Zn在KOH水溶液中的阳极溶解和钝化机理

本文用旋转圆盘电极、稳态极化曲线、交流阻抗及恒电流充电曲线等方法研究了Zn在常温(30℃)和低温(-20℃)的KOH水溶液中阳极溶解和钝化过程的规律。从而提出其反应机理,并用最优化程序在TRS-80微型计算机上计算了反应机理中基元反应的速度和动力学参数的最佳值。由动力学参数计算的φ~i关系定量地符合从阳极溶解至钝化前整条极化曲线实验数据。旋转圆盘电极的转速效应、交流阻抗值以及恒电流充电电量值也都与提出的反应机理相符合。

Modeling and simulation of 3D thermal stresses of large-sized castings in solidification processes

When heavy machines and large scaled receiver system of communication equipment are manufactured, it always needs to produce large-sized steel castings, aluminum castings and etc. Some defects of hot cracking by thermal stress often appear during solidification process as these castings are produced, which results in failure of castings. Therefore predicting the effects of technological parameters for production of castings on the thermal stress during solidification process becomes an important means. In this paper, the mathematical models have been established and numerical calculation of temperature fields by using finite difference method (FDM) and then thermal stress fields by using finite element method (FEM) during solidification process of castings have been carried out. The technological parameters of production have been optimized by the results of calculation and the defects of hot cracking have been eliminated. Modeling and simulation of 3D thermal stress during solidification processes of large-sized castings provided a scientific basis, which promoted further development of advanced manufacturing technique.

Long-term corrosion evolution associated with the structural heterogeneities of an Fe-based amorphous coating in H_(3)BO_(3)solution at various temperatures

Understanding the long-term corrosion behavior of neutron absorber materials in H_(3)BO_(3)solution is crucial for the materials applications in spent fuel storage.In this paper,long-term corrosion evolution for 180 d in relation to the structural heterogeneities of an Fe-based amorphous coating(AMC)in H_(3)BO_(3)solution at various temperatures was systematically investigated.Results indicate that the coating corrosion could be divided into three distinct stages.Initially,the corrosion resistance increased owing to the thickening and composition evolution of the passive films.Subsequently,the corrosion rate was kept almost constant in the second stage,which connected with the steady state of the passive film.Finally,the corrosion resistance of coating reduced gradually owing to the initiation and penetration of local-ized corrosion.Interestingly,it was revealed that the localized corrosion was initiated at the relatively Cr-depleted amorphous matrix in the deep pores of the coating.This could be attributed to the synergy of Cr-depletion and occlusive effect in the deep pores during long-term immersion.With the elevation of temperature,the localized corrosion was enhanced due to the accumulation of the H+in the pores to swiftly reach the critical conditions for passive film breakdown.This work provides insights into the long-term corrosion mechanism of Fe-based AMCs in H_(3)BO_(3)solution and offers meaningful contributions to the design of new corrosion resistant neutron absorbing coatings for spent fuel storage applications.

Effect of grain refinement on the hydrogen embrittlement of 304 austenitic stainless steel

The effect of grain size(in the range from 4 μm to 12 μm) on the hydrogen embrittlement(HE) of 304 austenitic stainless steel(ASS) was studied. HE susceptibility result shows that HE resistance increases with grain refinement. Electron backscattered diffraction kernel average misorientation(EBSD-KAM)mapping shows that the strain localization can be mitigated by grain refinement. Hence, strain localization sites which act as highways for hydrogen diffusion and preferred crack initiation sites can be reduced along with grain refinement, leading to a high HE resistance. Meanwhile, grain size shows no influence on the strain induced martensite(SIM) transformation during the hydrogen charging slow strain tensile test(SSRT). Hence, the SIM formed during hydrogen charging SSRT is not responsible for the different HE resistance of 304 ASSs with various grain sizes. Hydrogen diffusion is supposed to be controlled by a competition between short-circuit diffusion along random grain boundary(RGB) and hydrogen trapping at dislocations, leading to a maximum hydrogen diffusion coefficient in the 304 ASS with an average grain size of 8 μm.

Short-time Oxidation of Alloy 690 in High-temperature and High-pressure Steam and Water

The oxidation behavior of alloy 690 exposed to high-temperature and high-pressure steam and water at 280℃ for 1 h was investigated by scanning electron microscopy （SEM）, atomic force microscopy （AFM） and X-ray photoelectron spectroscopy （XPS）. In high-temperature and high-pressure steam, the oxide film is composed of an outermost Ni-rich hydroxides layer, an intermediate layer of hydroxides and oxides enriched in Cr, an inner oxide layer. The film formed in high-temperature water is similar to that in steam, except for missing the Ni-rich hydroxides layer. Samples with different surface finishes （electropolished, mechanically polished, ground, and as-received） were prepared for comparison. A general increase of the oxide thickness with the degree of surface roughness is observed. The equivalent oxide thicknesses lie in the range of 100-200 nm for the as-received samples, 150-250 nm for the samples ground to 400# and 10-20 nm for the samples ground to 1500#, mechanically polished, and electropolished.

Influence of cerium content on the corrosion behavior of Al-Co-Ce amorphous alloys in 0.6 M NaCl solution

The effect of cerium content on the corrosion behavior of Al-Co-Ce amorphous alloys in 0.6 M NaCl solution was investigated by cyclic polarization, Mott-Schottky and X-ray photoelectron spectroscopy techniques. Results indicated that the open circuit potential of Al-Co-Ce amorphous alloys displayed a decreased tendency with the increase in Ce content, and the amorphous alloy with 4 at.% Ce presented both the lowest passive current density and donor density indicating the best corrosion resistance, while adding excess Ce led to the reduced corrosion resistance of Al-Co-Ce alloys, Furthermore, it was found that a low Ce content is beneficial to the formation of a more protective passive film on Al-Co-Ce amorphous alloys, and the corrosion inhibition reactions of Al-Co-Ce alloys in 0.6 M NaCl solution were changed with the increase in Ce content and the detailed reasons were discussed.

Atom probe tomographic observation of hydrogen trapping at carbides/ferrite interfaces for a high strength steel

A three-dimensional atom probe （3DAP） technique has been used to characterize the hydrogen dis- tribution on carbides for a high strength AISI 4140 steel. Direct evidence of H atoms trapped at the carbide/ferrite interfaces has been revealed by 3DAP mapping. Hydrogen is mainly trapped on car- bide/ferrite interfaces along the grain boundaries. Slow strain rate tensile （SSRT） testing shows that the AIS14140 steel is highly sensitive to hydrogen embrittlement. The corresponding ffactographic mor- phologies of hydrogen charged specimen exhibit brittle fracture feature. Combined with these results, it is proposed that the hydrogen trapping sites present in the grain boundaries are responsible for the hydrogen-induced intergranular fracture of AISI 4140. The direct observation of hydrogen distribution contributes to a better understanding of the mechanism of hydrogen embrittlement.

The Influence of Pore Structures and Degree of Cross-Linking on Catalytic Properties of Aminomethyl Polystyrene Resin Supported Dendritic Copper Complexes

1 Introduction Immobilization of homogeneous catalysts onto polymer supports through covalent attachment has received wide attention because these materials offer advantage features of heterogeneous catalysis to homogeneous systems.The polymer-supported catalysts enhance their thermal stability,selectivity,recyclability and easy separation from reaction products leading to the operationally flexible[1-2].Such behaviour prompted us to know the effect of pore structures of polymer supporters on catalytic ...

Oxidation of Alcohols Using Oxygen as Oxidant Catalyzed by AlCl_3

1 Introduction The oxidation of alcohols to their corresponding aldehydes,ketones or carboxylic acids is of significant importance in organic chemistry,and the oxidation products represent important intermediates for the preparation of a various of other compounds[1,2].Catalytic oxidation methods,which employ a variety of metal-containing catalysts,such as Cu (Ⅰ)[3] and so on,developed quickly in recent decades.However,most of the metal containing catalysts are expensive and the reactions generally used...

Photo Catalytic Oxidation of Alcohols in Water under Natural Weathering Conditions in the Presence of Bromo Source

1 Results The oxidation of alcohols into the corresponding carbonyl compound is one of the most important functional group transformation in organic synthesis[1]. Traditionally,such transformations have been performed with stoichiometric inorganic oxidant or other high valent metal oxidant[2]. Despite a variety of systems for the catalytic oxidation of alcohols have been developed,there is ongoing interest in the search for new efficient and environmental friendly oxidation system.To the best of our kno...

富含油酸和亚油酸的油类对提高牛奶中共轭亚油酸含量的影响

选择40头荷斯坦奶牛,测定富含油酸和亚油酸的油类对提高牛奶中C18：2cis-9,trans-11共轭亚油酸和C18：1trans-11（VA）含量的影响。采用完全随机分组法,试验为期9周,最后6周为测定期。对照组的基础中日粮含粗饲料59%,试验组在此基础上分别添加4%的大豆油（SO）、4%的亚麻油（FO）以及2%的大豆油＋2％的亚麻油（SFO）。