Cost‐efficient conversion coatings for corrosion protection prepared by the sol‐gel process

For several years, chromate compounds were used as effective and inexpensive corrosion inhibitors. Studies showed that these materials were toxic and carcinogenic. A subsequent ban on these materials has led to extensive research to develop effective alternative inhibitors. The sol‐gel method appeared as an effective technique forming protective silane layers from hydrolyzed tetraethylorthosilicate (TEOS) and glycidoxypropyltrimethoxy silane (GPTMS) in an aqueous sol–gel process. The final cross‐linking of the layer is realized by heat treatment to form thin, fully dense, protective films of silane on diverse metal surfaces. Most sol‐gel layers use a considerable amount of solvent VOC (v olatile o rganic c ompound) in order to achieve a dispersion of silane with water. However, in a wide range of industries, the high amount of VOC is the major hindrance for the application of silane layers. This article shows a coating concept without VOC, which is cost‐efficient, effective for corrosion protection and applicable for metal surfaces. The corrosion protection effect is given by means of comprehensive impedance spectroscopy measurements.     

AFM characterisation of sol‐gel TiO2 films deposited on stainless steel

One‐layer, two‐layer and three‐layer titania films on AISI 304 stainless steel were deposited by sol‐gel process and dip‐coating method. Two sols were prepared by using titanium isopropoxide as a precursor, propanol as a solvent, nitric acid as a catalyst and acetylacetone for peptization. Both of the prepared sols contained the same amount of mentioned components, the only difference was in the addition of polyethylene glycol (PEG) as templating reagent to one of the sols. After calcination at 550°C, deposited films on the stainless steel substrate were characterized by atomic force microscope (AFM). Influence of layer number as well as addition of polyethylene glycol on morphology of titania films was analysed and discussed. Generally, by increasing the number of layers and by addition of polyethylene glycol, roughness parameters increase by changing surface topography. The surface topography analysis is very important when choosing the adequate industrial application of prepared layers.     

Structural and optical properties of nitrogen‐iron co‐doped titanium dioxide films prepared via sol‐gel dip‐coating: Effect of urea and iron nitrate concentration in the sol

In this study, nitrogen‐iron co‐doped titanium dioxide films were prepared via sol‐gel dip‐coating method using urea and iron nitrate as nitrogen and iron source, respectively. Nonmetal doping of TiO₂ have some disadvantages such as massive charge carrier recombination and losing the photo‐catalytic capability. Three different nitrogen‐iron co‐doped titanium dioxide sols with different urea and iron nitrate concentration were prepared. The resulting sols were homogeneous and transparent, and no precipitation was observed in any of them. It was observed that the film prepared with middle urea‐iron nitrate concentration sol got opaque in a short time after the dip‐coating process. All prepared films were characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy, scanning electron microscopy, confocal microscopy and ultraviolet–visible (UV‐Vis) spectroscopy. It was found that the concentration of the urea and iron nitrate in the sol had an effect on the crystal structure, microstructure, surface morphology and optical properties of the resulting films. Samples with middle concentrations had amorphous structure and bigger particle size. It was seen that sample with higher iron amount has lower band‐gap. It is concluded that we can prepare transparent anatase, transparent amorphous and opaque amorphous titanium dioxide films by changing the urea and iron nitrate concentration in the sol.     

含碳纳米管有机-无机复合涂层的制备与防护性能

为了改善铝合金材料的耐腐蚀性能, 研究了以正硅酸乙酯（TEOS）为主要原料, 加入一定量的KH-550, 并引入部分羟基化的多壁碳纳米管（MWCNTs-OH）进行复合, 以冰乙酸为催化剂, 采用溶胶---凝胶法在铝合金基体表面形成复合涂层。腐蚀电化学测试和扫描电镜分析结果表明, MWCNTs-OH的引入能够明显提高涂层的防护性能, 并有效防止涂层开裂。考察了MWCNTs-OH含量和热处理温度对涂层性能的影响。结果表明: MWCNTs-OH质量分数为0.04%、 热处理温度为130℃时制备的涂层性能最佳, 相应的试样在3.5wt%NaCl溶液中的腐蚀电流密度约为3.056×10-8A/cm2, 而同等实验条件下铝合金基体腐蚀电流密度为7.216×10-5A/cm2, 涂层的存在使腐蚀速率降低了3个数量级, 涂层对铝合金基体具有显著的防护效果。      

Development of corrosion protective polymeric coatings from a non‐edible seed oil

In this study, we have developed corrosion protective coatings material from Pongamia glabra seed oil. First, oil was converted to pongamia oil epoxy (POE). The resin was synthesized by the reaction of POE with phthalic acid to develop polyester (PE) and further treated with diethylene triamine (DTA) in different (20–35%wt) amount. The structural elucidation of POE and PE were carried out by FT‐IR, ¹H‐NMR and ¹³C‐NMR spectroscopic techniques. Thermal behavior of PE‐30 was studied by thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC). The coatings of PE‐DTA resins were prepared on mild steel strips to investigate their physico‐mechanical and corrosion performance. Corrosion protection of coated panels were examined in different corrosive media (3.5 wt% HCl, 3.5 wt% NaOH, 5.0 wt% NaCl) using potentiodynamic polarization and AC impedance. Thermal analyses revealed that PE‐30 may find application as eco‐friendly corrosion protective coating safely used up to 175°C.     

Controlled adsorption of titanium(IV) oxide particles on electroplated zinc coatings to improve the corrosion resistance of chromium(VI)‐free conversion layers

Adsorption of nano‐scaled titanium(IV) oxide particles on electroplated zinc is performed by a simple dip‐coating technique in an aqueous titanium(IV) oxide suspension prepared with a stirred media mill. X‐ray photoelectron spectroscopy, scanning electron microscopy and X‐ray fluorescence spectroscopy are carried out to investigate the composition of the zinc surface and the thickness and porosity of the adsorbed titania films. The zinc surface formed during the electrodeposition process is of oxyhydroxide nature and the thickness of the adsorbed titania particle layer is controlled by the pH value and the solid concentration of the suspension. In the range of 10 wt.%–30 wt.% titanium(IV) oxide, a linear dependence between the titania film thickness and the solid content of titania particles in the suspension is found. Highest film thicknesses are obtained in alkaline media (pH≥9). At 13.5 wt.% titania particles and pH values below pH = 2.4, the titania particle film is not closely packed and the zinc layer underneath is still visible in electron microscopy, which is a prerequisite for imbedding these particles by a thin second zinc layer for formation of a robust chromium(VI)‐free passivation layer containing the titania particles.     

Design of wear and corrosion resistant PVD‐coatings for magnesium alloys

Although magnesium alloys became popular in the first half of the 20^th century, the bad corrosion properties prevented their breakthrough in industrial mass production. Since the technology for the production of high purity alloys was introduced in the 1970s, magnesium alloys became more and more in the focus of industrial attention. Today magnesium alloys are state of the art in structural parts in automotive industry. Despite its outstanding properties like good castability, low density and nearly unlimited availability the negative aspects like weak corrosion and wear behaviour still limit the application of magnesium in industry [1]. So, the only economic solution is the deposition of a coating or a suitable surface treatment which provides both, wear and corrosion resistance. Today, plasma electrolytic anodisations are state of the art [2–5]. They provide acceptable corrosion resistance and protect the magnesium from mechanical damage due to their high hardness. On the other hand, their high porosity limits their use in combination with electrochemically noble materials, leading to galvanic corrosion [6]. In addition, the high surface roughness of the plasma electrolytic anodisations restricts their use in tribological applications, particularly under dry sliding conditions [7]. On the other hand, due to the high life time recommendations the application of magnesium in the automotive industries motion component field is a long term process. Nevertheless, there is a quite high industrial interest to apply magnesium in the motion component field in consumer applications like do‐it‐yourself or gardenig. Some examples are motor components of lawnmovers, motor saws or drills. Especially for these fields of application there are quite high demands on the corrosion properties due to undefined storage and the conditions during usage. In order to achieve smooth surfaces with high quality, the PVD technology moves into the centre of interest. Since the 1980s PVD coatings are well established and widely used for different industrial applications, mainly for steel and tool coatings. The authors were the first who carried out serious studies on the development of PVD coatings for magnesium alloys since 1999 [6, 7]. The extensive research activities lead to the recent development of a coating system, which provides both, good wear properties as well as good corrosion behaviour.     

镁合金超疏水环氧复合涂层的制备与性能EI北大核心CSCD

传统的超疏水表面的制备过程比较复杂,机械稳定性差,这严重制约了超疏水表面的实际应用。采用“黏合剂+纳米粒子”的方法,在镁合金表面制备一种无氟、持久稳定的超疏水环氧复合涂层。接触角测试结果表明,复合涂层的接触角最高可达160.2°,且在3.5%(质量分数)NaCl溶液中浸泡30天后,接触角仍然高达103°;EIS结果表明,在5个加速老化循环周期后,复合涂层的|Z|_(0.01 Hz)仍高于10^(9)Ω·cm^(2),展现出优异的耐盐雾性能和耐蚀性能;摩擦磨损实验结果显示,在19.6 N的载荷下机械摩擦8 h后,复合涂层的|Z|_(0.01 Hz)高达1.84×10^(9)Ω·cm^(2)。通过“空气垫”的屏障作用,复合涂层能够为镁合金提供高效且持久的腐蚀防护,“黏合剂+纳米粒子”策略为超疏水涂层的制备提供了新的思路。     

Al含量对镁铝合金大气腐蚀产物膜结构与性能的影响

采用X射线衍射(XRD)和扫描电镜能谱(EDS)面扫描分析技术,研究了Al含量对实验室模拟的潮湿大气中由NaCl盐粒诱发的3种镁合金腐蚀产物膜结构和成分的影响.结果表明,腐蚀产物主要为Mg(OH)2和Mg2(OH)3C1·4H2O,随着合金中Al含量的增加,腐蚀产物中Al参与生成的产物增多,但腐蚀产物膜的结构变得疏松多孔.采用电化学交流阻抗(EIS)测试了膜层的保护性.结果表明,3种不同Al含量镁合金腐蚀产物膜的保护性能均随着暴露时间的延长而提高;在相同的暴露时间内,镁合金中Al含量越高,腐蚀产物膜的阻抗值愈小,膜层的保护性愈差.其原因是Al的含量越高,腐蚀产物膜的结构变得愈加疏松和多孔.     

EURAXLES – A global approach for design,production and maintenance of railway axles: WP4 – “Tools,technologies and surface protection systems minimizing the negative influence of corrosion or surface damage on the free axle surface“

Work Package 4 “Tools, technologies and surface protection systems minimizing the negative influence of corrosion or surface damage on the axle surface” of the EURAXLES project aimed on development of practical solutions for wheelset protection systems to avoid corrosion and damages at the axles and thus minimizing the risk of axle failures. The work included investigations for improving the paint adhesion by grit‐blasting of the axle surface, alternative and innovative coating systems, recommendations for quality tests of painting and coatings and also investigation of unpainted axles.     

In vitro corrosion characterization and cell proliferation on surface‐modified Ti

Two types of surface treatments (Low pressure metal organic chemical vapor deposition (Ti‐MOCVD) and anodized Ti) have been conducted on Ti to improve their osteointegration properties in view of dental implant application. The two typologies of surfaces have been characterized in vitro both regarding the corrosion and the in biological behaviour in comparison with the Ti machined surface. The corrosion tests showed that both the surface treatments reduced markedly the corrosion rate compared to Ti machined. The biological tests showed that all specimens are cytocompatible and significant differences among them were detected. In particular WST1 tests showed more viable osteoblasts adhering to MOCVD specimens in comparison with the other surfaces.     

Effect of aluminum content on solidification microstructure and properties of Fe‐Cr‐B‐Al alloys

The microstructures and mechanical properties of eight kinds of Fe‐Cr‐B‐Al alloys containing X wt.%Al‐0.35 wt.%C‐10.0 wt.%Cr‐1.4 wt.%B‐0.6 wt.%Si‐0.8 wt.%Mn (X = 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0) were studied by means of optical microscopy (OM), scanning electron microscopy (SEM), X‐ray diffraction (XRD), Rockwell hardness and Vickers micro‐hardness testers. The results indicate that the as‐cast microstructure of aluminium‐free sample consists of the martensite, austenite and eutectic borocarbides, and the eutectic borocarbides are the mixture of (Fe, Cr)₂B and (Cr, Fe)₇(C, B)₃, and its hardness reaches 65 HRC. When a small amount of aluminium element (Al ? 1.0 wt.%) is added, the phase composition has no significant change, and the hardness excels 65 HRC. When the concentration of aluminium reaches 1.5 wt.%, the matrix of Fe‐Cr‐B‐Al alloy becomes pearlite and δ‐ferrite, leading to a sharply decrease of the hardness. The proportion of ferrite goes up along with increasing aluminium concentration, and the hardness of Fe‐Cr‐B‐Al alloy has slight decrease.     

Experimental investigation and life prediction of hot corrosion pre‐exposure on low‐cycle fatigue of a directionally solidified nickel‐base superalloy

Low‐cycle fatigue tests were conducted on the directionally solidified nickel‐base superalloy DZ125 at 850 °C in the unexposed and exposed specimens for 2, 15, 25 and 50 h in hot corrosion environment. The pre‐exposed specimen exhibited a lower life than unexposed specimens. Fatigue cracks in the unexposed specimens are initiated from defects near the surface, while the cracks of exposed specimens preferentially occur on the surface. Hot corrosion damage in fatigue life was found to be associated with the reduction of the bearing area. A novel life prediction methodology based on continuum damage mechanics was proposed to predict the experimentally observed decrease in low‐cycle fatigue life with increasing prior exposure time.     

Bulk preparation and characterization of mesoporous carbon nanotubes by catalytic decomposition of cyclohexane on sol–gel prepared Ni–Mo–Mg oxide catalyst

Multiwalled carbon nanotubes were synthesized using Ni–Mo–Mg oxide catalyst prepared by sol–gel technique. Carbon nanotubes were formed in situ by the reduction of nickel oxide (NiO) and molybdenum oxide (MoO₃) to Ni and Mo by a gas mixture of nitrogen, hydrogen and cyclohexane at 750 °C. Scanning Electron Microscopy (SEM) was used to confirm the formation of carbon nanotubes (CNTs). The pore size distribution of carbon nanotubes (CNTs) was investigated by N₂ adsorption and desorption. It was found that the pore size fell into the mesopore range: 2 < d < 50 nm. Interpretation was also made using Raman spectroscopy, Diffuse reflectance spectroscopy, X-ray diffraction and ESR spectra. This method is found to produce a very high yield weighing over 20 times of the catalyst. Based on the experimental conditions and results obtained a possible growth mechanism of the carbon nanotubes is proposed.     

The influence of the electroplating parameters on the conditions of deposited nickel‐iron coatings

Several specific electroplating parameters are varied to develop a manufacturing process for nickel‐iron coatings with low residual stresses and favourable structures and hardness values. Here, the produced coating conditions on the surface are characterised according to alloy compositions, microstructures, residual stresses, texture and microhardness as well as the elastic indentation modulus. The manufacture of the coatings was carried out in a laboratory electroplating plant. The process parameters are: electroplating in electrolytic baths with and without saccharin as an additive, with different iron content as well as with various current parameters. The results show significant influences of saccharin, as a bath additive, and of the pulse frequency during the reverse current pulse procedure on the coating conditions. Supplementary investigations are scheduled for determining the distributions of the conditions through the coating thickness. Similarly, micromechanical tests are planned. Process parameters with optimal conditions can then be selected from the determined process‐condition property relation. This is to subsequently serve as the basis for improving the manufacture of micro gear‐wheels. The micro gear‐wheels are produced by electroforming using the direct LIGA process.     

Investigation of wear resistance and microstructure of a newly developed chromium and vanadium containing iron‐based hardfacing alloy

Plasma transferred arc (PTA) welded Ni and Co‐based alloys have gained high acceptance in many industrial applications for the wear protection of components. Recently, the cost of nickel and cobalt is rising drastically. This paper presents the development of a cost‐effective high chromium and vanadium containing iron‐based hardfacing alloy with high hardness and wear resistance. The welding processing of the alloy is carried out by PTA welding of atomized powders. Investigations on powder production as well as on weldability are presented. The coatings are metallographically studied by optical microscopy, SEM, EDX and micro‐hardness measurements. The wear resistance properties of the coatings are examined using pin on disk, dry sand rubber wheel and Miller testing, the corrosion properties are determined by immersion corrosion tests. The newly developed iron‐based alloy has nearly the same wear resistance as Ni‐based alloys with fused tungsten carbides at a higher level of corrosion resistance and much lower cost.     

Integration of Multiple Plasmonic and Co‐Catalyst Nanostructures on TiO2 Nanosheets for Visible‐Near‐Infrared Photocatalytic Hydrogen Evolution

Utilization of visible and near‐infrared light has always been the pursuit of photocatalysis research. In this article, an approach is developed to integrate dual plasmonic nanostructures with TiO₂ semiconductor nanosheets for photocatalytic hydrogen production in visible and near‐infrared spectral regions. Specifically, the Au nanocubes and nanocages used in this work can harvest visible and near‐infrared light, respectively, and generate and inject hot electrons into TiO₂. Meanwhile, Pd nanocubes that can trap the energetic electrons from TiO₂ and efficiently participate in the hydrogen evolution reaction are employed as co‐catalysts for improved catalytic activity. Enabled by this unique integration design, the hydrogen production rate achieved is dramatically higher than those of its counterpart structures. This work represents a step toward the rational design of semiconductor–metal hybrid structures for broad‐spectrum photocatalysis.     

The effect of PVD coatings on the tensile strength and low‐cycle fatigue resistance of stainless steel and titanium alloys

PVD coatings applied to components form hard, stronger layers and generate high residual compressive stresses that limit the plastic deformation in surface layers of the base metal thus increasing its tensile strength and resistance to fatigue loading. The purpose of this paper is to experimentally determine the influence of the deposition of 2 to 16.5‐μm‐thick PVD coatings of TiN, Cr, (Cr+TiN), (TiC)N, (TiAl)N onto specimens of stainless steel 321 and titanium alloys of types MILT‐81556A and (10‐2‐3; 4966) on their tensile strength and low‐cycle fatigue resistance when the development of large elastic–plastic strains takes place. The tensile and low‐cycle fatigue tests were conducted under conditions of axial zero‐to‐tension cycle of the stress‐controlled loading on flat 1‐ to 1.5‐mm‐thick specimens in the initial state (uncoated specimens) and after application of a PVD coating, including those after pretensioning or after cyclic prestraining in the low‐cycle fatigue range. The deposition of PVD coatings is found to enhance the characteristics of tensile strength and low‐cycle fatigue resistance in the quasi‐static fracture range. The deposition of PVD coatings on specimens cyclically prestrained to the values of 53–86% of the number of cycles to fracture, changes the cyclic properties of the material and predetermines the fatigue fracture mode only.