The characteristics of a Pd–Ni/Pd–Cu double coating on 316L stainless steel and the corrosion resistance in stirred boiling acetic and formic acids mixture

A Pd–Ni/Pd–Cu double coating was deposited on stainless steel surface by electroplating. The microstructure and corrosion resistance of the double coating in strong reducing corrosive media were studied. In boiling 90 wt% acetic acid +10 wt% formic acid mixture containing 0.005 mol L⁻¹ NaCl with 900 r min⁻¹ stir, the corrosion rate of the double coating coated 316L stainless steel is one order of magnitude lower than that of Pd–Cu coated samples. The double coating shows lower porosity, higher hardness and elasticity modulus as well as higher adhesive strength, which may explain the better corrosion resistance in the testing environments.     

Multicomponent Hybridization Transition Metal Oxide Electrode Enriched with Oxygen Vacancy for Ultralong-Life Supercapacitor

Transition metal oxide electrode materials for supercapacitors suffer from poor electrical conductivity and stability, which are the research focus of the energy storage field. Herein, multicomponent hybridization Ni-Cu oxide (NCO-Ar/H₂-10) electrode enriched with oxygen vacancy and high electrical conductivity including the Cu_0.2Ni_0.8O, Cu₂O and CuO is prepared by introducing Cu element into Ni metal oxide with hydrothermal, annealing, and plasma treatment. The NCO-Ar/H₂-10 electrode exhibits high specific capacity (1524 F g⁻¹ at 3 A g⁻¹), good rate performance (72%) and outstanding cyclic stability (109% after 40,000 cycles). The NCO-Ar/H₂-10//AC asymmetric supercapacitor (ASC) achieves high energy density of 48.6 Wh kg⁻¹ at 799.6 W kg⁻¹ while exhibiting good cycle life (117.5% after 10,000 cycles). The excellent electrochemical performance mainly comes from the round-trip valence change of Cu⁺/Cu²⁺ in the multicomponent hybridization enhance the surface capacitance during the redox process, and the change of electronic microstructure triggered by a large number of oxygen vacancies reduce the adsorption energy of OH⁻ ions of thin nanosheet with crack of surface edge, ensuring electron and ion-transport processes and remitting the structural collapse of material. This work provides a new strategy for improving the cycling stability of transition metal oxide electrode materials.     

Study of vanadium-based chemical conversion coating on the corrosion resistance of magnesium alloy

In this study, magnesium alloy (AZ61) was immersed in vanadium containing bath with various conditions, such as the vanadium concentration, immersion time and bath temperature. The results indicate that increase of both vanadium concentration and immersion time produces a thicker conversion layer. However, when immersion time is too long, it will worsen the corrosion resistance due to the increasing of the crack density. The experimental parameter of bath temperature has no significant effect on corrosion resistance. Our results demonstrated that the better corrosion resistance coating can be obtained when the samples are submitted to an immersion in the conversion bath containing NaVO₃ with concentration of 30 g l⁻¹ for 10 min at 80 °C. The presented conversion treatment has its potential to replace the chrome-based conversion coating treatment.     

Characterization of passive oxide film on a Ti–5%Ta–1.8%Nb alloy on exposure to severe oxidizing conditions

This paper presents the results of a study on the characteristics of the passive oxide film that forms on the surface of an α + β Ti–5%Ta–1.8%Nb alloy, which possesses good corrosion resistance in severe oxidizing environment of boiling 11.5 M nitric acid. Through systematic structure–property studies, the microstructure with low corrosion rate (< 1 mpy) in liquid, vapor and condensate phases of nitric acid was identified. The characteristics of the passive film, which imparts corrosion resistance to the alloy, are influenced by its microstructure, temperature and concentration of the acid. The microstructure, thickness and composition of the oxide film were characterized using different techniques. TiO₂, Nb₂O₅ and Ta₂O₅ formed on exposure to vapor and condensate phases, while TiO₂ was observed on exposure to the liquid phase. Detailed microstructural studies showed that the passive film consists of nano-crystalline phases of titanium and tantalum oxides, predominantly anatase in an amorphous matrix. Based on these studies, the mechanism of corrosion of the alloy is derived.     

Scleral Lens Sensor for Ocular Electrolyte Analysis

The quantitative analysis of tear analytes in point-of-care settings can enable early diagnosis of ocular diseases. Here, a fluorescent scleral lens sensor is developed to quantitatively measure physiological levels of pH, Na⁺, K⁺, Ca²⁺, Mg²⁺, and Zn²⁺ ions. Benzenedicarboxylic acid, a pH probe, displays a sensitivity of 0.12 pH units within pH 7.0–8.0. Crown ether derivatives exhibit selectivity to Na⁺ and K⁺ ions within detection ranges of 0–100 and 0–50 mmol L⁻¹, and selectivities of 15.6 and 8.1 mmol L⁻¹, respectively. A 1,2 bis(o-aminophenoxy)ethane-N,N,-N',N'-tetraacetic-acid-based probe allows Ca²⁺ ion sensing with 0.02–0.05 mmol L⁻¹ sensitivity within 0.50–1.25 mmol L⁻¹ detection range. 5-Oxazolecarboxylic acid senses Mg²⁺ ions, exhibiting a sensitivity of 0.10–0.44 mmol L⁻¹ within the range of 0.5–0.8 mmol L⁻¹. The N-(2-methoxyphenyl)iminodiacetate Zn²⁺ ion sensor has a sensitivity of 1 µmol L⁻¹ within the range of 10–20 µmol L⁻¹. The fluorescent sensors are subsequently multiplexed in the concavities of an engraved scleral lens. A handheld ophthalmic readout device comprising light-emitting diodes (LEDs) and bandpass filters is fabricated to excite as well as read the scleral sensor. A smartphone camera application and an user interface are developed to deliver quantitative measurements with data deconvolution. The ophthalmic system enables the assessment of dry eye severity stages and the differentiation of its subtypes.     

Stability of plasma electrolytic oxidation coating on titanium in artificial saliva

Bioactive PEO coating on titanium with high Ca/P ratio was fabricated and characterized with respect to its morphology, composition and microstructure. Long-term electrochemical stability of the coating and Ti⁴⁺ ion release was evaluated in artificial saliva. Influence of the lactic acid and fluoride ions on corrosion protection mechanism of the coated titanium was assessed using AC and DC electrochemical tests. The PEO-treated titanium maintained high passivity in the broad range of potentials up to 2.5 V (Ag/AgCl) for up to 8 weeks of immersion in unmodified saliva and exhibited Ti⁴⁺ ion release <0.002 µg cm^?2 days^?1. The high corrosion resistance of the coating is determined by diffusion of reacting species through the coating and resistance of the inner dense part of the coating adjacent to the substrate. Acidification of saliva in the absence of fluoride ions does not affect the surface passivity, but the presence of 0.1 % of fluoride ions at pH ≤4.0 causes loss of adhesion of the coating due to inwards migration of fluoride ions and their adsorption at the substrate/coating interface in the presence of polarisation.     

Preparation of coatings with high adhesion strength and high corrosion resistance on sintered Nd–Fe–B magnets through electroless plating

Electroless Ni–P-based coatings have been deposited on sintered Nd–Fe–B magnets through applying ultrasonic irradiation and adjusting the [Cu²⁺]/[Ni²⁺] ratio in the solution. The effects of the ultrasonic power on the adhesion to the magnet substrate and the [Cu²⁺]/[Ni²⁺] ratio on the corrosion resistance of the coatings were investigated. It was found that the adhesion of the coating to the substrate could be greatly improved through applying ultrasonic irradiation. Maximum adhesion strength reached 56 MPa at 150 W. The results also showed that the addition of Cu²⁺ could improve the corrosion resistance of Ni–P-based coatings. When the [Cu²⁺]/[Ni²⁺] ratio was 0.02, the coating could be as long as 512 h free of corrosion in the neutral salt spray. The compact amorphous structure was responsible for the improved corrosion resistance of the coating.     

Effect of rare earth metals on microstructure and corrosion resistance of Zn–0·18Al coatings

Abstract

Effect of rare earth (RE) metals addition on the microstructure, formation of Fe–Zn intermetallics and corrosion resistance of the batch galvanising Zn–0·18Al coating were studied. Microstructure of the coating was observed using optical microscopy, scanning electron microscopy and transmission electron microscopy. Salt spray test and surface potential measurement were employed for corrosion resistance determination. The results show that the addition of RE can improve bath liquidity, refine surface spangles, stabilise the Fe₂Al₅ inhibition layer, decrease coating thickness and enhance corrosion resistance of the coating. However, corrosion resistance of the coating did not increase continuously with increasing RE content and the optimum RE content lies between 0·045 and 0·069% in the experiment. Mechanism of RE on the corrosion resistance of the galvanised coating was briefly analysed.     

钢线材硫酸盐体系电镀纳米晶锌镀层工艺研究

为了克服传统线材高速电镀锌工艺存在的镀层耐蚀性能差问题,研究了硫酸盐电镀纳米晶锌镀层的工艺.采用场发射扫描电子显微镜、透射电镜和X-射线衍射技术对镀锌层的表面形貌及晶粒尺寸进行了表征,利用极化曲线和线材缠绕试验对纳米晶锌镀层的耐蚀性能和延展性能进行了研究.结果表明:在基础硫酸盐镀液体系中,仅通过改变脉冲电镀参数并不能得到纳米晶锌镀层;而在含有唯一添加剂(晶粒细化剂1 g/L)的基础硫酸盐镀液体系中,通过对双脉冲电镀参数的优化,得到了平均晶粒尺寸为31 nm,结晶细密、平整、光亮的纳米晶锌镀层;该纳米晶锌镀层在低碳钢板材和线材表面重现性良好;纳米晶锌镀层的耐蚀性能优于传统粗晶锌镀层,且具有良好的延展性.     

Microstructure and properties of laser clad high-entropy alloy coating on aluminium

An AlCrFeNiCuCo high-entropy alloy (HEA) coating was synthesised on an aluminium substrate by laser cladding. Samples were characterised using an optical microscope, X-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy, a microhardness tester, and an electrochemical workstation. The results showed that the interface between the cladding layer and matrix was sound, while the HEA coating consisted of BCC and FCC solid solutions and an Al-rich phase resulting from substrate dilution. The microstructure of the clad layer comprised both columnar and equiaxed grains. The average microhardness of the coating was 550 HV_0.2, and it exhibited better corrosion resistance than the aluminium matrix in a 1?mol?L^?1 H₂SO₄ solution. The typical corrosion characteristic of the coating was pitting and localised corrosion.     

Investigation of the properties of nickel-boron/nano-diamond composite coatings upon pre/post heat treatment

The study has explored the physical and chemical properties of nickel-boron/nano-diamond composite coatings upon pre/post heat treatment. The nano-composite coatings were produced by electroless plating. In fact, the effects of using the nano-diamond additives (0 g l⁻¹, 0.1 g l⁻¹, 0.3 g l⁻¹, 0.5 g l⁻¹, 0.7 g l⁻¹) were investigated in pre/post heat treatment. According to the results, the micro-hardness of the nickel-boron/nano-diamond composite coating produced in the bath containing 0.5 g l⁻¹ nano-diamond additive reached to 1005 HV 0.05 upon post-heat treatment. Also, the corrosion resistance of the nickel-boron/nano-diamond composite coatings was modified by using the nano-additive or heat treatment. But, adding nano-diamond particles reduced the ductility and wear resistance of the nickel-boron coatings. We also found, modification of the properties (ductility and wear resistance) of the composite coatings was achieved by using the heat treatment.     

Synthesis and characterization of FeCoNiCrCu high-entropy alloy coating by laser cladding

The influences of Si (1.2 mol.%), Mn (1.2 mol.%) and Mo (2.8 mol.%) additions on the microstructure, properties and coating quality of laser cladded FeCoNiCrCu high-entropy alloy coating have been investigated. The multi-component alloy coating is found to be a simple face-centered cubic (FCC) solid solution with less component segregation and high corrosion resistance, microhardness and softening resistance properties. For the coating without Si, Mn and Mo additions, the microstructure is mainly composed of columnar and equiaxed grains with uniformly distributed alloying elements. The microhardness reaches 375 HV_0.5, which is about 50% higher than that of the same alloy prepared by arc melting technique. But the coating quality is very poor. While for the coating with Si, Mn and Mo additions, the coating quality is greatly improved, the microhardness increases to 450 HV_0.5, but the microstructure transforms to dendrite due to a slightly increase in component segregation.     

Effect of nitrogen on corrosion behaviour of a novel high nitrogen medium-entropy alloy CrCoNiN manufactured by pressurized metallurgy

A novel high nitrogen medium-entropy alloy CrCoNiN, which had higher strength and slightly lower ductility than CrCoNi alloy, was successfully manufactured by pressurized metallurgy. The microstructure and corrosion behaviour were investigated by microscopic, electrochemical and spectroscopic methods. The results indicated that nitrogen existed in the form of Cr₂N precipitates and uniformly distributed N atoms, and nitrogen alloying significantly refined the grain size. Besides, nitrogen enriched on the outmost surface of passive film and metal/film interface as ammonia (NH₃ and ${{\mathrm{N}\mathrm{H}}_4}^{+}$) and CrN, respectively. The significant improvement of corrosion resistance of CrCoNiN was attributed to the lower metastable pitting susceptibility together with thicker, less defective and more compact passive film.     

Electroplating of zirconium and aluminum hydroxide thin films following anodic dissolution of corresponding metal anodes in organic medium

Zirconium (IV) hydroxide or hydrate oxide films, which are typically difficult to prepare by electrochemical methods using aqueous solutions, are easily fabricated in an acetone bath using Zr anodes as the metal sources and a metal-free solvent containing halide ions as the supporting electrolyte. This method is also confirmed to be applicable to aluminum anodes. In the early stage of electrolysis, anodic oxidation of the metal anode proceeds in the presence of water as an impurity in the solvent. Subsequently, pitting corrosion of the oxide film on the metal anode occurs as a result of the action of halide ions. The corrosiveness of the halogen additive appears to be an important factor determining the dissolution or deposition of metal species in this stage. That is, Br^– is more active for electrochemical dissolution of a passive oxide film on the anode compared to I^–. Finally, Zr species are deposited on the cathode surface via reactions with cathodically generated hydroxide ions. In these processes, the metal plate acts as a soluble anode and as a metal source for electrodeposition. The coating of Zr (IV) hydroxide film on a stainless steel substrate is shown to act as an effective barrier against electrolytic corrosion.     

Pulse Electrocodeposited Ni–WC Composite Coating

In the present work, tungsten carbide (WC) particulate of average size 10 µm were electrocodeposited in the nickel metal matrix, to form metal matrix composite (MMC) coating over the EN8 steel substrate. The electrodeposition of Ni–WC particulate composite coating was carried out using the Watt's bath under the influence of varying current density and duty cycle. It was found that current density of 0.02 A/cm² was sufficient to start the codeposition kinetics. But, good quality of electrodeposition was obtained at a current density of 0.04 A/cm². The WC particulate entrapment and distribution of WC particles in Ni matrix according the variation in experimental parameters has been reported. The dense and compact microstructure was obtained at a current density of 0.04 A/cm² and duty cycle of 30%. Microhardness and corrosion resistance properties of composite coating were also evaluated and reported.     

The surface chemistry of 3-mercaptopropyltrimethoxysilane films deposited on magnesium alloy AZ91

Magnesium and its alloys have desirable physical and mechanical properties for a number of applications. Unfortunately, these materials are highly susceptible to corrosion, particularly in the presence of aqueous solutions. The purpose of this study is to develop a uniform, non-toxic surface treatment to enhance the corrosion resistance of magnesium alloys. This paper reports the influence of the coating bath parameters and alloy microstructure on the deposition of 3-mercaptopropyltrimethoxysilane (MPTS) coatings on magnesium alloy AZ91. The surface chemistry at the magnesium/MPTS interface has also been explored. The results indicate that the deposition of MPTS onto AZ91 was influenced by both the pH and MPTS concentration in the coating bath. Furthermore, scanning electron microscopy results showed that the MPTS film deposited uniformly on all phases of the magnesium alloy surface. X-ray photoelectron spectroscopy studies revealed that at the magnesium/MPTS interface, the molecules bond to the surface through the thiol group in an acid-base interaction with the Mg(OH)₂ layer, whereas in the bulk of the film, the molecules are randomly oriented.     

Effect of Rough-Surfaced Diamond Content on the Microstructure,Tribological Behavior,and Corrosion Resistance of Ni/Diamond Composite Coatings

This study fabricates certain Ni/diamond composite coatings using a coelectrodeposition method and then evaluates the effect of diamond content on the morphology, phase structure, microhardness, wear, and corrosion resistance of such coatings, while exploring their tribological and anticorrosion mechanisms. It is demonstrated that the addition of diamond can change the preferred orientation of Ni from (200) to (111), and its texture coefficient value can be boosted from 23.3% to 64.4% with the increase of diamond content. In the experiment, at a diamond content of 3 g L⁻¹, the deposited diamond particles are more and evenly dispersed across the composite, with the microhardness of nickel-based coatings reaching an optimum value of 613 HV. In addition, the coefficient of friction is reduced to a minimum value of 0.627, while the wear rate is kept at only 1.79 × 10⁻⁵ mm³ Nm⁻¹, indicating a high wear resistance. Electrochemical test results demonstrate that the Ni/diamond composite coatings produced at 3 g L⁻¹ create the maximum charge transfer resistance (5429.3 Ω cm²) and the minimum corrosion current density (2.19 μA cm⁻²), features that can deliver the best corrosion resistance.     

超声场中脉冲电沉积Ni-CeO_2纳米复合镀层的耐蚀性

在超声场中用脉冲电沉积法制备了Ni-CeO2纳米复合镀层,考察了镀层中CeO2含量及表面形貌,研究了镀层在10wt%HCl溶液中的耐蚀性,分析了超声作用下脉冲参数对镀层耐蚀性的影响.结果表明:脉冲参数和超声波对镀层中CeO2含量和微观组织均有影响,适宜的脉冲参数可以提高镀层中CeO2含量,细化镀层晶粒,而超声波可促使镀层晶粒进一步细化;Ni-CeO2纳米复合镀层的耐蚀性与镀层中CeO2含量、镀层晶粒大小及组织致密程度有关;在占空比0.2、脉冲频率1000Hz时超声作用下制备的镀层中CeO2含量较高,镀层晶粒细小、组织致密,腐蚀速率最低,表现出优良的耐蚀性.     

Influence of phytic acid concentration on performance of phytic acid conversion coatings on the AZ91D magnesium alloy

In this study, the phytic acid conversion coating, a new environmentally friendly chemical protective coating for magnesium alloys, was prepared. The influences of phytic acid concentration on the formation process, microstructure, chemical state and corrosion resistance of the conversion coatings on AZ91D magnesium alloy were investigated by means of weight gain measurement, field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS), respectively. And the depth profile of all elements in the optimal conversion coatings was analyzed by auger electron spectroscopy (AES).The results show that the growth, microstructure, chemical state and corrosion resistance of the conversion coatings are all obviously affected by the phytic acid concentration. The concentration of 5 g l⁻¹ corresponds to the maximum weight gain. The main elements of the coating are Mg, Al, O, P, and C, which are distributed gradually in depth. The functional groups of conversion coatings formed in higher concentration phytic acid solution are closer to the constituent of phytic acid than those formed in lower concentration phytic acid solution. The coatings formed in 1–5 g l⁻¹ are integrated and uniform. However, those formed in 20–50 g l⁻¹ have some micro-cracks on the α phase. The coating formed in 5 g l⁻¹ has the best corrosion resistance, whose open circuit current density decreases about six orders than that of the untreated sample, although the coatings deposited in 1–20 g l⁻¹ can all improve the corrosion resistance of AZ91D.     

Chemical composition and corrosion resistance of passive chromate films formed on stainless steels 316 L and 1.4301

The chemical composition and corrosion behavior of the natural and formed by chemical treatment in chromium-containing solution passive films on 316 L and 1.4301 stainless steel surfaces have been investigated by means of X-ray photoelectron spectroscopy and electrochemical in situ method of anodic polarization curves. It have been established that the oxide films formed by the chemical treatment have different chemical composition (Cr-enriched), color and reduced corrosion resistance compared to the natural passive films on both steels. The results have shown that the lower part of the oxide layer represents a uniform modified passive film and the upper one is a porous Cr³⁺-enriched film with an island-like structure. The latter permits a direct contact of the solution with the modified passive film which controls the corrosion resistance by the dissolution of the Fe³⁺ oxides present in the lower thinner layer.