to the abovementioned diamagnetic oxide glasses and rare-earth-rich oxide glasses, a brief review concerns the Faraday effect of oxide glasses containing large amounts of 3d transition metal ions as well as glass-ceramics comprising ferro- or ferri-magnetic nano-sized crystalline particles embedded in transparent glass matrices.
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.
Coagulation is a critical step in the water treatment process. As an important component of coagulation technology, the development and application of coagulants have always been a core focus of the industry. To address the challenges posed by complex water quality and improve the efficiency of coagulation, titanium-based coagulants are evolving from single-component formulations towards composite formulations. By optimizing synthesis conditions (such as molar ratio, alkalinity, reaction temperature, and reaction time) to alter the structure of single-component titanium-based coagulants, composite titanium salt coagulants can be prepared. These composite variants not only effectively overcome the limitations of single titanium salts and combine the coagulation characteristics of multiple reagents but also achieve efficient removal of various pollutants through synergistic effects between components. Consequently, composite titanium salt coagulants demonstrate superior coagulation performance.
This article provides a comprehensive review of the preparation, classification, application, current challenges, and future development strategies of composite titanium salt coagulants. It begins with an overview of current preparation methods, including slow alkali titration (SAT), electrodialysis (ED), stepwise/copolymerization methods, and the sol-gel method. Each technique has its unique characteristics in terms of control precision, product performance, and suitability for large-scale application. The SAT method is simple to operate, low-cost, and easily scalable, making it the most commonly used method for laboratory and industrial preparation of composite titanium salt coagulants. The ED method allows precise control over hydrolysis and polymerization processes, producing products with excellent performance; however, its higher cost and operational complexity have so far limited its application to laboratory and pilot-scale stages. Copolymerization/stepwise polymerization is suitable for preparing titanium salt-silicate composite coagulants with controlled structures, while copolymerization can produce titanium salt-metal salt composites with stronger synergistic effects. The sol-gel method can prepare dry gel coagulants that are convenient for storage and use, combining both coagulation mechanisms and adsorption. However, this technology is still in the laboratory research stage, and its cost and control techniques are key factors for future large-scale application.
Based on compositional differences, composite titanium salt coagulants can be classified into several types: titanium salt-metal salt, titanium salt-silicate, and titanium salt-organic polymer composite coagulants. Titanium salt-metal salt composite coagulants mainly include liquid or conventional composite titanium salt coagulants prepared by techniques such as SAT and ED, as well as dry gel-form composite titanium salt coagulants prepared by the sol-gel method. Both types of coagulants form titanium-containing bimetallic or multimetallic composite systems by combining titanium salts with metal salts such as aluminum, iron, and zirconium, thereby incorporating the coagulation advantages of multiple metals. Titanium salt-silicate composite coagulants are formed by copolymerizing/stepwise polymerizing titanium salts and polysilicic acid (PSiA). These coagulants combine the charge neutralization capacity of titanium salts with the adsorption and bridging ability of PSiA, significantly enhancing coagulation efficiency. Titanium salt-organic polymer composite coagulants are a category of composite titanium-based coagulants formed by combining titanium salts with organic polymer compounds (such as polyacrylamide, chitosan, starch, etc.). These coagulants integrate the highly efficient charge neutralization capacity of titanium salts with the adsorption and bridging capabilities of organic polymers, thereby significantly improving coagulation performance. Composite coagulants effectively overcome the problems associated with single titanium salts, such as significant pH fluctuations and poor storage stability. They demonstrate superior performance compared to traditional coagulants in specific areas, including ultrafiltration pretreatment, sludge conditioning, treatment of low-temperature and low-turbidity water, and removal of micropollutants. The sludge generated from their use can serve as a raw material for producing TiO2, providing a new pathway for resource recovery in water treatment processes and highlighting their unique application prospects. However, their adaptability in real water bodies, economic feasibility, and long-term ecological safety still require systematic evaluation.
Finally, this study outlines the challenges faced in transitioning composite titanium salt coagulants from laboratory research tolarge-scale engineering applications and proposes corresponding strategies to address them.
Although composite titanium salt coagulants demonstrate excellent performance, there are still some issues and challenges that need to be addressed. Future research can focus on the following aspects: (a) Enhancing Adaptability to Real Water Bodies. Currently, the complex composition of various actual water bodies imposes higher demands on the application of composite titanium salt coagulants. To ensure stable and efficient coagulation performance under complex water quality conditions, future efforts should focus on developing novel composite titanium salt coagulants with stronger specificity and broader applicability, thereby meeting the needs of more complex and demanding application scenarios. (b) Lower- Cost Preparation of Composite Titanium Salt Coagulants. At present, the preparation of composite titanium salt coagulants largely relies on complex processes such as SAT, ED, and sol-gel methods, which hinders their large-scale application. Future research should aim to develop simpler, greener, and more economically viable preparation pathways—for instance, utilizing industrial by-products or waste materials as raw materials—while optimizing the preparation process to reduce energy consumption and production costs. (c) Ensuring Ecological and Health Safety. Current research on the toxicity assessment of titanium-based coagulants has predominantly focused on TiCl4 and Ti(SO4)2. Future studies should strengthen investigations into titanium residue and its ecotoxicological effects during the use of composite titanium salt coagulants. Meanwhile, it is essential to employ a wider range of aquatic organisms (e.g., fish, shellfish, and aquatic plants) for ecotoxicity studies, and to further explore the migration, transformation, and long-term accumulation of residual titanium in water bodies and organisms. This will provide a scientific basis for comprehensively safeguarding water environments and human health.
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