近零膨胀多孔SiC/LAS陶瓷材料的制备与性能

采用分步加热法成功制备了纯度较高的各向同性负热膨胀为-6.2×10-6 K-1的β-锂霞石材料LiAlSiO4。将SiC、Li-AlSiO4与玻璃粉末按一定比例混合,在950℃烧结1 h制备了近零热膨胀系数的多孔SiC/LAS陶瓷材料。研究结果表明,LiAl-SiO4在950℃烧结过程中与玻璃粉反应生成一部分近零膨胀锂辉石材料LiAlSi2 O6,通过改变玻璃结合剂的体积分数,可以调控SiC/LAS陶瓷材料的热气孔率及材料的杨氏模量。当玻璃粉末的体积分数为25%时,多孔材料的气孔率为～24%,热膨胀系数为0.38×10-6 K-1。杨氏模量达到～59 GPa,接近理论计算值。     

SiC超细粉体分散性的研究进展

SiC超细粉体的分散是其应用的关键技术之一.综述了国内外近年来对SiC超细粉体分散方法的研究,并针对其研究现状提出了几个问题,以期对其分散和应用有所助益.     

THE MICROSTRUCTURE OF SOME LOW DIMENSIONAL MATERIALS(1)——Ultrafine Carbonyl Iron Powders and Laser-made SiCB Powders

利用电子能量损失谱、微衍射及高分辨电子显微术等方法观察和分析了直径为5—30nm的超细羰基铁粉和直径为30—80nm 的SiCB 超细粉。超细铁粉主要由中心核α-Fe 和外壳Fe_3O_4组成,其中部分超细粉完全被氧化,形成空心的γ-Fe_2O_3。激光制得的SiCB 超细粉由Si,SiC,SiB_6多相复合微粒组成,并有大量孪晶形成。     

一些低维材料的微观结构(一)——超细羰基铁粉和SiCB激光制粉

利用电子能量损失谱、微衍射及高分辨电子显微术等方法观察和分析了直径为5—30nm的超细羰基铁粉和直径为30—80nm 的 SiCB 超细粉。超细铁粉主要由中心核α-Fe 和外壳 Fe_3O_4组成,其中部分超细粉完全被氧化,形成空心的γ-Fe_2O_3。激光制得的 SiCB 超细粉由 Si,SiC,SiB_6多相复合微粒组成,并有大量孪晶形成。     

非晶态和纳米晶碳化硅薄膜的制备及力学性能

以SiC超细粉为原料、利用热等离子体PVD(TPPVD)技术快速制备出了优质非晶态和纳米晶SiC薄膜.用扫描电子显微镜、高分辨透射电子显微镜、X射线衍射和X射线光电子谱、红外分光谱对薄膜的微结构进行了观察和分析.用纳牛力学探针测量了薄膜的力学性能.研究结果表明,只有当基板温度低于600℃、粉末供给速度不超过20mg/min时可沉积非晶态SiC薄膜,最大沉积速度达到25nm/s;当基板温度在600℃～1000℃时沉积的β-SiC薄膜是晶粒大小为3 nm～5 nm的纳米晶薄膜,最大沉积速度达到230 nm/s.非晶态和纳米晶SiC薄膜的硬度分别达到33.8 GPa和38.6 GPa.     

用CO2激光法合成SiC超细粉

当前,人们注视于SiC、Ni_3N_4等陶瓷超细粉作为烧结原料。合成这些陶瓷超细粉比较新的方法之一是使用CO_2激光法。有关使用CO_2激光合成SiC、Si_3N_4等陶瓷超细粉的报导,目前有好几篇。但是,大部分的试制都是使用SiH_4气体作原料,并且在减压的条件     

喷雾冷冻干燥制备复合氧化物超细粉的研究

喷雾冷冻干燥(FD 法)制备的超细粉对于功能无机材料的合成具有重要意义。本文以制备陶瓷超导复合氧化物 BaPb_(1-x)Bi_xO_(?)超细粉为例,讨论了各种不同工艺条件对 FD 法制备过程的影响,所制备的超细粉在500℃时就形成单相复合氧化物,粒径<500(?),比表面可达55m~2/g。用同样条件制备的 YBa_2Cu_3O_(7-δ)复合氧化物陶瓷超导材料,具有 T_c(ρ=0)=90.6K 的高温超导电性。     

超细SiC片晶的制备方法

超细SiC片晶由于其高强度、高弹性模量和高导热系数已成为替代价值昂贵、制备技术复杂的SiC晶须的理想的增韧材料SiC片晶的制备方法有化学制备法和机械制备法。本文中详细介绍了用机械方法制备SiC片晶的设备与工艺过程,阐述了各种制备方法的工作原理及其优缺点,通过对各种制备方法的比较得出采用气流磨与分级机结合工艺是目前制备系列超细SiC片晶有效的和最经济的生产工艺。     

超声雾化法制备超细粉体的研究进展

随着对超细粉体性能的要求越来越高,超细粉体的制备问题引起了人们的关注。传统的方法制备超细粉体无法控制粉体的性能,而超声雾化在超细粉体粒径、粒径分布及形貌调控等方面的独特优势,逐渐成为超细粉体制备的前沿技术。为此,对超声雾化制备超细粉体的工作原理进行了综述,重点阐述了超声雾化技术、工艺参数对粉体粒径、形貌的调控机制,分析了目前超声雾化制备超细粉体存在的问题,并对该领域的未来应用和挑战进行了展望。     

SiC/C薄膜的制备及其力学性能

以SiC 超细粉为原料、采用热等离子体物理气相沉积( TPPVD) 技术快速制备出了高质量SiC/ C 薄膜, 最大沉积速度达到225 nm/ s, 高于常规物理气相沉积( PVD) 和化学气相沉积(CVD) 法两个数量级。用扫描电子显微镜、高分辨透射电子显微镜和X 射线光电子谱对薄膜的形貌和微结构进行了观察和分析, 并用纳牛力学探针测定了薄膜的力学性能。研究结果表明, 向等离子体中导入CH₄, SiC/ C 薄膜沉积速度增大, 薄膜中C 含量增加, 薄膜断面呈现柱状结构。薄膜硬度和弹性模量随薄膜中C 含量增加而降低, 在接触深度为40 nm 时由纳牛力学探针测得沉积薄膜的最大硬度达到38 GPa。     

Production of ultra fine SiC powder from SiC bulk by arc-plasma irradiation under different atmospheres and its application to photocatalysts

The production of ultrafine SiC powder from a SiC bulk (containing 10wt% Si) was examined by the arc-plasma method under different atmospheres such as argon, argon and hydrogen, argon and helium, and argon and nitrogen. No melting of SiC bulk occurred during arcplasma irradiation, and even pure argon gas was effective for the production of the ultrafine powder. The SiC powder produced has the structure of -SiC, compared to -structure of the bulk SiC. The average particle size of the SiC powder produced decreased to one-half of the value when hydrogen or helium was added to argon. Smaller particles of SiC are formed by the arc-plasma gases with a large thermal conductivity. The present results confirm that sublimation is a major process in the production of ultrafine SiC powder. The SiC powder is found to be effective as a photocatalyst for the decomposition of water.     

Microwave hybrid synthesis of silicon carbide nanopowders

Nanosized silicon carbide powders were synthesised from a mixture of silica gel and carbon through both the conventional and microwave heating methods. Reaction kinetics of SiC formation were found to exhibit notable differences for the samples heated in microwave field and furnace. In the conventional method SiC nanopowders can be synthesised after 105 min heating at 1500 °C in a coke-bed using an electrical tube furnace. Electron microscopy studies of these powders showed the existence of equiaxed SiC nanopowders with an average particle size of 8.2 nm. In the microwave heating process, SiC powders formed after 60 min; the powder consisted of a mixture of SiC nanopowders (with two average particle sizes of 13.6 and 58.2 nm) and particles in the shape of long strands (with an average diameter of 330 nm).     

超微粉末的研究

作者采用溶蒸发凝聚法制备了金属基超微粉末,采用化学反应法制备了氧化物超微粉主研究了超微粉末的制备工艺。了一种新型的超微偻末收集器,研究了超微合金 末中合金相的生成规律和机理,解决了超微粉末制备过程中一系列难题,实现了批量制备超微粉末。     

Microstructure and properties of alumina-SiC nanocomposites prepared from ultrafine powders

Alumina-Silicon Carbide nanocomposites were produced and studied under different aspects: characteristics of the starting materials, processing, microstructure and mechanical properties. The raw materials were two kinds of fine SiC powders (30 and 45 nm) and two Al₂O₃ powders (60 and 140 nm). Different compositions (amounts of SiC in the range 0.5–5 vol%) were performed and the characteristics of the resulting materials compared. The oxygen enrichment in SiC nanopowder due to specific powder treatments was controlled, in order to optimize powder processing routes. Densification tests of Al₂O₃-SiC powder mixtures were performed both by pressureless sintering and hot pressing route. The addition of SiC reduced the densification rate and favoured a refinement of the matrix. Improvement of mechanical properties over monolithic alumina was obtained in composites with the 45 nm SiC. The study pointed out that the critical factor for the success of these materials is the choice of the raw SiC powders in terms of grain size and state of agglomeration. The addition of this ultrafine SiC strongly affected the microstructural evolution, even at low volumetric fractions. The results do not substantiate any remarkable effect by dispersoids in the tested nanosize range.     

Sintering of ultrafine SiC powders prepared by plasma CVD

Ultrafine SiC powders with a nanometre particle size were synthesized by r.f. plasma chemical vapour deposition (CVD) using a chemical system of SiH₄−C₂H₄−Ar. The powder was also ultrapure with a grade of 99.999% purity. The product was polytype 3C−SiC and black in colour, in spite of its high purity, because of its ultrafine size. Silicon carbide is a difficult ceramic to sinter; it is possible to sinter it to full density with the aid of sintering additives. Ultrafine and ultrapure SiC powders were hot-pressed without sintering additives in the present study, in order to investigate the sintering behaviour. The CVD powders proved sinterable to 88% theoretical density without sintering additives. The present experiments revealed that powder treatment before firing was a key technology when using ultrafine powders as starting materials in the sintering process. The sintering behaviour of the powder was characterized by a large shrinkage. Phase transformation was negligible after hot pressing at 2200°C for 30 min.     

A Method to Adjust Dielectric Property of SiC Powder in the GHz Range

The SiC powders by Al or N doping have been synthesized by combustion synthesis, using Al powder and NH4Cl powder as the dopants and polytetra?uoroethylene as the chemical activator. Characterization by X-ray diffraction, Raman spectrometer, scanning electron microscopy and energy dispersive spectrometer demonstrates the formation of Al doped SiC, N doped SiC and the Al and N co-doped SiC solid solution powders, respectively. The electric permittivities of prepared powders have been determined in the frequency range of 8.2-12.4 GHz. It indicates that the electric permittivities of the prepared SiC powders have been improved by the pure Al or N doping and decrease by the Al and N co-doping. The paper presents a method to adjust dielectric property of SiC powders in the GHz range.     

超细镍粉的制备及还原生长机理研究

以联氨为还原剂,在硫酸镍水溶液中控制液相还原反应条件制备了超细镍粉,并讨论了超细镍粉的还原生长机理.通过实验分析了工艺参数对还原反应的影响,采用X射线衍射(XRD),扫描电镜(SEM),比表面积测定等分析手段对超细镍粉进行表征,结果表明:超细镍粉的形核和生长独立进行;温度、Ni2+浓度和pH值调控着溶液中镍离子的释放并...     

流化床气流磨粉碎制备超细SiC片晶的实验研究

超细SiC片晶由于其高强度、高弹性模量和导热系数已成为替代价值昂贵、制备技术复杂SiC晶须的理想的增韧材料。本文中通过对流化床气流磨粉碎机理,以及粉碎腔内工质压强与喷嘴个数对SiC颗粒形貌影响的研究,得出工质压强、喷嘴个数等参数对粉碎的颗粒形貌有很大的影响的结论,其中粉碎腔采用高的工质压强以增加粉碎强度。采用两喷嘴以增加颗粒互相撞击的几率是制备片状SiC粉的有效方法;采用流化床式气流磨加多级涡轮分级机的粉碎系统可以制备产品质量较好的多级别超细SiC片晶微粉。     

A coprecipitation technique to prepare ZnNb2O6 powders

A simple coprecipitation technique was successfully applied for the preparation of pure ultrafine single phase, ZnNb₂O₆ (ZN). Ammonium hydroxide was used to precipitate Zn²⁺ and Nb⁵⁺ cations as hydroxides simultaneously. This precursor on heating at 750°, produced ZN powders. For comparison, ZN powders were also prepared by the traditional solid state method. The phase contents and lattice parameters were studied by the powder X-ray diffraction (XRD). Particle size and morphology were studied by transmission electron spectroscopy (TEM).     

Effect of SiC Nanoparticles Content and Mg Addition on the Characteristics of Al/SiC Composite Powders Produced via In Situ Powder Metallurgy Method

In the present study, the effect of the nanosized SiC particles loading and Mg addition on the characteristics of Al/SiC composite powders produced via a relatively new method called “in situ powder metallurgy” (IPM) was investigated. Specified amounts of SiC particles (within a size range of 250 to 600 µm) together with SiC nanoparticles (average size of 60 nm) were preheated and added to aluminum melt. This mixture was stirred via an impeller at a certain temperature for a predetermined time. The liquid droplets created by this process were then subsequently cooled in air and screened through 250 µm sieve to separate micron-sized SiC particles from solidified aluminium powder particles containing nanosized SiC particles. Results of SEM and TEM studies together with microhardness measurements revealed that the commercially pure (CP) Al could not embed as-received SiC particles. However, the nanosized particles were distributed uniformly in the Al-1 wt% Mg powders. The process yield and microhardness of the Al-1Mg composite powders increased with increasing the contributed amount of nanosized SiC particles.