Electrochemical Separation of Multicomponent Tin-based Alloys in Salt Melts

The results obtained in a study of the electrochemical separation of multicomponent tin-based alloys in salt melts are presented. The influence exerted by electrolysis conditions on the discharge at the auxiliary electrode of a number of metals accompanying lead and tin was determined.     

Creation of thin oxide coatings and oxide nanopowders by anodic oxidation of metals in molten salts

We studied the feasibility of synthesizing ultrafine oxide powders by anodic oxidation of metals, such as zirconium and tantalum, in chloride + nitrate melts at temperatures above 830K. We showed that, varying the electrolyte composition, oxidation temperature, and anodic current density, one obtains either compact protective coatings on the specified metals or oxide powders with particle sizes of 50 to 200 nm.     

Metal extraction in activation analysis

Our investigations have shown the perspectives of pyrometallurgical methods in activation analysis based on metal extraction (ME). The technique of rapid micromelting (MM) not requiring special equipment has been developed. It has been shown that in non-mixed liquid metal-molten salt systems different elements such as noble, rare and dispersed ones can be quantitatively extracted from geological samples to be analyzed into metal collectors (bismuth, lead, tin, copper, iron, etc.). The same meltings have been supposed for extraction into the ionic salt melts of the impurity elements from the analyzed metals.     

Organic-Inorganic Insulating Coatings Based on Sol-Gel Technology

The approach for improving bending strength of temperature-resistant flexible ceramic electric insulating coatings prepared by sol-gel processing is considered. Starting suspensions, based on both tetraethoxysilane (TEOS)-derived modified sols and highly dispersed fillers such as Cr₂O₃, are used to deposit the coatings on metals and alloys. Some polymers and organic substances are tested as additives for improving flexibility of the ceramic coatings. The results of study of both bending strength and electrical strength of flexible hybrid organic-inorganic insulation formed on a nichrome wire are discussed. The data obtained on the chemical and phase structure of the coatings, which have been heat treated at temperatures from 95 to 1100°C, using DSC as well as X-ray scattering techniques are presented.     

Thin-layer chromatographic behavior and separation of alkaline earth metals on silica gel in aqueous sodium perchlorate solution

The thin-layer chromatographic behavior of alkaline earth metal ions (Mg2+, Ca2+, Sr2+, and Ba2+) in aqueous sodium perchlorate solutions on silica gel thin-layers impregnated with sodium hydroxide has been surveyed as a function of salt concentration. At salt concentrations above 2 mol 1(-1), the selectivity of the metals increased with a decrease in the crystal ionic radii; with further increases in salt concentration, the selectivity differences among the metals expanded remarkably. In the present systems, it was supposed that the cation exchange, the surface complexation, and the salting-out effect participate simultaneously in the adsorption of the metals on silica gel. Typical chromatograms for the mutual separation of the alkaline earth metals are presented.     

Electroactive conducting polymers for corrosion control

There is an intensive effort underway to develop new corrosion control coatings for structural metals. In part, this effort has been motivated by the desire to replace chromium(VI)-containing coatings currently used for corrosion control of iron and aluminum alloys. Cr(VI) has been shown to be hazardous to the environmental and to human health, and its use in many countries will be sharply curtailed in the coming years. Electroactive conducting polymers (ECPs) represent a class of interesting materials currently being explored for use in corrosion control coating systems, possibly as a replacement for Cr(VI)-based coatings. The electroactivity and the electronic conductivity (or semiconductivity) of ECPs set them apart from traditional organic coatings. As with chromate, interesting and potentially beneficial interactions of ECPs with active metal alloys such as steel and aluminum are anticipated, with concomitant alteration of their corrosion behavior. A review of this active research area will be presented in two parts. Here in Part 1, a general introduction to the topic of corrosion control by ECPs will be presented, including an overview of corrosion and its control by traditional methods, an introduction to ECPs and their properties, and a discussion of the processing issues surrounding the use of ECPs as coatings. Part 1 also includes a review of the literature on the use of ECPs as coatings (or components of coatings) on non-ferrous active metals, principally aluminum and aluminum alloys, although some work on zinc, copper, silver, titanium and silicon will also be described. In Part 2 of this review (to be published in the next issue of this journal), the rather extensive literature on the use of ECPs for the corrosion control of ferrous alloys (steels) will be reviewed. Electronic Publication     

Inorganic–organic sol gel hybrid coatings for corrosion protection of metals

Inorganic–organic hybrid coatings by sol–gel process are very suitable for fighting corrosion. Inorganic sols in hybrid coatings not only increase adhesion by forming chemical bonds between metals and hybrid coatings, but also improve comprehensive performances of polymer in the coatings. Different organic polymers or organic functionalities are introduced into gel network to achieve tailored properties, such as hydrophobic properties, increasing cross-linking density, etc. As for corrosion protection of metals organic components of hybrid coatings are selected to repel water and form dense thick films and reduce coating porosity. The factors, such as the ratio of inorganic and organic components, cure temperature, pigments in hybrid coatings, need to be optimized for attaining hybrid films with the maximum corrosion resistance. Electro-deposition technique offers relatively thick homogeneous defect-free hybrid coatings in comparison to dip or spin coating techniques. Green cerium ions and non-ionizable organic inhibitors are more developed in hybrid coatings nowadays than other corrosion inhibitors. Long-term corrosion resistance techniques of inhibitors are discussed. The inhibitors entrapped in the nanocontainers are doped in hybrid films to prolong release of the inhibitors to damaged zones, which is discussed in detail. Among all the nanocontainers of corrosion inhibitors the prospective techniques which show superior corrosion protection are cyclodextrin/organic inhibitor inclusion complexes and layer by layer assembly of organic corrosion inhibitors in nanocontainers. Super-hydrophobic property of hybrid coatings derives from low surface tension and surface roughness of hybrid coatings, which endues the films with excellent corrosion protection for metals, but the durable property of super-hydrophobic coatings needs to be improved for industrial application. An ideal multiple model of hybrid coatings for superior anti-corrosion of metals proposed is a combination of super-hydrophobic hybrid coatings and underlying hybrid coatings doped with sustained release of corrosion inhibitors on metal substrates.     

Effect of metals on melt oxidation of polyethylene

Oxidation of polyethylene (PE) melts in contact with metals (Cu, Pb, Au, Al, Zn, Ag) has been studied by infrared spectroscopy and differential thermal analysis (DTA). These metals may be divided into two groups, depending on their activity for oxidizing PE: namely, high-activity metals (Cu, Pb, Ag, Zn) and low-activity metals (Al, Au). During the oxidation of PE in contact with high-activity metals dissolution of the surface layer of metal is observed with accumulation of metal-containing compounds (salts of carboxylic acids) in the bulk of the polymer. With low-activity metals these phenomena are not observed. The rate of oxidation of PE on low-activity metals approaches the oxidation rate of nonmetals (polytetrafluoroethylene and inorganic glass). With certain high-activity metals (Cu, Pb) the process of oxidation is accelerated only in the early stage of oxidation; then the oxidation rate slows down and the oxidation process ceases. PE films separated from metal after being oxidized on it possess chemical memory, i.e., their oxidation rate depends on the nature of the metal with which they had been in contact, and on the duration of the contact oxidation. The effect of salts of carboxylic acids (metal stearates) on the oxidation of PE melts was also studied. Based on the data obtained, it is concluded that the rate of oxidation of PE melts on high-activity metals is controlled by metal-containing compounds which are the products of contact reactions.     

Simple preparation routes for corrosion protection hybrid sol‐gel coatings on AA 2024

In recent years, many hybrid inorganic‐organic systems have been proposed in order to replace the traditional conversion coatings on metals like aluminum, and some results have been promising. However, many proposed solutions are based on complicated processes which are not easy to be adapted to industrial scale. The aim of this study was to establish a simple process leading to the production of highly efficient corrosion protective hybrid sol‐gel coating systems for the aluminum alloys as replacement for the highly hazardous conventional chromate conversion coatings. Hybrid coatings have been realized by means of the sol‐gel process. CeO₂ and ZnO have been introduced as dispersions of nanoparticles in the system and used as corrosion inhibitors. The aim of this work was to obtain pore‐free coatings with increased barrier properties using nanoparticles that possess the double function of pore fillers and corrosion inhibitors. The proposed processes led to coating materials with good adherence to the aluminum substrate and an extremely long life in the accelerated neutral salt spray test according to DIN ISO 9227. Electrochemical impedance spectroscopy approves these results by high impedance values in the low‐frequency region of the Bode plot. Copyright © 2011 John Wiley & Sons, Ltd.     

Coexistence of Immiscible Liquid Phases in the LaPO<Subscript>4</Subscript>–SiO<Subscript>2</Subscript>–NaF–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> System

It was determined that the system LaPO₄–SiO₂–NaF–Nb₂O₅ within the temperature range 850–1200°C has regions of immiscibility of liquid phases (silicate and phosphate–salt melts). The coexisting melts have contrast chemical and phase compositions and structural-textural features, because of which the methods for extracting rare-earth elements and niobium from these melts differ. The silicate melts form glass, whereas the phosphate–salt melts have high crystallization ability. The mutual solubility of the liquid phases does not exceed 5%. The components of the system are contrastively distributed between the silicate and phosphate–salt melts. A fraction of 95–97% of niobium is extracted into the silicate melt, and 93–95% of La and P is extracted into the phosphate–salt melt.     

Wetting of a Charged Surface of Glassy Carbon by Molten Alkali-Metal Chlorides

Values of the contact angle of wetting of a surface of glassy carbon by molten chlorides of lithium, sodium, potassium, and cesium are measured by the meniscus weight method to determine the common factors of wettability of solid surfaces by ionic melts upon a change in the salt phase composition and a jump in electric potential. It is found that with a potential shift in the positive direction the shape of the curve of the contact angle’s dependence on the potential varies upon substitution of one salt by another: the angle of wetting shrinks monotonously in lithium chloride but remains constant in molten cesium chloride. This phenomenon is explained by the hypothesis that the nature of the halide anion adsorption on the positively charged surface of an electrode is chemical and not electrostatic. It is shown that the adsorption process is accompanied by charge transfer through the interface, with covalent bonding between the adsorbent and adsorbate.

     

Equilibrium and Transport Properties of Low-Melting Salts

An understanding of the physical and chemical phenomena and the structure of salt melts calls not only for kinetic and spectroscopic data but also for systematic studies on the equilibrium and transport properties of individual systems. The present article deals with the activity coefficients, transport numbers, and self-diffusion and interdiffusion coefficients of salt melts, and the results of consistent measurements of these quantities are reported.     

Electrodeposition of tungsten and molybdenum metals and their carbides from low-temperature halide-oxide melts

The electrodeposition of tungsten and molybdenum metals and their carbides from the halide-oxide melts at a temperature of 550°C is studied using cyclic voltammetry and potentiostatic and galvanostatic electrolyses. The conditions of concurrent electroreduction of fluoroxide complexes of tungsten and molybdenum with carbon dioxide and also with nickel and cobalt ions in the halide-oxide melts at 550°C are found. The optimal conditions for the production of tungsten and molybdenum metals, tungsten (molybdenum) carbides, and binary carbides of tungsten with nickel (cobalt) from the oxide-halide melts are determined.     

The Nanocrystalline Ceria Sol-Gel Coatings for High Temperature Applications

Sol-gel technology was utilized to produce nanocrystalline thin films of CeO₂ on substrates with different oxidation resistance at high temperatures. After deposition, the coatings were composed of CeO₂ crystallites with a size of 5 nm, randomly oriented on all the substrates. The annealing of gel deposited on Pt and Si substrates was accompanied by evaporation of water and other species and followed by growth of crystallites, without formation of any evident texture. Conversely, the annealing of coatings deposited on easy oxidizing substrates of Nr, Cr, or Ni−Cr alloys resulted in incorporation of CeO₂ crystallites into growing native oxide, and in slowing the oxidation rate. Examples of the application of CeO₂ ceramics as coatings deposited on selected metals and alloys for improving their oxidation performance are presented.     

Inter-Alkali-Metal Dative Bond in the MMN3− (M=Alkali Metal) Cluster

Alkali metals are generally Lewis acids. On the contrary, Lewis basic character of alkali metals forming donor – acceptor complexes is a very rare phenomenon. In this contribution, I have theoretically designed an anionic cluster MMN₃⁻ (M=alkali metals) on the basis of experimentally known reagent, alkali salt of azide ion MN₃, which shows unprecedented M:⁻→M donor-acceptor interaction. To the best of author's knowledge, the characterization of such donor-acceptor interaction among alkali metals is unprecedented. Formation of the 2c–2e donor-acceptor bonds have been confirmed by quantum theory of atoms in molecules and electron localization function analyses. The calculated bond dissociation energies are significant suggesting their possible spectroscopic identification.     

NaCl-NaBr系熔盐溶液的分子动力学研究

近年来，用计算机模拟馆公的结构和性质的研究已有较大进展[1，2]．但研究工作多集中在有阴离子相同、阳离子不同的盐组成的“同阴离子系”（commonanionsystems），而对由阳离子相同、阴离子不同的盐组成的“同阳离子系”（commoncationsystems）熔盐溶液则甚少研究．鉴于自然界和生产中同阳离子系也不乏实例，建立同阳离子系熔盐溶液的理论屯有必要．为止匕我们先选择NaCI－NaBr系熔盐溶液（同阳离子系的一个最简单的典型）为对象，开展分子动力学方法计算机模拟研究．1模型和计算方法采用标准文献中的计算模拟和方法，离子间劳用Fumi-…     

IR-Spectroscopic investigations on phosphated galvanized steel

Hopeite-type phosphate coatings in which zinc is replaced by other metals like nickel, manganese and magnesium are of great interest as conversion coatings on galvanized steel in the automotive and appliance industries. The analytical characterization of such coatings produced in special processes is not possible by XRD because the different types of hopeite are isomorphic. In this paper it is shown that the kind of metal substitution is responsible for certain specific features in the infrared reflection spectra. Furthermore the structural changes caused by dehydration due to heating of the coatings were studied and differences in the thermal stability of the different coatings thus could be observed.     

Electrosynthesis of metal-containing polymeric coatings based on 1-vinylimidazole and acrylamide

Possibility of electrochemical formation of metal-polymeric nanocomposites and coatings on purely iron and steel electrodes by combining the electrochemically initiated (co)polymerization of 1-vinylimidazole and acrylamide with the cathodic deposition of metals was studied. Polymeric coatings were formed by the method of contact exchange of metals. The structure and selected properties of metal-polymeric coatings were examined. It was found that silver nanoparticles are uniformly distributed in the polymeric matrix. A thermogravimetric analysis demonstrated that the metal-polymers synthesized possess a high thermal stability.     

Dynamic criterion of the complex formation and the structure of molten halides: To the fortieth anniversary of the autocomplex model for the structure of melts

The results of my latest research into molten halides of alkali and alkaline-earth metals by a method of Raman spectroscopy are reviewed. A dynamic criterion for the formation of complexes in melts is considered. The results that testify to the existence of instantaneous and short-lived autocomplexes in these liquids are analyzed in the light of an autocomplex model for the structure of melts.     

熔盐电化学的新进展

本文主要介绍熔盐体系、熔盐电池、熔盐电沉积金属以及合金、电合成化合物材料等方面的新进展 ,预期熔盐电化学在能源、环境保护和资源利用等领域中的应用 .