一步法合成高纯度碳化硅粉体的研究

利用液态硅为原料, 以碳和二氧化硅粉末组成的混合物作为催化剂, 通过液态硅与一氧化碳之间的气-液相碳热反应, 一步合成了高纯度的碳化硅微细粉体, 制得的碳化硅粉体的平均颗粒尺寸为D₅₀=0.41μm. 利用XRD、SEM、激光粒度分析和元素分析对粉体进行了表征, 并讨论了碳化硅粉体的形成机理.     

高密度耐热冲击烧结碳化硅

1 专利范围本专利是关于无压烧结碳化硅,特别是关于具有高密度,导电性好和强度高的无压烧结耐热冲击碳化硅陶瓷体。本专利还涉及到制造这种碳化硅陶瓷体的方法。     

烧结温度对包混/复合添加工艺制备多孔SiC陶瓷性能的影响

采用包混工艺合成了核壳结构的先驱体粉体,并引入一定量Al2O3、SiO2和Y2O3复合添加剂,通过成型、炭化和烧结工艺制备了多孔碳化硅陶瓷;分析了样品的物相、表面形貌、孔隙率、热导率、热膨胀系数、抗弯强度和抗热震性能。结果表明,在较低的烧结温度下制得了多孔碳化硅陶瓷,在1650℃烧结的多孔碳化硅陶瓷综合性能较好。     

溶胶凝胶原位成型陶瓷结合剂砂轮中碳化硅的改性

使用硅烷偶联剂KH550作为表面活性剂对碳化硅微粉表面进行改性,使用扫描电镜、X射线衍射仪、激光粒度分析仪和红外光谱仪等手段研究了改性前后微粉的形貌、表面性质、粒度分布及烧结体微观形貌。结果表明,硅烷偶联剂与碳化硅通过接枝反应在其表面形成包覆层,但是不改变其物相和结构。改性后碳化硅微粉的团聚减少,因此平均粒径减小;颗粒间的静电斥力和空间位阻增大,改善了碳化硅颗粒在溶胶中的悬浮稳定性和分散性。与未改性的SiC相比,用溶胶凝胶原位成型SiC/陶瓷复合材料改性后SiC与陶瓷的烧结体结构均匀,抗弯强度较高。     

聚碳硅烷低温烧结碳化硅网眼多孔陶瓷的研制

通过有机模板复制法,以聚碳硅烷(Polycarbosilane,PCS)为粘结剂和烧结助剂,通过离心工艺二次挂浆制备出低温烧结高强度碳化硅网眼多孔陶瓷.系统地研究了烧结温度、保温时间等工艺参数对制得的碳化硅网眼多孔体微观结构与性能的影响.研究结果表明:最佳烧结温度为1100℃,合适的保温时间为1h,且所制备的网眼多孔体的孔筋厚度均匀.用10PPI(pores per inch)和25PPI有机模板制得的网眼多孔体抗压强度分别为(1.08±0.21)MPa和(2.19±0.32)MPa,耐火温度高达1690℃,而且抗热震性能优良.当淬冷温度大约为1400℃,用25PPI有机模板,经PCS浆料二次挂浆制备的网眼多孔体的热震损伤参数(Dts)仅为0.36.     

不同含量PEG对固相烧结碳化硅陶瓷性能的影响EI北大核心

在以碳黑、碳化硼为烧结助剂的碳化硅陶瓷烧结过程中,通过引入聚乙二醇(PEG)为粘结剂,研究了不同PEG含量对碳化硅陶瓷密度和力学性能的影响。结果表明随着PEG含量的增加,碳化硅陶瓷的密度和力学性能表现为先增加后减小的规律。另外在碳化硅陶瓷烧结过程中增加保温时间,由于晶粒长大过快导致其密度和力学性能迅速下降,同时棒状晶粒的形成没有增加碳化硅陶瓷的韧性。     

碳化硅衍生碳/中间相沥青炭复合材料的制备及表征

通过聚碳硅烷和中间相沥青在320℃共混及不同温度热解、炭化、石墨化处理得到碳化硅/中间相沥青炭前驱体,然后采用Cl_2在1 000℃对前驱体进行刻蚀,成功制备碳化硅衍生碳/中间相沥青炭复合材料。采用偏光显微镜、X射线衍射、扫描电子显微镜、透射电子显微镜和拉曼光谱对产物的微观形貌和结构进行了表征,利用物理吸附仪分析其比表面积和孔结构特征。结果表明,随着热处理温度的升高,聚碳硅烷热解形成的SiC的晶体尺寸变大,同时沥青炭的石墨化程度也变高;刻蚀后碳化硅衍生碳的结构以无定形碳为主,有明显的石墨化碳层分散其中,样品的比表面积随热处理温度升高而减小,微孔孔径增大。     

复合陶瓷材料的生产

将二氧化硅细粉(10～150份重)撒在氮化硅和/或碳化硅(100份重)基体粒子表面上,与10～600份重的碳、10～300份重的碱金属卤化物或碱土金属、氮化硅和/或碳化硅用的准确数量的烧结助剂和形成碳化硅胡须用的准确数量的催化剂混合在一起,将混合物置于非氧化     

残余相和烧结温度对碳化硅陶瓷抗混酸腐蚀特性的影响（英文）

本工作主要研究了残余相和晶粒尺寸对碳化硅的抗混酸(HF-HNO_3)腐蚀特性。通过不同的烧结方法(固相烧结、液相烧结、反应烧结)制备出残余相不同的碳化硅材料。结果表明:与液相烧结碳化硅(LPS SiC)和反应烧结碳化硅(RB SiC)相比,固相烧结碳化硅(SSiC)具有更好的腐蚀抗性,这是由于残余相石墨的抗腐蚀性强,以及残余相在材料中形成不能相互联通的岛状结构。通过调节碳化硅的烧结温度,可以影响材料中的晶粒尺寸,研究结果发现相同烧结温度下随着残余相含量的增加,材料腐蚀失重线性增加,对曲线进行线性拟合,其Y轴截距的绝对值代表不含碳的试样在该烧结温度下的腐蚀失重。研究表明随着烧结温度由2100℃升高到2160℃,晶粒尺寸由2μm增加到6μm。此时其Y轴截距的绝对值分别为9.22(2100℃),5.81(2130℃),0.29(2160℃),表明晶粒尺寸的增加有利于提高材料的抗腐蚀能力。     

多孔碳化硅材料的制备及其催化性能

以糊精作为造孔剂及粘结剂,制备出了多孔碳化硅陶瓷。通过调节添加剂的含量,得到空隙率27％～70％的多孔陶瓷体,孔径呈现出明显的双峰分布。应用XRD和SEM手段对多孔陶瓷的形貌以及结构的分析表明,不同的烧结气氛对材料有着很大的影响。比较了有氧气气氛和在真空条件下烧结的多孔碳化硅材料性能,气孔率从60％明显下降到28％,材料强度从24MPa上升到90MPa。对材料的催化性能表征显示,用多孔碳化硅作为碳改性的氧碳化钼(MoC₃-C)催化剂载体,具有较高的选择性,达到70％,但活性仅20％,其原因尚需进一步研究。     

纳米碳化硅基复相陶瓷的分散和烧结技术研究进展

碳化硅陶瓷是一种高性能的陶瓷,具有高强度、高硬度、耐高温、耐化学腐蚀、高热导率、低热膨胀以及低密度等性能,广泛应用于各个工业领域以及航空航天领域.从纳米复相陶瓷制备过程中的分散方法以及碳化硅基陶瓷的烧结方法与烧结助剂等方面详细论述了目前有关碳化硅基纳米复相陶瓷的研究进展.     

Saturation of capillary pores in silicon carbide briqettes with liquid–phase carbon-containing solutions before the reaction-sintering

It has been studied the increasing of the carbon saturation of a porous silicon–carbide briquette by a multiple impregnation of oil coke solutions instead of a traditionally used lamp black hardphase powder or fine-dispersed graphite powder intended for a reaction sintering of silicon carbide aimed to decrease the free silicon part, which remains in the structure after sintering.     

成型温度对多孔SiC陶瓷性能的影响

以包混工艺合成了核-壳结构的先驱体粉体,并引入少量Al<,2>O<,3>,SiO<,2>和Y<,2>O<,3>作为复合添加剂,通过模压成型、炭化和烧结工艺制备了多孔碳化硅陶瓷;研究了成型温度对样品的孔隙率、密度、热膨胀系数、抗弯强度和热震性能的影响.结果表明:成型温度对多孔碳化硅陶瓷的孔隙率、密度、抗弯强度及热震性能均...     

Numerical modeling of liquid-phase infiltration in the process of sintering ceramic composites

The paper presents a numerical model for infiltration of porous preforms of ceramic materials in the process of sintering. The mathematical model of infiltration is based on the Richards equation and Van Genuchten formulas describing permeability properties of the porous structure and the infiltrant. A finite-element method and stable implicit finite-difference time scheme are applied for discretization of the Richards equation. Based on the outcome of solving test problems, a comparison of the numerical results with the results obtained by other researchers and with the experimental data, the numerical model has been proved adequate. The paper provides some findings of computer modeling of infiltration of liquid silicon into porous silicon carbide preforms of various geometries and dimensions.     

The features of photoluminescence from nanograins of gallium-doped cubic silicon carbide

The photoluminescence (PL) and photoexcitation spectra of carbonized porous silicon (por-Si) doped with gallium in the course of a high-temperature annealing were studied. It is shown that carbonization leads to the formation of a heterojunction between 3C-SiC nanograins and silicon quantum wires. The spectrum of PL from gallium-doped silicon carbide nanograins is shifted by 0.35 eV toward higher energies relative to the spectrum of bulk por-Si and exhibits several features related to the radiative annihilation processes involving phonons and donor-acceptor (N-Ga) pairs. The PL excitation spectra of carbonized por-Si display two resonance bands with the energies E ₁=2.8–3.1 eV and E ₂=3.2–3.7 eV.     

碳化硅轻型反射镜的研究进展

反射镜材料需具有低密度、高弹性模量、高热导率和低热膨胀系数.比较了不同反射镜材料的物理性能和机械性能,与传统光学材料对比,碳化硅具有优越的物理性能和热性能,被认为是轻型反射镜材料的首选.综述了碳化硅反射镜材料常用制备方法的特点.认为反应烧结法和热等静压法适用于制备SiC反射镜基体材料,化学气相沉积法适合用于基体材料增密和制备反射层,反应烧结法结合化学气相沉积工艺是制备SiC反射镜的高效低成本工艺.     

Structure, mechanical and functional properties of aluminum nitride-silicon carbide ceramic material

Two-phase ceramic composites of the dielectric-semiconductor type having different semiconducting phase content (aluminum nitride ceramics with uniformly distributed inclusions of silicon carbide of a certain size) have been produced by pressureless sintering. These composites are characterized by Vickers hardness HV (150 N) 9.5–15.8 GPa, Palmqvist fracture toughness 3.0–4.2 MPa m^0.5, bending strength 132–209 MPa, thermal conductivity 37–82 W/(m K), and by a coefficient of the microwave electromagnetic energy attenuation to 36.3 dB/cm. It has been found that as the size of silicon carbide grains in aluminum nitride-based ceramics increases, the thermal conductivity increases and microwave energy attenuation decreases, which is indicative of the decisive role of grain boundaries in scattering both phonons and microwave radiation.     

R-curve measurement of silicon nitride ceramics using single-edge notched beam specimens

R-curve behaviour of three kinds of silicon nitride-based ceramics has been studied using the single-edge notched beam (SENB) technique. If the notch is deep enough, the specimen shows stable fracture during the bending test, even when the sample is a brittle material. The conditions required to obtain stable fracture in the bending test are clarified by the analysis. The crack length of the specimen was also calculated from the changing load during the fracture test. In this study, coarse-grained silicon nitride shows a large increase of theR-curve. On the other hand, silicon nitride with silicon carbide whiskers shows noR-curve increase. The rise of theR-curve should be related to the microstructure of the ceramics, and especially to the grain size of the specimen, because silicon carbide whiskers are not large compared to the silicon nitride grains, and silicon carbide can reduce the grain growth of silicon nitride during sintering.     

Effect of structure of interfacial coating layer on mechanical properties of continuous fiber reinforced reaction sintered silicon carbide matrix composite

A dense silicon carbide matrix composite reinforced by Hi-Nicalon fibers CVD coated with boron nitride and silicon carbide was fabricated by slurry impregnation and subsequent reaction sintering with molten silicon. The effect of the structure and the thickness of the silicon carbide layer of the fiber coating on the mechanical properties of the composite were investigated. That is, three types of silicon carbide layers, namely a dense structure with a thickness of 0.15 m and two porous structures with a thickness of 0.15 m and 0.48 m, respectively, were investigated. As a result, excellent strength property of ceramic matrix composite (CMC) was obtained in the case of the dense silicon carbide (SiC) layer. The thickness effect of the SiC layer on the strength was smaller than that of the structure.