Spray-Drying Ceramic Powders

Spray-drying is a convenient process for producing a granulated, flowable powder of uniform bulk density. In this review the effect of feed slurry solids content, viscosity, binder type, and atomization technique on the granule character are discussed. Also, mechanisms of hollow granule formation and binder migration are reviewed.     

超声波场下辅助引发苯乙烯分散聚合反应的研究

通过实验设计,对超声波场下辅助引发苯乙烯(St)分散聚合反应的可行性进行了研究。结果表明:利用超声波空化作用产生的热点效应,油溶性引发剂偶氮二异丁腈(AIBN)裂解生成自由基可引发St的分散聚合反应。超声波场的工作参数(超声波输出功率、作用时间)对聚苯乙烯(PS)粒子的性能影响很大,适宜的超声波场聚合反应条件为400W×3.0h。     

超声波对润滑脂中固体添加剂分散作用的研究

研究了超声波对固体添加剂MoS2和WS2在复合磺酸钙基润滑脂中的分散作用.结果表明,超声波能在半熔体状态下的润滑脂中传播,并通过超声空化作用能较好地分散润滑脂中的固体添加剂微粒,提高润滑脂的抗磨性能.     

纳米陶瓷粉体的分散

介绍了纳米陶瓷粉体的几种主要分散机理：双电层(静电)稳定机制,空间位阻稳定机制,静电位阻稳定机制;根据不同的稳定机制可以得出相应的影响因素及控制方法。概述了目前纳米陶瓷粉体分散的研究现状,讨论了诸如表面活性剂、pH值、电解质等对分散效果的影响。     

表面活性剂在陶瓷料浆中的应用

本文综述了表面活性剂在陶瓷料浆稳定分散中的应用进展,说明了表面活性剂的分散机理,同时指出了表面活性剂在陶瓷料浆中的使用条件及发展方向。     

超声波场作用下苯乙烯的分散聚合反应机理研究

通过实验研究和理论分析,提出了超声波场作用下分散聚合的反应是分区域分阶段逐步进行的反应机理。在分散聚合反应过程中,成核机理为接枝共聚物聚结机理,稳定机理以接枝稳定机理为主,分散剂吸附为辅。聚合过程可分为5个阶段:自由基生成阶段、强化扩散阶段、均相溶液聚合阶段、聚结成核阶段和粒子增长阶段。     

Laser-Sintered Barium Titanate

Laser sintering of alkoxy-derived ultrafine BaTiO₃ powders was investigated. The temperature increases of the sample with laser irradiation were measured with a thermocouple. It was found that laser irradiation could generate enough heat to sinter ceramics. A slurry was prepared by mixing an alkoxy-derived BaTiO₃ powder, binder additives, solvent, and plasticizer. The slurry was tape cast and dried to give a green sheet. The green sheet was laser sintered and was then characterized by SEM, XRD, and density measurements. The effect of burnout before laser irradiation and the characteristic microstructure of laser-sintered BaTiO₃ are described.     

超声分散法制备表面修饰二氧化钛的研究

利用超声分散法以钛酸丁酯为主要原料,制备硬脂酸修饰二氧化钛粉体。并对产品进行了表征。通过正交实验方法获得了硬脂酸修饰的二氧化钛的最佳的制备工艺条件。结果表明:水/钛酸丁酯为0.75,pH为3,硬脂酸加入量为1.5 g、焙烧温度为500℃时硬脂酸修饰二氧化钛的油溶性最好。     

Solvothermal Synthesis and Characterization of Barium Titanate Powders

Cubic BaTiO₃ powders have been synthesized from gel powders after thermal treatment in an alcohol solution and characterized using X-ray diffractometry, transmission electron microscopy, and other techniques in detail. The borderline reaction conditions, such as the reaction temperature and time, for the synthesis of crystalline BaTiO₃ powder in different solvents are established. The single-phase BaTiO₃ powder has low agglomeration and seems to have a regular morphology. The formation of BaTiO₃ powders via solvothermal reaction is more difficult, in comparison to hydrothermal processing. The crystalline powders, which have a small particle size (∼20–60 nm) and narrow particle-size distribution, can be synthesized in methanol, ethanol, or n -propanol systems. Unlike the hydrothermal reaction, tetragonal-phase BaTiO₃ powders cannot be prepared via the solvothermal reaction, even with alkali catalysts.     

Effects of Solids Loading, pH, and Polyelectrolyte Addition on the Stabilization of Concentrated Aqueous BaTiO3 Suspensions

Colloidal stability of concentrated aqueous BaTiO₃ suspensions with ammonium salts of poly(acrylic acid) (PAA-NH₄) and poly(methacrylic acid) (PMAA-NH₄) as a function of pH and solids loading is investigated. For suspensions with solids loading less than 40 vol%, the required polyelectrolyte concentration to stabilize aqueous BaTiO₃ suspensions decreases with increasing pH, but remains relatively unchanged with increasing solids loading. As the solids loading continuously increases (e.g., >50 vol%), the required amount of polyelectrolyte increases, but exhibits a minimum at pH ∼ 9.2. The critical amount of polyelectrolyte needed to achieve colloidal stability of aqueous BaTiO₃ suspensions as a function of pH and solids loading is summarized in a three-dimensional stability map.     

超声波作用下反应体系组成对苯乙烯分散聚合反应规律的影响

研究了超声波作用下反应体系组成对苯乙烯(St)分散聚合反应规律的影响,表明超声波作用下的分散聚合反应并非一般的热引发分散聚合反应,超声波的空化作用可有效地、多途径地生成更多的自由基。掌握了聚合反应规律,可初步实现根据聚苯乙烯(PS)粒径及分布和聚合反应速率要求进行反应体系的配方设计。     

Slurry Chemistry Control to Produce Easily Redispersible Ceramic Powder Compacts

The slurry-based Three Dimensional Printing (3DP^TM) process requires the production of an easily redispersible powder bed from a well-dispersed slurry. Understanding and control of the interparticle potential in the dispersed state, as well as in the dry consolidated state, are important. The strength of the particle–particle interactions in the dry state determines the redispersion efficiency. One factor that controls the interparticle strength is the chemical stability of the ceramic powders in the dispersed state. For unstable powders, a partial dissolution and/or hydration of the powders can occur and eventually impede the redispersion by forming insoluble salt bridges at the necks of the particles. Redispersion of the powder bed can be improved substantially by weakening the strength of the particle–particle bonds. The formation of strong chemical bonds between particles should be avoided by adjusting the slurry pH to an appropriate range where the powders are chemically stable in the slurry. Replacement of the chemical bonds by soluble physical bonds, using a low-molecular-weight hydrophilic polymer, also reduces the interparticle strength and enhances redispersion.     

液相法制备BZP族磷酸盐陶瓷粉体分散性研究

用共沉淀法合成了单相的BaZr4(PO4) 6粉体 ,研究了两种不同的分散方法制得的BZP粉体的粒度分布及其烧结体的力学性能。结果表明 :与用有机高分子分散剂PEG改性处理相比较 ,采用低分子有机溶剂分散处理所制得的BZP粉体具有较窄的粒度分布 ,平均粒径 1 6 μm～ 1 8μm ,在同样的烧结条件下 ,烧结体的抗压强度也明显优于前者。另外 ,在液相反应中控制pH =7～ 1 1 ,可有效防止反过程中团聚体的形成     

超声分散法制备含锰的二氧化钛光催化剂及其表征

以钛酸四丁酯为主要原料,硫酸锰溶液为掺杂剂,采用超声分散法制备了含锰的二氧化钛光催化剂。并用X射线衍射(XRD)和透射电镜(TEM)对粉体的结构、粒径大小、物相、形貌等进行了表征。经500℃焙烧2h后,锰掺杂的二氧化钛粉末为锐钛型结构,其平均粒径为13nm,由于在XRD图谱上未发现有新相的生成,因此,可知锰离子是经过焙烧渗入到了二氧化钛的晶格中,掺杂所引起的变化主要是由于锰离子渗入二氧化钛晶格引起的。     

钛酸钡纳米粉体表面包覆方法的研究

钛酸钡纳米粉体的表面包覆不仅解决了粉体的团聚和分散问题，而且赋予粉体诸多的优异性能，因此粉体的表面包覆技术受到诸多关注并且已取得了一定的研充进展。文章主要综述了近年来钛酸钡纳米粉体表面包覆方法，以及包覆后对钛酸钡纳米粉体的表面性质乃至粉体的相结构和性质的改善作用。     

Effect of Dispersants on the Rheological Properties and Slip Casting of Concentrated Alumina Slurry

Slip casting is one of the most common forming techniques used in the fabrication of ceramics. To obtain successful casting results, one need first to fully deagglomerate the ceramic powders and get concentrated slurries with good rheological properties. In this work, the rheological properties of concentrated alumina slurries were studied as functions of solid contents and quantities of two different dispersants, i.e., sodium pyrophosphate and diammonium hydrogen citrate. It was found that these properties could be satisfactorily related to the maximum packing fractions which were determined from sedimentation experiments. Our results also indicated that an optimum deflocculation process can always lead to optimal casting and sintering results.     

Robocast Pb(Zr0.95Ti0.05)O3 Ceramic Monoliths and Composites

Robocasting, which is a computer-controlled slurry-deposition technique, was used to fabricate ceramic monoliths and composites of chemically prepared Pb(Zr_0.95Ti_0.05)O₃ ceramics. The densities and electrical properties of the robocast samples were equivalent to those obtained for cold isostatically pressed parts formed under a pressure of 200 MPa. Three-layer robocast composites that consisted of alternating layers of different sintered densities—93.9%/96.1%/93.9%—were fabricated using different levels of organic pore-former additions. Modification from a single-material to a multiple-material deposition robocaster was essential for the fabrication of composites that could withstand repeated cycles of saturated polarization switching under fields of 30 kV/cm. Furthermore, these composites withstood a poled ferroelectric-to-antiferroelectric phase transformation that was induced by a hydrostatic pressure of 500 MPa, during which strain differences on the order of 0.8% occurred between the composite elements.     

Microstructural Investigations of Barium Titanate-Based Material for Base Metal Electrode Ceramic Multilayer Capacitor

The microstructures of BME-X7R ceramics have been investigated by imaging and analytical TEM. By varying the sintering conditions (pressing, sintering temperature and atmosphere), the microstructure changes drastically, and dislocation loops can be observed. These defects most probably are caused by an ordering of oxygen vacancies in the lattice, and the density appears to be correlated to the oxygen partial pressure applied during the reoxidation step. For pressed and unpressed ceramic foils, a model for different sintering behaviors according to liquid-phase assistance is given that is based on a kinetically determined microstructure rather than thermodynamic equilibrium.     

基于空气耦合超声波的非金属陶瓷材料检测研究

针对非金属陶瓷材料的空气耦合超声波检测问题,建立空气耦合超声波经空气入射非金属陶瓷材料的数学模型及非金属陶瓷材料的空气耦合超声波检测有限元模型,通过matlab软件和ANSYS有限元软件联合仿真得到了非金属陶瓷材料的空气耦合超声波检测的频散曲线和各节点的接收信号,研究了空气耦合超声波在非金属陶瓷材料中的传播特性.结果表明,当频厚积小于2 MHz· mm,空气耦合超声波在非金属陶瓷材料氮化硅材料中存在A0,S0,SH0三种模态;当频厚积大于2 MHz· mm时,材料中存在较多的模态.随着声波传播距离越远,所接收到的A0模态和S0模态的信号幅值越小,且A0模态较S0模态幅值大,因此宜激发A0模态的空气耦合超声波检测和评价非金属陶瓷材料.     

超细钛酸锶陶瓷粉体的湿化学制备技术

随着钛酸锶电子陶瓷应用日益广泛,对其性能要求不断提高,所以制备超细钛酸锶粉体的湿化学制备技术越来越受到重视,制备超细钛酸锶粉体的湿化学方法主要包括:沉淀法,金属醇盐水解法,溶胶-凝胶法,微乳液法,水热法,燃烧合成法.本文简要阐述这6种主要湿化学合成工艺的研究进展,介绍了它们的优缺点,对各种方法进行了比较.