氮离子注入GCr15轴承钢改性的时效机理及摩擦学性能探讨

对１２年前经离子注入处理后的ＧＣｒ１５轴承钢表面耐磨性能的时间效应进行了探讨。发现离子注入材料的改性效果存在时间效应性。利用ＡＥＳ和Ｘ射线衍射分析发现，掺杂原子及材料表面吸附的氧原子的多元迁移和硬质相的生成是造成离子注入材料改性时效的原因。     

Diaminodiacid Bridges to Improve Folding and Tune the Bioactivity of Disulfide‐Rich Peptides

Disulfide‐rich peptides containing three or more disulfide bonds are promising therapeutic and diagnostic agents, but their preparation is often limited by the tedious and low‐yielding folding process. We found that a single cystine‐to‐diaminodiacid replacement could significantly increase the folding efficiency of disulfide‐rich peptides and thus improve their production yields. The practicality of this strategy was demonstrated by the synthesis and folding of derivatives of the μ‐conotoxin SIIIA, the preclinical hormone hepcidin, and the trypsin inhibitor EETI‐II. NMR and X‐ray crystallography studies confirmed that these derivatives of disulfide‐rich peptide retained the correct three‐dimensional conformations. Moreover, the cystine‐to‐diaminodiacid replacement enabled structural tuning, thereby leading to an EETI‐II derivative with higher bioactivity than the native peptide.     

Crystalline Hetero‐Stereocomplexed Polycarbonates Produced from Amorphous Opposite Enantiomers Having Different Chemical Structures

Stereocomplexation is the stereoselective interaction between two opposite enantiomeric polymers through an interlocked orderly assembly. Most studies focus on the stereocomplex formation from the crystalline opposite enantiomers having the identical structure; nevertheless, rare examples were reported regarding the crystalline stereocomplexes from enantiomeric polymers having different chemical structures. Herein we show a strategy for polymer orderly assembly through the formation of crystalline hetero‐stereocomplexed polymeric materials by the cocrystallization of amorphous isotactic polycarbonates with different chemical structures and opposite configurations. The behaviors in the crystalline state are significantly different from that of the component enantiomeric polymers or their homo‐stereocomplexes. This study is expected to open up a new way to prepare various semicrystalline materials having a wide variety of physical properties and degradability.     

A Chemically Triggered and Thermally Switched Dielectric Constant Transition in a Metal Cyanide Based Crystal

A dielectric constant transition is chemically triggered and thermally switched in (HPy)₂[Na(H₂O)Co(CN)₆] ( 2 , HPy=pyridinium cation) by single‐crystal‐to‐single‐crystal transformation and structural phase transition, respectively. Upon dehydration, (HPy)₂[Na(H₂O)₂Co(CN)₆] ( 1 ) transforms to its semi‐hydrated form 2 , accompanying a transition from a low‐dielectric state to a high‐dielectric state, and vice versa. This dielectric switch is also realized by a structural phase transition in 2 that occurs between room‐ and low‐temperature phases, and which corresponds to high‐ and low‐dielectric states, respectively. The switching property is due to the variation in the environment surrounding the HPy cation, that is, the hydrogen‐bonding interactions and the crystal packing, which exert predominant influences on the dynamics of the cations that transit between the static and motional states.     

Direct Detection of the Superoxide Anion as a Stable Intermediate in the Electroreduction of Oxygen in a Non‐Aqueous Electrolyte Containing Phenol as a Proton Source

The non‐aqueous Li–air (O₂) battery has attracted intensive interest because it can potentially store far more energy than today′s batteries. Presently Li–O₂ batteries suffer from parasitic reactions owing to impurities, found in almost all non‐aqueous electrolytes. Impurities include residual protons and protic compounds that can react with oxygen species, such as the superoxide (O₂^?), a reactive, one‐electron reduction product of oxygen. To avoid the parasitic reactions, it is crucial to have a fundamental understanding of the conditions under which reactive oxygen species are generated in non‐aqueous electrolytes. Herein we report an in situ spectroscopic study of oxygen reduction on gold in a dimethyl sulfoxide electrolyte containing phenol as a proton source. It is shown directly that O₂^?, not HO₂, is the first stable intermediate during the oxygen reduction process to hydrogen peroxide. The unusual stability of O₂^? is explained using density functional theory (DFT) calculations.     

Copper‐Catalyzed Trifluoromethylazidation of Alkynes: Efficient Access to CF3‐Substituted Azirines and Aziridines

A novel method for convenient access to CF₃‐containing azirines has been developed, and involves a copper‐catalyzed trifluoromethylazidation of alkynes and a photocatalyzed rearrangement. Both terminal and internal alkynes are compatible with the mild reaction conditions, thus delivering the CF₃‐containing azirines in moderate to good yields. The azirines can be converted into various CF₃‐substituted aziridines.     

Flexible,Stretchable, and Rechargeable Fiber‐Shaped Zinc–Air Battery Based on Cross‐Stacked Carbon Nanotube Sheets

The fabrication of flexible, stretchable and rechargeable devices with a high energy density is critical for next‐generation electronics. Herein, fiber‐shaped Zn–air batteries, are realized for the first time by designing aligned, cross‐stacked and porous carbon nanotube sheets simultaneously that behave as a gas diffusion layer, a catalyst layer, and a current collector. The combined remarkable electronic and mechanical properties of the aligned carbon nanotube sheets endow good electrochemical properties. They display excellent discharge and charge performances at a high current density of 2 A g^?1. They are also flexible and stretchable, which is particularly promising to power portable and wearable electronic devices.     

Copper as a Robust and Transparent Electrocatalyst for Water Oxidation

Copper metal is in theory a viable oxidative electrocatalyst based on surface oxidation to Cu^III and/or Cu^IV, but its use in water oxidation has been impeded by anodic corrosion. The in situ formation of an efficient interfacial oxygen‐evolving Cu catalyst from Cu^II in concentrated carbonate solutions is presented. The catalyst necessitates use of dissolved Cu^II and accesses the higher oxidation states prior to decompostion to form an active surface film, which is limited by solution conditions. This observation and restriction led to the exploration of ways to use surface‐protected Cu metal as a robust electrocatalyst for water oxidation. Formation of a compact film of CuO on Cu surface prevents anodic corrosion and results in sustained catalytic water oxidation. The Cu/CuO surface stabilization was also applied to Cu nanowire films, which are transparent and flexible electrocatalysts for water oxidation and are an attractive alternative to ITO‐supported catalysts for photoelectrochemical applications.     

Threading Chalcogenide Layers with Polymer Chains

Inserting polymers into a crystalline inorganic matrix to understand the structure, position, and the structure–property relationships of the resulting composites is important for designing new inorganic‐organic materials and tuning their properties. Single crystals of polymer‐chalcogenide composites were successfully prepared by trapping polyethyleneglycol within a selenidostannate matrix under surfactant‐thermal conditions. This work might provide a new strategy for preparing novel crystalline polymer‐inorganic composites through encapsulating polymer chains within inorganic matrices.     

Realizing both High Energy and High Power Densities by Twisting Three Carbon‐Nanotube‐Based Hybrid Fibers

Energy storage devices, such as lithium‐ion batteries and supercapacitors, are required for the modern electronics. However, the intrinsic characteristics of low power densities in batteries and low energy densities in supercapacitors have limited their applications. How to simultaneously realize high energy and power densities in one device remains a challenge. Herein a fiber‐shaped hybrid energy‐storage device (FESD) formed by twisting three carbon nanotube hybrid fibers demonstrates both high energy and power densities. For the FESD, the energy density (50 mWh cm^?3 or 90 Wh kg^?1) many times higher than for other forms of supercapacitors and approximately 3 times that of thin‐film batteries; the power density (1 W cm^?3 or 5970 W kg^?1) is approximately 140 times of thin‐film lithium‐ion battery. The FESD is flexible, weaveable and wearable, which offers promising advantages in the modern electronics.