Electrochemical behaviour of thin films of Co/Al layered double hydroxide prepared by electrodeposition

Thin films of controlled thickness of Co/Al layered double hydroxide with different Co and Al percentages have been electrosynthesized by the cathodic reduction of a 0.03 M Co and Al nitrate solution. The electrochemical behaviour of the films deposited on Pt or ITO electrodes has been deeply studied in 0.1 M NaOH solution. Our findings demonstrate that as soon as a potential is applied in the anodic direction, the films undergo an irreversible change of phase.     

正交实验法研究铝合金上镀硬铬

通过正交实验法,研究了铝合金上二次浸锌法镀铬工艺条件（镀液成分、镀液温度及电流密度）对镀层硬度和光亮性能的影响,确定了获得高硬度及光亮镀层的最佳工艺参数。     

A kinetic and electrochemical study of the zincate immersion process for aluminium

To plate aluminium, its surface is often first coated with a thin layer of zinc which is formed by immersion in an alkaline zincate solution. This paper describes a kinetic and electrochemical study of the zincate immersion reaction. Using an aluminium sample in the form of a rotating disc, the effects of varying the zinc concentration (0.01–0.5 m), disc rotation speed (66–1380 rpm), temperature (5–72°C), and sodium hydroxide concentration (1.5–9.0 m) on the kinetics were investigated. It was found that the reaction was usually first order. When the zincate concentration was 0.1 m, the reaction was chemically controlled with an activation energy of 35 ± 7 kJ mol^–1. At high zincate concentrations, high disc rotation speeds and low sodium hydroxide concentrations, a thin film of zinc metal was formed on the aluminium surface, blocking the subsequent reaction. It was found that the most compact and adherent zinc films were formed at high zincate concentrations. This finding is consistent with industrial practice. These results are explained using mixed potential measurements and Evans' diagrams.     

Reduction of graphene oxide films on Al foil for hybrid transparent conductive film applications

We report the reduction of graphene oxide (G-O) films on Al foil using hydrogen as a reducing agent generated during the etching of Al foil in an aqueous solution of hydrochloric acid (HCl). Complete etching of the Al substrate results in simultaneous reduction and a free standing film composed of stacked and overlapped reduced graphene oxide (RG-O) platelets. Generation of hydrogen at the G-O/Al interface increases the reduction efficiency of this method that is demonstrated in better electrical conductivity of the obtained films compared to the RG-O films reduced by the similar method but using remote Al foil in HCl solution and hydrazine reduced RG-O films. By transferring the free standing RG-O films onto Ag NW films, hybrid transparent conductive films (TCFs) with opto-electrical properties comparable to that of ITO films were obtained.     

Preparation and electrochemical properties of an electropolymerized polyacrylamide-based cross-linking copolymer film on 6063 Al alloy

An acrylamide-based cross-linking copolymer film was electrodeposited on 6063 Al alloy using ethylene glycol maleic rosinate acrylate (EGMRA) as the cross-linking agent. The corrosion resistance of polyacrylamide (PAA)-based films in the absence and presence of EGMRA was evaluated in 3.5 wt.% NaCl solution through polarization curves and electrochemical impedance spectroscopy. Compared with the uncoated Al alloy and electrodeposited film, the cross-linked film provided more effective protection for the Al alloy. The chemical structures and morphologies of the copolymer films were, respectively, analyzed using Fourier-transform infrared spectroscopy and scanning electron microscopy. Results confirmed that PAA-based cross-linking copolymer films were deposited on 6063 Al alloy.     

Characteristics of Optimized Al:ZnO sputtering targets prepared by nanostructured powder

Optimized Al:ZnO sputtering target was prepared by cold isostatic pressing (CIP) using nanostructured zinc oxide powder and aluminum oxide powder as raw material. Compared with the target prepared by conventional raw materials, the performance of the optimized Al:ZnO sputtering target is greatly improved. The microstructure of the optimized Al:ZnO sputtering target is refined and its average grain size is less than 5 μm with 99.7% theoretical density. Al:ZnO thin films of both optimized and conventional targets were prepared by RF magnetron sputter and their properties were characterized, respectively. The Al:ZnO thin films obtained by optimized target feature better uniformity and compactness, and the internal stress is −378.8 MPa, which is nearly 2/3 lower than that of the conventional target. The film obtained by optimized targets also features a 97% IR transmittance, 1.71 nm Rq surface roughness and non-offset (002) XRD peak. It can be speculated that the optimized Al:ZnO target has great potential to prepare micrometer scale Al:ZnO films and employed in thin-film ZnO device industry.     

Pyrrole-based silane primer for corrosion protection of commercial Al alloys. Part II. Corrosion performance in neutral NaCl solution

A chromate-free, direct-to-metal treatment using pyrrole-based silane (PySi) was developed for protection against corrosion of as-received commercial Al alloys, following the typical procedure for silane deposition. The protection performance of composite PPySi films, containing polysiloxane linkages and polypyrrole units, was evaluated in near neutral NaCl solution by simple corrosion tests such as single-cycle anodic polarization, corrosion potential monitoring and long-term immersion experiments. Control coatings of polymethylsiloxane (PMeSi) and electrochemically synthesized polypyrrole (Ppy) were also studied. The superior performance of PPySi with respect to PMeSi and Ppy was attributed to highly crosslinked, well-packed and adherent composite films of thickness of the order of microns, manifesting both barrier action and active protection. The use of pyrrole-based silane for corrosion protection of Al alloys constitutes a promising approach for effective replacement of chromium-based treatments in practical applications. Further investigation from the fundamental point of view is deserved.     

绝缘金属铝基板的制备及介电性能研究

采用阳极氧化的方法分别在浓度2%和4%的草酸体系下对金属铝基板表面进行了绝缘化处理。通过SEM对绝缘膜层进行了研究分析,并测试了膜层的介电性能。结果表明:浓度4%的草酸体系下得到的绝缘膜表面存在直径80nm左右的针状物,它可能是膜表面形成的Al(OH)3水合物。较大浓度的草酸电解液的溶解作用加剧了膜层断面开裂、膜质疏松等缺陷,严重影响着膜层的介电性能。     

Cathodic breakdown of anodic oxide film on Al and Al–Sn alloys in NaCl solution

The effect of cathodic polarisation on stability of defined oxide films on Al and Al–Sn alloys (with up to 0.40% Sn) has been investigated in a 0.5 M NaCl solution using the potentiostatic pulse method. The dependence of the cathodic current on time (in the period of 1, 10 and 100 s) was recorded on Al and Al–Sn alloys when subjected to a potential pulse from E_OCP to different negative values (up to −2.0 V). Anodic current responses to the return to the E_OCP were also recorded at three different time scales (1, 10 and 100 s). It has been established that the cathodic polarisation of passivated Al and Al–Sn alloys in a chloride solution is characterized by two regions of potentials with distinctly different phenomena: the range of low and high cathodic potentials (LCP and HCP). In the LCP range, the oxide film retains its properties, while in the HCP range cathodic breakdown and hydration of the oxide take place. The boundary between these two potential ranges shifts towards more negative potential values when the percentage of Sn in the alloy increases. The longer the duration of the cathodic pulse, the more positive the potentials at which the oxide film breakdown takes place. This shift is more marked with alloys containing higher percentage of Sn. Cathodic polarisation (duration of 100 s) activates alloys with 0.20% and 0.40% Sn for anodic dissolution.     

Electrochemical properties of Al and Al alloys relevant to corrosion protection in seawater environments

A series of electrochemical experiments on Al alloys were undertaken to determine their optimum protection potentials in seawater. With 1050 and 5456 alloys, passive films form during anodic polarization but are destroyed by the Cl in seawater, only to regrow as a result of the self-healing capacity of aluminum. The current density of 5456 Al alloy proved to be lower than that of 1050 as a whole. Any shift to more anodic or cathodic conditions in the potential range of-1.5∼-0.68 V resulted in a sudden increase in current density. Current densities in the high-strength 7075 Al alloy showed the greatest values. In contrast, the current densities of 5456 alloy, known to have excellent corrosion resistance in seawater, were the lowest in the range of -0.70∼-1.3 V, and we concluded that this potential range offered optimal protection.     

电流密度对Ti 6Al 4V微弧氧化膜形貌和性能的影响

采用NaAlO2-Na3PO4-NaF溶液体系,研究了电流密度对Ti 6Al 4V合金微弧氧化膜厚度、生长速率、表面形貌、粗糙度、组成相以及氧化膜耐蚀性、耐磨性等影响.结果表明,(1)在试验的电流密度范围内,氧化膜的厚度随电流密度的增大呈线性增大,但氧化膜的粗糙度却几乎呈指数增大,表面质量变差;(2)在质量分数为3.5%的NaCl溶液中显示了比Ti 6Al 4V钛合金更好的耐蚀性;(3)在干摩擦条件下,氧化膜的摩擦系数高于基体的,氧化膜的磨损机制为脆性断裂.     

Characterization and Piezoelectric Properties of Reactively Sputtered (Sc,Al)N Thin Films on Diamond Structure

Highly oriented wurtzite (Sc, Al)N films were deposited on a diamond/silicon by a co‐sputtering system. The results showed that the formation of Sc_xAl_1?xN alloys causes a lattice distortion during the phase transition, and this intermediate phase induces a large piezoelectric response. When the scandium concentration increased up to the solution limit of scandium in aluminum nitride (measured data are about 12 at.%), the piezoelectric coefficient of (Sc, Al)N film is four times larger than pure AlN layer. After annealing process, the d₃₃ value of (Sc, Al)N can be increased to a maximum of 20.073 pC/N.     

Effect of Al(III) as an Activator for Adsorbing Colloid Flotation

Abstract

The effect of Al(III) on adsorbing colloid flotation using Fe(OH)₃ as the coprecipitant and sodium lauryl sulfate as the collector was studied, and the results of foam separation were compared with the zeta potential of the floc before and after Al(III) being added to the solution. It was found that when Al(III) is used as an activator, the zeta potential of the floc is more positive, which presumbly gives the floc a stronger affinity for anionic surfactant adsorption, resulting in better separation efficiency. The working range of pH for an effective separation is extended and good separation efficiency can be achieved at pH values closer to neutral with the aid of Al(III). Furthermore, the separation efficiency is significantly improved for solutions containing interfering ions, such as sulfate, by using Al(III) as an activator.     

影响铝合金阳极氧化膜质量因素的研究

采用扫描电镜观察了铝舍金阳极氧化膜的微观结构,测定了氧化膜的硬度、厚度和失重,进而分析了氧化膜微观结构与其质量的关系。讨论了铝材中金属元素、氧化添加剂、氧化条件对膜层微观结构的影响。结果表明,氧化膜的微观结构与其性能相对应,当氧化膜具有明显的多边形孔的结构且致密时,其性能较好,铝合金中必须含有Mg和Si,且其比例要合适才能形成较好的氧化膜结构;添加剂和氧化条件对氧化膜结构的影响也较大。     

Effects of oxidation curing and Al atoms on the formation of near-stoichiometric freestanding SiC(Al) films derived from polyaluminocarbosilane (PACS)

The effects of oxygen pick-up and Al atoms on the formation and microstructure of freestanding SiC(Al) films by melt spinning of polyaluminocarbosilane (PACS) precursor were studied. PACS green films were cross-linked for 1 h, 2 h, 3 h and 4 h, pre-pyrolyzed at 900 °C, respectively. They were continuously pyrolyzed at 1800 °C to convert initial PACS into SiC(Al) ceramic films. Results reveal that the strict control of oxygen content during the oxidation curing is essential to produce near-stoichiometric SiC(Al) films. The microstructure of the dense films is a mixture of β-SiC crystals, α-SiC nano-crystals, C clusters and a small amount of Al₄O₄C and Al₄SiC₄. Al atoms which play important roles as both sintering aids and grain growth inhibitor are well distributed in the films due to the presence of stable composition and structure. SiC(Al) films with excellent mechanical properties would be attractive candidate materials for MEMS in harsh environments.     

Study of passivation of Al and Al-Sn alloys in borate buffer solutions using electrochemical impedance spectroscopy

Properties of thin oxide films on Al and Al-Sn alloys (with Sn content of 0.02, 0.09, 0.20 and 0.40 wt.%) formed either naturally or anodically in borate buffer solutions were investigated by means of electrochemical impedance spectroscopy. Equivalent circuits have been proposed that completely illustrate the Al(Al-Sn alloy)/oxide film/electrolyte systems examined, and properties of oxide films were determined. The stability (thickness and resistance) of oxide films has been found to increase with increased Sn content in the alloy, with increased passivation potential, and with longer time of anodising. The increase in temperature of anodising significantly reduces impedance in systems observed.     

A new sol-gel route to prepare dense Al2O3 thin films

Anew sol-gel route has been applied to synthetize dense Al₂O₃thin films from aluminum isopropoxide (Al(OPri)₃)as raw precursor material. The results show that, in the solution, acetylacetone (AcAc) and aluminum form a complex compound which effectively suppresses the growth of colloidal particles and makes the sol very stable. Al₂O₃thin films fabricated by spin-coating method and calcined at 500 °C for 3 h possess an amorphous structure and exhibit a highly homogeneous surface texture without evidence of holes or cracks throughout the film. Moreover, the prepared films display a low leakage current and a high transmittance. This new sol-gel route appears to be a highly promising method to synthetize dense Al₂O₃ thin films from Al(OPrⁱ)₃, and could provide a wide range of optical and electric applications.     

Al3+/Bi4Ti3O12薄膜的制备及其光催化性能表征

采用溶胶一凝胶法制备了掺 Al3+ 的Bi4 Ti3 O12 薄膜(Bl-xAlxTi3O12).采用分光光度法研究了薄膜对甲基橙溶液的降解,以及Al3+对薄膜的光催化效果影响.光催化结果表明,Al3+的掺杂量为 2atm% 时,薄膜的光催化效果最好,比未掺杂前提高 57.9%,且吸收边红移量为 36nm.     

Hydrogen incorporation in Ni–P films prepared by electroless deposition

Electroless NiP films, with 12 to 16 wt % P, were deposited from a moderately acid solution. Thermogravimetric analysis indicates the presence of occluded hydrogen in the layers, which desorbs upon heating. The amount of incorporated hydrogen decreases when the pH of the solution or the nickel sulfate concentration is increased; by contrast it increases with hypophosphite concentration. Cyclic voltammetry, using an electrochemical quartz crystal microbalance, confirms the existence of parasitic reactions, namely the reduction of protons of the solvent during the cathodic process and oxidation of hydrogen during the dissolution of the layers. This behaviour is in qualitative agreement with the proposed reaction scheme.     

脉冲电镀锌-铁合金

介绍了在锌酸盐溶液中脉冲电镀锌-铁合金工艺。研究了镀液中氧化锌、亚铁离子和络合剂浓度、脉冲电流参数对镀层中铁含量的影响,获得了铁的质量分数为0.3%~0.6%的电镀锌-铁合金工艺,并通过中性盐水浸泡实验确定了最佳耐蚀镀层的工艺条件。