The Effect of Iron Precursors in an Electrolyte on the Formation,Composition, and Magnetic Properties of Oxide Coatings on Titanium

The effect of iron sulfate and citrate addition into the base alkaline phosphate-borate-tungstate electrolyte on the peculiarities of plasma-electrolytic formation of coatings on titanium, their thickness, surface morphology, composition, and magnetic characteristics has been investigated. In the first electrolyte, dispersed particles of iron hydroxides and hydroxo salts are formed, whereas the second one comprises a true solution. Numerous Fe-containing crystallites of a size of ~50 nm united into agglomerates have been found in the suspension electrolyte with FeSO₄. Such coatings manifest ferromagnetic properties: coercive force Hc of the samples is 62 and 148 Oe at 300 and 2 K, respectively. In pores of the coatings obtained in the electrolyte with FeC₆H₅O₇ (true solution), the presence of crystallites is less clearly expressed, while crystallites themselves are larger and molten to a higher degree. At room temperature, such coatings are paramagnetic; at 2 K, they manifest ferromagnetic behavior with the Н _с value of up to 200 Oe. The available data enable one to associate ferromagnetic properties of the formed coatings with metals concentrated in pores.     

Iron Distribution and Ferromagnetic Characteristics of Fe-Containing PEO Coatings on Aluminum

Fe-containing oxide coatings fabricated by the plasma-electrolytic oxidation (PEO) method have been studied by means of scanning electron and magnetic force microscopy. The data comparison has demonstrated that ferromagnetic properties of the coatings are mainly associated with concentrating of iron in specific pores. A scheme has been suggested that would explain iron distribution in the course of the coating growth.     

The effect of the conditions of formation on ferromagnetic properties of iron-containing oxide coatings on titanium

Oxide coatings formed on titanium by plasma-electrolytic oxidation in a Na₃PO₄ + Na₂B₄O₇ + Na₂WO₄ + Fe₂(C₂O₄)₃ electrolyte-suspension at different current densities and different durations of treatment are shown to have ferromagnetic properties. The coercive force of the specimens reaches maximum values of 124 and 380 Oe at 300 and 10 K, respectively, when the thickness of coatings is about 3–5 mm. Crystallites with a mean size of ∼50 nm are found to be present in pores of the coatings. Based on the experimental data, combined with the results of theoretical modeling carried out previously, crystallites are concluded to be iron particles surrounded with a shell composed of oxides and/or hydroxides. The existence of crystallites and their spatial sizes determine the ferromagnetic properties of the coatings.     

Magnetoactive oxide layers formed on titanium by plasma-electrolytic technique

Two kinds of iron-containing coatings, specifically those obtained from electrolytes containing polyphosphate iron complexes (no. 1) and from electrolyte suspensions (no. 2), are formed and studied. According to the microprobe analysis, the iron content in the coatings is 6–7 at %. Coatings of type 1 are paramagnetic, while coatings of type 2 are ferromagnetic. The distribution of elements over the depth of coatings is heterogeneous and the typical components of the surfaces have different compositions. Iron and titanium are concentrated at the bottom and walls of pores. Upon annealing in air, iron and titanium phosphates crystallize in coatings no. 1, while maghemite is formed in coatings no. 2. Based on the results obtained, the supposition is made that the ferromagnetic properties of type 2 coatings are determined by the presence of fine-dispersed magnetite and/or maghemite particles in them, as well as titanium-magnetite and/or titanium-maghemite grains.     

Magnetic properties of plasma-electrolytic iron-containing oxide coatings on aluminum alloy

Applications of the plasma-electrolytic oxidation technique for the formation of magnetically active oxide coatings on aluminum and titanium are reviewed. Specimens of aluminum-, iron-, and tungsten-containing oxide layers on aluminum substrates with ferro- and ferrimagnetic properties are experimentally produced and studied, as well as specimens that can be remagnetized at certain external magnetic field intensities and specimens the magnetization of which is opposite to the external field. The existence of nano- and microscale crystallites, in which aluminum and metals from the electrolyte are accumulated, are found in pores of the coatings. The crystallites supposedly determine the magnetic properties of the specimens. A correlation between the Fe/Σ(W, Al) atomic ratio in crystallites and the magnetic properties of the systems studied is discovered.     

Composition and magnetic characteristics of plasma electrolytic oxide coatings on titanium

The results of studies of the composition and magnetic characteristics of coatings formed in different time periods on titanium in suspension electrolytes of compositions Na₃PO₄ + Na₂B₄O₇ + Na₂WO₄ + Fe₂(C₂O₄)₃ (PBWFe, рH 7.8) and Na₂НPO₄ + Na₂B₄O₇ + Na₂WO₄ + Fe₂(C₂O₄)₃ (P*BWFe, рН 7.4), as well as the characteristics of coatings fabricated in filtrates of both electrolytes, are presented. PBWFe and P*BWFe electrolytes contain colloid particles of iron hydroxides. Crystallites are contained in pores of PBWFe and P*BWFe coatings. The averaged Fe/Ti atomic ratio for crystallites in pores of PBWFe coatings formed in different periods of time is equal to ~2.6, while in pores of P*BWFe coatings it is equal to ~1.1. The samples with PBWFe coatings manifest ferromagnetic properties, while samples with P*BWFe coatings and those obtained in filtrates of both electrolytes are paramagnetics. It was shown that, for PBWFe and P*BWFe coatings formed in different time periods, the composition, thickness, and presence and composition of crystallites in pores, as well as magnetic and other controlled parameters, are fairly reproducible.     

Composition,structure, and photocatalytic properties of Fe-containing oxide layers on titanium

The composition, optoelectronic properties, and surface and cross-section morphology of coatings formed by the method of plasma electrolytic oxidation in electrolytes containing sodium phosphate or silicate with or without addition of K₃[Fe(CN)₆] have been investigated. The coatings were studied by the methods of spectrophotometry, X-ray diffraction analysis, electron microscopy, and X-ray photoelectron spectroscopy. The photocatalytic activity of oxide coatings was studied in the reaction of phenol degradation under ultraviolet irradiation in the presence of hydrogen peroxide. The highest photocatalytic activity in the reaction of phenol degradation in the presence of hydrogen peroxide was manifested by Fe-containing coatings formed in the silicate electrolyte with addition of 8.0 g/L of K₃[Fe(CN)₆].     

Plasma-electrolytic formation of Ta-containing oxide coatings on titanium. Their composition and properties

Coatings with a thickness of 2–18 μm that contain up to 20 at % tantalum and Ta₂O₅ oxide phase are formed in an aqueous NH₄[TaF₆]-containing electrolyte for 2 min. The coatings are pierced with pores with a size of from 0.5 to 2 μm. The number of pores in the coatings can be decreased by additionally applying a Ta-containing paste to the surface. The contact angle of the coatings in distilled water is 68°–85°. This approach is promising for application of Ta-containing coatings on titanium implants and stents for increasing their corrosion resistance, chemical inertness, and biocompatibility.     

Producing and studying oxide coatings containing manganese and nickel compounds on titanium from electrolyte suspensions

Regular effects of anion-active surfactants added to silicate electrolyte suspensions containing dispersed MnO₂ and NiO particles on the composition, properties, and catalytic activity of the oxide compositions produced on titanium by plasma-electrolytic oxidation are studied. In both cases, introducing surfactants is shown to result in similar changes in the surface relief, namely, an increase in the surface domains and height drops between crests and hollows, as well as a simultaneous decrease in the size and concentration of pores. At the same time, the elemental and phase compositions of the coatings, as well as their catalytic activity with respect to the CO oxidation, are determined by the nature of both the solid particles and surfactant used.     

热喷涂方法对Al_2O_3涂层层状结构的影响

热喷涂层由扁平粒子组成，呈层状结构。气孔不可避免地存在于涂层中，而这些气孔包括通常所指的微米级气孔以及亚微米级的气孔。亚微米级气孔由扁平粒子间的未结合界面和扁平陶瓷粒子内所产生的显微裂纹构成。业已开发成功陶瓷涂层的电镀技术，并利用电镀的钢在涂层断面上的分布，揭示热喷涂Al2O3涂层的的真实气孔结构的方法。该方法的最重要之处在于直观地揭示热喷涂层的扁平陶瓷粒子间的未结合界面。本论文将电镀技术应用于传统的等离子、低气压等离子以及爆炸喷涂法喷制的Al2O3涂层，用扁平粒子间平均结合率和扁平粒子的平均厚度为结构参数定量地评价涂层结构。考察热喷涂方法对扁平粒子间结合的影响。     

Compositions of Composite Polymer-Oxide Coatings on Aluminum from Pyrolytic Gas Chromatography Mass-Spectrometry Data

Data on the composition of the external polymer part of the composite polytetrafluoroethylene (PTFE) oxide coatings obtained on an aluminum substrate by plasma electrolytic oxidation (PEO) within a single stage are presented. The coatings were formed in an aqueous silicate electrolyte with addition of PTFE dispersed powder in a siloxane–acrylate emulsion. It has been established that the external polymer-like layer of the PTFE/PEO coatings does not represent a physical mixture of the siloxane–acrylate copolymer and PTFE particles, but is composed of fragments of them. A partial substitution of fluorine by hydrogen in fluorocarbons contained in the coatings has been revealed. The obtained data are crucial for expanding knowledge on the formation, structure, composition, and properties of the composite polymer-containing oxide coatings formed within a single stage by means of plasma electrolytic oxidation on the valve metal surface.     

The Microstructure and Wear Resistance of Microarc Oxidation Composite Coatings Containing Nano-Hexagonal Boron Nitride (HBN) Particles

The composite coatings containing HBN were prepared on 2024 aluminum alloy by microarc oxidation in the electrolyte with nano-HBN particles. The microstructure, surface roughness, phase composition, hardness, adhesion strength and wear resistance of composite coatings were analyzed by SEM, EDS, laser confocal microscope, XRD, Vickers hardness tester, scratch test and ball-on-disc abrasive tests. The results revealed that composite coatings were mainly composed of γ-Al₂O₃, α-Al₂O₃, mullite and HBN. With increasing the content of HBN particles in the electrolyte, the size and number of the pores on the surface of composite coatings decreased significantly. Compared to the MAO coatings without HBN, the composite coatings exhibited better wear resistance, as demonstrated by the lower friction coefficient and the lower wear rate.     

Biocidal Anodic Films on Titanium

Biocidal action of coatings on titanium samples, formed by anodic-arc method in electrolytes containing polyphosphates and acetates of Zn(II), Mg(II), Ni(II), and Mn(II), is studied. The strongest biocidal effects are exhibited by coatings formed in a sodium-hexametaphosphate-containing electrolyte and a two-component electrolyte containing sodium hexametaphosphate and zinc acetate. The biocidal properties of are presumably due to the metals" binary phosphates present in the coatings.     

镁合金微弧氧化过程中电源模式对颗粒掺杂的影响

目的采用含颗粒电解液是目前最常用制备具有更佳性能微弧氧化膜层的方法之一,主要研究微弧氧化过程中颗粒掺杂与电源模式的关系。方法在Y2O3颗粒质量浓度为0~10 g/L的电解液中,分别以单极脉冲和双极脉冲电源模式制备一系列微弧氧化膜层,并从表面形貌、表面元素组成、截面形貌及耐蚀性能等方面对膜层进行综合评价。结果分散在电解液中的颗粒带有负电荷,在微弧氧化过程中发生电泳现象。在单极脉冲电源模式下,颗粒受正电吸引而发生定向迁移,在试样附近聚集并且吸附至表面,从而参与下一步的微弧氧化膜层形成过程。随着电解液中颗粒浓度的提高,分散在微弧氧化膜层表面的Y2O3颗粒数量增多,膜层表面的Y元素含量增加,膜层变得致密,耐蚀性能因而提高。在双极脉冲电源作用下,由于电场的交替变化,颗粒难以聚集在试样周围,颗粒的掺杂只能通过随机熔融包覆进行,因而参与到微弧氧化过程中的颗粒数量较少。结论颗粒掺杂受电场力影响,在单极脉冲模式下,颗粒的掺杂浓度对膜层的性能影响明显;在双极脉冲电源模式下,负向电流的引入不利于颗粒掺杂至氧化膜层,颗粒的掺杂浓度对膜层的性能影响不明显。     

TC4 合金微弧氧化层的耐磨性和耐蚀性

目的对比不同电解液体系中制备的陶瓷膜层的耐磨损和耐腐蚀性能,判断实验条件下陶瓷膜性能最优的电解液体系。方法在相同的电参数工艺下,分别在Na Al O2,(Na PO3)6和Na2Si O3电解液体系中对TC4合金进行微弧氧化处理,处理时间为15 min。分析陶瓷层的表面形貌、成分和相结构。进行干摩擦条件下的摩擦磨损实验,对比TC4合金及三种陶瓷膜的耐磨性。通过测试极化曲线,对比TC4合金及三种陶瓷膜的耐蚀性。结果在Na Al O2,(Na PO3)6,Na2Si O3电解液体系中获得的陶瓷层表面呈现出多孔和局部凸起的相似表面特征,但相组成存在差异,主要相分别为Al2Ti O5,Al PO4和Ti O2。摩擦磨损实验表明,在10 N载荷下,以Si3N4陶瓷球作为摩擦配副,陶瓷层的磨损失重相对基材均显著减小,其中(Na PO3)6-陶瓷层失重约为基材的1/22。极化曲线分析表明,在模拟油田采出液作为腐蚀液的条件下,与TC4合金相比,陶瓷层的Ecorr显著正移,Jcorr明显减小,其中(Na PO3)6-陶瓷层的Ecorr从-0.311 V正移至0.777 V,Jcorr从9.634×10-7A/cm2减小到2.595×10-8A/cm2。结论微弧氧化处理能够显著改善TC4合金的耐磨性和耐蚀性,其中(Na PO3)6-陶瓷层的综合性能较好,有望满足TC4合金服役于油田环境时的要求。     

Electrochemical deposition of Fe–Mo–W alloy coatings from citrate electrolyte

Peculiarities of the electrochemical deposition of Fe–Mo–W coatings from citrate electrolyte containing iron(III) on the substrates of mild steel and gray cast iron are investigated. The effect of the salt concentration of alloying components and electrolysis modes on the quality, composition, and properties of the alloys is determined. It is shown that the alloys formed via nonstationary electrolysis exhibit a more uniform surface and lower content of impurities. The improved physical and mechanical properties as well as corrosion resistance of Fe–Mo–W coatings in comparison with the base metal can be considered as promising technologies for surface hardening and repair of worn items.     

Producing and investigating oxide coatings containing manganese and nickel compounds on titanium from electrolyte suspensions

Elemental and phase compositions, as well as the surface structure of oxide coatings formed on titanium by plasma-electrolytic oxidation in aqueous electrolyte suspensions containing dispersed MnO₂, NiO, and Mn₂O₃ particles with sizes of 5–10 μm, are determined. The coatings are investigated using X-ray spectral analysis, X-ray photoelectron spectroscopy, and X-ray phase analysis, as well as electron and atomic force microscopy. The amount of transient metals contained in the surface layer of the coatings is found to be determined by the concentration of oxide particles added to the solution, their nature, and the nature of the base solution. The relations discovered can be used when carrying out a directional formation of coatings containing the necessary oxide systems, including their mixtures with particular component ratios.     

纳米铁纤维与羰基铁粉共混制备轻质宽带吸波涂层材料

为降低羰基铁粉吸波剂的密度、提高介电常数,采用轻质、高介电常数的纳米铁纤维与羰基铁粉共混,制备了轻质宽带吸波涂层.研究了纳米铁纤维含量对复合吸波剂微波电磁与吸收特性的影响.结果表明,随纳米铁纤维含量的提高,复合吸波剂的介电常数和磁导率增大.当复合吸波剂中纳米铁纤维含量(质量分数)为2.2%-4.4%时,吸波涂层有更低的面密度和更宽的有效带宽,这是由于在一定范围内提高介电常数,可以改善吸波涂层的匹配吸收特性.     

电解液组成对纯钛微弧氧化膜结构及光催化活性的影响

分别在钨酸钠和磷酸二氢钾电解液中制备了纯钛的微弧氧化(MAO)膜,利用SEM、EDX、XRD分析了膜层的形貌、元素分布及相组成,并测试了2种膜层的光催化活性.结果表明,纯钛在2种电解液中均形成粗糙多孔的微弧氧化膜层,但钨酸钠溶液中形成的膜层表面的孔洞尺寸较小、分布较均匀.膜层的元素组成和相组成与电解液成分有关,钨酸钠溶液中的膜层由W、Ti、O元素组成,W在膜层中近似均匀分布,锐钛矿与金红石的含量比(质量比)为27:73,而磷酸二氢钾电解液中的膜层由P、Ti、O元素组成,P从表面向内层逐渐增加,锐钛矿与金红石的含量之比则为84:16.吸光度测试结果表明,钨酸钠溶液中制备的膜层光催化活性高于磷酸二氢钾溶液中制备的膜层的光催化活性.     

One-step electrochemical process for the formation of poly(N-methylpyrrole) coatings on steel in different media

Poly (N-methylpyrrole) coatings have been successfully formed on steel by a one-step electrochemical process in different media. Electropolymerization was performed in aqueous medium with low monomer concentration and in a mixed aqueous/organic media with higher monomer concentrations. Ethanol (EtOH) and N,N-dimethylformamide (DMF) were chosen as the organic components of the mixed solvents and oxalic acid was used as the electrolyte. The effect of process parameters on the formation of poly(N-methylpyrrole) was systematically investigated. The composition and morphology of the coatings were also studied by elemental analysis, FT-IR and scanning electron microscopy (SEM). Our results reveal that the formation and properties of poly (N-methylpyrrole) coatings were all dependent on the solvent composition and other process parameters. The amount of poly(N-methylpyrrole) formed on steel increased with time and applied current for all the solvent-electrolyte systems. For the electropolymerization performed in distilled water-oxalic acid solution, the amount of polymer coatings formed decreased with increased electrolyte concentration. In contrast, the amount of polymer coatings formed on steel in distilled water:ethanol (1:1)-oxalic acid and distilled water:DMF (1:1)-oxalic acid systems, increased with increasing electrolyte concentration. By controlling the electrochemical parameters, smooth, uniform and strongly adherent coatings could be formed onto steel substrates.