A three-dimensional (3D) multiple phase field model, which takes into account the grain boundary (GB) energy anisotropy caused by texture, is established based on real grain orientations and Read–Shockley model. The model is applied to the grain growth process of polycrystalline Mg (ZK60) alloy to investigate the evolution characteristics in different systems with varying proportions of low-angle grain boundary (LAGB) caused by different texture levels. It is found that the GB energy anisotropy can cause the grain growth kinetics to change, namely, higher texture levels (also means higher LAGB proportion) result in lower kinetics, and vice versa. The simulation results also show that the topological characteristics, such as LAGB proportion and distribution of grain size, undergo different evolution characteristics in different systems, and a more serious grain size fluctuation can be caused by a higher texture level. The mechanism is mainly the slower evolution of textured grains in their accumulation area and the faster coarsening rate of non-textured grains. Therefore, weakening the texture level is an effective way for implementing a desired homogenized microstructure in ZK60 Mg alloy. The rules revealed by the simulation results should be of great significance for revealing how the GB anisotropy affects the evolution of polycrystalline during the grain growth after recrystallization and offer the ideas for processing the alloy and optimizing the microstructure.
Bismuth-oxygen moieties are beneficial for highefficiency electrochemical CO 2 reduction (CO 2 RR) to produce formate; however, preserving bismuth-oxygen moieties while applying a cathodic potential is challenging. This work reports the preparation of ultrathin Bi 2 O 2 O/Bi 2 O 2 (OH)(NO 3 ) nanosheets (BiON-uts) by in-situ tailoring of hydrogen bonds in a Bi 2 O 2 (OH)(NO 3 ) precursor. The BiON-uts exhibits a formate faradaic efficiency of 98 % with higher partial current density than that of most reported bismuth-based catalysts. Mechanistic studies demonstrate that the ultrathin nanosheet morphology facilitates ion-exchange between BiON-uts and the electrolyte to produce Bi 2 O 2 CO 3 as intermediate, and adsorption of CO 2 with surface Bi 2 O 2 O. DFT calculations reveal that the rate-limiting first electron transfer is effectively improved by the high electron affinity of Bi 2 O 2 CO 3 . More importantly, high-efficiency CO 2 RR in turn protects the bismuth-oxygen moieties from being reduced and thus helps to maintain the excellent CO 2 RR activity. This work offers an interactive mechanism of CO 2 RR promotion and bismuthoxygen moiety preservation, opening up new opportunities for developing high-performance catalysts.
Surface metallization of continuous carbon fibers (CFs) can improve the properties of the interface between the CFs and the metal matrix of the metal based composites. In this study, copper was coated on the surface of continuous CFs by electroplating in acidified copper sulfate electrolyte system. The effects of electroplating parameters such as current density, plating time, plating temperature and the pH value of electrolyte solution on the electroplating of the copper thin films on CFs were studied. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to determine the microstructure of the copper coatings, and its composition and crystal structure. The thermal gravimetric analysis (TGA) was used to study the thermal stability of the CFs after electroplating. The results showed that high quality copper-coated CFs can be obtained under the optimized plating parameters as follows: the current density 3~4mA/cm2, electroplating time 10~20min, the temperature and the pH value of electrolyte solution 3.0~4.0, 20~30°C respectively. The coatings were uniform and smooth, which were adhered to CFs. XRD patterns indicated that the copper coatings were mainly composed of pure copper. And TGA results identified an increase in thermal stability of the copper coated CFs.
The initial stages of copper electrodeposition in acid copper sulphate/sodium citrate bath were investigated with varying copper and sodium citrate concentrations. Different electrochemical measurements, including linear sweep voltammetry, cyclic voltammetry, and chronoamperometry were introduced to the study. The Scharifker-Hills model was introduced to identify the nucleation model with analysing current transients. It was observed that the increase of copper ions inhibited the cathodic polarization behaviour for the reduction of ions. On the contrary, sodium citrate promoted the cathodic polarization behaviour. The chronoamperometry results indicated that without the sodium citrate, the nucleation process corresponded to instantaneous nucleation and three-dimensional diffusion limited growth, although obvious deviations were observed. While the addition of sodium citrate changed the deviations and caused that the initial deposition kinetics followed well with the mechanism of instantaneous nucleation.
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