Hydration of lanthanides and actinides in solution

Hydration studies of lanthanides and actinides are reviewed. In their trivalent state, the two series of elements have similar hydration and hydrolytic behavior. The solid hydrates adopt the tricapped trigonal prism (CN=9) structures whereas in solution, diffraction and solution measurements support a change in hydration number from 9 to 8 with decreasing ionic radii. Thermodynamics of hydration, rates of solvolysis and preferential solvation in mixed solvents are discussed. Changes in hydration and hydrolytic characterization with oxidation state of the central ion are also reviewed.     

Synthesis and properties of zinc nanoparticles: The role and prospects of radiation chemistry in the development of modern nanotechnology

Zinc-containing nanoparticles stable in the liquid phase are synthesized by the radiation chemical reduction of zinc ions in solutions of inverse micelles. The effects of the absorbed radiation dose and the size of the micelle water pool on the spectral characteristics of samples are studied. The HPLC and electron microscopy results indicate that the composition of nanoparticles synthesized depends on the salt nature. Original Russian Text ? A.A. Revina, E.V. Oksentyuk, A.A. Fenin, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 6, pp. 613–618.     

Triboluminescence of crystals and suspensions of inorganic salts of lanthanides

It is found that the triboluminescence spectra of crystalline hydrates of inorganic salts of Ln³⁺ (Ce³⁺, Pr³⁺, Gd³⁺, Eu³⁺, Tb³⁺, and Dy³⁺) during mechanical trituration and ultrasonic treatment (22 kHz) of crystal suspensions in perfluorodecalin (in the sonotriboluminescence) exhibit gaseous and solid-state components. The first component contains emission lines of N2 in an electric discharge. The spectrum of the second component coincides with the photoluminescence spectrum of the crystals, including ions that cannot be excited due to the absorption of emission from N₂: Ce³⁺, Pr³⁺, and Gd³⁺. Among the different salts of Ln³⁺, the highest intensity of luminescence is observed in sulfates; the highest yields of tribo- and sonotriboluminescence are characteristic of the Ce³⁺ salts. The triboluminescence of Ln³⁺ nitrates is not registered. Possible mechanisms of excitation of the Ln³⁺ ions are discussed. The main source of the solid-state component of the triboluminescence of Ln³⁺ salts is assumed to be the electroluminescence typical of crystalline phosphors. It is shown that, along with lines of N₂, the spectrum of the triboluminescence observed in the atmosphere of He, Ar, and O₂ contains lines of these gases.     

Cation-promoted supramolecular assembly of bivalent metal tetra-15-crown-5-phthalocyaninates: Controlling the architecture of supramolecular aggregates

Cation-promoted supramolecular assembly of cobalt(II) and ruthenium(II) tetra-15-crown-5-phthalocyaninates is comparatively studied using the electronic absorption and infrared spectroscopy. The effects of the nature of the receptor and substrate on the architecture of the supramolecular aggregates formed are discovered. By contrast to Cu(II), Zn(II), and Ni(II) tetra-15-crown-5-phthalocyaninates, Co(II) and Ru(II) complexes are found to demonstrate sodium-potassium selectivity determined by the peculiarities of supramolecular structures formed upon the interaction with the cations.     

Structural chemistry and magnetism of dicyclopentadienidehalides of lanthanides Part 8: terbiumdicyclopentadienidebromide [Tb(C5H5)2Br]2

A single-crystal X-ray structural investigation of [Tb(C₅H₅)₂Br]₂ revealed the [Sc(C₅H₅)₂Cl]₂-type structure, space group P2₁/c, with a = 1407.6(2) pm, b = 1644.7(2) pm, c = 1370.6(9) pm, β = 93.46(3)°, V = 3167(2) × 10⁶ pm³, D_c = 2.322 g cm⁻³ and Z = 6 dimers (R = 0.036 for 4627 reflections with I > 3σ(I)). The metal centres have the pseudosymmetry C_2v. Magnetic susceptibility data show Curie-Weiss behaviour between 213 and 6 K with θ_p = −4.5(3) K and a magnetic moment μ = 9.8(1) μ_B close to the Tb³⁺ free-ion value (9.72 μ_B). Below 6 K, deviations from Curie-Weiss behaviour are observed, and at 5.3 K a maximum in the susceptibility is detected which may be caused by intradimer antiferromagnetic spin coupling. The magnetic properties are compared with the prediction of various models, starting from cubic crystal fields and isotropic intramolecular exchange interactions, followed by extension to lower crystal field symmetry (orthorhombic) and anisotropic contributions to the spin coupling. However, a reasonable agreement between the measured and calculated data was not obtained. As in [Gd(C₅H₅)₂Br]₂, the low-temperature behaviour is governed by effects which cannot be described by spin coupling models in the generally accepted form.     

Flexible film systems: Current understanding and future prospects

The electrical and mechanical properties of metal films on polymer Substrates are of interest for use inflexible electronic devices and sensors. In these Systems, film deformation mechanisms are comparable to those from free-standing films but the influence of the Substrate and the Interface on the film properties is yet to be fully understood. This understanding is critical to further design improvements and advanced in situ characterization holds the promise of making this possible. With the aid of such techniques direct Observation of failure and deformation mechanisms has become possible.     

Nanostructured ceramics in medical devices: Applications and prospects

Nanostructured materials may possess unique capabilities for specific interactions with cells, proteins, and DNA. This article reviews several classes of nanostructured ceramics with unique biological functionalities that are being considered for use in medical devices. The properties of calcium phosphate nanoparticles (Nano-CaPs™) and diamond-like carbon-metal nanocomposite films are described in detail. For more information, contact Roger J. Narayan, Georgia Institute of Technology, School of Materials Science and Engineering, 771 Ferst Drive, Northwest, Atlanta, GA 30332-0245; (404) 894-2823; fax (404) 894-9140; e-mail roger.narayan@mse.gatech.edu.     

Structural characteristics and the temperature derivative of the electrical resistivity of liquid lanthanides

The technique of an analysis is described and structural characteristics of liquid metals are calculated in terms of the model of hard spheres whose diameters asymptotically tend to zero with increasing temperature. The structure factor of a liquid refractory metal near the first maximum has been established to only weakly depend on temperature. A sufficient condition for the validity of the hard-sphere model has been formulated. On the example of many liquid lanthanides, it has been shown that the model satisfying this condition relatively well reproduces not only the structure factor of the melt but also its electrical resistivity in the vicinity of the melting point of the metal. With increasing temperature, the resistivity ρ of trivalent lanthanides increases monotonically, whereas in the case of divalent metals Eu and Yb smooth minima appear in the temperature dependences of ρ. An analysis of the results of calculations suggests that the hard-sphere model used in terms of the electron theory can relatively well describe properties of at least those liquid metals which crystallize into lattices with a packing fraction η ≥ π √3 /8.     

Self-repairing oxides to protect zinc: Review,discussion and prospects

Zinc is protected in the short term by chromate conversion coatings. The Cr (VI) based surface layer has the unique ability to self-repair which is attributable to the aqueous properties of its constituent ions. The thermodynamic feasibility of achieving chromium-like protection for the short term using other candidates is reviewed. Long-term protection of zinc is naturally affected by its own corrosion products (patina), which form a multilayered structure. The role of this patina in protecting the underlying metal is also reviewed, and processes within the patina, including the interaction between its various layers, are elaborated and discussed.     

Chromatography: Method of investigation of surface chemistry and interface processes

This paper discusses application of gas and liquid chromatography to studies of surface chemistry and various materials. Examples of studying adsorption processes from gas and liquid media with application of the chromatography technique are given. It is shown that the information on the structure of the material obtained using the chromatography technique allows predicting the regularities of chromatographic retention for molecules of different structures and various sorbents. The chromatography technique is frequently used in studies of nanomaterials and stable nanoparticles. It is shown that the chemical properties of surfaces modified by nanoparticles can be advantageously used in gas and liquid chromatography techniques. Much attention is given to molecular statistical calculations of adsorption on carbon sorbents in gas and liquid chromatography. The possibilities of the technique regarding prediction of retention of various sorbates and specification of structural parameters of molecules are demonstrated. Methodological and preparative aspects of a new area, micellar chromatography of nanoparticles, are considered. Options of liquid chromatography for separation, including preparative separation, identification, and classification, are shown.     

Beta-titanium alloys and prospects of their development

A classification of β-titanium alloys based on a structural factor and reflecting the special features of physical, mechanical, and technological properties of each group is suggested. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 11–14, December, 1998.     

激光焊接技术的研究现状与展望

激光技术在制造业中的应用是目前各国的研究重点,随着工业发展对高效、环保、自动化的需要,激光技术的应用迅速普及制造业的许多领域.在此基础上,激光焊接工艺将成为激光应用的重要方面之一.本文概述了激光焊接的发展现状,简单介绍了采用激光技术进行焊接的基本原理及其优缺点.详细描述了激光器的研发、等离子体控制、焊接过程的自动化检测和各种先进激光焊接技术.通过介绍激光焊接在具体领域(如汽车业、造船业等)的应用,充分说明激光技术在焊接制造中的优越性,并对激光焊接的发展前景做了具体的展望.     

电焊机行业的特点与展望

从市场容量、产品种类、涉及学科领域以及焊接设备在焊接生产中的地位等方面阐述了电焊机行业的特点;指出电焊机行业中企业兼并、整合的特点,并展望了行业的发展前景。     

铝合金材料发展现状, 趋势及展望

铝合金因其密度低,比强度高等特性,被广泛应用到航空航天、军事工业等领域.与其他焊接工艺相比,变极性等离子弧焊接在大型铝合金结构件加工方面具有突出优势. 针对轻金属合金等离子弧焊接过程中匙孔难以自由闭合的问题,提出了气电分离时序脉冲等离子弧环焊缝收弧方法,对比研究了环焊缝收弧方法与手工钨极惰性气体保护焊(tungsten inert gas welding, TIG焊)填补法焊缝匙孔闭合处的微观组织与力学性能. 结果表明,通过调节焊接起弧、收弧策略,实现了等离子弧匙孔自由闭合,焊缝收弧区成形良好,组织为均匀的等轴晶;抗拉强度为329.9 MPa,断后伸长率为16.3%,比TIG填补法的抗拉强度提高了22.91%,断后伸长率提高了55.24%. 平均硬度值为78.9 HV0.2,热影响区硬度呈下降趋势,熔合线处硬度呈升高趋势,焊缝区硬度波动范围为75 ~ 81 HV0.2.

     

Supramolecular bisporphyrin cages: Design and ways of self-assembly of supramolecular bisporphyrin structures for molecular nanomotors and nanosensors

Self-assembly of supramolecular ensembles of coordination bisporphyrins was studied in reactions of meso-tetrakis(3-hydroxyphenyl)porphyrinatozinc with LaCl₃, MnCl₂, CrCl₃, and SnCl₂ and exodentate ligands (1,4-diazabicyclo[2.2.2]octane and 4,4’-bipyridyl). A design and ways of self-assembly of bisporphyrins structures were developed. Original Russian Text ? Yu.P. Yashchuk, V.S. Tyurin, I.P. Beletskaya, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 6, pp. 608–614.