Search

Based on their characteristics, transition metal layered double hydroxides have been of great scientific interest for their use in supercapacitors. Up until now, severe aggregation and low intrinsic conductivity have been the major hurdles for their application. In this work, nickel–iron sulfide nanosheets (NiFeSx) and carbon nanotubes (CNTs) were synthesized on diatomite using chemical vapor deposition and a two-step hydrothermal method to overcome these challenges. Synthesis of this composite successfully exploits the synergistic effect of multicomponent materials to improve the electrochemical performance. Diatomite is selected as a substrate to provide preferable surroundings for the uniform dispersion of nanomaterial on its surface, which enlarges the active sites that come in contact with the electrolytes, significantly improving the electrochemical properties. Combined with high conductivity and a synchronous sulfurization effect, the NiFeSx@CNTs@MnS@Diatomite electrode delivered a high specific capacitance of 552F g−1 at a current density of 1 A g−1, a good rate capability of 68.4% retention at 10 A g−1, and superior cycling stability of 89.8% capacitance retention after 5000 cycles at 5 A g−1. Furthermore, an asymmetric supercapacitor assembled via NiFeSx@CNTs@MnS@Diatomite and graphene delivered a maximum energy density of 28.9 Wh kg−1 and a maximum power density of 9375 W kg−1 at a potential of 1.5 V. This research lays the groundwork for ideal material preparation as well as a rational design for the electrode material, including property enhancement of diatomite-based material for use in supercapacitors.

Corrosion inhibitor microcapsules were prepared by centrifugation-coating method and the influence factors on the morphology of microcapsules were discussed. Process technology was optimized by orthogonal design method, with the rotational speed of turntable at 500 r/min, the fan speed at 400 r/min, the speed of peristaltic pump at 15 r/min and the jet pressure at 0.20 MPa. Analysis on the surface morphology, thermal stability and mechanical properties of microcapsules revealed that the obtained microcapsules had high drug loading rate and good mechanical strength, and higher weight gain rate of wall material can obtain thicker wall. Their release rates measured in the simulated concrete pore solution showed that microcapsules with higher weight gain rates had slower release rate, polymethyl methacrylate as wall material released faster than ethyl cellulose.

Magnesium alloys, the advanced lightweight structural materials, have been successfully applied in the manufacturing field. Unfortunately, their poor corrosion resistance restrains the potential wide applications. In this work, anti-corrosion coatings were fabricated via the in-situ growth of the corrosion inhibitors intercalated magnesium-aluminum layered double hydroxide (Mg–Al LDH) on AZ31 magnesium alloy and then post-sealing it by a super-hydrophobic coating. SEM, XRD, EDS, FTIR, XPS and contact angle test were conducted to analyze physical/chemical features of these coatings. Potentiodynamic polarization curves and electrochemical impedance spectroscopy were recorded to assess the anti-corrosion performance of prepared coatings. Surprisingly, Mg–Al LDH with molybdate intercalation and lauric acid modification achieves the excellent corrosion inhibition performance (99.99%) due to the multicomponent synergistic effect such as the physical protection of Mg–Al LDH, the corrosion inhibition of molybdate and super-hydrophobic properties of lauric acid. This work presents a scientific perspective and novel design philosophy to fabricate the efficient anti-corrosion coating to protect magnesium alloys and then expand their potential applications in other field. Keywords: Magnesium alloy, Superhydrophobicity, LDH films, Corrosion inhibitor, Corrosion resistance

Due to the diverse H

Fly ash is an industrial by-product that is widely used in the cement industry. Traditional methods used to investigate the influence of fly ash on the hydration behavior of cement are destructive and cannot accomplish a continuous tracing of the hydration process. In this study, the influence of fly ash incorporation on the hydration process of cement is evaluated using measured electrochemical data obtained from the electrochemical impedance spectroscopy approach. A novel equivalent circuit model that considers the electrochemical characteristics of cement during the hydration process is proposed to investigate the electrochemical property of the blended cement. The resistance parameter of the model, Rct1, was found to have a positive correlation with hydration degree and compressive strength during hydration. With this parameter, the method can be used to non-destructively trace and characterize the effects of fly ash incorporation on the cement hydration process.

Preparation of two-dimensional hybrid nanoarrays with porous structure and multiple active components is considered as an effective strategy to improve the electrochemical performance of supercapacitors. Herein, etched CoAl LDO/MnO2 was in-situ prepared on Ni foam by a simple hydrothermal process and subsequent alkali etching treatment. The morphologies and structures of synthetic nanocomposites were examined by XRD, SEM, TEM, EDS, BET and XPS. The nanocomposites present unique hybrid nanoarrays in which etched CoAl LDO nanoarrays form a core and worm-like MnO2 nanosheets create a shell. The electrochemical properties of etched CoAl LDO/MnO2 electrodes were examined by CV, CC and cycling tests. The results exhibit an excellent areal specific capacitance of 991 mF cm−2, desirable rate capability and outstanding cycling stability of 79.87% retention over 10000 cycles. The asymmetric supercapacitor using etched CoAl LDO/MnO2//AG achieves the maximum energy density and power density of 16.6 Wh kg−1 and 5000 W kg−1, respectively. The excellent electrochemical performance of the as-prepared material suggests its potential application for clean energy storage.

In this paper, a novel capillary absorption model is proposed to investigate the capillary absorption process of cementitious materials. This model mainly consider the influence of tortuosity of the capillary pores of cement paste, which is the key factor affecting the capillary absorption process. The proposed model is verified by the capillary absorption process of paste samples with different water/cement ratios. The absorption height and water content profile of testing samples are measured by X-ray computed tomography. The results show that the proposed capillary absorption model that takes the tortuosity of capillary pores into consideration is suitable for investigating the capillary absorption process of water in cementitious materials.

Cracking is a major form of failure in cementitious materials. In this study, the cracking process in a mortar is non-destructively investigated using an in-situ X-ray computed tomography (XCT) method. A novel image-processing method that allows for 3D visualization of the cracking process and for the distinction between pores and cracks is proposed to identify cracks inside concrete structures. With the proposed method, the fracture process in a mortar can be visualized, and quantitative information regarding the amount of solid, pores, and cracks inside the mortar can be obtained. Based on the experimental results, three fracture stages were observed: a compression stage, an expansion stage, and a cracking stage, which is consistent with the concrete compression failure process fracture theory.

In this paper, electrochemical impedance spectroscopy (EIS) is used as a non-destructive testing method for investigating the cracking behavior of two kinds of cement-based materials with/without fiber, which are engineered cementitious composites (ECC) and plain mortar. The experimental results show that the cracking patterns and deflection-load curves of plain mortar and ECC are different when the external load reaches to the first-cracking load and ultimate load. The EIS results show that the parameter value of Rct and plural modulus value Z in fractured mortar increase several hundred times compared with correspondingly origin plain mortar. Moreover, the semi-circle presents in the fractured mortar at high frequency and the diagonal lines are deviated from less than 45 deg at low frequency, and the phase angle (θ°) in cracked mortar decreases as the frequency decreases in Bode plots. However, the values of Rct and Z in cracked ECC increase dozens of times compared to origin ECC, and the phase angle decreases as the frequency decreases. The variation of Rct in Nyquist plots, and the stability and smoothness of Bode plot sensitively reflect the cracking degree of cementitious system. In this paper, it is proposed that as a non-destructive method, electrochemical impedance measurement can be used to evaluate the cracking behavior of cement-based materials.

The chloride-induced corrosion of reinforcement in concrete is a serious problem. In this study, the chloride ion migration in cement materials blended with fly ash or/and slag is studied by the electrochemical impedance spectroscopy (EIS) method. A novel equivalent circuit model Rs(Q1(Rct1W1))(Q2(Rct2W2)) is established to analyze the chloride ion migration. The results indicate that increasing the amount of fly ash or/and slag enhances the resistance to chloride ion migration. The chloride ion migration depth can be qualified by an equation that is a function of the parameter (Rct1) of the circuit model. With this function, the chloride ion migration depth in cement materials replaced with fly ash or/and slag can be predicted by EIS method.

The main purpose of this study is to non-destructively monitor the formation and development of corrosion products in reinforced mortar with the help of X-ray micro computed tomography (X-ray µCT). A new method based on the relationship between the linear attenuation coefficient and CT number as well as greyscale value is built to identify different type of corrosion products. Based on this method, two categories of corrosion products including iron oxides and iron hydroxides are identified in this research. Additionally, the corrosion mechanism and the interaction between different types of corrosion products are discussed according to the characteristics of corrosion evolution. Furthermore, the volumetric expansion ratio of corrosion products is quantified (from 2.71 to 3.97). This method provides a new angle to investigate the formation and development of reaction products, which contributes to further understand the corrosion process in reinforced concrete.

Mg-Al layered double hydroxides intercalated with nitrite ions was prepared by three different methods: calcined-rehydration (R-LDH), hydrothermal (H-LDH) and coprecipitation (C-LDH) method. The products were characterized and the results indicated that C-LDH had the highest intercalated rate of anions. The ion substitution test also verified C-LDH exhibited the largest adsorption capacity of chloridion. The inhibition efficiency and corrosion current density of C-LDH from electrochemical test both had the better performance than R-LDH and H-LDH over immersion time. Therefore, C-LDH could had the best anticorrosion in a long period and its mechanism of corrosion protection was also discussed.

Electrical resistance tomography (ERT) method is proposed to visually investigated of the defect in cementitious materials. Specimens with one precast defect are made with different water-cement (w/c) ratio and detected using the embedded electrodes. The experimental images are assessed with a similarity evaluation method based on color histogram. In addition, the electrical resistivity and moisture content of the specimens are measured simultaneously to explore its effects on the quality of the imaging results. The results show that the moisture content is the main factor influencing the resistivity of the specimens in the early hydration reaction while the w/c ratio becomes the main factor effecting the resistivity after the early hydration reaction. For the multi-defect detecting, the influence of electrical soft field effect cannot be neglected. The experiment results imply that ERT technique has potential in defect detection and in-situ monitoring in cement mortar.