International Journal of Applied Ceramic Technology最新文献

Carbon nanotubes (CNTs) were in-situ grown in the shallow surface of carbon/carbon (C/C) composites with a bulk density of 0.7-0.8 g/cm³, and then they were further densified by pyrocarbon (PyC). After that, a novel CNT-induced C/C composite (CNT-C/C) with a reinforced surface layer was prepared. Since CNTs optimized the spatial nucleation of PyC in the surface layer greatly, a porous isotropic layer with a lower coefficient of thermal expansion was obtained, alleviating the thermal contraction and inducing a compressive stress surface layer after cooling. This structure can effectively resist the initiation and propagation of cracks and improve the mechanical properties of C/C composites. The flexural strength, modulus, and fracture toughness of surface layer enhanced CNT-C/C increase by 53.7%, 13%, and 31.6% than that of the baseline, respectively.

To evaluate the applicability of 80% dense boron carbide (B₄C) for control rods in high-temperature gas-cooled reactors (HTGRs), a sintered body was fabricated from nuclear-grade powder via vacuum hot-pressing (2100°C, 20 MPa). Its microstructure, temperature-dependent mechanical/thermophysical properties (RT–1000°C), and thermal shock resistance were systematically investigated. The microstructure shows the grains form an interconnected skeletal structure with uniformly distributed pores, beneficial for helium release. Compressive strength decreased from 1.46 (RT) to 0.90 GPa (1000°C), while the elastic modulus decreased from 285.5 to 266.4 GPa. The critical irradiation dose was calculated as ∼2.19×10²⁶ cap/m³, indicating enhanced swelling tolerance due to porosity. The thermal expansion coefficient increased from 3.05 × 10⁻⁶°C⁻¹ (RT) to 6.02×10⁻⁶°C⁻¹ (1100°C), and thermal conductivity decreased from 9.77 W/(m·°C) to 6.29 W/(m·°C). Predicted thermal conductivity values fell below 4 W/(m·°C) for burnups >5×10²⁶ cap/m³. After 60 and 100 thermal shock cycles (1000°C ↔ 125°C), compressive strength decreased by 13.4% and 16.0%, respectively, with transgranular fracture dominating. Theoretical evaluation of the critical temperature difference revealed that rapid cooling from high temperature induces microcracking. This study provides essential data and theoretical support for assessing the in-core safety of porous B₄C under HTGR conditions.

This study evaluates the load-bearing performance of oxide ceramic matrix composites (Ox-CMCs) reinforced with continuous fibers, which contain fiber interruptions caused by the manufacturing process. Two different lap joint designs are evaluated: stepped and overlaying lap joints. Bending, tensile, and compression tests show a lower strength of the lap joints compared to an undamaged composite. The failure of stepped lap joints is primarily attributed to the propagation of a main crack in the porous ceramic matrix, that is not bridged by any fibers. Hence, sintering temperature has a positive effect on the strength. Overlaying lap joints exhibit higher strength, especially with the sintering temperature of 1200°C, with strength increasing further with longer overlap lengths. On the other hand, higher sintering temperatures do not lead to any improvement in strength due to the superimposed effect of limited crack deflection mechanisms and decreased fiber strength. In contrast to the strength, the stiffness of all lap joints remains consistent with that of the undamaged composite. In summary, if an interruption in the fiber layers of an Ox-CMC structural element is unavoidable, overlaying lap joints with the longest possible overlap length, that is acceptable from a structural design standpoint, is recommended to enhance strength.

The concern with greenhouse gas emissions has justified efforts to increase energy efficiency in industrial processes. In the ceramics sector, the firing stage accounts for the highest fuel consumption. Excess oxygen in firing gases is one factor that increases fuel consumption. Oxygen fractions above 8% are usually applied to oxidize organic carbon from humic acids in plastic clays. Low oxygen levels combined with high humic acid content promote the occurrence of the defect known as black core. This study aimed to apply ozonation to reduce humic acid levels, thus minimizing the formation of black core in atmospheres with low oxygen content. An industrial powder composition was exposed to four ozone concentrations, ranging from 12 to 64 g O₃/Nm³, for up to 6 h. Test specimens were produced to evaluate effects under firing in an atmosphere with 1% O₂. Additional technological characterizations were performed to assess any changes in relevant properties during the manufacturing stage. Ozonation under the applied conditions led to a 25% reduction in the incidence of black core, without affecting other product characteristics. The proposed method allows for a reduction in the oxygen content during firing, potentially reducing fuel consumption by approximately 3%.

The electric-field-modulated photoluminescence (E-PL) performance of rare-earth-doped ferroelectric (FE) materials has been widely studied. However, the hysteresis effect in FE materials limits the tunability of E-PL modulation. Antiferroelectric (AFE) materials possess a reversible AFE-FE phase transition, inducing changes in crystal structure that can significantly affect the E-PL intensity. In this work, Sm/Mn-codoped silver niobate ceramics (ASMNx, x = 0, 0.5, 1, 1.5, 2) were fabricated via the tape-casting method, and the AFE properties, thermal stability, and E-PL performance were systematically investigated. The results show that the addition of Sm and Mn ions effectively inhibits the growth of grains and enhances the AFE properties. Upon irradiation at 480 nm, the samples exhibit a down-conversion PL effect, and the PL intensity increases with increasing Sm³⁺ doping concentration. The in situ modulation of the PL intensity is reversibly achieved through the E-induced AFE-FE phase transition. Among them, ASMN1 shows the best tunability of −30.18% at 300 kV cm⁻¹. The excellent E-PL tunability in the lead-free ASMNx ceramics contributes to the broad applications in optical information storage, optical communication, and multifunctional optoelectronic devices.

Continuous alumina fiber-reinforced alumina composite (Al₂O_3f/Al₂O₃) is an ideal material for developing high-performance aero-engine hot section components. In the present work, the air oxidation and steam corrosion behaviors of Al₂O_3f/Al₂O₃ at 1000°C–1200°C were investigated. X-ray diffractometer, scanning electron microscope, and transmission electron microscope were applied to analysis the composition, fracture morphology and microstructure of the Al₂O_3f/Al₂O₃. The degradation in the properties of the component was analyzed by nanoindentation. The results show that the strength of Al₂O_3f/Al₂O₃ decreases significantly after steam corrosion. The higher temperature leads to a greater degradation in the strength of Al₂O_3f/Al₂O₃ after steam corrosion. The damages of the composites are closely related to fiber strength and interfacial bonding strength. Fiber grain coarsening causes the reduction of the fiber strength, while strong interfacial bonding leads to the failure of the fiber toughening mechanisms.

This article investigates the impact of second-phase additives on the structure and mechanical properties of zirconium diboride (ZrB₂)-based ceramic materials. The materials obtained were characterized by X-ray diffraction, scanning electron microscopy, and Vickers hardness (HV) analysis. As a result, in the temperature range of 1800–2000°C, dense ceramic materials with a fine-grained structure and uniform distribution of secondary phases were obtained. Additives such as molybdenum disilicide (MoSi₂), silicon carbide (SiC), molybdenum carbide (Mo₂C), and tungsten carbide (WC) lowered the sintering temperature compared to the sintering of pure ZrB₂. HV measured at loads from 1 to 20 kg showed a weak dependence of hardness on the load. Maximum hardness values were achieved for the three-component ceramics ZB₂ + 15 vol.% SiC + 5 vol.% Mo₂C and ZB₂ + 15 vol.% SiC + 5 vol.% WC (HV₂₀ = 18.68 GPa and 19.33 GPa, respectively) due to increased density of the materials and small grain sizes. The addition of 15 vol.% MoSi₂ leads to an increase in the fracture toughness (5.04 MPa*m^1/2) and grain boundary strength (0.58 GPa). This points to the formation of grain boundary states with increased strength (σ_f = 0.48 GPa).

This research work investigates the high-temperature corrosion behavior of ceramic coatings comprising alumina and carbon nanotube-reinforced alumina (1, 3, and 4.5 wt.% CNT) deposited on T23 boiler steel using plasma spraying. The coated and uncoated samples were exposed for 1000 h at 900°C in a 250 MW operational thermal power plant boiler to simulate real service conditions. Corrosion performance was analyzed using thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The CNT-reinforced ceramic coatings significantly reduced the corrosion rate to 28.27 mpy (mils per year), compared to 110.64 mpy for alumina-only and 328.54 mpy for uncoated steel, owing to improved microstructural integrity and reduced porosity. While the findings demonstrate the coatings' strong applicability for high-temperature environments, the study is limited to a specific boiler condition and exposure duration, suggesting the need for broader validation under diverse operational parameters. These coatings have direct practical implications for improving boiler durability, reducing maintenance costs, and enhancing operational reliability. Furthermore, this work contributes to sustainable development goals by supporting energy efficiency, industrial innovation, and responsible consumption and production. The research offers original insights into the real-world performance of CNT-reinforced ceramic coatings for advanced corrosion protection in thermal power applications.

Ultra-high temperature ceramics (UHTCs) are valued for their exceptional mechanical, thermal properties, and oxidation resistance. Among UHTCs, zirconium diboride (ZrB₂) reinforced with silicon carbide (SiC) has emerged as a promising candidate for extreme environment applications due to its exceptional combination of high melting point, thermal conductivity, oxidation resistance, and mechanical strength. While most UHTC research has focused on monolithic structures, functionally graded materials offer a novel pathway to further enhance performance by gradually transitioning composition between constituent materials. In this work, a custom-built direct ink writing (DIW) additive manufacturing system with active in-line mixing was implemented to fabricate functionally graded ZrB₂–SiC ceramics. Rheologically optimized aqueous suspensions of ZrB₂ and SiC were formulated with matched viscosity profiles for co-extrusion. The system enabled continuous and discrete gradient structures by varying composition in real time during printing. Post-processing involved binder burnout and hot pressing to achieve densification. The graded samples exhibited high relative density (∼93%) and 25% increase in hardness from the ZrB₂-rich to SiC-rich regions. The elastic modulus in the gradient samples exceeded 517 GPa, which is 2% higher than monolithic ZrB₂ and 78% higher than monolithic SiC. These findings demonstrate the viability of DIW for fabricating dense, graded UHTCs with tunable mechanical properties.

Silicon carbide (SiC) ceramics are promising for molten salt reactor (MSR) applications, but their poor machinability necessitates reliable joining technologies. This study investigates SiC joining using pure Ag filler combined with magnetron-sputtered refractory metal coatings (W, Mo, and Ti). All joints achieved sound metallurgical bonding: Ti coating reacted completely with SiC to form TiC and Ti₅Si₃; W coating partially reacted to generate W₂C, WC, and minor W₅Si₃ with residual W; and Mo coating reacted to form Mo₂C and MoSi₂ with remaining Mo. Corrosion tests conducted in FLiNaK molten salt at 700°C for 100 h showed that Mo/Ag joints exhibited the best resistance with a corrosion depth of approximately 8.62 µm, followed by W/Ag joints at 56.75 µm while Ti/Ag joints suffered complete failure. The shear strengths were measured as 103.10 ± 6.86 MPa for Ti/Ag, 95.39 ± 7.48 MPa for W/Ag, and 59.17 ± 8.60 MPa for Mo/Ag brazed SiC joints. The Mo/Ag brazing system shows promise for SiC joining in MSR environments, with potential for further optimization.