Galvanic Coatings Research Articles

Application of some thin galvanic coatings to create a hydrogen decorption barrier from palladium

Application of some thin galvanic coatings to create a hydrogen decorption barrier from palladium

VOLTAMPEROMETRY OF Co–Mo ALLOY DEPOSITION

At present, cobalt–molybdenum alloys are among the most functional galvanic coatings characterized by the following properties: magnetic, chemical resistance, catalytic activity, high wear resistance and corrosion resistance, including in aggressive environments. This paper is devoted to the study of the production of cobalt-molybdenum coatings from simple and complex electrolytes. The effect of ligands, such as trilon B and ammonium sulfate, on the alloy deposition process has been investigated in this paper. The kinetics of the process of electrodeposition of a coating from a polyligand ammonium–trilonate electrolyte on a copper electrode was studied using methods of linear voltammetry in a potentially dynamical regime with variation of the scanning speeds of a potential of 1–100 mV / s. The kinetic regularities of the restoration of cobalt ions in the following systems are studied: – cobalt sulfate; sulphate – cobalt – trilol B; – cobalt – ammonium sulfate and – cobalt – trilol B – ammonium sulfate with different concentrations. The nature of cathode peaks and the mechanism of electrode processes are determined by the analysis of volt-ampere characteristic dependences, and the Semerano criterion is calculated. Based on the Rendls–Shyevchik equation for the irreversible process, the coefficient of diffusion of the electrically active compound was determined and the rate constant of the charge transfer stage was calculated on the basis of J. Hohstein’s equation. Moreover, the product of the transfer coefficient for the number of electrons of the irreversible stage is calculated by the angular coefficient. The mechanism and kinetic equations of alloy deposition from a polyligand electrolyte in general and in separate stages are proposed. The electrochemical behavior of the – sodium molybdate system at various pH values in an acidic environment.

The Use of a Bipolar Electrochemical Polarization for the Development of Measuring and Process Equipment

Электрохимическая биполярная поляризация твердотельного электрода реализуется в случае специальной схемы включения электродов, когда в электрохимической ячейке между двумя электродами, подключенными к источнику электрического тока, помещают электрод, не имеющий с внешней цепью электрического контакта. При протекании тока между первой парой электродов силовые линии тока взаимодействуют с третьим электродом, вызывая в нем «наведенную» поляризацию. Это явление использовано здесь для разработки измерительной техники. Наиболее эффективно оно для разработки схемы полярографа с твердотельным электродом. Предложенная в статье схема полярографа включает две электрохимические ячейки: полярографическую и электрохимическую. В первой смонтирован проволочный платиновый электрод, поляризуемый биполярно. Он оснащен подвижным контактом для измерения текущего значения потенциала, во второй - рабочий электрод и электрод сравнения. Потенциал, измеренный на проволочном электроде, подается на вход потенциостата. На выходе потенциостата синхронно формируется токовый сигнал. Ток с выхода потенциостата пропускается через рабочий электрод так, чтобы величина потенциала рабочего электрода совпадала с потенциалом проволочного электрода в точке касания его подвижным контактом. Предложено также устройство для количественного измерения сквозной пористости гальванических катодных покрытий. Калибровочная зависимость связывает результаты контактного измерения пористости и силы тока коррозии, протекающего в микрогальванических парах в порах покрытия. Потенциал корродирующего в стационарных условиях исследуемого образца подается на вход потенциостата, ток на его выходе соответствует плотности тока коррозии детали. Далее рассматривается устройство для детоксикации организма и лечения путем электрохимического синтеза натрия гипохлорита и элементарного водорода в токе крови непосредственно в кровеносном сосуде из компонентов, входящих в состав крови, на поверхности проволочного электрода, введенного в кровеносный сосуд и поляризуемого при помощи пары накладных электродов.

Methods for Determining the Quality of Galvanic Chromium Coating

The surface and microsections of the cross-section of the chromium coating samples were studied. The microhardness of the coating and the base material was tested, their metallographic studies were conducted. The analysis of the microstructure showed that the base metal of 45 and 38XA steel of all samples is in the normalized state. The analysis of the microstructure of the samples subjected to surface HFC hardening (high frequency currents) showed that the temperature of heating during quenching is insufficient, and it leads to a lower strength and hardness of the layer. The sample with a lower hardness of the chromium coating has a higher coating viscosity and resistance to wear. The sample with the highest microhardness of the coating is characterized by increased brittleness. The hardness of the metal substrate and its structure does not affect the properties of the chromium coating layer.

Application of zirconium carbide: assessment, determination of dominant trends and prospects

The analysis and systematization of information on the application of zirconium carbide in modern technology: in the production of hard alloys and products from them, in technologies of anti-emission coatings, surface modification of powder materials. Prospective directions are indicated: a component in composite materials technologies, a modifying phase of galvanic metal matrix composite coatings, a functional component of wettable coatings for cathodes of alumina reduction cells.

Physico-mathematical model of the mechanism of galvanic coating by nanoscale materials

The article proposes a physico-mathematical model of the mechanism of hardening of galvanic coatings by nanoscale materials. It has been established that the mechanism of hardening is most strongly influenced by structural transformations occurring in nanocomposite coatings. Based on the physical processes taking place in modified by nanoscale materials galvanic coatings, the physico-mathematical model of the mechanism of their hardening was substantiated and investigated. The presented model allows predicting the degree of hardening of nanocomposite coatings depending on the nanodispersed materials and the distance between them in the coating.

Separation of cations of heavy metalsfrom concentrated galvanic drains

When applying galvanic coatings, soluble salts of heavy metals such as iron, copper, nickel, zinc, cadmium, chromium and other metals are used, toxic cations enter the water, with subsequent migration to the biosphere. To date, many methods have been developed for cleaning galvanic sewage, which cannot be considered sufficiently effective. The joint sorption of divalent cations of copper, nickel and cadmium from concentrated aqueous solutions was investigated. Calculation and experimental methods were used to determine the separation conditions of the bivalent ion systems that differed and close in sorption properties on the aminophosphonic polyampholyte Purolite S950 in a natrium form. It is shown that the cadmium (II) cations can be isolated from solutions containing copper (II) or nickel (II) cations even at the height of the sorption layer of 0.13 m due to the difference in the defining characteristics of the cations. This layer height can be used not only in a chromatographic column, but also in a concentrating cartridge. Separation of the copper (II) and nickel (II) close to the sorption properties requires an absorbing layer of 0.76 m, which can only be used in a chromatographic column, but not for a concentrating cartridge. In this paper, the degrees of ion separation in various sorption conditions are calculated. The applicability of the conductometric method for controlling the ion exchange process is shown not only when the free cations are isolated from aqueous solutions but also bound to complexes.

Hardening parts by chrome plating in manufacture and repair

In the engineering industry, galvanic coatings are widely used to prolong the service life of the machines, which contribute to the increase in the strength of the parts and their resistance to environmental influences, temperature and pressure drops, wear and fretting corrosion. Galvanic coatings have been widely applied in engineering, including agriculture, aircraft building, mining, construction, and electronics. The article focuses on the manufacturing methods of new agricultural machinery parts and the repair techniques of worn parts by chrome plating. The main attention is paid to the unstable methods of chromium deposition (in pulsed and reversing modes) in low-concentration electrolytes, which makes it possible to increase the reliability and durability of the hardened parts operation by changing the conditions of electrocrystallization, that is, directed formation of the structure and texture, thickness, roughness and microhardness of chromium plating. The practical recommendations are given on the current and temperature regimes of chromium deposition and composition of baths used for the restoration and hardening of the machine parts. Moreover, the basic methods of machining allowances removal are analysed.

Wear Resistance of Nickel–Cobalt–Polytetrafluoroethylene Composite Electrolytic Coatings Deposited from Chloride-Containing Electrolyte

The development and implementation of novel galvanic coatings with abnormally high microhardness, wear resistance, and corrosion resistance are the focus of modern machine-building. The galvanic deposition of composite electrolytic coatings (CECs) is an efficient method of improving their properties. In this paper, a chloride-containing electrolyte has been proposed for obtaining a wear-resistant nickel–cobalt–polytetrafluoroethylene CEC. The effect exerted by electrolysis modes and electrolyte compositions on some physicomechanical properties (wear resistance and corrosion resistance) of a nickel–cobalt–polytetrafluoroethylene composite electrolytic coating deposited from chloride-containing electrolyte has been studied. The potentialities of using the deposited layer as wear- and corrosion-resistant coating.

Using fuzzy rule-based knowledge model for optimum plating conditions search

The paper discusses existing approaches to plating process modeling in order to decrease the distribution thickness of plating surface cover. However, these approaches do not take into account the experience, knowledge, and intuition of the decision-makers when searching the optimal conditions of electroplating technological process. The original approach to optimal conditions search for applying the electroplating coatings, which uses the rule-based model of knowledge and allows one to reduce the uneven product thickness distribution, is proposed. The block diagrams of a conventional control system of a galvanic process as well as the system based on the production model of knowledge are considered. It is shown that the fuzzy production model of knowledge in the control system makes it possible to obtain galvanic coatings of a given thickness unevenness with a high degree of adequacy to the experimental data. The described experimental results confirm the theoretical conclusions.

Evaluating the Replacement of Galvanic Cr Coatings

Evaluating the Replacement of Galvanic Cr Coatings

Формирование износостойких покрытий на алюминиевом сплаве АЛ9 гальваническими, детонационными и газофазными методами

This paper reports the comparative assessment of coatings on aluminum alloy Al9 obtained through different methods of surface strengthening under conditions of products wear operation. It is shown that galvanic coatings allow increasing surface hardness up to 4500 Pa and they may be recommended for products with wear operation with small specific load. Surface strengthening by oxides with the use of the detonation method of plating allowing the formation of layers with higher hardness (9000 MPa) may be recommended for products with wear operation under higher specific loads. For products operating with wear under hard conditions of loading, particularly, in aggressive environment (chemical engineering) there are recommended gas-cycle coatings consisting of metal-organic compounds of chromium with hardness up to 16 000 MPa.

Study of the Performance of Copper Coatings Formed by Electroplating and Deformation Cladding with a Flexible Tool

The results of comparative tests of copper coatings formed by electroplating and deformation cladding with a flexible tool (DGFT) under ultimate loads that cause breakage and burrs have been presented. The number of cycles of lateral bending that cause the copper coating to peel and the sample to break, as well as coefficient of sliding friction and the wear of samples during the friction of a lubricant-free spherical indenter on the flat surface of the copper-plated steel disks with substrate hardnesses of 20, 50, and 70 HRC, have been accepted as the performance standards. During the peeling test under bending, it has been found that cladded coatings were not peeled off from the basic material, even in the case when experimental samples were broken, and the peeling of coating in the samples with galvanic coatings has been observed on half of the first bending cycle. Based on the results of the tribotechnical tests, it has been found that copper coatings formed using the above technologies contribute mainly to a reduction in the coefficient of sliding friction on friction surfaces compared to samples without coatings. However, under loads that cause burrs, galvanic coatings have smaller values of the coefficient of sliding friction compared to cladded coatings.

Effects of surface hydroxylation on adhesion at zinc/silica interfaces.

The weak interaction between zinc and silica is responsible for the poor performance of anti-corrosive galvanic zinc coatings on modern advanced high-strength steels, which are fundamental in the automotive industry, and important for rail transport, shipbuilding, and aerospace. With the goal of identifying possible methods for its improvement, we report an ab initio study of the effect of surface hydroxylation on the adhesion characteristics of model zinc/β-cristobalite interfaces, representative of various surface hydroxylation/hydrogenation conditions. We show that surface silanols resulting from dissociative water adsorption at the most stable stoichiometric (001) and (111) surfaces prevent strong zinc-silica interactions. However, dehydrogenation of such interfaces produces oxygen-rich zinc/silica contacts with excellent adhesion characteristics. These are due to partial zinc oxidation and the formation of strong iono-covalent Zn-O bonds between zinc atoms and the under-coordinated excess anions, remnant of the hydroxylation layer. Interestingly, these interfaces appear as the most thermodynamically stable in a wide range of realistic oxygen-rich and hydrogen-lean environments. We also point out that the partial oxidation of zinc atoms in direct contact with the oxide substrate may somewhat weaken the cohesion in the zinc deposit itself. This fundamental analysis of the microscopic mechanisms responsible for the improved zinc wetting on pre-hydroxylated silica substrates provides useful guidelines towards practical attempts to improve adhesion.

Zamena prevlaka kadmijuma na delovima oružja prevlakama volfram-disulfida

Galvanic cadmium coatings were applied on the material in order to improve some properties such as: corrosion resistance, improved tribological properties, chemical stability, etc. The paper describes the properties of the cadmium coating and a replaceable coating as well. Cadmium is a very toxic element, so its use in EU coun­tries and around the world is limited or completely eliminated. During the process of deposition of the cadmium coating, it is necessary to comply with the relevant legislation in order to protect living and working environment. As an alternative to cadmium coatings, zinc coatings, zinc nickel alloys, tin-zinc coatings and aluminum coatings obtained in vacuum are most commonly applied. As one of the possible replacement of the cadmium coating, there is a coating of nano-based tungsten-disulfide. The paper presents the results of testing the properties of tungsten-disulfide coatings in nanoparticles and their comparison with cadmium coatings.

Investigation of the wavelength dependence of laser stratigraphy on Cu and Ni coatings using LIBS compared to a pure thermal ablation model

In this study, galvanic coatings of Cu and Ni, typically applied in industrial standard routines, were investigated. Ablation experiments were carried out using the first two harmonic wavelengths of a pulsed Nd:YAG laser and the resulting plasma spectra were analysed using a linear Pearson correlation method. For both wavelengths the absorption/ablation behaviour as well as laser-induced breakdown spectroscopy (LIBS) depth profiles were studied varying laser fluences between 4.3–17.2 J/cm^2 at 532 nm and 2.9–11.7 J/cm^2 at 1064 nm. The LIBS-stratigrams were compared with energy-dispersive X-ray spectroscopy of cross-sections. The ablation rates were calculated and compared to theoretical values originating from a thermal ablation model. Generally, higher ablation rates were obtained with 532 nm light for both materials. The light–plasma interaction is suggested as possible cause of the lower ablation rates in the infrared regime. Neither clear evidence of the pure thermal ablation, nor correlation with optical properties of investigated materials was obtained.

Improving Adhesion at the Alumina/Zinc Interface by Stainless Steel Buffers

The weak interaction between zinc and alumina is responsible for a poor performance of anticorrosive galvanic zinc coatings on modern advanced high strength steels. In this context, we report a theoretical study on the effect of realistic multicomponent metal buffers on the adhesion strength of a model α-alumina(0001)|zinc interface. Relying on results of ab initio calculations on relevant individual oxide|oxide, oxide|metal, and metal|metal interfaces (separation and interface energies), we determine by Monte Carlo simulations the thermodynamically preferred sequence of components in a multicomponent buffer, as a function of buffer composition and oxygen conditions. We find that stainless steel buffers considerably enhance the overall strength of the alumina|zinc interface. Most importantly, we show that a partial oxidation of multicomponent buffers, which is unavoidable under realistic conditions, does not degrade their performance. This advantageous property relies on the separation of metal and oxide components in the buffer and on the resulting suppression of weakly interacting oxide|zinc and moderately strong alumina|metal interfaces. More generally, owing to the possibility of selective oxidation and component segregation, multicomponent buffers appear as promising solutions for adhesion improvement at weakly interacting metal|oxide interfaces.

THE SUBSTANTIVE FACTORS COMPLEX INFLUENCE ON THE SURFACE LAYERS' INTERNAL TENSIONS IN THE STEEL HARDENED CAR'S PARTS

Досліджено актуальне питання комплексного впливу режимів електролізу на структуру та величину внутрішніх напружень у поверхневих шарах різної товщини насталених автомобільних деталей. Встановлено, що на якість насталених покриттів значною мірою впливають такі вагомі чинники як густина струму, температура та кислотність електроліту. Для визначення комплексного впливу вагомих чинників на внутрішні розтягувальні напруження у поверхневих шарах насталених деталей за різної їх товщини застосовано системний підхід, вихідною передумовою якого є прагнення з максимальною повнотою врахувати початкові та вихідні характеристики об'єкту. На підставі застосування методу планування експерименту отримано регресійні рівняння, які дають змогу оцінити взаємовплив густини струму, кислотності та температури електроліту на внутрішні напруження у поверхневих шарах різної товщини насталених автомобільних деталей. За результатами аналізу регресійних рівнянь й оцінки числових значень та знаків їх коефіцієнтів з'ясовано, що для різної товщини покриття сила й характер впливу чинників є неоднаковими, що дасть змогу вдосконалити технологічні процеси відновлення автомобільних деталей електролітичним нарощуванням.

Experimental Investigation and Artificial Neural Network Modeling of Warm Galvanization and Hardened Chromium Coatings Thickness Effects on Fatigue Life of AISI 1045 Carbon Steel

In the present study, the main purpose is investigation of the coatings thickness effect on the fatigue life of AISI 1045 steel. Herein, two different coatings of warm galvanization and hardened chromium have been used on the specimens. Fatigue tests were performed on specimens with different coating thicknesses of 13 and 19 µm. In the high-cycle level, S–N curves are extracted with 13 points for each sample. The results show that the galvanized coating is the most appropriate coating with low thickness, but with significant increasing of coating thickness, the best choice is hardened chromium coating. However, artificial neural network (ANN) has been used as an efficient approach instead of various and costly tests to predict and optimize the engineering problems. In this study, fatigue life of AISI 1045 steel was modeled by means of ANN. Back propagation (BP) error algorithm is developed to network’s training. The experimental data are employed in order to train the network. ANN’s testing is accomplished using test data which were not used during networks training. Amplitude stress and thickness of coatings are regarded as input parameters, and fatigue life is gathered as an output parameter of the network. A comparison was made between experimental and predicted data. The predicted results were in admissible agreement with experimental ones, which indicate that developed neural network can be used for modeling the mentioned process.

Coating of a substrate with surface preliminarily treated with intensive flows of high-speed electrons and plasma using a magnetron

This paper presents results of the research in influence of preliminary surface treatment on adhesion of film to substrate (St8 or brass-target, CU, Ni-film). The preliminary treatment has been conducted by two methods: first, by compressive plasma flow with charge duration ∼100μs, plasma formation rate (15-20)×103 m/s; second, by low-energy high-current electron beams with pulse duration 2-3 μs and electron energy up to 30 keV. The investigation shows the strong influence of preliminary sample treatment and processing parameters on adhesion of film to substrate and final roughness. Experimental investigations have revealed the best adhesion of film to substrate, and the smoothest film is corresponding to the mode with preliminary LEHCEB irradiation with electron energy of 25, 30 keV. It was shown that the alternation of deposition with LEHCEB irradiation has resulted in large-scale surface smoothing: the surface has become glassy whereas craters of 10-20 μm have formed. It was shown that the magnetron-covered samples can withstand the saline mist for twice as long as samples with galvanic coatings.