Sb_xSn_(1-x)O_2固溶体系电学性能与导电机制研究

本文报道以均匀共沉淀法制得 Sbx Sn1 -x O2 体系半导体气敏材料 ,研究了固溶体组成与电导的变化规律 ,并对导电机制进行了讨论。结果表明 :x<0 .30时均可生成固溶体。微量 Sb(x=0 .0 4 )的掺入即能提高 Sn O2 电导一个数量级 ,在 x≤ 0 .0 4区间电导都呈上升趋势 ,其后一直到固溶范围内随着 X增加 ,电导反而缓慢下降。根据体系中存在的 Sb°Sn和 Sb′Sn两种缺陷 ,讨论了其电导变化和导电机制。认为平衡 Sb°Sn 2 e′=Sb′Sn对上述导电机制起决定作用。XPS分析对 Sb5 、Sb3 的含量进行了确认 ,交流阻抗谱的测试结果从另一角度对电导行为加以证实。     

Modeling the growth and molecular structure of conductive polymers: Application to poly(dialkoxybenzene)s

A modeling strategy, based on (i) quantum semiempirical calculation of the electronic structure of the successive intermediate oligomers and (ii) evaluation of the activation energy of the successive coupling reactions by use of the frontier orbital model, has been used to study the growth of a wide set of conductive polymers and is illustrated with poly(1,2-dialkoxybenzene) and poly(1,4-dialkoxybenzene) generated by electrochemical oxidation of the corresponding monomer. These monomers have been chosen because they are known to yield polymers of completely different structures. The strategy, which is designed to be as little computer time-consuming as possible, allows us to predict a growth trend in agreement with the structure inferred from spectrochemical experiments. In the case of poly(1,2-dialkoxybenzene) it suggests the formation of a cyclic tetramer as a byproduct detected in small quantities by means of MALDI spectroscopy. This modeling strategy allows one to describe the electronic modifications induced by the growth of a highly conjugated structure. It suggests that oxidation of the successive oligomers at high doping level and quinonic deformation are key factors for the growth of long and regular polymer structures     

Poly(ethylene oxide)/poly(2vinylpyridne)/lithium perchlorate blends as solid polymer electrolytes: Composition/property/structure interrelationship

Poly(ethylene oxide) (MW 600,000)/poly(2vinylpyridine) (MW 200,000)/LiClO₄ blends have been prepared by the solution blending process. The ionic conductivities of the blends containing lower weight fractions (15, 17.5, 20 and 22.5%) of poly (2vinylpyridine) initially increases as the salt content is increased, reaches a maximum at an ethylene oxide/Li⁺ mole ratio of 10 and decreases as the salt content is further increased. Blends, which have higher weight fractions of poly(2vinylpyridine) (25 and 35%) display different electric behavior, i.e., the ionic conductivity continously increased as the salt content is increased to an ethylene oxide/Li⁺ mole ratio of 2. Thermal, ⁷Li solidstate NMR and semiempirical MNDO molecular orbital studies indicate that this contrasting behavior may be explained by the structure and ratios of the solvates (mixed solvate or homosolvate) of LiClO₄ present in the blends. © 1995 John Wiley & Sons, Inc.     

导电炭黑在聚丙烯/极性聚合物体系中的选择性分散及其对导电性能的影响

以聚丙烯(PP)和极性聚合物的共混物为基体材料,以导电炭黑为填料,通过熔融共混制备导电复合材料。探讨了导电炭黑在两相基体中的分散情况以及双基体各组分比例对复合体系结构形态和导电性能的影响。SEM测试结果表明:炭黑粒子选择性地分散在极性乙烯-丙烯酸共聚物(EAA)树脂或尼龙6(PA6)中。EAA相在PP基体中呈棒状伸长结构,且随着EAA树脂含量的增大,在PP基体中形成更多更为连续的棒状伸长结构,使体积电阻率迅速下降。当在体系中加入PA6,mPP/mPA6=80/20时,PA6在PP基体中形成相互连接的纤维状分散结构,显著降低了复合体系的体积电阻率。电性能测试结果表明:材料在相同导电炭黑含量下的体积电阻率相对单基体体系可降低3~7个数量级。     

Carbon Nanotubes Act as Conductive Additives in the cathode of Lithium Ion Batteries

The layered compounds LiCoO2, LiNiO2 and spinel compound LiMn2O4 have served as very effective cathode active materials in lithium ion rechargeable batteries. Generally, their high conductive resistance easily results in a serious polarization and poor utilization of active materials.In order to make full use of the active materials and increase the capacity, the charge-discharge rate and the cycle life of lithium ion batteries, conductive additives are often added into the above cathode materials to form a conductive network. Carbon materials, such as carbon black, graphite powders and chemical vapor deposit carbon fibers have been widely used as conductive additives owing to their high electrical conductivity and chemical inertness. To effectively utilize the active materials, the contents of these carbon additives in the cathode often reach up to 10～20wt%. This leads to a great need for binder, for example, 10wt% or more. It follows therefore a considerable increase in volume of the lithium batteries and lower energy density because of the large amount of carbon additives and binder in the cathode.By substituting carbon nanotubes (CNTs) for carbon black, graphite powders or chemical vapor deposit carbon fibers, much conductive additives and binder are saved, and the cathode with only 3～5wt% of conductive additives CNTs shows excellent rate capacity. At the discharge rate 0.5C,2.0C and 3.0C, the LiCoO2 cathode with CNTs exhibits discharge capacity up to 134mAh/g, 126 and 120mAh/g, respectively. The explanation is given as follows. Firstly, their microstructure and graphitic crystallinity are very important for electron transport. CNTs employed in the experiments comprise an array of complete graphite sheets seamlessly wrapped into cylindrical tubes which are concentrically nested like the rings of a tree trunk. Thus, the process of -electrons transport occurs in graphite sheet in super-conjugative manner when they move from one end to the other end in CNTs. Apparently, the CNTs' microstructure does good to electron transport. On the other hand,being highly graphitic (concluded from XRD patterns), CNTs also displays high electron conductivity. Secondly, being smaller in diameter, CNTs possess much larger number of primary particles in unit mass than other carbon materials. Hence, it results in a lower percolation threshold in the case of CNTs. Finally, owing to their high surface energy, CNTs fallen into nano-materials tend to aggregate and then form firm webs effectively entrapping LiCoO2 particles during the preparation of the cathode to guarantee their close contact with the active materials.Accordingly, effective electron channels are provided to lessen the polarization loss.     

Molecular design of a π‐conjugated single‐chain electronically conductive polymer

This study demonstrates that single‐chain π‐conjugated systems can be made electrically conductive by modifying the molecular structures of both ends of the oligomers making up a polymer. That is, the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gaps of a fairly long polyyne‐type oligomer with appropriately modified molecular structures at both ends are found to be on the order of thermal energy by calculations using density functional theory (DFT) with B3LYP functionals. This result applies to molecular structures with characteristic bond alternations. The peculiar bond alternations are caused by competition between two effects of the bond alternations of the two mutually perpendicular π‐conjugated systems, which partially cancel each other out. It is probable that we can design one‐dimensional polymers with HOMO–LUMO gaps small enough to be conductive by combining the above‐mentioned oligomers with each other as monomer units in the polymer. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Synthesis and characterization of novel sulfonated naphthalenic polyimides as proton conductive membrane for DMFC applications

To prepare proton conductive membrane for direct methanol fuel cells (DMFC), a novel sulfonated aromatic diamine monomer, 1,4-bis(4-amino-2-sulfonic acid-phenoxy)-benzene (DSBAPB) was synthesized and characterized by ¹H NMR and FT-IR. Then a series of sulfonated polyimides (SPIs) were prepared from DSBAPB with 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) and a non-sulfonated diamine, 4,4′-oxydianiline (ODA) via one-step high-temperature polymerization method. The sulfonation degree of the SPIs can be controlled by changing the mole ratio of sulfonated monomer to non-sulfonated monomer. The obtained SPI membranes exhibit desirable proton conductivity ranged from 7.9 × 10⁻³ to 7.2 × 10⁻² S cm⁻¹ and low methanol permeability of less than 2.85 × 10⁻⁷ cm² s⁻¹. Furthermore, the hydrolysis stability of the obtained SPIs is better than the BDSA based SPIs caused by the flexible structure.     

Structures, energy bands and conductivities of (Me_3NEt)[Pd(dmit)_2]_2 and (NEt_4)[Pd(dmit)_2]_2

The electrical conductive molecular crystals (Me3NEt)[Pd(dmit)2]2 and (NEt4)[Pd (dmit)2]2 (dmit = 4,5-dimercapto-1,3-dithiole-2-thione) have been prepared, and their crystal structures and conductivity-temperature curves have been determined. The fact that the conductivity at room temperature of (Me3NEt)[Pd(dmit)2]2 (a = 58 Ω· cm-1) is much higher than that of (NEt4)-[Pd(dmit)2]2(cr= 2.2 Q~1 ?cm'1) has been rationally explained by the results of energy band calculations. (MeNEt3)[Pd(dmit)2]2 belongs to monoclinic system, P21/m space group and (NEt4)[Pd (dmit)2]2 belongs to triclinic system, P1 space group. The structural conducting component of the crystals is the planar coordinative anion [Pd(dmit)2]05- which forms the face-to-face dimmer [Pd(dmit)2]2-. These dimers have been further constructed to be a kind of two-dimensional (2-D)conductive molecular sheet by means of S…S intermolecular interactions. The tiny difference of the above 2-D molecular sheets of the two title crystals has resulted in one     

复合型炭系导电发热涂料的研究

采用复合型炭系填料石墨、炭黑、煅烧石油焦、石墨纤维、炭纤维和碳化硅粉末等与合成改性树脂经机械混合及不等温固化,制得并联导电发热涂料;利用扫描电镜、伏安法体积电阻率测试仪和电参数测定仪对涂层进行测试分析.研究结果表明:在安全电压下,该涂料具有加热迅速、使用安全、热效率高等特点,而且热传导和热辐射性能优良;在填料含量相同时,复合型炭系填料优化配方后所制得的涂层比单一填料具有更优良的导电特性;炭系填料与纤维匹配后构成了三维空间网络导电粒子链结构,更利于导电和发热;在60 V电压下,通电14 min,自制电热壁画涂层表面温度达到134.8 ℃;树脂基体改性后电发热涂料的附着力提高,耐温变性和耐热性等能力增强.     

高精度微型凸缘无磁钢轴承套圈加工

通过对不导磁材料高精度凸缘轴承套圈的加工工艺进行探讨，在轴承套圈磨加工时，采用了导磁附件，二级工装，粘导磁片的方法，使无磁钢凸缘微型轴承套圈的加工转化为常规轴承套圈的加工。