氮化硅结合碳化硅窑具材料

本文介绍了氮化硅结合碳化硅窑具的制造工艺原理及生产工艺技术，报道了该窑具的材料性能和各类窑具的品种特点。氮化硅结合碳化硅材料以其优异的性能，独特的成形技术和氮化工艺，可生产出轻量化、组合化的现代窑具。     

高档发优质反应结合氮化硅结合碳化硅窑具的制备

本文研究了高档优质Ｓｉ３Ｎ４结合ＳｉＣ窑具的工艺过程，并且论述了制备这处高档优质窑具的工艺参数。     

氧氮化硅结合碳化硅窑具材料研究

利用热力学分析了氧氮化硅结合相的生成机理。探讨了硅粉加入量对氧氮化硅生成量、材料的各项理化性能以及抗氧化性能的影响。结果表明：氧氮化硅的含量随Ｓｉ含量的增加而增加,制品的常温耐压强度和荷重软化温度相应提高     

提高氮化硅结合碳化硅窑具使用性能的研究

氮化硅结合碳化硅窑具的抗热震性能被破坏、不合理的支撑方式、承重变形因素导致其使用性能降低,影响了氮化硅结合碳化硅窑具的使用寿命。本研究制备了氮化硅结合碳化硅窑具,并结合生产实际主要研究了如何提高材料的抗氧化性、抗热震性以及其他高温理化性能,使氮化硅结合碳化硅窑具使用寿命延长。     

碳化硅窑具材料的研制方法介绍及展望

本综述了各种窑具材料生产工艺及使用性能,认为今后的研究重点应放在研制低成本高性能的SiC窑具材料上。     

碳化硅窑具材料的研究

本文采用正交设计试验法,研究了SiC颗粒级配、结合相用量及外加糊精用量对SiC窑具材料性能的影响。经试验确定取:SiC颗粒级配为粗:中:细=55:20:25,结合相用量19wt％,外加糊精3wt％。     

Silicon Nitride–Silicon Carbide Refractories Produced by Reaction Bonding

Silicon nitride-silicon carbide refractories have been prepared by reaction bonding. The percentage of silicon nitride in the refractory was varied from 5 to 45 wt%. The modulus of rupture of refractories increases with an increase of temperature, whereas thermal expansion decreases. These refractories are resistant to molten non-ferrous metals but are attacked by molten cast iron.     

Reaction-Bonded and Superplastically Sinter-Forged Silicon Nitride–Silicon Carbide Nanocomposites

Silicon nitride–silicon carbide (Si₃N₄–SiC) nanocomposites were fabricated by a process involving reaction bonding followed by superplastic sinter-forging. The nanocomposites exhibited an anisotropic microstructure, in which rod-shaped, micrometer-sized Si₃N₄ grains tended to align with their long axes along the material-flow direction. SiC particles, typically measuring several hundred nanometers, were located at the Si₃N₄ grain boundaries, and nanosized particles were dispersed inside the Si₃N₄ grains. A high bending strength of 1246 ± 119 MPa, as well as a high fracture toughness of 8.2 ± 0.9 MPa·m^1/2, was achieved when a stress was applied along the grain-alignment direction.     

Silicon Nitride–Silicon Carbide Nancocomposites Fabricated by Electric-Field-Assisted Sintering

Starting with Si-C-N(-O) amorphous powders, and using the electric field assisted sintering (EFAS) technique, silicon nitride/silicon carbide nanocomposites were fabricated with yttria as an additive. It was found that the material could be sintered in a relatively short time (10 min at 1600°C) to satisfactory densities (2.96–3.09 g/cm³) using 1–8 wt% yttria. With decreasing yttria content, the ratio of SiC to Si₃N₄ increased, whereas the grain size decreased from ∼150 nm to as small as 38 nm. This offers an attractive way to make nano-nanocomposites of silicon nitride and silicon carbide.     

Preparation of Aluminum Nitride–Silicon Carbide Nanocomposite Powder by the Nitridation of Aluminum Silicon Carbide

Aluminum nitride (AlN)–silicon carbide (SiC) nanocomposite powders were prepared by the nitridation of aluminum-silicon carbide (Al₄SiC₄) with the specific surface area of 15.5 m²·g⁻¹. The powders nitrided at and above 1400°C for 3 h contained the 2H-phases which consisted of AlN-rich and SiC-rich phases. The formation of homogeneous solid solution proceeded with increasing nitridation temperature from 1400° up to 1500°C. The specific surface area of the AlN–SiC powder nitrided at 1500°C for 3 h was 19.5 m²·g⁻¹, whereas the primary particle size (assuming spherical particles) was estimated to be ∼100 nm.     

Silicon Carbide Monofilament-Reinforced Silicon Nitride or Silicon Carbide Matrix Composites

SiC-monofilament-reinforced SiC or Si₃N₄ matrix composites were fabricated by hot-pressing, and their mechanical properties and effects of filaments and filament coating layers were studied. Relationships between frictional stress of filament/matrix interface and fracture toughness of SiC monofilament/Si₃N₄ matrix composites were also investigated. As a result, it was confirmed experimentally that in the case of composites fractured with filament pullout, the fracture toughness increased as the frictional stress increased. On the other hand, when frictional stress was too large (>about 80 MPa) for the filament to be pulled out, fracture toughnesses of the composites were almost the same and not so much improved over that of Si₃N₄ monolithic ceramics. The filament coating layers were found to have a significant effect on the frictional stress of the SiC monofilament/Si₃N₄ matrix interface and consequently the fracture toughness of the composites. Also the crack propagation behavior in the SiC monofilament/Si₃N₄ matrix composites was observed during flexural loading and cyclic loading tests by an in situ observation apparatus consisting of an SEM and a bending machine. The filament effect which obstructed crack propagation was clearly observed. Fatigue crack growth was not detected after 300 cyclic load applications.     

Reactive Infiltration of Si-Mo Alloyed Melt into Carbonaceous Preforms of Silicon Carbide

A MoSi₂/reaction-bonded SiC composite was prepared from a preform of petroleum coke and commercial SiC powders (in weight ratios of 0.5 and 0.6), following reactive infiltration of a Si-Mo melt (molybdenum concentration of 7–29 wt%) made from elemental powder. The resulting material had a relative density of >90% of the theoretical density and, on a microstructural scale, contained SiC and MoSi₂, in addition to unreacted carbon and silicon. The SiC and MoSi₂ boundary was smooth and sharp, with no sign of any reaction. The occasional presence of an intermediate zone between SiC and MoSi₂ was detected; this zone contained silicon, iron, and aluminum, the formation of which may be related to the presence of impurities in the silicon and SiC.     

Reactivity of Aluminum Nitride Powder in Aqueous Silicon Nitride and Silicon Carbide Slurries

The reactivity of AlN powder with water in supernatants obtained from centrifuged Si₃N₄ and SiC slurries was studied by monitoring the pH versus time. Various Si₃N₄ and SiC powders were used, which were fabricated by different production routes and had surfaces oxidized to different degrees. The reactivity of the AlN powder in the supernatants was found to depend strongly on the concentration of dissolved silica in these slurries relative to the surface area of the AlN powder in the slurry. The hydrolysis of AlN did not occur if the concentration of dissolved silica, with respect to the AlN powder surface, was high enough (1 mg SiO₂/(m² AlN powder)) to form a layer of aluminosilicates on the AlN powder surface. This assumption was verified by measuring the pH of more concentrated (31 vol%) Si₃N₄ and SiC suspensions also including 5 wt% of AlN powder (with respect to the solids).     

Silicon Carbide/Silicon and Silicon Carbide/Silicon Carbide Composites Produced by Chemical Vapor Infiltration

Composites of SiC/Si and SiC/SiC were prepared from single yarns of SiC. The use of carbon coatings on SiC yarn prevented the degradation normally observed when chemically vapor deposited Si is applied to SiC yarn. The strength, however, was not retained when the composite was heated at elevated temperatures in air. In contrast, the strength of a SiC/C/SiC composite was not reduced after this composite was heated at elevated temperatures, even when the fiber ends were exposed.     

Microstructure of Silicon Carbide Whiskers Synthesized by Carbothermal Reduction of Silicon Nitride

The microstructure of silicon carbide whiskers synthesized by carbothermal reduction of silicon nitride has been studied using transmission electron microscopy. All of the whiskers examined are single crystals, and grow in the (111) crystallographic direction. Two different forms of stacking faults and microtwins were observed; in one the planar defects are normal to the whisker growth direction, and the other has the defect planes at an angle of about 70° to the growth axis, while both forms of the defects are on the [111] closed-packed planes. Without the addition of catalyst, droplets containing metallic impurities were not found at the tips of the whiskers synthesized by the present process. A core and outer regions were observed in the single-crystal whiskers, which may be evidence that the whiskers were formed by a two-stage mechanism.     

SiC纳米线增强反应烧结碳化硅陶瓷的性能研究

以单晶SiC纳米线作为增强体,碳化硅-碳为陶瓷基体,在1550℃下,采用反应烧结制备碳化硅基陶瓷复合材料(SiCnf/SiC).结合X射线衍射、万能试验机和扫描电镜等检测和分析,研究SiC纳米线对复合材料的微结构和力学性能的影响.研究表明:与未加入SiC纳米线的反应烧结碳化硅陶瓷相比,添加SiC纳米线的复合陶瓷的抗弯强度和断裂韧性都得到显著的提高,抗弯强度提高了52％,达到320 MPa(SiC纳米线含量为12wt％),断裂韧性提高了40.6％,达到4.5 MPa· m1/2(SiC纳米线含量为15wt％);反应后的SiC纳米线仍然可以保持原有的竹节状结构,且随着SiC纳米线的加入,复合陶瓷的断口可以观察到SiC纳米线拔出现象.但由于SiC纳米线“架桥”的现象,添加过量的纳米线会降低复合陶瓷的密度和限制复合陶瓷力学性能的提高.同时还讨论了SiCnf/SiC的增强机理.