Kinetics of crystallization processes in some glass ceramic products

The paper presents the kinetic study of the crystallization processes which take place in basalt glasses containing variable amount of nucleation agent (CaF₂, 310%). The activation energies have been calculated using Kissinger's equation and verified with the Ozawa-Flynn-Wall equation. In this order, the DTA curves have been registered with different heating rates, between 4 and 20 degrees/min. A correlation equation between the activation energy and the amount of nucleation agent (% of CaF₂) was established. By X-ray diffraction it was proved that the crystalline phase formed in the crystallization process represents a pyroxenic solid solution, Ca(Mg,Fe)SiO₃. This revised version was published online in July 2006 with corrections to the Cover Date.     

导电共聚物衍化新策略制备硫、氮共掺杂碳纳米管及其对改善PtCu纳米晶分散性与甲醇电催化氧化的促进作用

有效调控碳纳米材料的几何和电子结构的协同效应和缺陷是获得优良电化学性能的关键.然而,如何设计一种具有优势结构的杂化材料及对其电催化机理的认识尚不清楚.本文提出了一种聚(3,4-乙撑二氧噻吩)/聚苯胺导电共聚物热解策略来制备S和N共掺杂多壁碳纳米管(MWCNTs),发现改变前驱体溶液中两种单体的比例可以调控掺杂MWCNT...     

导电高分子在神经界面电极中的应用

神经界面电极作为人体和外部器件间信息融合的媒介, 为人们进一步探究神经系统高级功能的机制提供了有效工具. 传统的神经电极多以金属和半导体材料为主, 这两类材料因具有惰性材料的特性及优越的 导电性能而成为早期神经电极的主要制备材料, 但由于其刚性过大和光滑表面导致的机械失配及与生物组织间过高的电化学阻抗限制了神经电极的进一步发展. 导电高分子作为一种有机导电材料, 同时具备柔软性 (杨氏模量约在0.01~10 GPa)和导电性(高掺杂度的导电高分子的电导率在金属范围, 10⁰~10⁵ S/cm)的特征, 是制备神经电极的有效材料. 近年来, 人们利用导电高分子材料对传统电极材料进行改性甚至替代, 以提高电极比表面积、 减小界面阻抗, 并提高电极检测的灵敏性; 同时减小电极与组织间的应变失配, 减少炎症反应, 并进一步在导电高分子中引入功能性生物大分子, 减少生物组织对电极的排异反应, 增加电极在体内长期植入的稳定性. 本文讨论和总结了导电高分子材料在神经电极中的应用, 分别对导电高分子作为涂层修饰神经电极、 全导电高分子材料神经电极及导电高分子复合材料神经电极等展开讨论, 分析了导电高分子在神经界面电极中的应用前景及存在的问题, 以期对神经界面电极在脑科学和生物电子医疗等前沿领域的进一步发展提供参考.     

A simple approach to porous low-temperature-sintering BaTiO3

Porous tetragonal BaTiO 3 ceramic was successfully prepared by a combination of hydrothermal and low-temperature-sintering method.The hollow TiO2@BaCO 3 as the sintering precursor was synthesized via a simple hydrothermal method,and then porous BaTiO 3 was generated by calcining the hollow TiO2@BaCO 3 precursor at 900 ℃ without additive.The hollow TiO2@BaCO 3 structure plays two important roles in the preparing of the porous BaTiO 3 ceramic.First,the TiO2@BaCO 3 hollow structure provides high surface areas and increases the contact points between BaCO 3 and TiO2,which can reduce the sintering temperature of the BaTiO 3 ceramic.Second,the cavity of the ordered arranged TiO2@BaCO 3 hollow sphere shows important influence on the porous structure,and the pore size of the as-prepared porous BaTiO 3 ceramic can be tuned from several nanometers to hundreds nanomters by changing the sintering temperature.The formation mechanism of the porous BaTiO 3 ceramic was proposed.     

Highly adhesive metal plating on Zylon fiber via iodine pretreatment

Highly adhesive metal plating was performed on poly(p-phenylene-2,6-benzobisoxazole) fiber named Zylon^® via iodine pretreatment followed by electroless plating. First, iodine components were selectively doped into the inner part of the fiber near the surface through iodine vapor exposure. The doped iodine was converted to palladium iodide particles by treating with palladium chloride solution. After the reduction of the iodide to metal palladium particles, electroless copper plating was conducted on the fiber. A uniform copper layer was deposited on the fiber surface and exhibited high durability in durability tests such as ultrasonic exposure, tape peeling-off, and corrosion in NaCl solution. This durability was attributed to the palladium particles formed at the fiber surface that served as an anchor for the plated layer as well as an electroless plating catalyst. The plated fibers also possessed electrical conductivity. Although the tensile strength of the Zylon^® fiber decreased from 5.8 to 4.9 GPa after undergoing the pretreatment and plating processes, the light shielding effect improved the light resistance of the plated fibers in terms of tensile properties. After 18 days of xenon lamp exposure, the plated fibers retained 74% of its initial strength, whereas that of untreated fibers decreased to 43%.     

On the local coordination of Fe in Fe2O3-glass and Fe2O3-glass ceramic systems containing Pb, Na and Si

The effect of the composition and casting temperature on the structural role of Fe in a series of binary (Fe₂O₃-PbO and Fe₂O₃-Na₂O) and ternary (Fe₂O₃-PbO-SiO₂) glass and glass ceramic materials is studied by means of X-ray fluorescence (XRF) mapping, X-ray absorption fine structure (XAFS) and Mössbauer spectroscopies. According to the Mössbauer results the majority of Fe exists in the Fe⁺³ state. The XRF maps reveal that Fe-rich islands evolve into the vitreous matrix of ternary samples that contain more than 40 wt% Fe₂O₃. In these samples the XAFS results disclose that 40-43 at.% of the Fe atoms belong to the Fe-rich microcrystalline islands formed by Fe_xO_y oxides. Furthermore, the structural role of Fe⁺³ in the ternary glasses is found to depend on the Fe₂O₃ content. Finally in the binary Fe₂O₃-PbO systems the majority of Fe⁺³ is octahedrally coordinated in the Fe₂O₃ and/or PbFe₁₂O₁₉ crystalline phases.     

铪掺杂对锆钛酸钡钙陶瓷电学性能的调控

用固相反应法制备了B位Hf掺杂的Ba_0.95Ca_0.05 Zr_0.05Ti_0.95-xHf_x (BCZ_0.05T_(0.95-x)-xH) (x=0、0.02、0.04、0.06和0.08)陶瓷。研究B位同时含有Hf、Zr、Ti三种元素时,BCZ_0.05T_(0.95-x)-xH陶瓷的相结构变化与电学性能的差异。XRD测试结果表明：Hf₄₊^融入晶格,造成晶格膨胀。BCZ_0.05T_(0.95-x)-xH(x=0、0.02)陶瓷的XRD测试结果表明,该体系中存在明显的四方相与正交相共存的多晶型相转变(PPT),但正交相逐渐转变为主晶相;BCZ_0.05T_(0.95-x)-xH (x=0.04、0.06)陶瓷的XRD结果表明,四方相进一步减少,三方相却逐渐增加;当x继续增大到0.08时,XRD测试发现该体系只存在正交相和三方相结构。SEM测试发现,随着Hf的掺杂量增加,晶粒尺寸逐渐减小。剩余极化随Hf掺杂量的增加先增大再减小,在x为0.02时取得最大值,Hf掺杂显著降低矫顽场(Ec)。压电测试结果表明BCZ_0.05T_0.96-0.04H陶瓷具有最大压电系数(d₃₃=259 pC/N)。     

低应变率下硅铝质泡沫陶瓷复合材料的力学性能研究

以泡沫陶瓷复合材料在防护工程中的应用为背景,利用MTS(Material Test System,材料试验机)对该型材料进行了准静态压缩实验。得到了应变率在10-5~10-3s-1范围内的应力应变曲线,并对实验结果进行了理论分析和数值模拟。研究表明,泡沫陶瓷复合材料的力学性能在准静态一维应力压缩条件下显示出明显的应变率效应,同时其应力应变曲线可用一种经验的脆性材料本构模型进行较好地拟合。而在一维应变压缩条件下,材料的应力应变曲线则显示出明显的三段式特征:弹性段、平台段和密实段,同时材料的吸能幅值随着应变率的增大而增加。     

Modification of submicron ceramic under pulse loading

Abstract

The explosive loading may be successfully employed to modify submicron rapidly solidified ceramic powders (? 0.5 mcm in mean diameter) of nanocrystalline structure at several structural levels, e.g., for a qualitative morphological variation of particles (their fragmentation) with the change in fractal dimensions of a specific surface and for an additional defect saturation of a crystal structure. This has been shown to favour activation of the stabilized submicron ZrO₂ powder.