Effect of bath concentration and curing time on the structure of non-functional thin organosilane layers on aluminium

The corrosion resistance of aluminium alloys can be improved by different surface treatments such as painting. A pre-treatment based on chromate is the current method used to increase the corrosion resistance and the adhesion of the organic layer. Silane films seem to be an interesting alternative system to replace the toxic chromates. In this paper, the characterisation of bis-1,2-(triethoxysilyl)ethane (BTSE) thin layers has been evaluated by coupling optical techniques like spectroscopic ellipsometry (SE) and infra-red spectroscopic ellipsometry (IRSE) along with electrochemical methods (electrochemical impedance spectroscopy (EIS)). This approach has been chosen to have a better understanding of the protection provided by these organosilane thin films. It will be demonstrated that the BTSE bath concentration modifies the thickness of the layers and that the curing of this thin film can also improve the barrier properties by forming a denser layer.     

Correlation of morphology and barrier properties of thin microwave plasma polymer films on metal substrate

The barrier properties of thin model organosilicon plasma polymers layers on iron are characterised by means of electrochemical impedance spectroscopy (EIS). Tailored thin plasma polymers of controlled morphology and chemical composition were deposited from a microwave discharge. By the analysis of the obtained impedance diagrams, the evolution of the water uptake ?, coating resistance and polymer capacitance with immersion time were monitored and the diffusion coefficients of the water through the films were calculated. The impedance data correlated well with the chemical structure and morphology of the plasma polymer films with a thickness of less than 100 nm. The composition of the films were determined by means of infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The morphology of the plasma polymer surface and the interface between the plasma polymer and the metal were characterised using atomic force microscopy (AFM). It could be shown that, at higher pressure, the film roughness increases which is probably due to the adsorption of plasma polymer nanoparticles formed in the plasma bulk and the faster film growth. This leads to voids with a size of a few tens of nanometers at the polymer/metal interface. The film roughness increases from the interface to the outer surface of the film. By lowering the pressure and thereby slowing the deposition rate, the plasma polymers perfectly imitate the substrate topography and lead to an excellent blocking of the metal surface. Moreover, the ratio of siloxane bonds to methyl-silyl groups increases which implies that the crosslink density is higher at lower deposition rate. The EIS data consistently showed higher coating resistance as well as lower interfacial capacitance values and a better stability over time for the film deposited at slower pressure. The diffusion coefficient of water in thin and ultra-thin plasma polymer films could be quantified for the smooth films. The measurements show that the quantitative evaluation of the electrochemical impedance data requires a detailed understanding of the film morphology and chemical composition. In addition, the measured diffusion coefficient of about 1.5×10⁻¹⁴ cm² s⁻¹ shows that plasma polymers can act as corrosion resistant barrier layers at polymer/metal interfaces.     

Formation of ultra-thin amorphous conversion films on zinc alloy coatings: Part 2: Nucleation, growth and properties of inorganic-organic ultra-thin hybrid films

Within the two parts of this contribution a detailed investigation of the formation of ultra-thin amorphous conversion coatings on hot dip galvanised steel is reported. The second part deals with the nucleation, growth and the barrier properties of these ultra-thin films on model substrates. The chemical composition as well as the film growth kinetics of the phosphoric acid and complexing organic macromolecules within the conversion layer system on a hot dip galvanised steel substrate have been determined by infra-red reflection absorption spectroscopy (IRRAS) and X-ray photoelectron spectroscopy (XPS). Film nucleation was studied by atomic force microscopy (AFM) that revealed the initial formation of individual nanoscopic islands, which depends strongly on the initial surface chemistry. Cyclovoltammetry (CV) and potentiostat measurements were performed to characterise the blocking of ion transfer and electron transfer reactions on the modified surface. An excellent correlation with the barrier properties of the film with the state of film growth and the composition of the inorganic/organic nanocomposite layer was observed. The investigations are a basis for the understanding and future development of thin conversion films on zinc alloy surfaces. Finally, Scanning Kelvin Probe measurements showed the inhibiting effect of the conversion treatment under the conditions of atmospheric corrosion.     

Electrochemical and morphological properties of zirconium conversion coating in the presence of nickel ions on galvanized steel

A hexafluorozirconic acid-based conversion coating was applied on a galvanized steel substrate and the influence of nickel ion from nickel sulfate solution (in zirconium solution and in a separate solution) on the corrosion resistance behavior and morphology of zirconium conversion coating was investigated. Electrochemical impedance spectroscopy and DC polarization were conducted in 3.5 wt% NaCl solution in order to optimize practical conditions of zirconium conversion coating and NiSO₄ solution on the galvanized steel substrate. Field emission scanning electron microscopy and X-ray photoelectron spectroscopy were employed to study the morphology and composition of the coated surfaces. Results revealed that the conversion coating obtained from solution containing zirconium and nickel ions (Zr + Ni) did not improve corrosion resistance and uniformity of the coating in comparison with Zr conversion coating in optimized condition. However, a positive effect was obtained from samples coated with separate solutions of zirconium and nickel (Zr–Ni). Improved corrosion resistance and morphology of Zr-based conversion coating were observed in Ni²⁺ concentration, pH, and immersion time of 10 g/L, 6 and 300 s, respectively. Morphology and surface composition analysis proved that two separate layers of conversion coating containing zirconium, zinc, and nickel oxide/hydroxide compounds were formed in the case samples that were treated by separate solutions. This led to better uniformity and higher thickness of the coating. Finally, adhesion strength of epoxy organic coating on galvanized steel with and without conversion coating was investigated by pull-off measurement. Zr–Ni conversion coating in optimum conditions had a positive effect on adhesion of organic coating in comparison with blank sample and samples pretreated with Zr and Zr + Ni conversion coatings through increased surface roughness and physical interlocking.     

Corrosion inhibition of magnesium by combined zirconia silica sol-gel films

The inhibition of Mg (AZ91D) corrosion by thin sol-gel films was studied. The sol-gel films were prepared by the traditional acid or base-catalyzed hydrolysis and condensation, and finally deposited by dip coating. Two different sol-gel monomers were used: phenyltrimethoxysilane (PTMOS) and zirconium(IV)tetra-1-propoxide (ZrTPO). Films were made of each of the individual monomers and by depositing first a PTMOS film followed by ZrTPO-based film. The corrosion inhibition of the films and their characterization were examined by different methods including potentiodynamic polarization, contact angle measurement, adhesion test, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS).We found that while the ZrTPO-based film did not show a significant corrosion inhibition, the PTMOS-based film provided moderate protection. Interestingly, the combined film exhibited superior corrosion inhibition as compared with the other films.     

聚苯胺修饰纳米ZnO薄膜及其光致阴极保护性能

从金属材料腐蚀特性及腐蚀保护要求出发,首先利用阳极氧化法制得ZnO薄膜,再通过恒电位法将ZnO薄膜用聚苯胺修饰得到ZnO/PANI复合薄膜。采用扫描电镜分析（SEM）、X射线衍射分析（XRD）、光电流、开路电位（OCP）及电化学阻抗等方法对制得的ZnO薄膜和ZnO/PANI复合薄膜进行物性分析和光电性能评价。研究表明：成功制得ZnO/PANI复合薄膜,且表现出优良的腐蚀保护性能。OCP实验表明,ZnO/PANI复合薄膜腐蚀保护性能与纳米ZnO薄膜相比提升了2～3倍。其中,光照后ZnO薄膜的光电流增加7μA,OCP下降5mV,复合薄膜的光电流增加22μA,OCP下降13mV。最后,失重实验对两种薄膜的光致阴极保护性能的分析数据显示,ZnO薄膜和ZnO/PANI复合薄膜都能对316L不锈钢和Q235碳钢起到光致阴极保护效果,但复合薄膜对316L不锈钢的保护效果尤为明显,其受腐蚀速率与在ZnO薄膜保护状态下相比降低了1倍以上。     

Preparation and corrosion resistance studies of nanometric sol-gel-based CeO2 film with a chromium-free pretreatment on AZ91D magnesium alloy

Magnesium alloy, although valuable, is reactive and requires protection before it can be applied in many fields. In this study, a novel protective environmental-friendly gradient coating was performed on AZ91D magnesium alloy by non-chromate surface treatments, which consisted of phytic acid chemical conversion coating and the sol-gel-based CeO₂ thin film. The surface morphologies, microstructure and composition of the coatings were investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The corrosion resistance of the coatings was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. The effects of the concentration, layers, temperature of heat treatment of CeO₂ sol on the anti-corrosion properties of the gradient coating for magnesium were also investigated. The results showed that the gradient coating was mainly composed of crystalline CeO₂. According to the results of electrochemical tests, the corrosion resistance of AZ91D magnesium alloy was found to be greatly improved by means of this new environmental-friendly surface treatment.     

Corrosion protection of carbon steel by thin films of poly(3-alkyl thiophenes) in 0.5 M H2SO4

Poly(3-octyl thiophene) (P3OT) and poly(3-hexylthiophene) (P3HT) dissolved in toluene were deposited onto 1018 carbon steel and corroded in 0.5 M H₂SO₄. P3OT and P3HT films were chemically deposited by drop casting onto 1018-type carbon steel with two surface finishing, i.e. abraded with 600-emery paper and with alumina (Al₂O₃) particles of 1.0 μm in diameter (mirror finish). Their corrosion resistance was estimated by using potentiodynamic polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy, EIS, techniques. In all cases, polymeric films protected the substrate against corrosion, but the protection was improved if the surface was polished with Al₂O₃ particles of 1.0 μm in diameter. The polymer which gave the best protection was P3HT because the amount of defects was much lower than that for the P3OT films. The polymers did not act only as a barrier layer against aggressive environment, but they improved the passive film properties by decreasing the critical current necessary to passivate the substrate, increasing the pitting potential and broadening the passive interval.     

Electrochemical investigation of high-performance silane sol–gel films containing clay nanoparticles

Silane sol–gel coatings are widely used as adhesion promoters between inorganic substrates, such as metals, and organic coatings. The aim of these pre-treatments is to enhance the corrosion protection performance of the organic coating improving the adhesion to the substrate and acting as a barrier against water and aggressive ions diffusion. It is a matter of fact that the silane sol–gel pre-treatments do not provide an active protection against corrosion processes except for the partial inhibition of the cathodic reaction. Inorganic pigments can improve the barrier properties of the silane sol–gel film, enhancing the resistance against corrosion. In this study, different amounts of montmorillonite nanoparticles were added to a water based silanes mixture in order to improve the barrier properties of the sol–gel coating. Hot dip galvanized steel was used as substrate. The sol–gel film consists of a combination of three different silanes, GPS, TEOS and MTES. The clay nanoparticles used in this study were mainly neat montmorillonite. The proper concentration of filler inside the sol–gel films was determined comparing the corrosion resistance of silane layers with different nanoparticles contents. Additionally, the effect of CeO₂ and Ce₂O₃ enriched montmorillonite particles. The EIS analysis and the polarization measurements demonstrated that the optimal amount of neat montmorillonite nanoparticles is about 1000 ppm. The same electrochemical techniques highlighted the limited effect of the cerium oxides grafted to the clay nanoparticles on the corrosion resistance of the silane sol–gel film. The TEM analysis proved the presence of a nano-crystalline structure inside the silane sol–gel film due to the formation of crystalline silica domains.     

Stearic acid grafted chitosan/epoxy blend surface coating for prolonged protection of mild steel in saline environment

Chitosan (CS) is a promising candidate for green anticorrosive coating owing to its film forming nature, complexation with metals, biocompatibility, and varied surface functionalization. This paper illustrates the surface properties of chitosan film which is modified by grafting with stearic acid via a water-soluble coupling agent, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). The interaction between chitosan and stearic acid were investigated theoretically by Gaussian 09 package. The purified co polymeric films so formed were characterized by FTIR-ATR, NMR, XRD, TGA, CHNSO, SEM, AFM and EDX techniques. Stearic acid grafted CS film was developed on mild steel surface via dip coating technique and investigated for its corrosion resistance in 3.5% NaCl via electrochemical techniques. EIS measurements and potentiodynamic polarization studies have proven that the grafted CS when blended with epoxy resin offers better corrosion protection to mild steel in saline environment. The coating offers prolonged protection for the metal surface with enhanced barrier properties and hydrophobic nature.     

Application of corrosion inhibitors in water-borne coatings

Modification of an acrylate-based model dispersion by different additives which should act as corrosion inhibitors during the flash-off time of the dispersion film on a mild steel surface has been investigated. It is shown that mercapto compounds with a second functional group are capable of interaction with both the substrate surface and the functional groups of the polyacrylate film. Such additives bring about sufficient corrosion inhibition without adversely affecting other properties of the acrylate dispersion. Thus coatings with pronounced barrier properties on steel sheets are built up. The corrosion protection properties of the additives in the liquid dispersion as well as in the coatings formed on steel sheets have been characterized by electrochemical impedance spectroscopy.     

Improving the corrosion resistance of a-C:H film by a top a-C:H:Si:O layer

During the deposition of a-C:H film, defects (pinholes or discontinuities) caused by excessive stress will inevitably appear, which will reduce the corrosion resistance of the a-C:H film. In this study, top a-C:H:Si:O layers (thickness of approximately 0.3 μm) on the surface of a-C:H films were deposited on a large scale by PACVD technology using acetylene (C₂H₂) and/or hexamethyldisiloxane (HMDSO) as reactants, to improve the corrosion resistance of a-C:H films while ensuring the appropriate overall hardness of the films. The corrosion behaviors of the films were studied by electrochemical impedance spectroscopy (EIS) and Tafel polarization. We found that the a-C:H/a-C:H:Si:O films possess a lower electrolyte penetration rate due to their stronger capacitance characteristics. In addition, the corrosion current density of the a-C:H/a-C:H:Si:O films (10^?10 A cm^?2) were reduced by 2 orders of magnitude compared to the a-C:H film (10^?8 A cm^?2), and by 3 orders of magnitude compared to 316 stainless steel (10^?7 A cm^?2). The impedance results obtained by EIS were simulated using appropriate equivalent circuits, and the corresponding electrical parameters were used to further verify the electrochemical protection behavior of the top a-C:H:Si:O layer.     

不锈钢金属双极板TiW和TiTa膜的制备及性能

针对质子交换膜燃料电池金属双极板耐蚀性和导电性有待提高的问题,本文用磁控溅射双靶共溅的方法,在316L不锈钢基体表面沉积TiW和TiTa两种非贵金属膜层。通过X射线衍射、扫描电子显微镜-能谱仪、X射线光电子能谱仪、电化学和接触电阻测试等方法,表征了涂覆膜层后不锈钢的微观结构、表面形貌、化学组成、耐腐蚀性和导电性。实验结果表明,磁控溅射制备得到的TiTa膜表面较为均匀,且TiTa膜沉积的不锈钢具有较好的耐腐蚀性,其恒电位极化电流密度能够维持在0.3μA/cm²;从导电性来看,TiW膜与碳纸之间的接触电阻小于TiTa膜。综合考虑材料的各项性能,认为沉积TiTa膜的316L不锈钢有用作金属双极板材料的潜力。     

Electrochemical synthesis and corrosion performance of poly(pyrrole-co-o-anisidine)

The electrochemical synthesis of poly(o-anisidine) homopolymer and its copolymerization with pyrrole have been investigated on mild steel. The copolymer films have been synthesized from aqueous oxalic acid solutions containing different ratios of monomer concentrations: pyrrole:o-anisidine, 9:1, 8:2, 6:4, 1:1. The characterization of polymer films were achieved with FT-IR, UV–visible spectroscopy and cyclic voltammetry techniques. The electrochemical synthesis of homogeneous-stable poly(o-anisidine) film with desired thickness was very difficult on steel surface. Therefore its copolymer with pyrrole has been studied to obtain a polymer film, which could be synthesized easily and posses the good physical–chemical properties of anisidine. The kinetics and rate of copolymer film growth were strongly related to monomer feed ratio. The introduction of pyrrole unit into synthesis solution increased the rate of polymerization and the substrate surface became covered with polymer film soon, while this process required longer periods in single o-anisidine containing solution. The protective behavior of coatings has been investigated against steel corrosion in 3.5% NaCl solution. For this aim electrochemical impedance spectroscopy (EIS) and anodic polarization curves were utilized. The synthesized poly(o-anisidine) coating exhibited significant protection efficiency against mild steel corrosion. It was shown that 6:4 ratio of pyrrole and anisidine solution gave the most stable and corrosion protective copolymer coating.     

喷墨打印头陶瓷喷孔的皮秒激光加工研究

喷墨打印头的喷孔直径一般为几十微米,材料一般是有机薄膜、不锈钢薄片等。针对有机膜等作为喷嘴板材料的缺陷,采用氧化锆陶瓷代替,以提高耐磨能力和耐腐蚀性。采用皮秒激光打孔方法,可在多种材料上加工出直径几十微米的小孔,包括聚酰亚胺（厚度50μm）、氧化锆陶瓷（厚度120μm）和铜片（厚度70μm）。通过控制不同的参数变化,可制备出孔径约20μm、孔间距为140μm的喷孔阵列。对比不同参数下喷孔尺寸和微观形貌发现,较高功率密度、较低单点停留时间有助于得到圆孔,减少重铸层。     

Investigation of nanostructured Al-based quasicrystal thin films for corrosion protection

Quasicrystals belong to a particular type of solids, which consist of highly symmetric atom clusters. The structure is neither periodically ordered, as in crystalline materials, nor amorphous, as in a glass. Recent work has shown that thin film quasicrystal coatings can have unique properties such as very high electrical and thermal resistivities and very low surface energy, which may result in interesting corrosion properties. For example, aluminum alloy based quasicrystals are insulator alloys containing about 70% of aluminum. Other interesting properties involving, for instance, adhesion, corrosion, friction, and hardness suggest that quasicrystal coatings are promising materials for a variety of industrial applications.

The corrosion related properties of aluminum alloy based quasicrystal thin film coatings have been studied on coated AA2024 substrates. The thin film deposition parameters are briefly discussed. Results of the microstructural, surface chemistry, and surface energy analysis of the quasicrystal films are presented. The corrosion protection properties of the films have been studied by potentiodynamic scan and electrochemical impedance spectroscopy. Analysis of the electrochemical data indicates that nanostructured quasicrystal films significantly resist corrosion of AA2024-T3 substrates in a constant immersion environment.     

Novel hybrid sol-gel coatings for corrosion protection of AZ31B magnesium alloy

This work aims to develop and study new anticorrosion films for AZ31B magnesium alloy based on the sol-gel coating approach.Hybrid organic-inorganic sols were synthesized by copolymerization of epoxy-siloxane and titanium or zirconium alkoxides. Tris(trimethylsilyl) phosphate was also used as additive to confer additional corrosion protection to magnesium-based alloy. A sol-gel coating, about 5-μm thick, shows good adhesion to the metal substrate and prevents corrosion attack in 0.005 M NaCl solution for 2 weeks. The sol-gel coating system doped with tris(trimethylsilyl)-phosphate revealed improved corrosion protection of the magnesium alloy due to formation of hydrolytically stable Mg-O-P chemical bonds.The structure and the thickness of the sol-gel film were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The corrosion behaviour of AZ31B substrates pre-treated with the sol-gel derived hybrid coatings was tested by electrochemical impedance spectroscopy (EIS). The chemical composition of the silylphosphate-containing sol-gel film at different depths was investigated by X-ray photoelectron spectroscopy (XPS) with depth profiling.     

A comprehensive study of the green hexafluorozirconic acid-based conversion coating

The effect of four practical parameters (deposition temperature, time, bath pH and concentration of Zr) on electrochemical and morphological properties of zirconium based conversion coating (ZrCC) on cold rolled steel (CRS) substrates was investigated. DC polarization and electrochemical impedance spectroscopy (EIS) measurements were used for electrochemical studies. Micro structural characterization was carried out by FE-SEM, AFM and EDS. The optimal conditions were determined as follows: solution temperature 20–30 °C, immersion time 60–120 s, pH = 4 and acid concentration of 4% vol. In such condition, corrosion resistance values were maximum and uniformity was improved. Microscopical observations revealed that ZrCC comprises a two-layered structure. The film formation mechanism of ZrCC was discussed in detail. After achieving the optimum conditions, epoxy nanocomposites were applied on ZrCC treated CRS samples and corrosion performance of fully painted system was investigated. Finally the adhesion strength of subsequently applied organic coating on ZrCC treated substrates was measured by pull-off technique which exhibited considerable high values.     

Electrochemical deposition and characterization of polyaniline-graphene nanocomposite films and its corrosion protection properties

Polyaniline and polyaniline-graphene nanocomposite films were electrochemically deposited by cyclic voltammetry on 310 stainless steel electrode. The corrosion resistance of polyaniline and polyaniline-graphene nanocomposite covered 310 stainless steel substrates was estimated using potentiodynamic polarization and electrochemical impedance spectroscopy techniques in 5000 ppm NaCl aqueous solution at room temperature. Potentiodynamic polarization results show, which corrosion potentials shift to anodic regions in the presence of polyaniline-graphene nanocomposite compared to the pure aniline film. The electrochemical measurements also indicated that the inhibition efficiency for polyaniline-graphene nanocomposite and polyaniline are about 97 % and 73 %, respectively.     

Electrochemical study of TEOS,TEOS/MPTS,MPTS/MMA and TEOS/MPTS/MMA films on tin coated steel in 3.5% NaCl solution

This work compares the anticorrosion features of siloxane layers as eco-friendly alternatives for chromium passivation process on industrials tin coated steel and unravels the influence of each component of the film. The films were prepared with synergistic blends of siloxanes as tetraethyl orthosilane (TEOS), 3-methacryloxy-propyl-trimethoxysilane (MPTS) and methyl methacrylate (MMA). To assess the influence of each component, five different films were prepared: TEOS-based, MPTS-based, TEOS/MPTS, MPTS/MMA and TEOS/MPTS/MMA. The corrosion resistance of the coatings was evaluated by means of open circuit potential, anodic polarization curves and electrochemical impedance spectroscopy measurements, and the anticorrosion properties discussed based on electrical equivalent circuit fitting. Coated surfaces were analyzed using atomic force microscopy and the coatings’ thicknesses were evaluated by means of glow discharge optical emission spectroscopy. The results plainly showed the efficiency of the anticorrosion properties of the film in a 3.5 wt.% NaCl solution and have clearly revealed the improvement of the protective properties of the coating when the MPTS was added to the formulations, pointing this component as the main responsible for the coating anticorrosion action. The addition of MMA to the formulation led to formation of coatings with low long term anticorrosion protection, which was ascribed to the low thickness.