反应烧结工艺对碳化硅陶瓷微结构及性能的影响

研究了脱胶温度、加硅量、升温速率及重烧次数对反应烧结碳化硅陶瓷金相组织、体积密度、力学性能和微观结构的影响.结果表明:经800℃脱胶,硅与碳化硅生坯的质量比为0.9∶1,升温速率为1.0 ℃/min时,反应烧结碳化硅陶瓷产品的性能最好,体积密度为3.09 g/cm3,维氏硬度为26.82 GPa,弯曲强度为388 MPa,断裂韧性为4.49MPa·m1/2.对渗硅不充分的不合格品进行重烧可以有效提高产品的致密度和力学性能,但是,重烧次数过多会引起晶粒粗化,从而导致力学性能下降.     

Effect of Processing Parameters on Phase and Microstructure Evolution in RBAO Ceramics

Important parameters controlling the reaction-bonding of Al₂O₃ (RBAO) process are Al content, particle size, and green density. Successful fabrication of high-strength bodies requires fine and homogeneous powders. Low milling intensity does not lead to the required particle fineness, whereas overmilling causes extensive oxidation and hydrolyzation of Al. Oxidation of Al during milling is enhanced by ZrO₂ additions. As much of the Al should be oxidized by solid/gas reaction as possible. Milled RBAO precursor powder contains physically-adsorbed and chemically-bonded (aluminum hydroxide) water. Decomposition of chemically-bonded water promotes cracking in the temperature range 450–550°C. Bloating of RBAO occurs when the surface region becomes dense before complete decomposition of aluminum hydroxide in the interior of the body.     

Microstructure of Platelet-Reinforced Ceramics Prepared by the Directed Reaction of Zirconium with Boron Carbide

The microstructure of a ZrB₂-platelet-reinforced ZrC _x composite was examined using transmission electron microscopy and X-ray diffraction. The composites, which are formed by the reaction of molten Zr with B₄C, contain a small amount of residual Zr, the amount of which can be varied by altering the processing conditions. Results on two different materials are reported, one with a low Zr content, ∼2.5 vol%, and the other with a very low Zr content, ∼0.5 vol%. In the former, metallic Zr was found at triple points and as a grain boundary phase between the boride and carbide, and to a lesser degree between the boride grains. In the latter, it was only found as a ternary Zr–ZrB₂–ZrC _x eutectic at the triple points. Both materials showed a nearly random distribution of the boride and carbide constituents, though specific crystallographic relationships were found between the various constituents.     

Microstructure and Properties of Plasma Ceramics

Plasma spraying, originally a surfacing technology used for ceramic coating of metal and nonmetal substrates, is suitable for producing large, full ceramic bodies, such as plates and tubes, in situ to almost the desired dimensions; i.e., conventional methods of designing by molding and casting green bodies followed by sintering are not required. These "plasma ceramics" exhibit characteristic mechanical and thermomechanical properties. Their porous laminar grain structure results in low E -modulus and strength, and in extreme thermal shock resistance, which is enhanced by the comparably high fracture resistance of the material. Because of these properties and their low hardness, plasma ceramics can be easily machined with almost conventional methods of metal processing.     

Study on Structure Evolution and Reaction Mechanism in Microwave Pre-oxidation

Journal of Inorganic and Organometallic Polymers and Materials - Microwave pre-oxidation was compared with conventional pre-oxidation process in 180–280 °C, and the mechanism of...     

Influence of Temperature on Microstructure and Mechanical Property of Si-B-O-N Ceramics Fabricated by in-situ Reaction Method

为满足新型透波陶瓷工程应用需要,利用硼酸脱水得到的氧化硼与氮化硅在 1400～1800 ℃原位反应制备 Si–B–O–N 陶瓷。借助 X 射线衍射仪、X 射线光电子能谱仪、Fourier 变换红外光谱分析仪和扫描电子显微镜研究了热处理温度对 Si–B–O–N 陶瓷物相组成、结构及力学性能的影响。结果表明：氧化硼和氮化硅的原位反应在 1600 ℃以上完成,所得产物为氮化硼和掺杂硼、氮元素的石英玻璃,其体积分数分别为 30%和 70%;原位反应结束后,随温度提高,氮化硼生长速率逐渐加快,晶粒尺寸由纳米级逐渐长大为亚微米级,非晶相中硼、氮元素含量逐渐降低;受氮化硼纳米晶强化作用以及非晶相结构影响,在 1700 ℃获得的 Si–B–O–N 陶瓷力学性能较好。     

Microstructure of Barium Titanate Ceramics

The microstructure of polycrystalline barium titanate as seen in polished and etched specimens is more complicated than that in the single crystal. The greater complexity is revealed in the form of a banded structure which is considered to be due to the stress configuration arising from mutual impingement of randomly oriented grains during the cubic-tetragonal phase transformation.     

Microstructure of Lead-Magnesium Niobate Ceramics

Lead-magnesium niobate ceramics were processed with excess MgO and by precalcining MgO and Nb₂O₅. Transmission electron microscopy revealed sub-micrometer MgO inclusions in the perovskite phase. The pyrochlore phase exists as submicrometer rectangular crystals in an amorphous PbO matrix. The composition of the pyrochlore phase was calculated to be Pb_2.25Mg_0.27Nb_1.79O₇.     

Microstructure and Deterioration in Steatite Ceramics

Pitting in steatite ceramics was found to occur as a result of (1) deterioration with time, the familiar aging phenomenon, and (2) secondary recrystallization, which takes place immediately after fabrication. Differences in microstructural and other features observed in the two cases are pointed out.     

Microstructure Development in Mullite-Cordierite Ceramics

The evolution of the microstructure in mullite-cordierite bodies containing 36 wt% cordierite has been studied in samples fired at 1490°C for varying times. This material reaches its final density very quickly once the cordierite becomes molten. However, densification, which is not accompanied by any significant coarsening of the mullite phase, appears almost entirely to result from particle–particle rearrangement. Consequently, the ultimate density of these materials appears to be limited by the inability of molten cordierite to penetrate all mullite-mullite grain boundaries.     

Mapping Ceramics Research and Its Evolution

We show here how a simple data mining of bibliographic records can be used to follow and help understand the evolution of a research domain, at a level that cannot be captured by reading individual papers in a field of this size. We illustrate the approach by investigating 43 yr of research on ceramic materials, covered by 253 000 bibliographic records. The patterns of keywords used reveal the trends and the evolution of research ideas and priorities within the field. Simple, interactive tools based on co‐word network analysis help us better appreciate the organization and relationships of ideas or individuals, and hopefully allow identification of unexplored concepts, connections, or approaches on a given topic.     

Texture Development and Microstructure Evolution in Liquid-Phase-Sintered α-Alumina Ceramics Prepared by Templated Grain Growth

Texture development in alumina that contains calcia and silica and has been templated with platelet-shaped α-Al₂O₃ particles has been evaluated. The texture fraction is shown to be related directly to template growth. Texture quality is controlled by the template concentration, decreasing at template concentrations of >10%, as a result of template–template interactions during tape casting. Almost fully textured alumina has been obtained at template concentrations of ≥20%. The growth of template grains is much more rapid in the radial direction and is shown to be inversely related to the thickness of the grain-boundary liquid. The activation energy for growth (376 kJ/mol) and the inverse relation with the grain-boundary thickness indicate that template growth in the radial direction is controlled by Al³⁺ diffusion.     

滑石质日用细瓷的显微结构及性质

叙述了日用滑石瓷结构中的各种物相比例,主晶相类型、粒径大小及其分布状态、性质,个绍了其具有晶体小、结构细微、光学性质相似,具有同质异构体的独特显微结构,探讨了显微结构与生产工艺、各项性能的相互依赖关系。     

放电等离子烧结致密单相钛三铝碳二的反应机理

以3Ti/1.1Al/1.9C混合粉末为原料,采用放电等离子烧结(SPS)技术,利用X射线衍射仪、扫描电子显微镜和透射电子显微镜等分析方法,研究了致密单相Ti3AlC2三元层状化合物的合成机理,详细探讨了烧结温度对产物合成的影响,提出了一种SPS制备致密单相Ti3AlC2的反应机理。结果表明:利用SPS技术,在1 350℃保温10min的条件下,可以获得致密度大于99%的层状致密单相Ti3AlC2材料。最终产物中TiC的残留与原料中C含量有密切关系,适当降低原料中C含量有利于最终产物中TiC的消除。致密单相三元层状化合物Ti3AlC2的合成过程中,AlTi3和TiAl是形成TiC和Ti2AlC的主要中间相,而Ti3AlC2是由TiC与Ti2AlC反应生成的。     

A Microstructure Study of Barium Titanate Ceramics

Polishing and etching techniques suitable for the metallographic examination of polycrystalline barium titanate ceramics are described. Interpretation of the photomicrographs reveals information which may be correlated with the electromechanical properties.     

氧化铝/氮化铝陶瓷显微组织研究

氮化铝具有良好的热学、电学和机械等性能,是理想的电子封装材料和高性能陶瓷基板材料.本文研究了AlN加入量和烧结温度对Al2O3/AlN复相陶瓷相组成和显微组织的影响.结果表明该陶瓷在1400～ 1550℃烧结时,AlN被部分保留,少量氧原子进入AlN晶格,烧结生成4种铅锌矿结构新相,有利于提高复相陶瓷热导率;氮化铝含量和烧结温度的提高,有利于形成大尺寸晶粒.     

Mechanical Strength and Microstructure of Zinc Oxide Varistor Ceramics

ZnO-based varistor ceramics were sintered under various conditions to optimize their mechanical strength. For highest strength, the optimum sintering temperature was 1070°C or below. At higher maximum temperature, the strength decreased because of grain coarsening and the increasingly inhomogeneous distribution of secondary phases thereby induced. Fracture typically started from holes associated with hollow or poorly compacted sprayed granules. All series contained the same type of critical flaws, but, depending on the sintering temperature, the fracture toughness changed, which led to different strengths. At sintering temperatures above 1050°C, the density started to decrease slightly because of swelling attributed to the pressure of gas entrapped in closed pores.     

Microwave-Assisted Reaction Sintering of Bismuth Titanate-Based Ceramics

Bismuth titanate-based ceramics, pure and doped with 5 mol% WO₃, were prepared by reaction-sintering using a microwave oven. High densities, ≥96% of theoretical density were achieved with very short thermal treatments, with soaking time ranging from 5 to 15 min. Relatively small platelet-like grains were formed, and microstructure seemed not to be strongly affected by doping nor soaking time. Electrical measurements were performed and, as expected, a decrease of electrical conductivity was observed in WO₃-doped materials. The results of reaction-sintered samples, both conventional as well as microwave sintered, are compared with those of samples prepared with previously calcined powders and sintered using microwaves as well as a conventional electric furnace.