International Journal of Applied Ceramic Technology最新文献

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.

This article reports on the development of a spark plasma sintering (SPS)-assisted sol-gel method for the synthesis of dense pellets, belonging to the series of InGaO₃(ZnO)_m homologous phases, where m is an integer. We show that using this synthesis route, the sintering temperature is significantly decreased down to 950–1000°C as compared to 1150°C using solid-state synthesis methods, which enables a very good control of the materials stoichiometry by suppressing any cation volatilization. Therefore, dense single-phase pellets can be obtained for the m values from 1 to 5. However, for larger m values, different layer stackings are observed within single individual crystallites, raising some questions about the thermodynamic stability of InGaO₃(ZnO)_m crystal structure with m > 5. Besides, a significant preferential orientation of the pellets has been observed, linked to the platelet shape of the grains, which can be controlled to some extent by tuning the SPS conditions.

Ca_1-xY_xMnO₃ and Ca_1-xY_xMn_1-yNb_yO₃ (0 ≤ x, y ≤ 0.07) thermoelectric ceramics were fabricated via microwave-assisted calcination followed by conventional sintering. The effects of substituting Ca with Y and Mn with Nb on the microstructure and power factor (PF) were systematically investigated. The results indicate that the crystal structure of CaMnO₃ remains unchanged upon doping. Electrical conductivity increases, while the absolute value of the Seebeck coefficient decreases with increasing dopant concentration in both series of compounds. Consequently, the PF for Ca_1-xY_xMnO₃ increases continuously within the range of doping amount (0 ≤ x ≤ 0.07), whereas that of Ca_1-xY_xMn_1-yNb_yO₃ initially increases with x = y ≤ 0.02, and then decreases for 0.02 < x = y ≤ 0.06. In addition, the PF increases for all samples as the temperature increases. The maximum PF achieved are 127 µW m⁻¹ K⁻² for Ca_1-xY_xMnO₃ (x = 0.07), and 154 µW m⁻¹ K⁻² for Ca_1-xY_xMn_1-yNb_yO₃ (x = y = 0.02). These results demonstrate that the co-doping of CaMnO₃ with Y/Nb is more effective in improving the electronic transport characteristics than single Y-doping.

This work aimed at investigating the effect of different Er₂O₃ content on the mechanical properties and coloration of silicon nitride ceramics. All samples were prepared by gas pressure sintering at 1800°C for 2 h. The addition of Er₂O₃ led to a denser microstructure consisting of distinctive rod-like Si₃N₄ grains with higher aspect ratio, with the fracture toughness and flexure strengths as 10.77 ± 0.08 MPam^1/2 and 970 ± 27 MPa, respectively. The chromaticity of sintered samples was measured by spectrophotometer. With the increase of Er₂O₃ content, the color of pink-orange Si₃N₄ ceramics was gradually getting darker. Scanning transmission electron microscope (STEM) results showed that core–shell structures existed in the β-Si₃N₄ matrix, and the core and shell were pore and Er-rich liquid phase, respectively, which served as the chromogenic center in Si₃N₄ ceramics. Results showed that the combination of Er₂O₃ with MgO was effective for the development of Si₃N₄ ceramics with pink-orange color and high mechanical properties.

Hard substrate using Zn₂V₂O₇ ceramics having low sintering temperature were prepared and its feasibility as a substrate material for a microstrip patch antenna has been investigated. The crystal structure of Zn₂V₂O₇ ceramics were studied using X-ray diffraction and X-ray photoelectron spectroscopy techniques. Microhardness analysis indicated good resistance to indentation and deformation, with average apparent hardness values of 1.04 ± 0.07 GPa and 0.90 ± 0.06 GPa for applied loads of 1 and 10 N, respectively. Zn₂V₂O₇ substrates exhibited a coefficient of thermal expansion of 2.6 ppm °C⁻¹ and thermal conductivity of 0.65 W m⁻¹ K⁻¹ at room temperature. A permittivity of 7.1 and a loss tangent of 8.754 × 10⁻⁴ was measured using split post dielectric resonator cavity with Q × f value of 36 012 GHz at 3.75 GHz. A microstrip patch antenna was designed with copper tape as the ground plane and the radiating patch on the opposite faces of the substrate. The fabricated antenna had a return loss of −13.01 dB at 2.45 GHz. Three-dimensional radiation pattern of the antenna at 2.44 GHz indicated that radiation efficiency is −3.255 dB, and total efficiency is −4.762 dB, which is moderately efficient. These findings suggest Zn₂V₂O₇ as substrate material for microstrip patch antennas, offering potential advantages in terms of structural integrity and thermal stability.

Four different binders, namely, calcium aluminate cement, silica sol, hydratable alumina (HA), and mono-aluminum phosphate, are used separately in a high alumina castable composition to compare their effects on the properties development. The castables were prepared using commercial-grade materials using a distribution coefficient of 0.23, as per the Dinger and Funk model. Cement-bonded castable was added with additives, like flow modifier (fume silica), deflocculant, and anti-setting agent, and HA-bonded castable was added with deflocculant. All the castables with different bonding systems were processed as per conventional manufacturing technique and heat treated at three different temperatures. The castables showed corundum as the major phase post-firing with a minor anorthite phase for a cement-bonded one and a mullite phase for the silica sol–bonded one. Density and cold crushing strength were found to be higher for the cement-bonded one, whereas the hot strength was higher for the HA-bonded one, and thermal shock resistance was higher for the silica sol–bonded castable.

Tungsten carbide cermet coatings, prepared by high-velocity oxygen-fuel (HVOF) spraying, possesses advantages such as near-complete density, high hardness, and bonding strength. It is environmentally friendly, low in carbon emissions, suitable for remanufacturing processes, and offers benefits over electrolytic hard chrome. This paper reviews the deposition characteristics of tungsten carbide particles and the structure of coatings, as well as the latest developments in friction properties of HVOF coatings (including friction and high-temperature friction in seawater environments), cavitation erosion, and fatigue properties, existing problems, and solutions are reviewed. Although the HVOF spaying has a wide prospect in material surface protection and green low-carbon remanufacture, tracing to the source for the spraying quality is of hysteresis property. Therefore, the control from multi-aspects is needed.

Efficient, nondestructive, and cost-effective detection of the hollow ratio in ceramic powder remains an urgent technical challenge in the industrial field. In this study, a novel image recognition-based method for detecting the hollow ratio of ceramic powder was proposed. Using 8 mol% yttrium-stabilized zirconia powder as the research subject, a mapping relationship between the physical structure of hollow particles and their optical imaging characteristics was established. By conducting targeted image enhancement on the characteristics of ceramic particles, a high-resolution image annotation dataset was constructed, and the detection performance of the YOLOv5s, YOLOv8s, YOLOv9s, and YOLOv11s models was systematically compared. The results indicate that the YOLOv11s model demonstrates superior overall detection performance. Building upon this finding and integrating the OpenCV scale calibration algorithm, automatic statistical analysis of particle size distribution (D10, D50, D90) and hollow ratio was achieved, significantly enhancing both efficiency and accuracy. This study highlights the promising application potential of the proposed method in the field of powder metallurgy.

Cariri Stone is a type of limestone extensively quarried in the region of Cariri, Ceará (Brazil). However, its extraction process generates large volumes of waste—up to 70% of the total extracted material—which is often disposed of improperly, resulting in significant environmental impacts. This study explored the technical feasibility of incorporating Cariri stone waste (CSW) as an alternative raw material in porous ceramic formulations based on kaolin and alumina. Compositions were developed with CSW content ranging from 10% to 28%. Test specimens were shaped by uniaxial pressing (40 MPa) and subjected to sintering at temperatures of 1100°C, 1150°C, 1200°C, and 1250°C. The sintered specimens were characterized in terms of apparent porosity, bulk density, water absorption, mercury intrusion porosimetry, total porosity, linear shrinkage, and three-point flexural strength. Microstructural aspects and thermal behavior were also evaluated. It was observed that compositions containing 21% and 28% of waste exhibited higher porosity, good dimensional stability, and flexural strength reaching values around 38 MPa. The anorthite was the predominantly crystalline phase. Mullite and gehlenite were also identified. The results demonstrated that CSW has the potential to produce sustainable and innovative porous ceramics with good dimensional stability and mechanical resistance.