Collection of Ceramics Served under High Temperature and Extreme Enviroment(202312)
The batch stability of ceramic powders is a core indicator that manufacturers of ceramic products are most concerned about, yet has long been undocumented. In this study, the similarity of Si3N4 powders produced in different batches was quantitatively evaluated by taking combustion-synthesized Si3N4 powders as the sample. A system of powder performance evaluation parameters covering static physicochemical and dynamic flowability indices was firstly constructed. Then, all performance data of Si3N4 powders in this parameter system were retested. Subsequently, the consistency evaluation data of Si3N4 powders were obtained using the cosine similarity method and the Euclidean distance method. The results show that both methods based on this parameter system can reflect the similarity between batches of powders and quantitatively show the differences between them. Calculation results of the two methods are mutually verified. For powders judged to be dissimilar, differences in the process were traced to find the key link in the consistency between the Si3N4 powders and the raw silicon powders. For powders judged to be highly similar, they were classified as the same class. These study provides a quantitative basis for the classification of different batches of silicon nitride powders. The “Powder Consistency Evaluation System” established in this work presents an effective evaluation tool and quantitative basis for batch stability (performance consistency) of silicon nitride powder.
SiC ceramics with high thickness and high density are highly advantageous for armor protection, but it is difficult to produce bulk SiC ceramics with thicknesses more than 100 mm. This work was concentrated on the problems of easy cracking and non-densification in the thick SiC ceramic sintering, and degreasing products as well as pressure-incomplete degreasing process were investigated. In order to degrease thick ceramics, phenolic resin’s pyrolysis residue was examined using TG-MS. Formaldehyde and other small-molecule byproducts of breakdown were quickly eliminated, but macromolecule byproducts like dimethylphenol were easily retained in the core, leading to the noncompact sintering of thick ceramics. After degreasing optimization, the blank’s surface-core density is almost constant, ranging from 1.81 to 1.84 g/cm3. In contrast, the test group shows no cracking or deformation after sintering at 2150 ℃, and both surface and core of the large thickness ceramics obtain a density up to 3.14 g/cm3 with similar microstructure. The fracture strength of the core is (411±84) MPa, while the fracture strength of the surface is (433±48) MPa. According to the investigation, the ceramic core’s insufficient degreasing is the primary reason for the cracking and poor density.
With the rise of the third-generation wide-bandgap semiconductors represented by SiC and GaN, power electronic devices are developing rapidly towards high output power and high power density, putting forward higher performance requirements on ceramic substrate materials used for power module packaging. The conventional Al2O3 and AlN ceramics are inadequate for the new generation of power module packaging applications due to low thermal conductivity or poor mechanical properties. In comparison, the newly developed Si3N4 ceramics have become the most potential insulating heat dissipation substrate materials due to its excellent mechanical properties and high thermal conductivity. In recent years, researchers have made a series of breakthroughs in the preparation of high strength and high thermal conductivity Si3N4 ceramics by screening effective sintering additive systems and optimizing the sintering processes. Meanwhile, as the advancement of the engineering application of coppered Si3N4 ceramic substrate, the evaluation of its mechanical, thermal, and electrical properties has become a research hotspot. Starting from the factors affecting thermal conductivity of Si3N4 ceramics, this article reviews the domestic and international research work focused on sintering aids selection and sintering processes improvement to enhance the thermal conductivity of Si3N4 ceramics. In addition, the latest progress in the dielectric breakdown strength of Si3N4 ceramic substrates and the evaluation of properties after being coppered are also systematically summarized and introduced. Based on above progresses and faced challengies, the future development direction of high strength and high thermal conductivity Si3N4 ceramic substrates is prospected.
As a high-temperature-resistant structural reinforcement material with excellent performance, alumina continuous fiber has been widely used in various fields. However, its large-scale preparation is still a great challenge due to the technical difficulty. Herein, the alumina continuous fibers were prepared using self-made aluminum sol and commercially available silica sol as precursors, in which the microstructure and composition of aluminum sol were studied to reveal their excellent spinnability. Preparation of alumina-based gel continuous fibers with length longer than 1500 m was realized by Sol-Gel combined dry spinning technology. After calcination at 1100 ℃ for 30 min, the continuous ceramic fiber composed of γ-Al2O3 and amorphous SiO2 with the diameter and mean tensile strength of 10 μm and 2.0 GPa was successfully obtained. Microstructure analyses revealed high relative density of the ceramic fibers, in which the γ-Al2O3 nanocrystals with size of 10-20 nm uniformly distributed in amorphous SiO2, resulting in excellent mechanical properties. This preparation process is environment-friendly, simple and controllable, showing great potential in practical application. The test for high temperature resistance revealed that the alumina continuous fiber can work for a long time at 1000 ℃ while it can endure as high as 1300 ℃ for a short-time service.
Polymer derived ceramic is one of the effective methods for producing ultra-high temperature ceramics and powders, but effect of source material type on precursor cross-linking degree and ceramic yield has rarely been reported. Here, TaC precursors were synthesized using two carbon sources and poly-tantalumoxane (PTO). Phase composition and microstructure of TaC ceramic powders from different carbon sources, tantalum/carbon mass ratios, and pyrolysis temperatures were characterized. It was found that PF-3 resin with C=C was effective in promoting the cross-linking of PTO and increasing the ceramic yield. When the mass ratio of PTO to PF-3 Resin was 1 : 0.25 and PTO to 2402 Resin was 1 : 0.4, TaC ceramic powders could be obtained at 1400 ℃ without residue Ta2O5. Ceramic yields of ceramic powders were 54.02% and 49.64%, and the crystal sizes were 47.2 and 60.9 nm, respectively. Therefore, PF-3 resin is able to reduce crystal size while increasing ceramic yield, but has less impact on the powder purity and particle size. The purity of TaC ceramic powders derived from different carbon sources are 96.50% and 97.36%, respectively, meanwhile the median diameters are 131 and 129 nm, respectively.
Porous silicon nitride (Si3N4) ceramics can be widely used in various fields, such as sound and shock absorption, filtration and so on, due to its high porosity and outstanding properties of ceramics. However, conventional preparation methods, such as gas-pressure/pressureless sintering, sintering reaction-bonded sintering and carbothermal reduction sintering, perform long sintering time, high energy consumption and high equipment requirements, which makes the preparation of porous Si3N4 ceramics expensive. Therefore, it is of great importance to explore a rapid and low-cost preparation method. In recent years, the direct preparation of porous Si3N4 ceramics by self-propagating high temperature synthesis (SHS) has showed great potential of which the heat released from the nitridation of Si powder could be used for the in-situ sintering of porous Si3N4 ceramics. In present paper, researches relating to the initiation of the SHS reaction, and microstructural evolution, mechanical properties, and reliability of the fabricated Si3N4 ceramics are summerized systematically. Porous Si3N4 ceramics with complete nitridation, excellent grain morphology and outstanding mechanical properties and reliability are obtained by adjusting raw materials and process parameters. Furthermore, the relationship between properties of grain boundary phase and high-temperature mechanical properties of SHS-fabricated porous Si3N4 ceramics is reviewed. Finally, the development direction of the self-propagating high temperature synthesis of porous Si3N4 ceramics is prospected.
Si3N4-BN-SiC composites present desirable potential for engineering applications because of their improved mechanical properties and oxidation resistance. In present work, Si3N4-BN-SiC composites were successfully fabricated by combustion synthesis using Si, Si3N4 diluent, B4C, and Y2O3 as initial powders. BN and SiC were in situ introduced into Si3N4 ceramics by the reaction between Si, B4C, and N2 gas. The obtained Si3N4-BN-SiC composites were composed of elongated β-Si3N4 matrix and hollow spherical composites. The formation mechanism of the hollow spherical microstructure was investigated. The results show that the generated SiC and BN particles and glass phase cover on the raw materials, and hollow spherical microstructure is formed when raw particles are depleted. Furthermore, the impacts of B4C content on the mechanical properties of Si3N4-BN-SiC composites were investigated in detail. The in-situ introduction of BN and SiC is beneficial to improving mechanical properties of the composites to some extent. Finally, Si3N4-BN-SiC composites with bending strength of 28-144 MPa, fracture toughness of 0.6-2.3 MPa·m 1/2, Young's modulus of 17.4-54.5 GPa, and porosity of 37.7%-51.8% were obtained for the samples with 0-20% (in mass) B4C addition.
Melt-grown oxide eutectic ceramics possess a large area of clean and firmly bonded phase interfaces through liquid-solid phase transformation, which makes them present excellent high-temperature properties such as strength retention, creep resistance, thermal stability, oxidation and corrosion resistance. As a result, directionally solidified oxide eutectic composite ceramics have been regarded as one of candidates for new generation of high temperature structural materials which can service above 1400 ℃ in oxidation environment for a long period. In recent years, laser additive manufacturing based on melt growth has developed into the most promising technique for preparing ultrahigh-temperature oxide eutectic ceramics due to its unique advantage in one-step fabricating highly dense parts with large sample size and complex shape. In this paper, laser additive manufacturing technology was summarized in terms of forming principle, technical features and classification. The research status and the encountered technical problems in additively manufacturing melt-grown oxide eutectic ceramics were reviewed. Moreover, the research progress on laser additive manufacturing oxide eutectic ceramics was introduced from the aspects of laser forming process, solidification defect control, solidification microstructure evolution, and mechanical properties. Finally, the key bottlenecks of realizing engineering applications of the laser 3D-printed oxide eutectic ceramics were pointed out, and the future development directions of this field were prospected. The focus of the future work can be summarized into four points: developing high-quality spherical eutectic ceramic powders, preparing large-scale eutectic parts with complex shapes, accurate controlling solidification defects, as well as strengthening and toughening eutectic composites.
Ultra-high temperature composite ceramic matrix composites ZrC-SiC, ZrB2-ZrC-SiC and HfB2-HfC-SiC were fabricated by precursor infiltration and pyrolysis method. The ultra-high temperature ceramic phases in the materials were characterized by submicron/ nanometer uniform dispersion distribution. Ablation behaviors of ZrC-SiC, ZrB2-ZrC-SiC and HfB2-HfC-SiC matrix composites under atmospheric plasma and on-ground arc-jet wind tunnel were investigated comparatively. The main factors that affect design for ultra-high temperature composite ceramic matrix composites were summarized. The result shows that, compared with traditional SiC-based composites, ultra-high temperature composite ceramic matrix composites have a solid-liquid two-phase dense oxide film formed in situ on the surface of the composites after ablation. Synergistic effect of the two phases has achieved effects of erosion resistance and oxidation resistance, which plays a very important role in hindering the loss of liquid SiO2 and greatly improves the ultra-high temperature ablation performance of the materials. On this basis, the important factors that should be considered in the matrix design of ultra-high temperature composite ceramic matrix composites are obtained. The above results have instructional significance for the ultra-high temperature and the limited life application of ceramic matrix composites.