Effects of dissolution on plastic deformation and cracking of metals

The effects of surface dissolution on plastic deformation of metals, and the operating mechanisms, depend on many variables: stress; frequency of stress fluctuations; strain rate; temperature; metallographic constituents and their distribution; surface films; adsorbed species; surface energy; electrochemical potential and current; dissolution morphology; crack tip geometry; dislocation mobility; and the chemistry at the crack tip in the environment as well as in the metal. The manifestation of these variables in different relative proportions in different systems causes a variety of metal/environment interactions, the most extreme of which are stress-corrosion cracking and corrosion fatigue. During simultaneous action of stress and dissolution, stress-corrosion cracking occurs only with specific metal/environment combinations within critical electrochemical-potential ranges, whereas corrosion fatigue develops at dissolution rates greater than a critical value. In addition to these forms of degradation, the dissolution process may inject defects — such as vacancies, divacancies, or dislocations — into the metal lattice, with resulting alteration in dislocation behaviour and plastic-deformation characteristics. Dissolution may also influence the films that normally exist on metal surfaces and, consequently, the dislocation arrangements which depend on these films. This review is a systematic presentation and discussion of those critical — and sometimes controversial — experiments that elucidate the effects at an atomic level of surface dissolution on plastic deformation of metals.     

DFT study of metal cation-induced hydrogelation of cellulose nanofibrils

We report a density functional theory study of cation-induced bonding between carboxylated cellulose nanofibrils (CNFs). We describe a methodology of using cleaved cellulose crystal unit cells to develop simple surface and molecular models of charged CNFs. We compare bond lengths, binding energies, and displaced solvation volumes for interfibril models intercalated with alkali, alkaline earth, main group, or transition metal cations, surrounded by an implicit solvent. We characterize the type of bonding interactions that occur between metal cations, Mⁿ⁺ and carboxylated CNF surfaces by calculating the electronic density of states and Mayer bond orders. We find that Mⁿ⁺–O interactions for alkaline earth metal systems are predominantly electrostatic whereas transition metal cations form stronger, more covalent bonds with enhanced valence orbital overlap. Our results show that multivalent—as opposed to monovalent—ions can create CNF networks by effectively crosslinking multiple fibrils through surface carboxylate anions. Our computational results agree with empirical models of metal–carboxylate binding, while also providing a deeper understanding of the bonding mechanisms for different cations. Our findings help to explain trends in recent CNF hydrogelation experiments, and we also predict the existence of two new hydrogels—CNF-Mg²⁺ and CNF-Zr⁴⁺.     

Artificial Allosteric Receptors

Cooperative effects in the binding of two or more substrates to different binding sites of a receptor that are a result of a conformational change caused by the binding of the first substrate—also referred to as the effector—are called allosteric effects. In biological systems, allosteric regulation is a widely used mechanism to control the function of proteins and enzymes in cellular metabolism. Inspired by this a lot of efforts have been made in supramolecular chemistry to implement this concept into artificial systems to control functions as molecular recognition, signal amplification, or even reactivity and catalysis. This review gives an up‐to‐date overview over the different approaches that have been reported ever since the first examples from the late 1970s/early 1980s. It covers both homo‐ and heterotropic examples and is divided according to the nature of the effector—cationic, anionic, or neutral—effectors and systems that use combinations of those.     

Investigation of the state of palladium in the Pd/SO4/ZrO2 system by diffuse-reflectance IR spectroscopy

The Pd/ZrO₂ and Pd/SO₄/ZrO₂ systems were investigated by diffuse-reflectance IR spectroscopy using CO as the probe molecule. For the Pd/ZrO₂ system, the behavior of the metal is characteristic of the weak metal-support interaction. Intense bands attibuted to the bridging CO species indicate the formation of large metal particles in the reduced systems. Modification of the ZrO₂ support with SO₄ ^2? anions leads to an increase in the metal—support interaction and makes the metal more resistant to reduction. On the surface promoted by SO₄ ^2? anions, metal particles with a positive charge (Pd⁺ and Pd^δ+) were observed. The smaller the size of the metal clusters and the higher degree of oxidation of sulfur, the stronger the influence of acidic protons and surface sulfur compounds on the metal.     

Calculation of the optimal experimental conditions for liquid—liquid extractions with diethyldithiocarbamic acid

A simple mathematical treatment of the liquid—liquid extraction of metals with diethyldithiocarbamic acid is given. The expressions derived can be applied directly in practical work and have been checked against experiments with some metals. The metal extraction constants for the carbon tetrachloride—water and chloroform—water systems are listed.     

Review of the molar heats of chemisorption and chemabsorption by crystalline oxides and the surface “homogeneity versus heterogeneity” problem

To obtain a solution of the surface “homogeneity versus heterogeneity” problem, the results of microcalorimetric measurements of the dependences of the molar heats of chemisorption and chemabsorption of different gases on the amounts of chemisorbed or chemabsorbed gases in more than 20 gas/metal-oxide systems, in which the molar chemisorption heats are coverage-independent over rather wide ranges of the surface coverages, are presented. In order to approach the states of the metal oxide samples to those in real catalytic processes catalyzed by these oxides, the coverage dependences of the heats of chemisorption of gases at the samples were measured for a number of gas/metal-oxide systems against the chemisorbed amounts of not only the gas under study but also of another gas chemisorbed previously. The calorimetric data-set is supplemented with data obtained by other methods capable of helping to solve the surface “homogeneity versus heterogeneity” problem. These data are discussed together with the data on chemisorption in more than 40 gas/metal systems for which homogeneity of the surfaces was stated in our previous review. The entire set of the measurements was published for several decades by about 40 different composite authors. The chemisorption and chemabsorption mechanisms are discussed. It is concluded that thermally stabilized powder metal and metal oxide surfaces are homogeneous relative to the chemical ability of their atoms in chemisorption and catalytic processes in line with Langmuir’s opinion and the band theory of solids.     

SCF MO pseudopotential studies of chemisorption hydrogen + Pt(111) clusters

The Ewig—van Wazer NOCOR pseudopotential scheme is sued, with minor modifications, in SCF MO calculations on the interaction of a hydrogen atom with clusters of up to four platinum atoms. The electronic structures of the clusters and the nature of the metal—hydrogen bond are investigated; the results are compared with those of extended Hückel theory for the same systems.     

Alkali and alkaline-earth ion vibrations in solvent cages,coordination compounds,glasses and related systems

Alkali metal ion—oxygen donor solvent cages as well as coordination compounds, alkali metal oxide glasses and oxyanion salts of alkali metals exhibit low-frequency bands in the infrared spectrum characteristic of the cation—oxygen polyhedra. Similar bands are seen with nitrogen donors. Alkaline earth ions also show such absorption bands due to quantised vibration of cations. These bands not only provide a means of establishing the nature of cation coordination in diverse systems, but also serve as probes to examine ion-solvent interactions.     

PHOTOPOLYMERIZATION IN THE MICELLAR SYSTEMS Ⅳ THE PHOTOSENSITIZATION EFFECTS OF THE BENZOPHENONES WITH DIFFERENT CHARGE IN IONIC MICELLAR SYSTEMS*

The photosensitization effects of the benzophenone derivatives having different charges, such as cationic BP(BP—CH_2—N~+ (C_2H_5)_3Br~-) (PKT-1), anionic BP(BP—COONa) and the neutral BP in the various ionic micellar systems were studied. From the photopolymerization of MMA initiated by the various BP/TEA in different micellar systems, the results obtained show that the polymerization rate is in the order of PKT-1>BP>BP—COONa in the SDS anionic micelle. On the contrary, the order changes to BP—COONa>BP>PKT-1 in the CTAB cationic mieelle, and to BP—COONa≈PKT-1>BP in the PKT-3 functional micelle. It is noteworthy that the PKT-1/SDS system is more efficient with its quantum yield more than 50 times compared with that of simple BP/H_2O system.     

TiO2/UV/O2和TiO2/UV/N2体系降解水中对氯硝基苯

以商用TiO₂P25为催化剂,分别在TiO₂/UV/O₂和TiO₂/UV/N₂两种体系下进行降解对氯硝基苯(pCNB)试验.采用ESR对两种体系下光催化反应形成的·OH进行测定,利用LC-MS对两种体系下反应形成的中间产物进行了定性和定量分析,最后对pCNB降解过程中氯和硝基的存在形式进行了研究.结果表明:TiO₂/UV/O₂体系的催化降解效果要明显优于TiO₂/UV/N₂体系;两种反应体系都有·OH产生,并且TiO₂/UV/O₂体系产生的·OH的量多于TiO₂/UV/N₂体系产生的·OH的量;TiO₂/UV/O₂体系形成的中间产物的种类要多于TiO₂/UV/N₂体系形成的,苯环上的氢、氯、硝基均可被·OH取代形成对硝基酚(pNP)、5-氯-2-硝基酚(5-C-2-PN)等酚类物质;两种体系下均有Cl^-和NO₂^-存在,其中Cl^-生成势与pCNB的去除势一致,只有TiO₂/UV/O₂体系中存在NO₃^-.     

Studies in some new initiator systems for vinyl polymerization. Part I. Molecular halogens or halates as one component

Several new initiating systems involving a molecular halogen, halates, or perhalate as one of the components and a reducing metal salt, ammonia, an amine or an organic compound as the other component, have been introduced for the aqueous (and in a few cases the non-aqueous) polymerization of methyl methacrylate. Some of the resulting polymers have been subjected to endgroup analysis by the application of the ultrasensitive dye techniques recently developed in our laboratory. Reducing metal salt—halogen-initiated polymers are found to incorporate hydroxyl and halogen endgroups, while polymers initiated by amine—halogen systems incorporate hydroxyl and halogen as well as amino endgroups. However, in the ammonia—halogen system polymers incorporate only halogen endgroups. On the basis of the results of the endgroup analysis of the polymers an attempt has been made to explain the probable initiation mechanism with regard to the nature and identity of the initiating species involved in such processes.     

The Persistent Radical Effect in Organic Synthesis

Radical–radical couplings are mostly nearly diffusion‐controlled processes. Therefore, the selective cross‐coupling of two different radicals is challenging and not a synthetically valuable transformation. However, if the radicals have different lifetimes and if they are generated at equal rates, cross‐coupling will become the dominant process. This high cross‐selectivity is based on a kinetic phenomenon called the persistent radical effect (PRE). In this Review, an explanation of the PRE supported by simulations of simple model systems is provided. Radical stabilities are discussed within the context of their lifetimes, and various examples of PRE‐mediated radical–radical couplings in synthesis are summarized. It is shown that the PRE is not restricted to the coupling of a persistent with a transient radical. If one coupling partner is longer‐lived than the other transient radical, the PRE operates and high cross‐selectivity is achieved. This important point expands the scope of PRE‐mediated radical chemistry. The Review is divided into two parts, namely 1) the coupling of persistent or longer‐lived organic radicals and 2) “radical–metal crossover reactions”; here, metal‐centered radical species and more generally longer‐lived transition‐metal complexes that are able to react with radicals are discussed—a field that has flourished recently.     

Selected properties of Pt(111) modified surfaces: A DFT study

Density functional theory calculations were employed to investigate the electronic properties of a Pt(111) surface modified with foreign atoms. The effects of alloying platinum with molybdenum, palladium, and tin changed the interaction between adsorbate orbital and metal d band. This letter discusses the interaction between metal atoms and adsorbate and its influence on electronic structure rearrangement of the species—changes that must be taken into account to explain the behavior of catalytic systems and sensors. Mo/Pt(111) and Sn/Pt(111) exhibited lower susceptibility to poisoning by CO, compared with pure platinum. Both Pt-based materials are expected to find utility in electrodes for alcohol and hydrogen oxidation.     

离子液体介导CO2化学转化研究进展

The efficient utilization of carbon dioxide (CO₂) as a C1 feedstock is of great significance for green and sustainable development. Therefore, the efficient chemical conversion of CO₂ into value-added products has recently attracted a lot of research attention in recent years. The transformation of CO₂ generally requires high-energy substrates, specific catalysts, and harsh reaction conditions due to its high thermodynamic stability and kinetic inertness. Consequently, several efforts have been dedicated toward the development of high-performance catalysts and new reaction routes for CO₂ conversion over the last few decades. To date, many routes of convert CO₂ into value-added chemicals have been proposed, together with the development of heterogeneous and homogeneous catalysts. Among the advanced catalysts reported to date, ionic liquids (ILs) have been widely investigated and show great potential for the efficient, selective, and economical conversion of CO₂ into highly valuable products under mild conditions, even under ambient conditions. Some task-specific ILs have been designed with unique functional groups (e.g., —OH, —SO₃H, —NH₂, —COOH, and —C≡N), which can act as the solvent, absorbent, activating agent, catalyst, or cocatalyst to realize the transformation of CO₂ under metal-free and mild conditions. In addition, a variety of catalytic systems composed of ILs and metal catalysts have also been reported for the transformation of CO₂, in which the combination of the IL and metal catalyst is responsible for CO₂ conversion with high efficiency. In this review article, we summarize the recent advances in IL-mediated CO₂ transformation into chemicals prepared via C—O, C—N, C—S, C—H, and C—C bond forming processes. ILs that can chemically capture CO₂ with high capacity are first introduced, which can activate CO₂ via the formation of IL-based carbonates or carbamates, thus realizing the transformation of CO₂ under metal-free and mild conditions. Recent progress in IL-mediated CO₂ transformations to form carbonates and various kinds of N- and S-containing compounds (e.g., oxazolidinones, ureas, benzimidazolones, formamides, methylamines, benzothiazoles, and other chemicals) as well as CO₂ hydrogenation to give formic acid, methane, acetic acid, low-carbon alcohols, and hydrocarbons has been summarized in this review with a focus on the reaction routes, catalytic systems, and reaction mechanism. In these reactions, ILs can simultaneously activate the substrate via strong H-bonding in addition to activating CO₂, and the cooperative effects among the ionic and molecular species and metal catalysts accomplish the reactions of CO₂ with various kinds of substrates to afford a wide range of value-added chemicals. Finally, the shortcomings and perspectives of ILs are discussed. In short, IL-mediated CO₂ transformations provide green and effective routes for the synthesis of high-value chemicals, which may have great potential for a wide range of applications.     

Elektromotorisches Verhalten von Glaselektroden in flüssigem Ammoniak

Glass electrodes behaving as protodes or alkali cation electrodes in aqueous systems respond to the protonated solvent in liquid ammonia at — 38°C and can be used to measure the activity of NH₄⁺. Deviations in the response to the activity of NH₄⁺ are shown to be due to an alkali metal function (alkaline error) of the glass electrodes. The selectivity of glass electrodes for different alkali metal cations changes drastically from water to liquid ammonia.     

金属离子Na+ , Li+ , Mg2+与硫酸根离子形成的无水缔合物种的从头算量子化学研究

计算并讨论了Na+, Li+和Mg2+ 3种离子与SO42-离子形成离子缔合物的结构以及阳离子的结合对ν1-SO42-频率的影响. 结果表明, 在缔合物结构方面, 阳离子数目越少, 离子间斥力越小, 越容易形成阳离子与硫酸根间距离更短, 结合更紧密的双齿缔合结构; 而当阳离子数目增加时, 特别是当具有2个正电荷的Mg2+离子数目较多时, 离子间的斥力使多离子团簇不稳定, 易形成阳离子与硫酸根间距离更长的单齿缔合结构. 有2种阳离子作用可影响ν1-SO42-频率, 一种是极化作用, 可使ν1-SO42-频率红移; 另一种是成键作用, 可使ν1-SO42-频率蓝移. 当金属离子数目≤2时, 阳离子的极化作用占主导地位, 第一个阳离子能使ν1-SO42-频率发生红移, 而当阳离子数目增多时, 不同方向结合的其它阳离子可以削弱第一个阳离子的极化作用, 因此导致多离子团簇中ν1-SO42-频率红移的减小. 当阳离子数目≥3时, 极化作用影响减小, 成键作用占据主导地位, 导致ν1-SO42-频率更大蓝移的单齿缔合结构取代双齿结构, 并使多离子团簇中的ν1-SO42-频率继续发生蓝移.     

多肽基金属离子传感器

多肽基金属离子传感器作为一种基于多肽序列而设计的新型传感器,越来越受到研究者的关注.多肽作为一类重要的生物小分子,具有合成方法成熟、简便、成本低,且能够以多齿配位状态与金属离子结合等优点.多肽基传感器对金属离子具有高灵敏性和高选择性,且可以通过调节多肽序列进一步优化.与其他类型传感器相比,多肽基金属离子传感器具有良好的...     

Covalent Grafting of Carbon Nanotubes with a Biomimetic Heme Model Compound To Enhance Oxygen Reduction Reactions

The oxygen reduction reaction (ORR) is one of the most important reactions in both life processes and energy conversion systems. The replacement of noble‐metal Pt‐based ORR electrocatalysts by nonprecious‐metal catalysts is crucial for the large‐scale commercialization of automotive fuel cells. Inspired by the mechanisms of dioxygen activation by metalloenzymes, herein we report a structurally well‐defined, bio‐inspired ORR catalyst that consists of a biomimetic model compound—an axial imidazole‐coordinated porphyrin—covalently attached to multiwalled carbon nanotubes. Without pyrolysis, this bio‐inspired electrocatalyst demonstrates superior ORR activity and stability compared to those of the state‐of‐the‐art Pt/C catalyst in both acidic and alkaline solutions, thus making it a promising alternative as an ORR electrocatalyst for application in fuel‐cell technology.     

Properties of hybrid materials incorporating tetrabutyl titanate and tetraethoxysilane with ethylene-propylene nonconjugated diene terpolymer (EPDM-ENB) via sol-gel process

New flexible hybrid materials had been synthesized successfully by incorporating ethylene-propylene nonconjugated diene terpolymer (EPDM—ENB), which had been functionalized with 3-aminopropyl trimethoxysilane (APS), with highly reactive tetrabutyl titanate and tetraethoxysilane. The materials with low inorganic content displayed high transparency due to the formation of covalent bonds between the polymer chains and the inorganic network in the hybrids. The titanium systems were found to be more compatible than the corresponding silica hybrid materials of equal alkoxide content. As the inorganic content increased, the dynamic tensile modulus of the hybrid showed significant improvement over pure EPDM—ENB in the region above T_g of EPDM—ENB. For the EPDM—ENB/TiO₂ hybrids, when the total metal alkoxide content is fixed, the properties of the hybrids were not affected by partial replacement of tetrabutyl titanate with tetraethoxysilane. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2403–2409, 1997