立方氮化硅粉体的超高压烧结特性

以冲击波合成的立方氮化硅(γ-Si3N4)粉体为原料,添加Y2O3-Al2O3-La2O3系烧结助剂,进行了超高压烧结,研究了在不同烧结温度与压力下,烧结样品的相对密度、力学性能、物相变化及显微结构.经5.4～5.7 GPa和1670～1770 K,保温保压15 min超高压烧结后,烧结制备的氮化硅陶瓷主要由长柱状晶粒组成,显微结构均匀,y-Si3N4已完全转化为β-si3N4.烧结样品的最高相对密度与Vickers硬度分别为99.16%,23.42GPa.     

微波烧结制备陶瓷材料的研究进展

微波烧结是一种新型的利用微波加热来对材料进行烧结的方法,它是一种快速制备高质量新型材料和使传统材料具有新的性能的技术手段。简要介绍了微波烧结的发展史、基本原理、制备陶瓷材料的研究进展、微波烧结技术存在的一些问题,并对微波烧结技术的前景进行了展望。     

陶瓷材料微波烧结工艺与机理研究现状

微波烧结作为一种新型材料烧结技术,在陶瓷材料制备领域受到越来越多的关注.与传统烧结技术相比,微波烧结具有快速高效、节能环保以及改善材料微观结构,提高材料性能的优点.本文介绍了传统烧结和微波烧结的特点,对比了传统烧结和微波烧结陶瓷材料的烧结工艺和力学性能;列举了运用微波烧结法制备的典型结构陶瓷的烧结工艺及其力学性能;全面综述了陶瓷材料微波烧结机理;最后提出了微波烧结在未来发展中亟待解决的问题.     

微波烧结陶瓷结合剂金刚石砂轮研究

为了提高陶瓷结合剂金刚石砂轮的性能,采用微波烧结技术,通过一系列试验,分析了陶瓷结合剂金刚石砂轮的微波烧结温度、陶瓷结合剂含量和金刚石磨料粒度对其性能的影响。结果表明:微波烧结温度是影响陶瓷结合剂金刚石砂轮性能的最主要因素,远超其余二者;陶瓷结合剂金刚石砂轮试样的洛氏硬度和抗弯强度在740 ℃时达到极大值且气孔率较小,此时洛氏硬度为66 HRB,抗弯强度为76.5 MPa,气孔率为17.8%;由微观组织观察可知陶瓷结合剂金刚石砂轮在740 ℃时可以实现陶瓷结合剂对金刚石磨料的均匀包裹,并且气孔较少。     

烧结助剂对低温制备碳化硅多孔陶瓷性能的影响

分别采用十二烷基苯磺酸钠、氢氧化钠以及NaA分子筛残渣为烧结助剂,碳粉为造孔剂,干压法成型,在1150℃空气气氛下烧结制备碳化硅多孔陶瓷支撑体。考察了助剂添加量对微结构、平均孔径、孔隙率以及抗热震性等方面的影响;分析了添加助剂的低温烧成机理。研究结果表明：三种添加剂均有助于提高支撑体的气体渗透性、抗弯强度和耐热震性;添加NaA分子筛残渣助烧结剂获得的碳化硅多孔陶瓷各项性能最佳,气体渗透率为1300 m³/(m²·h·kPa),强度可达27 MPa,且抗热震性能良好。     

ZrO2陶瓷的微波烧结制备及其性能

以微波热解制备的氧化锆粉体为原料、氧化钇为烧结助剂,采用微波烧结方式制备氧化锆陶瓷,研究了不同氧化钇含量对氧化锆陶瓷的微波烧结行为、物相组成、显微结构及致密化的影响。结果表明:在微波烧结过程中,随着Y_2O_3含量的增加,ZrO_2陶瓷的物相从m-ZrO_2逐渐转变为m-ZrO_2与t-ZrO_2(c-ZrO_2)并存,且ZrO_2陶瓷的晶粒随着烧结助剂含量的增加而逐渐变小,样品致密度下降。当烧结温度为1 450℃时,微波烧结获得的未添加烧结助剂的样品致密度达到99%,远远高于传统电阻烧结所获得样品的致密度。     

一种高烧结活性氧化铝粉体的制备方法

本发明提供了一种制备高烧结活性氧化铝粉体的方法。其特征在于以含铝无机盐为主要原料，碳酸氢铵为沉淀剂，生成NH4Al(OH)2CO3，更确切地说，铝无机盐为硝酸铝，氯化铝和硫酸铝铵中一种，含铝的无机盐浓度为0．1－1mol/L，碳酸氢铵浓度为1-4mol/L，反应温度为5－50℃，沉淀陈化时间2－24h，沉淀物经去离子水洗涤至无在1100－1200摄氏度煅烧，使之转变为α－Al2O3，晶粒尺寸小于400nm的亚微米及纳米级氧化铝粉体，该方法制取的氧化铝粉体具有硬团聚少和烧结活性高的特点，非常适合于高档氧化铝陶瓷材料的制备。     

微波烧结制备碳化硅粉体的研究

以乙炔炭黑和硅粉为原料,采用微波烧结技术合成制备了粒度不同的碳化硅粉体.研究了反应温度和保温时间对碳化硅粉体产率和粒度的影响.结果表明:在900℃反应30 min,所得产物的主要物相为β-SiC和仍残余少量金属Si.随着反应温度的升高,产物中SiC的含量不断增加,残余金属Si的含量则明显下降.当反应温度升高至1100℃以上时,则得到单相的β-SiC.在1200℃下反应5min,产物中主要物相为SiC,存在着少量未反应的金属Si,当反应时间延长到15 min时,即得到单相的β-SiC.     

微波烧结技术及其在制备催化剂中的应用

介绍了微波烧结技术的原理和特点,通过采用微波烧结技术制备了钙钛矿型复合氧化物载体及相应的Pd负载钙钛矿型催化剂。结果表明,相对于常规载体和催化剂的制备方法而言,微波烧结法操作简便、材料损耗少、效率高,可以节约大量的时间和能耗,同时制备的载体和催化剂具有较大的比表面积、较均匀的活性组分分布、相对较高的催化活性。     

不同烧结温度制备的双相磷酸钙生物陶瓷及其力学性能研究

以煅烧缺钙磷灰石制备的双相磷酸钙(BCP)粉体为原料,采用热压烧结的方法制备了一种可用于骨替代、力学性能优良的生物陶瓷材料.研究了烧结温度对BCP陶瓷力学性能、物相组成和微观形貌的影响.当烧结温度为1100℃和1150℃时,BCP陶瓷的物相组成为HA和β-TCP,断裂方式以穿晶断裂为主;当烧结温度为1200℃时,BCP陶瓷的物相组成为HA和α-TCP,断裂方式为穿晶和沿晶混合断裂模式.当烧结温度为1150℃时,BCP陶瓷的弯曲强度和断裂韧性最高,分别为98 MPa和0.99 MPa·m1/2.     

Sintering of the Mechanochemically Activated Powders of Hexagonal Boron Nitride

Pressureless sintering of hexagonal boron nitride (BN) was performed using a powder activated by mechano-chemical treatments. Physical properties of the sintered BN bodies depend on the type of starting powder and the conditions of the treatments. The BN body, which was obtained at 2000°C using an appropriate activated powder, was 99 wt% pure and was excellent in mechanical and physical properties, in spite of its low density (1.64 g/cm³).     

Sintering of Spherical Glass Powder under a Uniaxial Stress

The sintering of spherical borosilicate glass powder (particle size 5 to 10 μm) under a uniaxial stress was studied at 800°C. The experiments allowed the measurement of the kinetics of densification and creep, the viscosities for creep and bulk deformation, and the sintering stress which was found to increase with density. The data show excellent qualitative agreement with Scherer's theory of viscous sintering. In addition, the quantitative comparison between theory and experiment shows good agreement; the measured viscosity of the bulk glass was ∽1×10⁹ P (∽1×10⁸ Pa·s) compared to ∽3×10⁹ P (∽3 Pa·s) obtained by fitting the data with Scherer's theory.     

Hot compaction of polyoxymethylene,part 1: Processing and mechanical evaluation

The hot‐compaction of polyoxymethylene powders in the solid state, otherwise pressure‐assisted sintering, is studied as an alternative way to the melt‐compression or injection molding processes. A native powder issued from suspension polymerization has been used, together with powders obtained from grinding of melt‐extruded pellets. The experimental conditions were optimized with regard to temperature, pressure, and time. Temperature is the most sensitive parameter of the process. Sintering at temperature close to the onset of the melting range turned out to be necessary for an efficient welding of the powder particles, as judged from mechanical properties. Despite a strong loss of ductility, the sintered samples have been easily machined out into strips for mechanical testing. A significant increase in crystallinity is observed for the sintered samples, as compared with the compression‐molded ones, accompanied with a nearly twofold increase of the Young's modulus. Scanning electron microscopy revealed that rupture of the sintered samples involves both inter‐ and intra‐granular fracture. Welding of the crystallites via molecular diffusion at the particle interface is suggested to be the mechanism of sintering. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1274–1284, 2006     

烧结法制微晶玻璃的机理研究

微晶玻璃是近些年来在材料科学上的一项重大发现,在国防尖端技术和建筑业等多种领域起到了举足轻重的作用。微晶玻璃更具有高机械强度、绝缘性和良好的耐酸耐碱性等优点,本文通过烧结法就微晶玻璃的材料特征、微观结构和性能、降低烧结温度的方法等做了详细的介绍。     

原料预合金化对微波无压烧结金刚石工具性能的影响

以Fe₆₀Cu₄₀预合金粉和单质粉为基础原料,利用微波无压烧结在850 ℃制备了FeCu/WC基金刚石复合材料刀头。通过探讨物料在微波场中的升温特性设计了微波无压烧结制度。采用扫描电子显微镜（SEM）、万能试验机、激光拉曼光谱等表征手段,对比研究了预合金粉和单质粉微波烧结样品的组织形貌等微结构信息,并获得了样品的硬度、致密度、横向断裂强度等力学性能。结果表明,与常规烧结方法相比,微波强化烧结可将温度降低至900 ℃以下,金刚石颗粒没有出现石墨化转变;FeCu/WC基配方在850 ℃微波烧结样品的洛氏硬度、相对致密度、横向断裂强度分别达到102.7 HRB、98.5%、1 035 MPa。并对微波烧结的强化机制和原料预合金化对于基体的增强机理进行了初步探讨,微波无压烧结对于预合金粉体金刚石刀头的制备表现出良好的应用前景。     

Mechanical and physical characterization of polyoxymethylene processed by high‐velocity compaction

Conventional polymer processes, such as injection and extrusion, require the melting of the polymer. High‐velocity compaction (HVC) allows the processing of polymer powders via sintering without the need of a melting stage. It opens up a new horizon for polymers that have processing issues linked to the melting stage. Because of chemical degradation above the melting point and significant shrinkage, the injection of semicrystalline polymer polyoxymethylene (POM) is often problematic. Nascent, highly crystalline POM powder has been successfully processed by HVC, and this process appears to be an interesting alternative to injection for certain applications. POM processed by HVC has a remarkably high stiffness but is brittle. A microstructural investigation, involving differential scanning calorimetry experiments and scanning electron microscopy, has been conducted to explain these unusual mechanical properties. It appears that in POM processed by HVC, the stiffness is due to particularly high crystallinity, and brittleness is intrinsic to nascent POM powder. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

An oscillatory pressure sintering of zirconia powder: Densification trajectories and mechanical properties

The densification trajectories and mechanical properties of zirconia ceramics obtained by oscillatory pressure sintering (OPS) process were investigated, during the sintering process an oscillatory pressure was applied at three stages. Current results indicated that at intermediate stage the oscillatory pressure revealed a favorable improvement of mechanical properties compared with conventional hot pressing (HP) and pressureless sintering (PS) procedures, while the enhancement was not obvious at initial stage. When the oscillatory pressure was applied at final stage, the OPS specimens exhibited the highest bending strength and hardness of 1455 ± 99MPa and 16.6 ± 0.31GPa compared with the PS and HP specimens. Considering the high elastic modulus and Moiré patterns observed in the OPS specimen, the oscillatory pressure applied at intermediate and final stages was detected to facilitate the sliding of grain boundary, plastic deformation of monolithic grains, the removal of pores and the strengthening of atomic bonds.     

Electrical transport and thermoelectric properties of Ca0.8Y0.2−xDyxMnO3−δ (0 ≤ x ≤ 0.2)

Ca_0.8Y_0.2?xDy_xMnO_3?δ (0≤x≤0.2) samples were fabricated by the solid‐state reaction method, and their thermoelectric properties were studied from 500°C to 800°C. Upon the substitution of Dy³⁺ for Y³⁺ in the Ca_0.8Y_0.2?xDy_xMnO_3?δ, the electrical and thermal conductivities gradually decreased with increasing Dy³⁺ concentration, whereas the absolute value of the Seebeck coefficient significantly increased. The Ca_0.8Dy_0.2MnO_3?δ showed the largest value of dimensionless figure of merit (0.180) at 800°C as a result of the combination of the largest absolute value of the Seebeck coefficient and the lowest thermal conductivity. We believe that the Ca_0.8Dy_0.2MnO_3?δ is a promising thermoelectric material at high temperatures.     

Development of WC–ZrO2 Nanocomposites by Spark Plasma Sintering

In the present work, we report the processing of ultrahard tungsten carbide (WC) nanocomposites with 6 wt% zirconia additions. The densification is conducted by the spark plasma sintering (SPS) technique in a vacuum. Fully dense materials are obtained after SPS at 1300°C for 5 min. The sinterability and mechanical properties of the WC–6 wt% ZrO₂ materials are compared with the conventional WC–6 wt% Co materials. Because of the high heating rate, lower sintering temperature, and short holding time involved in SPS, extremely fine zirconia particles (∼100 nm) and submicrometer WC grains are retained in the WC–ZrO₂ nanostructured composites. Independent of the processing route (SPS or pressureless sintering in a vacuum), superior hardness (21–24 GPa) is obtained with the newly developed WC–ZrO₂ materials compared with that of the WC–Co materials (15–17 GPa). This extremely high hardness of the novel WC–ZrO₂ composites is expected to lead to significantly higher abrasive-wear resistance.