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In this paper, MnO2/CNTs composite materials have been studied and fabricated by hydrothermal-assisted chemical oxidation. Oxidation reactions of KMnO4 with MnSO4 and CNTs to form the composites were carried out at 140°C for 20 h. The obtained materials were morphologically observed by FESEM, analyzed for elemental composition by EDX, phase composition by XRD, and thermogravimetric analysis. Results show that the materials were composite of rod-shaped α-MnO2 crystals, diameter from 20 to 30 nm, about 1 μm long, with scattered CNTs. The electrochemical properties of the materials were studied by cyclic voltammetry (CV) and chronopotentiometry (CP) methods. CNTs have improved electrochemical properties of the materials, the discharge rate increased two times and the specific capacity increased 20% higher compared to α-MnO2 with the same fabricated conditions. The MnO2/CNTs 1% material has the best properties, the specific capacity reaches 113 mAh/g, the electrode can still work well after 100 charge-discharge cycles. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to enhance to corrosion protection of NiZn-plated steel by electroplating multilayer coating. Design/methodology/approach: The multilayer coating consists of three layers on mild steel substrate, such as Cr3+ chromate conversion layer (CCC), electrodeposited nanosilica zinc-nickel composite layer (ZnNiSi) and electrodeposited zinc-nickel alloy layer (ZnNi). Its morphology, composition and corrosion behaviour were investigated by various methods. Findings: Polarization curves indicated that polarization resistance and corrosion current density of CCC/ZnNiSi/ZnNi/Fe (6.956 kO.cm2; 2.56 µA.cm−2) were two times higher and five times lower than that of ZnNiSi/ZnNi/Fe (3.42 kO.cm2; 12.52 µA.cm−2), respectively. From electrochemical impedance spectroscopy data, charge transfer resistances were 1.344, 2.550 and 2.312 kO.cm2 for ZnNi, ZnNiSi/ZnNi and CCC/ZnNiSi/ZnNi, respectively. Salt spray test indicated that after 48 h, surface of ZnNi and ZnNiSi was covered by white rust, whereas no white rust was observed on surface of CCC/ZnNiSi/ZnNi. After 600 h, there were red rust spots (1% surface coverage) on surface of Zn-Ni, whereas only white rust was observed on both ZnNiSi/ZnNi (100% surface coverage) and CCC/ZnNiSi/ZnNi (10% surface coverage). Originality/value: Multilayer coating enhanced significantly the corrosion protection for steel, as compared to the single-layer coating. [ABSTRACT FROM AUTHOR]