New polymerization of dienes and related monomers catalyzed by late transition metal complexes

This article reviews recent studies on the polymerization of 1,6-heptadienes and 2-aryl- and 2-alkoxy-1-methylenecyclopropanes catalyzed by Co, Fe, and Pd complexes. Co and Fe complexes with bis(imino)pyridine ligands catalyze the cyclopolymerization of 1,6-heptadiene in the presence of MMAO to produce the polymer, which contains five-membered rings in the monomer units. The polymers with cis- or trans-five-membered rings are obtained selectively, depending on the complex used in the polymerization. The catalyst, prepared from the Co complex having a bis(imino)pyridine ligand and MMAO, promotes the polymerization of 2-aryl-1-methylenecyclopropanes without ring-opening. The reaction under ethylene atmosphere produces alternating copolymer of the two monomers to yield the polymers composed of the C4 repeating unit with a 1,1-cyclopropanediyl group. The alternating copolymer of ethylene and 7-methylenebicyclo[4.1.0]heptane undergoes thermal rearrangement to afford the polymer with CC double bond in main chain. A radical pathway is proposed. Dinuclear π-allylpalladium complexes with bridging Cl ligands initiate living polymerization of 2-alkoxy-1-methylenecyclopropanes, which accompanies ring-opening of the monomer, to afford the polymers composed of the C₃ repeating units having alkoxy and vinylidene groups. A cyclic dinuclear π-allylpalladium complex reacts with 2-alkoxy-1-methylenecyclopropane in the presence of pyridine to produce the living polymer with macrocyclic structures. Block copolymerization of the two monomers that contain OR or O(CH₂CH₂O)R as the substituents on the three-membered ring, results in the polymers with hydrophobic and hydrophilic segments.     

硬质合金烧结技术的发展

硬质合金问世以来,其烧结工艺技术的发展经历了好几个阶段。本文就这些阶段的主要内容进行介绍,并对其先进性和不足方面的问题进行比较。目的旨在促进各硬质合金厂家根据自己的实际情况,选择适当的烧结工艺和装备。     

返滴定法测定硬质合金中的铁、镍和钴

利用运滴定法消除镍对二甲酚橙指示剂的封闭作用,在pH5．5～6．0先测得铁、镍和钴的总量,再利用镍、钴在强碱性溶液中有效稳定常数不同及铁可波三乙醇胺掩蔽的特性,用钙盐返滴定法测得镍和钴分量．此方法不需分离,简便、快速,应用于含镍、铁和钴的硬质合金中铁、镍和钴的测定,结果令人满意．     

Kinetics and mechanism of low-temperature ozone decomposition by Co-ions adsorbed on silica

Kinetics and mechanism of low-temperature ozone ((5–50) × 10⁻³ mol/m³ in the gas–air mixture) decomposition by Co-catalysts supported on silica have been studied. Co-ions adsorbed on silica react with surface oxygen species, thus resulting in an active catalyst. Low concentrations of Co-ions form a monolayer on the surface. Their specific catalytic activity remained constant, but sharply decreased at higher concentrations due to a formation of polynuclear Co-complexes. Ozone decomposition may occur either as a stoichiometric or catalytic process, depending on the ozone and catalyst concentrations. The turnover number increases with ozone concentration reaching a saturation point. It also increases with Co-concentration in the beginning, but drops at a concentration >1 × 10⁻⁴ mol/g. The mechanism of the reaction is discussed.     

环戊二烯基钴配合物的研究进展

综述了环戊二烯基钴化学的研究进展,着重介绍了其配合物的类型、合成方法、反应性及其在炔烃和腈环加成反应中的催化作用.     

Influence of deposited particles of Ni and Co on the passivity of aluminium

The cathodic deposition of transition metals allows obtaining surface conditions similar to those found in alloys and to study the anodic processes occurring on them. In this work, some aspects dealing with the influence of the presence of electro-deposited particles on the growth of anodic oxide films at potentials lower than 10 V in neutral acetate buffer solution were analysed by conventional electrochemical techniques supported by SEM and TEM. At the first stages of anodization, the particles lose progressively their contact with the substrate due to the growth of the aluminium oxide film leaving a defective structure. Thus, at potentials higher than 0.9 V SSE, the electrical contact of particles is established by tunnelling through localized states generated by defects in the band-gap. This, in turn, leads to the formation of preferential conductive paths. Thus, the dissolution/passivation of particles and the evolution of oxygen on them at higher anodic potentials could be observed. At potentials higher than 4 V, defects are released towards the oxide/electrolyte interface and the behaviour of pure aluminium oxide is observed again.     

YBa_(1-x)Ca_xCo_2O_(5+δ)(x=0,0.1,0.15,0.2,0.25,0.3)体系的制备和物性研究

用溶胶凝胶法制备了钙钛矿钴氧化物YBa1-xCaxCo2O5+δ(x=0,0.1,0.15,0.2,0.25,0.3),系统研究了材料的热膨胀性能和电输运性质.结果表明,热膨胀系数随着Ca的掺杂量x的增加而减小,x=0.30掺杂样品在400℃-800℃温区内具有最小的平均热膨胀系数约为12.34×10-6K-1;掺杂样品在中低温下的电输运机制符合小极化子模型,x=0.30掺杂样品也具有较高的电导率约为126Scm-1,在800℃时的热膨胀系数与固体电解质YSZ最相近.     

茜素红褪色动力学光度法测定痕量钴

在pH 8.0的氨-氯化铵介质中,以聚氧乙烯醚-200（PEG-200）为活化剂,Co催化溴酸钾氧化茜素红褪色,建立了动力学光度法测定痕量Co的新方法。该方法检出限为2.0×10-7g/L;线性范围0.01~0.21μg/50 mL;最大相对标准偏差为4.3%。该法用于湖水及生产排水的测定,结果满意;加标回收率在96.0%~105.0%。     

Experimental and theoretical research on interfacial reaction of solid Co with liquid Al

Interfacial reaction between solid Co and liquid Al was investigated with immersion tests and theoretical modeling. The microstructure characterization indicated that a Co₂Al₅ intermetallic layer was formed at solid–liquid interface during the immersion test. The modeling results indicated that the corrosion rate of a solid metal in a liquid metal was controlled by both the formation and dissolution of the intermetallic layer. In Co–Al reaction system, the formation and dissolution of the Co₂Al₅ layer reached an equilibrium state in a very short time, and the corrosion of the Co matrix was mainly dominated by the dissolution of the Co₂Al₅ layer.     

Interfacial reaction between Co–Cr–Mo alloy and liquid Al

The interfacial reaction between Co–Cr–Mo alloy and liquid Al was investigated using immersion tests. Microstructure characterization indicated that the Co–Cr–Mo alloy was corroded by liquid Al homogeneously, with the formation of a (Co,Cr,Mo)₂Al₉ layer close to alloy matrix and “(Cr,Mo)₇Al₄₅ + Al” layer close to Al. Kinetics analysis showed that the corrosion of the Co–Cr–Mo alloy followed a linear relationship with the immersion duration. Compared with pure Co–liquid Al reaction system, the alloying of Cr and Mo changed the solid–liquid interface structure, but the corrosion of the solid metal was still dominated by the dissolution of an intermetallic layer.