International Journal of Applied Ceramic Technology最新文献

This work addresses the challenges in brazing thermohydraulic sealings involving dissimilar materials, specifically 316Ti stainless steel and alumina, which have significantly different coefficients of thermal expansion (CTEs) and elastic constants. Traditional brazing methods require complex interlayers or extensive metallization steps, leading to issues such as dimensional changes, braze voids, and inadequate corrosion resistance due to prolonged high-temperature exposure. A novel laser-based brazing technique utilizing a diode laser is introduced to create high-quality, localized joints while preserving the integrity of the parent materials. The study systematically optimizes laser process parameters using finite-element modeling and the Taguchi method to achieve the desired bead geometry and thermal stress distribution with minimal heat input. Comparative analysis between laser active brazing (LAB) and conventional furnace brazing was conducted through metallography, shear testing, and autoclave testing. Results indicate that LAB parameters significantly affect bead thickness and shear strength, with laser-brazed joints demonstrating superior quality and stability post-autoclave testing compared with furnace-brazed joints. The thermodynamic and kinetic aspects of the brazing process were also analyzed. In conclusion, the LAB method for brazing 316Ti to alumina proves to be a successful and efficient alternative, with joint properties meeting or exceeding those of traditional furnace brazing.

Graphite/geopolymer composite is a promising smart material that can be used in various applications. This paper reports the design of strong self-heating graphite/geopolymer composites with high graphite percentages up to 120 wt% of metakaolin. The physical, mechanical, electrical, and electrothermal performance of composites were investigated; the compressive strength was tested at various ages and the electrothermal performance was tested using AC and DC voltages. The results showed that a compromise between high compressive strength and high electrothermal conversion can be achieved when a specific balance between the percentage of the graphite and the water content is established. The current study specified the reason for the deterioration of the electrothermal performance of the graphite/geopolymer composites, that is, the formation of a barrier layer between the electrode and the sample surface; it has been found that this can be avoided by removing the free ions from the geopolymer via washing. A composite with 47 ± 1 MPa compressive strength and stable electrothermal performance of 98°C at 6 DC volts can be prepared using 90 wt% graphite and 57 mL water content. This work is a step in the future innovation of smart construction using self-heating and antifreezing construction materials.

In this work, ZrW₂O₈-coated ZrC composite powders are synthesized by solid-state reaction method using ZrC and WO₃ powders. Thermodynamic analysis shows that when the molar ratio of ZrC to WO₃ is larger than 5:4, ZrW₂O₈ cannot be synthesized by solid reaction of ZrC and WO₃. The favorable molar ratio of ZrC to WO₃ for solid reaction synthesis ZrW₂O₈ is 1:2. After reacted below 800°C for 8 hours, only ZrC in the ZrC and WO₃ mixture powders partially reacts with oxygen to form ZrO₂. And there is no detectable reaction between WO₃ and the formed ZrO₂ to produce ZrW₂O₈. ZrC and WO₃ can synthesize ZrW₂O₈ at 900°C. ZrW₂O₈-coated ZrC composite powders can be synthesized using powder mixtures with molar ratio of ZrC:WO₃ = 1:1.7 and ZrC:WO₃ = 1:1.9 after heat treatment at 1000°C for 4 hours. The synthesized ZrW₂O₈-coated ZrC particles show cubic shape with obvious particles growth. The exothermic oxidation reaction of ZrC leads to a significant increase in local temperature, which is believed to trigger partial reaction between ZrO₂ and WO₃ to form ZrW₂O₈.

The development of vat photopolymerization (VPP) 3D printing technology has created the conditions for the fabrication of complex structured Si₃N₄ ceramics. However, Si₃N₄ ceramics produced through VPP often lack sufficient mechanical properties, which limiting their applications. This study introduces short carbon fibers (C_f) into the VPP-Si₃N₄ ceramics, combined with the polymer infiltration and pyrolysis (PIP) process, to prepare C_f/Si₃N₄ composites. The effect of C_f content on slurry preparation, green part printing, and mechanical properties of the C_f/Si₃N₄ composites was systematically investigated. The results indicate that C_f significantly enhances the mechanical properties of C_f/Si₃N₄ composites. At 6 wt.% C_f content, the samples exhibit the highest strength and fracture toughness, reaching 183.2 MPa and 6.2 MPa·m^1/2, respectively, representing increases of 29.7% and 92.3% compared to samples without C_f. The improvement in mechanical properties is partly due to the ‘pinning effect’ of C_f, which enhances interlayer bonding strength in the printed green parts, positively impacting the overall mechanical properties of the composites. Additionally, inherent toughening mechanisms of C_f, such as fiber pull-out, crack deflection, and crack bridging, further enhance the composite's mechanical properties. This study confirms the feasibility of using C_f to enhance the mechanical properties of VPP-Si₃N₄ ceramic.

Particle grading is a reliable method to improve mechanical properties of reaction-bonded silicon carbide (RBSC) ceramics. This work aims to explore the effects of particle grading on thermal and mechanical characteristics of RBSC ceramics. Results showed that the powder grading enabled to increase sintering density of silicon carbide (SiC) ceramics. The use of large particle SiC powder in grading led to a 28% increase in thermal conductivity but a 22% decrease in bending strength. Meanwhile, the addition of finer SiC powder exerted minimal effect on thermal conductivity but noticeably increased bending strength by 10%. Therefore, properly adjusting particle size in grading allows for the control of residual Si content and microstructure, thereby simultaneously increasing thermal conductivity and bending strength of the material.

Pressureless sintering processing was adopted to fabricate transparent aluminum oxynitride (AlON) ceramics by using magnesium oxide (MgO) as a sintering additive into synthetic single phased aluminum oxynitride powder. Under the condition of adding 0.6 wt% magnesium oxide, the relative density of aluminum oxynitride ceramics increased from 98.67% with no addition to 99.9% after being held at 1800°C for 24 h, coupled by a reducing of average grain size from 190 µm to 130 µm. The optical linear transmittance of the AlON ceramic sample (thickness 1.2 mm) reached 84.2% at the wavelength of 1100 nm. The microstructural characterizations by energy dispersive spectroscopy and atom probe tomography indicated that the doping Mg element was uniformly dispersed inside aluminum oxynitride grains of as-sintered ceramics. It was demonstrated that magnesium oxide played a key role in inhibiting the movement of grain boundaries, eliminating pores, leading to the fully densification of aluminum oxynitride ceramics.

Low-cost ceramic membrane support is important for the filtration performance of a asymmetry filtration membrane. In this study, the oil-based drilling cutting pyrolysis residues (ODPRs) were used as raw materials incorporating with fly ash, and carbon particles were used as pore-forming agents to prepare high-flux low-cost ceramic membrane supports. Besides the strength of the supports was decreased with increased carbon particles addition and size, the porosity, pore size and consequently the Darcey permeability k₁ and pure water permeability of the support were increased with the increased carbon particle addition and size. The chemical stability of the support was deteriorated with the increased carbon particles addition. A leaching test on the support with 10% 12 µm carbon particle addition indicates that the support obtained by using the ODPRs incorporating with fly ash as raw materials is safe for aqueous filtration. This study showcased the utilization of ODPRs as a primary resource to manufacture a high-permeability support for water filtration. This approach aligns with the principles of sustainable development, following a waste-to-product-to-environment pathway.

In this work, a flow field model of WC–12Co powder sprayed by high-velocity air fuel (HVAF) was established based on the computational fluid dynamics (CFD) method. The macro–micro coupled thermodynamic model of coating multilayer growth process was established based on the birth and death element method. The temperature and velocity of the particles in the combustion flame were applied to the coating growth model, and the transient evolution of the coating temperature and thermal stress was revealed. The results show the temperature and thermal stress of coatings increase with the increasing the number of spraying layers, and their incremental gradient gradually decreases with the increasing the number of deposition layers. The peak temperature of the coating surface reaches 1494 K, and the peak thermal stress of the first coating reaches 2693 MPa. The maximum stress of spraying particles appears at the contact edge of particles. Further preparation of WC coating, through the hardness, friction, and wear, corrosion tests verify that WC–12Co coating can effectively provide the TC18 substrate performance. The microhardness of WC–12Co coating was approximately three times that of TC18 substrate. The average friction coefficient and corrosion rate of the coating are 0.15 and 0.06 mg/cm²/h lower than that of the substrate, respectively.

Conventional aluminum nitride (AlN) ceramics exhibited insufficient mechanical properties expected from their potential applications in the presence of dynamic loads and intensive stresses caused by thermal shock. In this study, the mechanical properties of AlN ceramics were enhanced by toughening them using AlN whiskers (AlN_w) via gel casting followed by low-temperature sintering at 1650°C. The addition of AlN_w simultaneously increased the bending strength, toughness and thermal conductivity of the AlN ceramics. The maximum values of the bending strength, toughness, and thermal conductivity of 9.0 wt% AlN_w/AlN were 303.92 MPa, 3.92 MPa·m^1/2 and 186.53 W·m⁻¹·K⁻¹, respectively, which were higher than those of the AlN ceramics by 39.93%, 61.31% and, 15.61%, respectively. The AlN_w in AlN_w/AlN ceramics tightly bonded with the ceramic matrix, leading to two characteristic toughening mechanisms in the ceramics: crack pinning and deflection at irregular grain boundaries caused by doped whiskers, as well as bridging and stress relaxation caused by whiskers incorporated with the grains. Moreover, the one-dimensional morphology of AlN_w can provide a channel for quick photon transport, thereby enhancing the thermal conductivity of AlN_w/AlN.

Steelmaking has shown an increasing concern toward nonmetallic inclusions, leading to new technologies in the secondary metallurgy of steel. Although the typical inclusion removal procedure is by injecting inert gas into the ladle, this vessel does not fulfill all the requirements to accept a porous structure tailored to produce “clean steels.” Consequently, the spotlight has moved to the tundish, the last vessel before solidification, in which gas injection can continuously operate. Therefore, this work focuses on understanding the influence of typical gas flow rates (10–60 NL/min) on the kinetics of inclusion flotation, considering two bubble diameters (0.6 and 1.1 mm). For this purpose, experimental measurements were conducted in a water model, where glass hollow spheres played the role of inclusions, and their concentration was fitted by an exponential decay. In general, injecting bubbles into the system contributed positively to a faster and greater flotation of particles. The smaller bubbles led to a higher maximum efficiency, whereas the larger ones allowed a shorter time scale (i.e., a faster removal), defining a trade-off to tune the bubble size. Regarding the gas flow rate, the results indicate an optimum range to decrease the time scale, and suggestions for bubble curtains in tundishes are drawn.