Crystallization of Fine, Chemically Prepared Lead Lanthanum Zirconate Titanate Powders at Low Temperature

Fine, homogeneous lead lanthanum zirconate titanate (PLZT) powder prepared by the hydrolysis of an aqueous nitrate solution with ammonia gas exhibits high reactivity when calcined. The minimum temperature for crystal formation in PLZT is 400°C. The kinetics of crystallization between 400° and 600°C are studied isothermally by XRD. The isothermal crystallization process is best fitted to a first-order equation derived for a random, nucleation-controlled system on a large number of small particles with an activation energy of 297 kJ/mol. Characterization of the powder by XRD line-broadening and BET surface-area examination in the range 400° to 500°C shows a microstructure consisting of ∼20-nm subunits agglomerated into ∼60-nm particles. Each subunit evidently generates a single nucleus, which grows within that subunit.     

Stabilized Barium Titanate Ceramics for Capacitor Dielectrics

The effects of additions of La₂O₃ and La₂O₃-3TiO₂ on the electronic properties of barium titanate have been investigated. It has been found that small additions of these components markedly increase the lifetime of this material subjected to dc fields of 50 v per mil at 200°C.     

Improved Compaction in Multilayer Capacitor Fabrication

The most common defects found in multi-layer ceramic capacitors are derived from residual porosity formed when solvents and binders are released from a ceramic green body. Without a well-controlled compaction technique, defects between sheets in the stacked body are often present, leading to lamination problems. This paper suggests alternative approaches, using compaction applied before and/or after the process of binder burnout with the intention of reducing the number of stacking-generated defects and the volume of voids formed after binder burn-out. Barium titanate tapes and stacked multilayer electroded discs have been investigated and characterised by microstructural examination and density measurement. The resulting properties are described, and the behaviour of the multi-layers discussed in terms of the microstructure and processing procedures. It is shown that the porosity content of sintered samples compacted at 300 MPa is approximately half that of samples compacted at 30 MPa when both are sintered at 1300°C for 2 h. A further improvement of densification can be achieved by a postcompaction treatment after binder burn out.     

Zino Oxide Varistors Made from Powders Prepared by Amine Processing

A powder preparation process suitable for varistor production was developed. The mixed acidic solution containing varistor components was added to the diethylamine solution to coprecipitate all components. The resulting mixtures were washed, dried, and calcined to produce active and uniform composition powders. Large nonlinearity coefficient (α∼ 50) were achieved in varistors fabricated from these powders by sintering in the entire range 1100° to 1250°C. Large breakdown fields were also achieved with decreasing sintering temperature. The breakdown voltage per grain boundary of these varistors was approximately 5.2 V.     

Processing and Microstructure of Mullite-Zirconia Composites Prepared from Sol-Gel Powders

A high-purity stoichiometric mullite precursor was obtained by hydrolysis of the alkoxides Al(OC₃H₇)₃ and Si(OC₂H₂)₄. Fully sintered mullite ceramics can be prepared from sol-gel powders by sintering them at 1600°C for 4 h in air with the addition of 15 to 20 Vol% ZrO₂ or 1 to 3 mol% Y₂O₃ or both. Introduction of 1 to 3 mol% Y₂O₃ aids the retention of tetragonal ZrO₂; the volume fraction of t -ZrO₂ retained increases with increasing Y₂O₃ content. The maximum t -ZrO₂ retained reaches 34% in a matrix of synthetic mullite with 3 mol% Y₂O₃, but most of this t -ZrO₂ does not undergo stress-induced transformation during grinding.     

High-Temperature Behavior of Chemically Treated Silicon Nitride Powders

The mechanical properties of chemically treated, then sintered, Si₃N₄ was studied. Raw materials consisted of two types of Si₃N₄ produced by the nitridation of silicon. The chemical treatment involved leaching in different acids (HCl, HNO₃, HF, and combinations thereof). The powders were sintered by hot isostatic pressing with 2.5% yttria, and the high-temperature properties of the resultant materials were evaluated by the stepped-temperature stress rupture (STSR) method (24-h hold time at 150-MPa stress at 1000°, 1100°, 1200°, 1300°, and 1400°C). A significant decrease in high-temperature performance was observed for acidleached powders, especially when HF-containing acids were used.     

Excellent Polyimide Dielectrics Containing Conjugated ACAT for High-Temperature Polymer Film Capacitor

In order to meet the requirements of polymer dielectric materials for high thermal stability and excellent dielectric properties in the application of high-temperature film capacitors, a series of polyimide (PI) films are fabricated by introducing a self-synthesized aniline trimer (ACAT) with a conjugated structure in this work. Since the conjugated ACAT in the main chains of PI improves the electron polarization and carrier mobility of the PI molecular chains, the dielectric constant of the ACAT-PI films is greatly enhanced (4.4–7.4). Meanwhile, the dissipation factor does not increase apparently (0.002–0.013). The dielectric properties are stable even when the temperature is up to 200 °C, the thermal degradation temperature is as high as 450 °C, and the mechanical properties are also excellent (70–105 MPa). Among all the films, the PI film with 5 mol% ACAT exhibits the maximal energy density of 3.6 J cm⁻³ under the field of 426 kV mm⁻¹, the high tensile strength (90 MPa) and the excellent thermal stability (T_d5 = 515 °C). The work paves the way to prepare high-temperature polymer dielectric film materials with high energy storage density.     

化学法制备纳米氧化铁颜料研究进展

综述了纳米氧化铁化学制备方法的研究进展，对胶体化学法、水热法、固相法、沉淀法和水解法等化学制备方法进行了探讨。通过分析比较，对未来纳米氧化铁的化学制备提出了几点建议。     

Temperature-Stable Dielectrics Based on Chemically Inhomogeneous BaTiO3

The dielectric properties and chemical homogeneity of BaTiO₃ ceramics sintered with additions of the pseudophase "CdBi₂Nb₂O₉" were investigated using SEM, TEM, STEM, and EDX. In materials showing the "X7R" dielectric temperature characteristic, the microstructure exhibits the grain core-grain shell structure. The perovskite material in the shell shows a temperature characteristic determined by mixed crystals of BaTiO₃ with the complex perovskites Ba(Bi_1/2Nb_1/2)O₃ and Ba(Cd_1/3Nb_2/3)O₃ having an approximate Curie point of -80°C. The chemical inhomogeneity emerges during a process of reactive liquid-phase sintering. Application of too-high sintering temperatures leads to uniform distributions of the additives via solid-state diffusion and to the loss of the X7R characteristic.     

High-Performance Reversed-Phase Flash Chromatography Purification of Peptides and Chemically Modified Insulins

Preparative reversed-phase HPLC is the established method for the purification of peptides, but has significant limitations. We systematically investigated the use of high-performance reversed-phase flash chromatography (HPFC) to rapidly purify laboratory-scale quantities of crude, synthetic peptides and chemically modified insulins. We demonstrated these methods for a diverse set of peptides, including short, medium, and long peptides. Depending on the purity profile of the peptide, HPFC can be used either as the sole purification method, or as a pre-purification method prior to final HPLC purification. Furthermore, HPFC is suitable for the purification of peptides that are not fully in solution. We provide guidelines for the HPFC of synthetic peptides and small proteins, including the choice of columns, eluents, and gradients. We believe that HPFC is a valuable alternative to HPLC purification of peptides and small proteins.     

多层陶瓷电容器用纳米复合粉添加剂的制备研究

采用溶胶-凝胶法及超临界干燥技术按多层陶瓷电容器磁粉添加剂配方比例制备Bi、Sr、Ce、Mn和Si的化合物纳米复合粉.以DTA、SEM、XRD等检测方法对纳米复合粉的表面形貌、粒度、晶相组成等进行表征.研究结果表明:温度为50℃,pH值为-0.25,H2O/TEOS=9/1(V/V),并加入占TEOS体积5%的硅烷偶联剂KH570,可以制备得到复合物体系的稳定凝胶.以无水乙醇为超临界萃取剂,进行超临界干燥,煅烧温度约高于700℃,得到分散性较好的纳米复合粉体,粉体一次颗粒径约为40～60hm,粉体形貌近似球型.复合粉的主要晶相为Bi2SiO5、CeO2和sr2Mn205.     

Processing of Tape–Cast Laminates Prepared from Fine Alumina/Zirconia Powders

This paper addresses the effect of thermocompression pressure, shear deformation of green laminates, and postsinter HIPing on the microstructural homogeneity of cast tapes and laminates prepared from fine Al₂O₃, and Al₂O₃/ ZrO₂, powders. Green density increases with increasing thermo–compression pressure. Sintered densities, however, depend more on the macroscopic uniformity in the green tapes. When density gradients develop within the individual green tapes (because of improper drying), sintering is constrained in two dimensions and densities remain low. Postsinter HIPing does not significantly increase the sintered densities because of the retention of open porosity within the individual tape–cast layers. The use of a revised thermocompression process involving shear deformation results in higher sintered densities and complete densification after HIPing. Sintered densities increase with the degree of shear strain during green–state deformation processing. Thus, green-state deformation can improve homogeneity in laminates. A further variation of the shear deformation process has also been developed that allows the formation of complex shapes from tape–cast laminates in the green state, while retaining layer integrity.     

Mechanical Properties of Hot Isostatically Pressed Zirconia-Toughened Alumina Ceramics Prepared from Coprecipitated Powders

Amorphous Al₂O₃–ZrO₂ composite powders with 5–30 mol% ZrO₂ have been prepared by adding aqueous ammonia to the mixed solution of aqueous aluminum sulfate and zirconium alkoxide containing 2-propanol. Simultaneous crystallization of γ-Al₂O₃ and t -ZrO₂ occurs at 870°–980°C. The γ-Al₂O₃ transforms to α-Al₂O₃ at 1160°–1220°C. Hot isostatic pressing has been performed for 1 h at 1400°C under 196 MPa using α-Al₂O₃– t -ZrO₂ composite powders. Dense ZrO₂-toughened Al₂O₃ (ZTA) ceramics with homogeneous-dispersed ZrO₂ particles show excellent mechanical properties. The toughening mechanism is discussed. The microstructures and t / m ratios of ZTA are examined, with emphasis on the relation between strength and fracture toughness.     

Effect of Chemically Synthesized Aluminum Foil on Solid State Polypyrrole Capacitor

The purpose of this study is to explore the effect on capacitance features of the solid state high performance polypyrrole capacitor with the chemically synthesized aluminum foil. Atomic force microscope (AFM) was used to analyze the surface structure of the chemically synthesized aluminum foil for the experiment and distribution of polypyrrole on the surface of the foil was observed and analyzed through scanning electron microscope (SEM) and energy dispersive x-ray spectrometer (EDS). Finally, evaluation of electric performance was conducted so as to establish the parameters for the surface structure of the chemically synthesized foil with the best series capacitance features.     

Sintering of Chemically Synthesized Lead(II) Selenide Fine Powders

PbSe fine powders were synthesized from a liquid-phase reaction of lead-ascorbic acid complex and sodium selenosulfate. The resultant powders were sintered up to nearly theoretical density by controlling the sintering atmosphere and by optimizing the sintering temperature and time. The highest sintered density, 99.7% relative to the theoretical density of 8.27 103 kg/m3, was attained when a powder compact was sintered at 998 K for 6 h under a flow of argon containing 3% H2 gas. Powder compacts could be sintered to higher than 98% when the sintering temperature was 1073 K or lower. When the sintering temperature or time exceeded the optimum range, considerable volatilization of the component occurred, resulting in a decrease in the sintered density. The use of a powder bed was found to be effective in suppressing the volatilization of the component.     

A Review of Developments and Current Trends in Ceramic Dielectrics Used for Capacitor Applications

A review is made of currently produced titanate ceramic dielectric materials designed for close-tolerance temperature-compensating and for general purpose capacitors. Data are presented on capacitors made from semiconducting titanate dielectrics in which the capacitance values range from 50 to 400 times higher than values obtainable in similar sized units of conventional dielectric material having a dielectric constant of 6000.     

Modeling and Simulation of Electrostatic Adhesion Force in Concentric-Ring Electrode Structures of Multilayer Dielectrics

Recently, electrostatic adhesion force (EAF) has gained considerable interest for handling dielectric materials. EAF arises from the non-uniform electrical field generated between electrostatic adhesive with special electrode patterns and materials after alternative polarity potentials are applied to the electrodes. In this paper, a theoretical analytical model was derived from electrostatic adhesion fields of concentric-ring electrode (CRE) structures in cylindrical coordinates on multilayer dielectrics. Because polarization on different mediums is complex, the field was divided into four layers to receive corresponding boundaries. With respect to the reproducibility of the CRE structure along the radial direction, the field was further divided into rectangular section shapes according to the Neumann boundary conditions. The surface roughness of the dielectric material, amplitude of the applied voltages, and properties of the different dielectric layers were also accounted for in the modeling, because they have a remarkable effect on the adhesion field. Based on this model, EAF was also calculated by the Maxwell stress tensor. Several critical factors influencing the EAF were analyzed through comparison of the finite element method simulation with theoretical calculations. The results were in good agreement with each method.     

化学法制备纳米氧化铁顔料研究进展

综述了纳米氧化铁化学制备方法的研究进展,对胶体化学法、水热法、固相法、沉淀法和水解法等化学制备方法进行了探讨.通过分析比较,对未来纳米氧化铁的化学制备提出了几点建议.