Performance evolution of geopolymer repair materials in seawater
YANG Jingfei;CHEN Siyuan;WANG Shize;JIAO Wenxuan;CAO Wenkai;LI Weihua;[Objective] Slag-based geopolymers exhibit good resistance to chemical erosion, but they have limitations in practical applications. Incorporating low-reactivity metakaolin can improve their workability and enhance their erosion resistance. [Method] Slag/metakaolin geopolymers were prepared with water glass as an activator. Their mechanical properties, chloride ion content, and product composition under seawater erosion conditions were studied, accompanied by thermogravimetric analysis(TGA). [Result] The addition of an appropriate amount of metakaolin increased the mechanical properties of slag-based geopolymers after seawater erosion. At a metakaolin content of 10%, the flexural strength and compressive strength of the slag-based geopolymer after 180 days of seawater exposure increased by 13.5% and 5.9%, respectively. Furthermore, compared to the metakaolin-free slag-based geopolymer, its total chloride ion content, free chloride ion content, and bound chloride ion content were all lower. After seawater erosion, Mg(OH)2 precipitate formed on the surface layer within 5 mm depth of the geopolymer samples, leading to increased compactness and reduced interaction with aggressive ions in seawater. [Conclusion] Combined with the inherent stability of slagbased geopolymer in erosive environments, the incorporation of metakaolin endows the geopolymer with superior resistance to seawater erosion.
Corrosion protection of composite steel interfaces in marine environments using acrylic resin composite coatings containing stainless steel flakes
ZHANG Xiaoyan;WANG Shuai;LONG Jun;ZHENG Kaihong;MAO Lingbo;ZHENG Zhibin;[Objective] To address the issue of premature corrosion failure at the interface of a composite steel with a stainless steel–carbon steel–stainless steel structure when exposed to marine environments, an acrylic resin composite coating containing stainless steel flake fillers was applied to the cut edges of the composite steel. [Method] The corrosion behavior of the coating in simulated marine environment was evaluated by neutral salt spray testing and electrochemical measurement and to elucidate its protection mechanism on the composite steel interface. [Result] The coating consisted of a compact layered structure formed by the oriented arrangement of stainless steel flakes within the acrylic resin matrix, which effectively improved the corrosion resistance of the notch. The protection performance of the coating was attributed to the labyrinth effect of the flake fillers and the physical shielding provided by the compact corrosion products formed at the interface. [Conclusion] The failure of the coating originated from the permeation of corrosive media and the accumulation of corrosion products at the interface, ultimately leading to blistering and cracking of the coating.
Corrosion behavior of 2A97 Al–Li alloy in typical tropical marine atmospheric environment
DING Feng;JIA Jinghuan;JIANG Guojie;MU Chunhui;XUN Lijiao;ZHAN Zhongwei;SUN Zhihua;[Objective] The corrosion behavior and patterns of 2A97 Al–Li alloy in tropical marine atmospheric environment was studied to establish a corrosion rate prediction model along with an indoor accelerated testing method. [Method] Three typical tropical island-reefs(A, B, and C) were selected as exposure test sites for multi-cycle natural environment exposure tests. Environmental parameter monitoring data were combined with grey relational analysis to identify key environmental factors influencing corrosion. A power-function regression method was employed to develop a predictive model for corrosion rate over time. Meanwhile, an indoor comprehensive accelerated corrosion test was designed and conducted to verify its consistency with outdoor exposure results. [Result] At reefs A and B, average rainfall was the predominant factor affecting the corrosion rate, with grey relational coefficients of 0.855 and 0.704, respectively; at reef C, relative humidity was the main factor, with a grey relational coefficient of 0.727. The established power-function prediction models showed high coefficients of determination(R2 > 0.93), and the prediction errors for the 2-year corrosion rate were all below 15%. The indoor accelerated test results agreed well with the outdoor exposure trends, confirming the validity of the indoor accelerated testing method. [Conclusion] The corrosion behavior of 2A97 Al–Li alloy in tropical marine environments is closely related to relative humidity and rainfall. The power-function regression model can be used to predict its long-term corrosion rate. The developed indoor accelerated testing method can effectively simulate the actual environmental corrosion process, providing a scientific basis for material service life assessment and protection design.
Concentration-dependent corrosion inhibition of sodium lignosulfonate for pure zinc in saline-alkali soil leachate
LIU Chenhui;LIU Guangming;LU Yiliang;ZHU Yanbin;HUANG Zebang;ZHANG Lingling;GAN Chongwen;WEI Jijun;[Objective] To inhibit the corrosion of pure zinc used for grounding purposes in the Tianjin Binhai New Area. [Method] The effect of sodium lignosulfonate(SLS) on the corrosion behavior of zinc in a saline-alkali soil leachate was examined by measuring potentiodynamic polarization curves, electrochemical impedance spectra(EIS), and Mott-Schottky curves. The relevant adsorption isotherm model was also studied. [Result] SLS acts as a cathodic inhibitor. As its mass concentration increased within the range of 0-60 mg/L, the corrosion current density of Zn in the saline-alkali soil leachate gradually decreased, while the corrosion potential shifted positively. The adsorption film resistance and polarization resistance gradually increased, leading to higher charge transfer resistance and a reduced corrosion rate, with the inhibition efficiency progressively rising. Mott-Schottky curve analysis revealed that the adsorption film formed on the Zn surface exhibited n-type semiconductor characteristics. When the SLS mass concentration was increased from 0 mg/L to 60 mg/L, the donor density of the adsorption film on the Zn surface gradually decreased, and the flat band potential gradually increased. The semiconducting nature of the adsorption film did not change significantly, but the defect concentration decreased, enhancing the material's corrosion resistance. Fitting of the adsorption isotherm showed that in the saline-alkali soil leachate with SLS additions up to 60 mg/L, the adsorption behavior of SLS on the Zn surface conformed to the Langmuir adsorption isotherm model. This adsorption was a spontaneous process controlled by a mix of physical and chemical adsorption. [Conclusion] At addition levels not exceeding 60 mg/L, SLS effectively inhibits the corrosion of Zn in the saline-alkali soil leachate through a spontaneous and mixed adsorption mechanism on the Zn surface.
Study on corrosion of vehicle window rails made of 6061 aluminum alloy in 3.5% NaCl solution
YUAN Wenhao;CHEN Yajun;ZHANG Yiding;ZHANG Zichen;[Objective] The corrosion mechanism of 6061 aluminum alloy and the influence of corrosion products on the corrosion process were discussed. [Method] Through saline immersion test, corrosion morphology observation, product composition analysis, and electrochemical measurement, the effect of corrosion products on the corrosion process of 6061 aluminum alloy in 3.5% NaCl solution was studied. An immersion corrosion model for the aluminum alloy considering the influence of corrosion products was established, and the key parameters such as current density, corrosion depth, and corrosion product concentration in the system were analyzed. [Result] During a 7-day period, as the corrosion products accumulated, the corrosion rate of 6061 aluminum alloy decreased from 1.521 × 10-1 mm/a to 4.35 × 10-2 mm/a, and the corrosion current density dropped from 5.46 × 10-6 A/cm2 to 3.07 × 10-6 A/cm2. The generated products such as Al_2O3 and Al(OH)3 made the corrosion layer structure more compact, effectively blocking the contact between the corrosive medium and the substrate as well as the diffusion and transport of charged particles, thereby slowing down the corrosion process. The simulation results showed that the increase of Al(OH)3 concentration hindered the ion diffusion and migration, weakening the electrochemical corrosion effect. The corrosion depth measured experimentally was in good agreement with the simulation values, with an error of less than 10%. [Conclusion] The corrosion products synergistically slow down the corrosion process of 6061 aluminum alloy through a compact barrier structure and kinetic inhibition. This provides a scientific basis for corrosion assessment and protection of aluminum alloys in engineering applications.
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