Synthesis and rapid expansion in supercritical carbon dioxide through porous sintered metal plate of poly(1,1,2,2‐tetrahydroperfluorodecyl acrylate)

Poly(1,1,2,2‐tetrahydroperfluorodecyl acrylate) [poly(TA‐N)] was synthesized in dry benzene using AIBN as an initiator at 60°C. The effects of the monomer concentration (C_m), initiator concentration (C_i), and reaction time on the polymerization were investigated. The results of DSC and TGA showed that when the C_i remains constant, the higher the C_m value is, the better the thermal character for the product in the range of experiments. When the reaction was conducted for 30 h, polymerization is almost completed. The C_i should remain lower than 0.25 g/100 g monomer when the C_m is lower than 15 g/L. When the C_m is higher than 15 g/L, the C_i should be increased slightly. When the C_m remains constant, it was observed that an increase in the C_i increases the yield (mass of polymer after reaction/mass of monomer before reaction). On the other hand, the melting (T_m) and decomposition (T_d) temperatures of the reaction product decrease, except when the C_m reaches 20 g/L and the reaction time is 30 h. High purity CO₂ was continuously pumped using a high pressure syringe pump. Rapid expansion of poly(TA‐N) in supercritical CO₂ happened under control through a porous sintered metal plate. The poly(TA‐N) morphology was analyzed with a scanning electron microscope. An amorphous polymer was formed at a preexpansion temperature of 45°C. Fibers were formed at temperatures of around 60–80°C. An increase of the temperature slightly increases the particle size. At 105°C, most of the particles are spheres and dendrites. The corresponding CO₂ flow rate upon expansion was 2.5–5.0 ± 0.3 L/min (STP) and the pressure drop was 2 MPa. At the higher CO₂ flow rate, the spheres and dendrites became smaller. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2763–2768, 2003     

自熔性烧结含碳球团铁连晶形成动力学过程

链连晶是保持含碳球团热强度的金属骨架。在还原气氛条件下，反应温度600～700℃时，金属铁雏晶形成；铁连晶的形成存在一个临界温度700～750℃。实验表明，低于这个临界温度，即使长时间保温，铁连晶也不易形成；只有当加速率足够大时才会导致铁连晶的形成。在温度确定后，碳的固溶过程是时间的函数，在极短的时间内快速升温是提高含碳球团强度的有效途径。     

Tetragonal Tungsten Bronze Niobate, K0.2Sr0.4NbO3: A New Material for Capacitors with Flat Dielectric Curves

A new ceramic for capacitors, which exhibits flat dielectric curves with relative permittivity values (ɛ) as high as 3000 (Y7R or X7R class), has been synthesized. Use of a niobate, K_0.2Sr_0.4NbO₃ (KSN), with a tetragonal tungsten bronze structure (TTB), as a major phase for the fabrication of such ceramics is shown for the first time. Nevertheless, the addition of perovskites as minor agents—PbMg_1/3Nb_2/3O₃ (PMN)—is necessary to obtain stable temperature. Moreover, the use of lithium salts as sintering agents has been shown to be important for the fabrication of these ceramics.     

Ferroelectric Properties of Tungsten Bronze Morphotropic Phase Bounary Systems

Tungsten bronze ferroelectrics which have a morphotropic phase boundary (MPB) can have a number of enhanced dielectric, piezoelectric, and electrooptic properties compared to more conventional ferroelectric materials. The structural and ferroelectric properties of several MPB bronze systems are presented, including data from sintered and hot-pressed ceramics, epitaxial thin films, and bulk single crystals. Included among these are three systems which had not been previously identified as morphotropic. The potential advantages and limitations of these MPB systems are discussed, along with considerations of the appropriate growth methods for their possible utilization in optical, piezoelectric, or pyroelectric device applications.     

Voltammetric behaviour of an archeaological bronze alloy in aqueous chloride media

The interface archaeological bronze alloy‐chloride media was characterized by using linear sweep rate cyclic voltammetry. The electrochemical behaviour of the Cu‐Sn alloy being different from pure copper and pure tin. In fact, the voltammograms show an anodic peak and two cathodic peaks. Surface examination revealed a compact layer which spread over the ancient material. The influence of different parameters such as scan rate, chloride concentration and repetitive cycling on the voltammetric response of the archaeological bronze was also studied. The results indicate that patina layer formation is a spreading process over the electrode surface leaving only small pores. Diffusion of the halide controls the growing rate of this layer. Two other anodic peaks are evidences when potential cycling increases. The oxidation became more difficult as a result of a constant layer thickness.     

铁青铜含油轴承烧结及烧结温度的研究

本文叙述了在锡青铜粉中加入铁粉研制成铁青铜烧结轴承材料，其铁含量的加入与收缩率、耐磨性的关系，并得出铁粉的最佳加入量为４０％。根据铁－铜合金的烧结原理及状态图，得出铁铜合金的材料的烧结温度随铁粉加入量的增加而增高，最佳烧结温度为８２０－８５０℃。     

高强度低硅青铜QSi1.8-0.5棒材生产工艺

介绍了高强度低硅青铜QSi1.8-0.5的研制过程,并对两种生产工艺进行了分析和对比,认为采用加工率控制性能可以获得所需力学性能,更适于规模化生产。     

硅灰石在烧结焊剂中的应用研究

通过研究硅灰石的矿物组成和物理性能以及化学组成等 ,对照烧结焊剂熔渣的化学组成进行了硅灰石在烧结焊剂中应用的试验。试验结果显示 ,硅灰石具有改善烧结焊剂的焊接工艺性能和熔敷金属力学性能的作用。     

Microstructures and thermal conductivities of reaction sintered SiC ceramics

Abstract

Reaction sintered SiC ceramics were prepared by the silicon melt infiltration method over temperatures of 1450?1550°C. The effects of the carbon and silicon contents of the starting materials as well as the sintering temperature and time on the thermal conductivities and microstructures of the ceramic materials were studied. The thermal conductivities and microstructures of the samples were characterised using thermal conductivity measurements, X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy and mercury injection porosimetry. The results showed that sintering temperature and time as well as the carbon and silicon contents of the green specimens are the main factors affecting the microstructure and porosity of reaction bonded SiC ceramics. Increasing the reaction temperature and time decreased the porosity of the ceramics. This was due to the infiltration of the silicon melt into the ceramic specimens. The thermal conductivity and porosity of the sample sintered at 1550°C for 3 h in an argon atmosphere were 102·5 W m K^?1 and 0·3% respectively.     

三维数字重建在青铜器修复中的应用研究

如何利用数字化手段将文物碎片进行三维重建是当前考古学家和历史学家关注的问题。利用三维激光扫描仪获取了青铜器陶范残片的数据,利用人机交互的方式去除噪声点,利用变分法的隐式曲面建立点云数据的曲面,利用最邻近点法实现点云数据的转换,利用分形插值的方法进行三维曲面上的空洞修补,利用逆向工程和三维建模软件调整陶范模型的形状、纹饰、结构,对陶范进行反转法线处理,得到青铜器碎片。然后计算旋转轴,将青铜器碎片沿轴均匀排列,得到三维青铜器模型,并对缝隙进行修补。运用二维图像处理软件对需要进行纹理映射的纹饰进行修订,最后利用三维打印软件修复转换过程中的片面破损,并进行三维打印,得到真实的青铜器样本。从得到的青铜器来看,纹饰完整,器形规整,完全满足设计的要求。