Structural and physicochemical properties of silver-rich Ag–Al alloys

The X-ray diffraction, Scanning Electron Microscopy, Differential Scanning Calorimetry, dilatometric and electrical conductivity measurements were used to study the structural and physicochemical properties of selected silver-rich alloys from Ag–Al system. All the studied alloys, containing from 10 to 37 at. % of Al (Ag₉₀Al₁₀, Ag₈₅Al₁₅, Ag₇₇Al₂₃, Ag₇₅Al₂₅, Ag₇₂Al₂₈, Ag₇₀Al₃₀, Ag₆₃Al₃₇), were prepared from high purity metals by melting in a glove-box filled with a high purity argon atmosphere. The obtained X-ray diffraction patterns and microstructure observation of alloys containing up to 15 at. % of Al suggested that in this range only solid solution of silver exists. The thermal analysis showed heat effects related to phase transitions in Ag–Al system. In addition, the thermal expansion studies revealed an anomalous behavior in expansion for some composition of alloys associated with the phase transition. The electrical conductivity values rapidly changed, which may be associated with the formation of different phase areas in the Ag–Al system.Based on the results obtained in this work and critically reviewed literature data a thermodynamic re-optimization of the binary Ag–Al system using CALPHAD method was proposed. A good agreement between calculation and experiment was found.     

Characterization of superficial modification of ferrous rusted substrates subjected to dechlorination-electrochemical process

Preservation of archaeological artefacts after their removal from saline media is a difficult task due to the chloride content of the oxide layers which are unstable in atmospheric conditions, especially if the relative humidity exceeds 85%. For this reason, removal of chlorides from rust layers is one of the priorities of conservationists or restorers of historical artefacts. However, removal of chloride ions is not an easy procedure because of the many considerations involved in the process. In this research, artificially pre-rusted iron samples and an actual historical cannonball were subject to a dechlorination process in a potassium hydroxide solution to measure constant chloride release in a bulk solution. After the chloride removal process, a commercial protective layer was applied to the rust for stabilization purposes. It was calculated that the kinetics of the dechlorination process is driven by diffusion behaviour following Fick’s second law. When this diffusion process prevails, the dechlorination extraction affects the integrity of rust layers as is demonstrated with scanning electron microscopy and X-ray diffraction analyses. It was proven that the chloride removal procedure causes the studied iron layers to stiffen, provoking superficial modification and, in some cases, fractures of the rust. By means of electrochemical impedance spectroscopy it was calculated that the magnitude of the positive effect of the dechlorinated samples depends on the protective features of the rust. Therefore, this research reveals that an efficient chloride removal procedure depends on the electrochemical properties of the dechlorination process and the initial morphology of the iron rust.     

Fabrication of composites from different carbon content ferrous powders adopting thermomechanical processes

In this research, deep consolidation technique is utilized for processing of low and high carbon content ferrous powders to manufacture composite material. High carbon content ferrous powders were used as reinforcing material. The powder particles were allowed to mix with low carbon content ferrous powders in 50:50 weight percent for fabrication of composites. The composites were heat treated at three different temperatures (i.e., 800°C, 900°C, and 1000°C). The changes in microstructure, microhardness, the grain size, and bonding among powder particles were studied. Refinement of grains was observed and this led to improved hardness enabling the processed material to be used as a suitable composite. Abrasive wear tests were carried out using a laboratory tribometer in dry reciprocating sliding contact against Sic abrasive paper. The outcomes demonstrate that the abrasive wear resistance was notably affected by the treatment temperature and hardness of the composites.     

Recent advances during CH4 dry reforming for syngas production: A mini review

Given the continuing issues of environment and energy, methane dry reforming for syngas production have sparked interest among researchers, but struggled with the process immaturity owing to catalyst deactivation. This review summarizes the recent advances in the development of efficient and stable catalysts with strong resistance to coking and metal sintering, including the application of novel materials, the assessment of advanced characterizations and the compatibility to improved reaction system. One feasible option is the crystalline oxide catalysts (perovskite, pyrochlore, spinel and LDHs), which feature a fine metal dispersion and surface confinement effect via a metal exsolution strategy and exhibit superior reactivity and stability. Some new materials (h-BN, clays and MOFs) also extend the option because of their unique morphology and microstructure. It also is elaborated that progresses were achieved in advanced characterizations application, leading to success in the establishment of reaction mechanisms and attributions to the formed robust catalysts. In addition, the perspective described the upgrade of reaction system to a higher reaction efficiency and milder reaction conditions. The combination of efficient reaction systems and robust catalysts paves a way for a scaling-up application of the process.     

In2S3-NiS co-decorated MoO3@MoS2 composites for enhancing the solar-light induced CO2 photoreduction activity

In₂S₃-NiS co-decorated MoO₃@MoS₂ (INS/MoO₃@MoS₂) heterojunctions were prepared in nonthermal plasma via the in-situ sulfurization for enhancing the solar-light photocatalytic conversion of CO₂ into CH₄ and CO at 423 K. In contrast with hexagonal h-MoO₃ nanorods, CH₄ and CO yields were enhanced by h-MoO₃@MoS₂ and In₂S₃/MoO₃@MoS₂, while the increased CH₄ yield and decreased CO yield were obtained by INS/MoO₃@MoS₂ and NiS/MoO₃@MoS₂. The optimal 3-INS/MoO₃@MoS₂ with a nominal NiS-In₂S₃ content of 5.0 wt% and a In/Ni molar ratio of 2:1 exhibited the best photoreduction activity of CO₂, of which CH₄ and CO yields were 49.11 and 6.19 μmol g⁻¹ h⁻¹, respectively. It's ascribed to the tight interface for enhancing the visible-light absorption capacity and reinforcing the transfer and separation of charge carriers. S-rich sites and O vacancies were favorable for the adsorption and photoreduction of reactants on the bulks surface. The nonthermal plasma induced in-situ sulfurization was thus a promising route to fabricate metal sulfides-based heterojunctions.     

Visible-light-enhanced catalytic hydrolysis of ammonia borane using RuP2 quantum dots supported by graphitic carbon nitride

Hydrolytic dehydrogenation of ammonia borane (AB) driven by efficient catalysts has attracted considerable attention and is regarded as a promising strategy for hydrogen generation. Herein, RuP₂ quantum dots supported on graphitic carbon nitride (g-C₃N₄) were successfully prepared by in-situ phosphorization, yielding a highly efficient photocatalyst toward AB hydrolysis. The catalysts were characterized by field-emission scanning electron microscopy, transmission electron microscopy, x-ray diffraction, x-ray photoelectron microscopy, inductively coupled plasma atomic emission spectroscopy, UV–visible diffuse reflectance spectroscopy and photoluminescence spectroscopy. A conventional water-displacement method was employed to record the hydrogen volume as a function of reaction time. Owing to visible-light irradiation, the initial turnover frequency of the AB hydrolysis was significantly enhanced by 110% (i.e., 134 min^?1) at room temperature. Furthermore, the apparent activation energy decreased from 67.7 ± 0.9 to 47.6 ± 1.0 kJ mol^?1. The photocatalytic hydrolysis mechanism and catalyst reusability were also investigated.     

Investigating the influence mechanism of hydrogen partial pressure on fracture toughness and fatigue life by in-situ hydrogen permeation

In this work, we investigate the influence mechanism of hydrogen partial pressure on fracture toughness and fatigue life of a high strength pipeline steel. Both fracture toughness test and fatigue life test are carried out under different hydrogen partial pressure. The experimental results show that with the increasing of hydrogen partial pressure, fracture toughness and fatigue life decrease and the decrease trends gradually flatten out. Hydrogen has a larger effect on fatigue life than fracture toughness. Only 3% hydrogen gas can cause a 67.7% decrease of fatigue life. The in-situ hydrogen permeation test is performed respectively in 2 MPa, 5 MPa and 8 MPa hydrogen partial pressure. With the increasing of hydrogen partial pressure, the increase trend of hydrogen permeation current gradually tends to be gentle, which indicates that the hydrogen atoms entering into the material gradually become saturated. This result can be used to clarify the influence mechanism of hydrogen partial pressure on fracture toughness and fatigue life.     

Modeling of compressive strength of cemented sandy soil

This paper attempted to show the application of particle swarm optimization in the prediction of the compressive strength of cement sandy soil from the curing period, porosity of sample and percentage of cement. The results of the study show that the unconfined compressive strength of the cement stabilized sandy soil increases with an increasing cement content curing time period. Moreover the compressive strength decreases with an increasing porosity. The compressive strength improvement due to cement treatment has a larger increase in samples with less porosity. In addition, particle swarm optimization algorithm is and accurate technique in estimation of compressive strength of cement stabilized sandy soil. In order to compare of existing correlations, a total number of 100 unconfined compressive tests and 15 scanning electron microscope tests have been conducted on cemented Babolsar sand. It can be concluded that compared to existing correlations models, particle swarm optimization algorithm models give more reliable prediction about compressive strength of cement satblized sandy soil. Moreover, the sensitivity analysis of the polynomial model shows that cement content and porosity have significant impact on predicting unconfined compressive strength.     

Preparation and properties of modified graphene oxide incorporated waterborne polyurethane acrylate

In this study, a new modifier (KPG) was prepared by modifying graphene oxide with γ‐glycidoxypropyl trimethoxysilane (KH560) and polydimethylsiloxane (PDMS). KPG was in turn added to aqueous urethane acrylate for the fabrication of waterborne polyurethane polyacrylate emulsion modified with KH560‐PDMS composite (KPG/WPUA). Textural characterizations of the KPG/WPUA coating were achieved via Fourier transform infrared, SEM, TGA and AFM techniques, which revealed that the KPG/WPUA film possessed a smooth surface. The synthesized KPG/WPUA films were tested for mechanical properties, hydrophobicity and acid/water corrosion performance which suggested their highly hydrophobic surface. KPG/WPUA with 0.1% KPG showed a contact angle of 118.35°, 30.35° higher than that of pristine WPUA. The KPG/WPUA film exhibited higher thermal stability, i.e. a 5% weight loss temperature of 305 °C, which was 30 °C higher than that of pristine WPUA film. The Young's modulus and elongation at break of the KPG/WPUA film were 34.1 MPa and 74.88% respectively, which were higher than that of WPUA film. Furthermore, KPG/WPUA films exhibited greater resistance (without obvious blistering and the white spotting phenomenon) to H₂O₂, HCl and water corrosion than pristine WPUA. The superior performance of KPG/WPUA films was attributed to the network chain structure formed upon the introduction of KPG into WPUA. The outstanding performance of KPG/WPUA films in terms of mechanical properties, thermal stability and high resistance to acidic and water corrosion makes them interesting alternative contenders for target applications. © 2019 Society of Chemical Industry     

酸性尾矿废弃地生态修复技术进展

酸性尾矿废弃地废石含有硫化物，在雨水的淋溶作用下会产出硫酸，加剧废弃地的酸化，增加企业环保成本，而生态修复工作就是从源头上控制废弃地的酸化。根据尾矿废弃地酸化机理，结合国内外最新研究进展，分析了生态修复技术现状；概述了隔离覆盖、改良剂改良、植物修复、微生物法等多种处理方法在实践中的适应性及优缺点，并分别介绍了隔离覆盖-植物修复技术、原位改良-植物修复技术在Reden煤矿、永平铜矿的成功应用案例。针对酸性尾矿废弃地的特点，单一处理方法具有较大的局限性，需要采用联合工艺进行治理，隔离覆盖-植物修复技术、原位改良-植物修复技术因见效快、效果好、操作简单，势必成为将来研究的主要方向。