Chromium Electrodeposition Research Articles

Analysis of Nucleation Phenomena for Metallic Chromium Coatings Formed on Nanostructured Surfaces By of a Pulsed Laser

Obtain metallic chromium (Cr0) deposits by trivalent chromium in aqueous solution have some disadvantages respect to hexavalent chromium. The obtention of this coatings are not considered feasible to directly from a simple dissolution. The chromium III in aqueous solution presents an octahedral structure [Cr(H2O)6]+3[3], so the baths for the trivalent chrome require complex forming agents. It is also found that is difficult to obtain the same thickness with chromium III as using chromium VI, J. Mcdougall et al[4] report that it is difficult to obtain deposits greater than 2 µm from trivalent chromium, attributed to microstructural differences, causing the properties of the chromium coatings be diminished compared with the hexavalent chromium. A form to controlled the phenomena associated with the nucleation of the trivalent chromium electrolytic deposits is nanostructuring the surface sustrate where the electrodeposit is formed. This can do by pulsed laser-induced phenomenon change microstructure of the bulk. Some authors have reported significant improvements using treatments earlier of coats by pulsed lasers (femtosecond) [5][6][7]. The optimized characteristics reported are: Better Adherence, friction coefficients lower, even the nucleation type can be epitaxial. Therefore, in the present project proposes electrochemical characterization by polarization curves, electrochemical impedance spectroscopy and cyclic voltammetry for substrates of 1008 carbon steel polished and nanostructured by a pulsed laser with pulse ultra-fast. Also structural and morphologic by scanning electron microscopy, X-ray diffraction, etc., Chronoamperometry was used for analyzed the nucleation phenomena on substrates polished and nanostructured materials. [1] S. G. O. J., “Obtención de un Recubrimiento de Cromo Decorativo a Partir de Soluciones de Cromo Trivalente,” Ing. E Investig., vol. 26, pp. 75–83, 2006. [2] D. L. Snyder, “Decorative chromium plating basics,” Met. Finish., vol. 110, no. 2, pp. 14–21, 2012. [3] H. Chun et al., “Molecular and Electronic Structure of Octahedral o -Aminophenolato and o -Iminobenzosemiquinonato Complexes of V ( V ), Cr ( III ), Fe ( III ), and Co ( III ). Experimental Determination of Oxidation Levels of Ligands and Metal Ions,” no. V, pp. 4157–4166, 2001. [4] J. Mcdougall and S. Ma, “Chromium electrodeposition using a chromium ( III ) glycine complex,” vol. 28, 1998. [5] C. Yao et al., “The influence of femtosecond laser repetition rates and pulse numbers on the formation of micro/nano structures on stainless steel,” J. Alloys Compd., vol. 722, pp. 235–241, 2017. [6] X. Chen, Q. Yan, and Q. Ma, “Applied Surface Science Influence of the laser pre-quenched substrate on an electroplated chromium coating / steel substrate,” Appl. Surf. Sci., vol. 405, pp. 273–279, 2017. [7] P. Zhang, L. Chen, J. Chen, and Y. Tu, “Material removal effect of microchannel processing by femtosecond laser,” Opt. Lasers Eng., vol. 98, no. June, pp. 69–75, 2017.

Peculiarities of chromium electrodeposition from water − dimethylformamide solutions

Electrodeposition of chromium from both CrCl2- and CrCl3-containing dimethylformamide (DMF)–water solutions is studied. It is found that the process of chromium deposition from Cr(II)-containing solutions is stable during the whole period of electrolysis, while the rate of electrodeposition from Cr(III)-containing electrolytes gradually decreases. To explain the experimental results, it has been assumed that the film consisting of chromium oxide and hydroxide species is formed in the near-cathode region during electrolysis in Cr(III)-based baths. The physical properties of this film are critical for chromium electrodeposition. It is necessary to maintain the negative potential sufficient for Cr(II)→Cr electroreduction at the electrode-film interface for the sustained chromium plating. Under such conditions, thick (up to 100 μm) Cr–C coatings of good quality can be deposited.

Effect of Caprolactam and Acrylamide on the Kinetics of Chromium Electrodeposition Process from Sulfate-Oxalate Bath

Effect of Caprolactam and Acrylamide on the Kinetics of Chromium Electrodeposition Process from Sulfate-Oxalate Bath

Physicochemical properties of ionic liquid mixtures containing choline chloride, chromium (III) chloride and water: effects of temperature and water content

The effects of water addition and temperature on some physicochemical properties of room temperature ionic liquids containing chromium chloride, choline chloride and water in the molar ratio of 1:2.5:x (where x = 6, 9, 12, 15 or 18) have been studied. The density, viscosity, surface tension and conductivity of the liquid mixtures were measured for the temperature range of 25 to 80 °C. Increasing both water content and temperature resulted in decreasing density, surface tension and viscosity and increasing electrical conductivity. The average void radii (hole sizes) for the liquid systems under study were calculated; they were in the range of 1.21 to 1.82 A. The average hole size was stated to grow with increasing both temperature and water content in the mixture. The variation of the average void radii correlates with the change in viscosity and conductivity. The activation energies of viscous flow and conductivity diminishes with increasing water content in the liquid mixture. There is a strong linear correlation between conductivity and fluidity which indicates that the conductivity of the ionic liquid mixtures is generally controlled by the ionic mobility. A moderate viscosity and higher conductivity of the Cr(III)-containing ionic liquids with extra-water addition (at x > 9) make them suitable for the development of chromium electrodeposition processes.

Direct electro-deposition of metallic chromium from K2CrO4 in the equimolar CaCl2-KCl molten salt and its reduction mechanism

Spongiform metallic chromium was obtained directly from K2CrO4 in the equimolar CaCl2-KCl molten salt by electrolysis at 1173K and this reduction mechanism was discussed. The chemical composition and microstructure of the products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The reduction mechanism was analyzed by cyclic voltammetry, square wave voltammetry and potentiostatic electrolysis. K2CrO4 is soluble in the molten chlorides. The soluble CaCrO4 was easily formed in the molten CaCl2-KCl before electrolysis and dissociated to Ca2+ and CrO42−. The CrO42− was firstly electro-reduced to CaCr2O4 by a three-electron-transfer process and CaO was released simultaneously. The generated CaO with a high solubility was dissolved into the CaCl2-KCl molten salt and electro-reduced to metallic calcium. As the electrolysis proceeded, the amount of released CaO increased and more CaO was electro-reduced to Ca. CrO42− can be reduced to CaCr2O4 by electrolysis and calcium reduction simultaneously. Then, CaCr2O4 was further reduced to metallic chromium by the dissolved Ca in the near-cathode region. However, the inclusion of a little CaCr2O4 brought oxygen into metallic Cr powders.

Superhydrophobic surface fabricated on iron substrate by black chromium electrodeposition and its corrosion resistance property

The fabrication of superhydrophobic surface on iron substrate is carried out through 20min black chromium electrodeposition, followed by immersing in 0.05M ethanolic stearic acid solution for 12h. The resultant superhydrophobic complex film is characterized by scanning electron microscope (SEM), disperse Spectrometer (EDS), atomic force microscope (AFM), water contact angle (CA), sliding angle (SA) and X-ray photoelectron spectroscope (XPS), and its corrosion resistance property is measured with cyclic voltammetry (CV), linear polarization and electrochemical impedance spectroscopy (EIS). The results show that the fabricated superhydrophobic film has excellent water repellency (CA, 158.8°; SA, 2.1°) and significantly high corrosion resistance (1.31×106Ωcm−2) and excellent corrosion protection efficiency (99.94%).

Development of a brazing process for the production of water- cooled bipolar plates made of chromium-coated metal foils for PEM fuel cells

Beside lithium batteries, PEM fuel cells are the most promising strategy as a power source to achieve the targets for introducing and increasing the usage of electric vehicles. Due to limited space and weight problems, water cooled, metallic bipolar plates in a fuel cell metal stack are preferred in motor vehicles. These plates are stamped metal sheets with a complex structure, interconnected media-tight. To meet the multiple tasks and requirements in use, complex and expensive combinations of materials are currently in use (carbon fiber composites, graphite, gold-plated nickel, stainless and acid resistant steel). The production of such plates is expensive as it is connected with considerable effort or the usage of precious metals. As an alternative, metalloid nitrides (CrN, VN, W2N, etc.) show a high chemical resistance, hardness and a good conductivity. So this material category meets the basic requirements of a top layer. However, the standard methods for their production (PVD, CVD) are expensive and have a slow deposition rate and a lower layer thicknesses. Because of these limitations, a full functionality over the life cycle of a bipolar plate is not guaranteed. The contribution shows the development and quantification of an alternative production process for bipolar plates. The expectation is to get significant advantages from the combination of chromium electrodeposition and thermochemical treatment to form chromium nitrides. Both processes are well researched and suitable for series production. The thermochemical treatment of the chromium layer also enables a process-integrated brazing.

Electrodeposition of Nanocrystalline Chromium Coatings Based on 1-Butyl-3-Methylimidazolium-Bromide Ionic Liquid.

The electrochemical behavior of trivalent chromium reduction from 1-butyl-3-methylimidazolium-bromide ([BMIM]Br) ionic liquid is studied. The result of cyclic voltammetry shows that the Cr(III) reduction is irreversible and occurs in two steps, Cr(III)to Cr(II), and Cr(II) to Cr(0), respectively. In the electrochemical impedance spectroscopy measurements, the preferable equivalent circuit is made to fit the experimental data. The effects of electroplating parameters on coating thickness and electrodepositon rate are investigated by potentiostatic method on Cu electrode from Cr(III)-[BMIM]Br solution. The results show that the temperature and depositing potential have great effect on the coating thickness and electrodeposition rate. The surface morphology and composition of deposited Cr are investigated using scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS). SEM analysis shows that chromium electrodeposits obtained on Cu electrodes present a ball-like structure. EDS analysis shows that the coatings are composed of Cr. Moreover, the corrosion resistance of the as-deposited chromium layer is evaluated using polarization curves. The results show that the corrosion resistance of the chromium coatings obtained at higher potential is better.

Analysis of SEM digital images to quantify crack network pattern area in chromium electrodeposits

Abstract Scanning electron microscopy (SEM) is one of the primary methods used to inspect a wide range of materials, including metallic coatings. The use of software for image collection, analysis and, to some degree, interpretation is commonplace. However, no software seems to have been developed to quantify the cracks of chromium coatings. In the present paper SEM images are binarized using a proper threshold calculated from the histogram of images, once they have been filtered from nodules and background. The method uses the second derivative of the histogram obtained with the Laplacian of Gaussian (LoG), together with Prewitt vertical edge detector in some cases; then spatial cracked area can be quantified with much more accuracy than the subjective visual assessment that is usually done in the morphological analysis of the electrodeposits. The procedure has been automated so that the operator can straightforwardly obtain the result of the crack density from the original SEM image after some minor decisions orientated by the software, which is free on request from the authors. Manual computation has also proven to provide adequate results, but it takes longer and has limitations when highly cracked images are involved. The method could be probably extended to any kind of electrodeposits.

Feature descriptors from scanned images of chromium electrodeposits as predictor parameters of surface roughness and crystallographic texture

Feature descriptors extracted from scanned images of chromium electrodeposits are proposed as predictor parameters of surface roughness and crystallographic texture. First-order statistics of the images histogram, second-order statistics extracted from the gray-level co-occurrence matrix (GLCM), PC1 and PC2 scores from image PCA, and wavelet-based texture signatures have been extracted. A vector of 25 feature-descriptors variables was generated for characterizing each sample. Partial least squares (PLS) regression has been used to predict a value for deposit roughness (Ra) from the extracted image features and the value was compared with the one obtained from a stylus profilometer. The best result was obtained when a number of 13 variables were kept and the rest discarded. A RMSE of 0.0656 was obtained for external samples and no significant differences were proven to exist for 95% confidence level between the two methods under comparison. Partial least squares–discriminant analysis (PLS-DA) has been shown to be an adequate algorithm to correctly classify the chromium samples between those with low and high crystallographic T(110) texture coefficient. In this case, 6 variables of the 25 originally measured are enough to get proper results. The values found for both specificity and sensitivity were 1.00 and the percentage of correctly classified (%CC) samples was 100% in the calibration, the cross-validation, and the prediction sets. The proposed method can avoid the use of the X-ray diffractometry whenever a high precision of the texture coefficient value is not necessary.

Specific electrical conductivity of chromium plating and nickel plating electrolytes

The paper presents the results of measuring specific electrical conductivity (SEC) of chromium and nickel plating electrolytes with the help of a non-contacting conductivity meter of the CRAB-d 064 type in temperature intervals corresponding to the working ranges of electrochemical deposition processes. A schematic diagram of the apparatus for the measurement of electrolyte SEC is presented. Electrolytes based on chromium compounds of varying degrees of valence (Cr3+ Cr6 +) and a standard nickel electrolyte (Watts electrolyte) were chosen as the objects of study. The dependence of the SEC of electrolytes on their temperature is analyzed, a comparative assessment of the impact of temperature on the electrical conductivity of various chroming electrolytes is given.
 The influence of addition of nanoparticles of aluminum oxide and silicon carbide with the dispersion of 40-100 nm and a specific surface area of 23-32 m2 / g on the amount of electrical conductivity of an oxalate-sulfate electrolyte for chromium plating at a specified temperature is investigated. The study of nanosuspensions showed that the addition of nanoparticles of different nature with the concentration of 5-10 g / l to an electrolyte has no significant effect on the value of SEC.
 To evaluate the relationship between the electrolyte conductivity and process parameters of electrodeposition of chromium and nickel coatings a qualitative assessment of chromium and nickel current output was performed and bar graphs showing the ratio of the values of the electrolyte electrical conductivity and the metal current output are presented. It has been established that the electrical conductivity of electrolytes and the metal current output are parameters that do not depend on each other.

Electrodeposition of black chromium–cobalt alloy based on trivalent sulfate electrolyte

This study is aimed to improve the corrosion resistance, adhesion strength, and color of trivalent black chromium coatings on steel substrates by using chromium sulfate bath and chromium chloride bath. The effects of the electrodeposition current density on the trivalent black chromium coatings were studied. Surface morphology and chemical composition of coatings have been investigated using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) techniques. The protective behavior from substrates of trivalent black chromium coatings was studied in (3.5 wt. % NaCl) solution by potentiodynamic polarization technique. The better protective behavior from substrates was shown by coatings that formed in chromium sulfate bath. The coatings deposited at low current densities (10 A/dm2) showed high cobalt content because cobalt is more easily reduced than chromium on a cathode. The enhancement of the driving force caused chromium and cobalt to change into oxides and hydroxides when current density increased to more than 30 A/dm2. The best homogeneity of the black color, the degree of blackening and the protective behavior from substrates of coatings occurred at current density 50 A/dm2. The results of XPS indicated that the coatings contained not only chromium oxides and hydroxides but also cobalt oxides and hydroxides. Of all the constituent compounds, Co3O4 was the most dominant in influencing the degree of blackness.

Electrodeposition of mixed chromium metal-carbide-oxide coatings from a trivalent chromium-formate electrolyte without a buffering agent

The electrodeposition of mixed chromium metal-carbide-oxide coatings on low carbon mild steel from a trivalent chromium-formate electrolyte without a buffering agent is investigated at a rotating cylinder electrode enabling precise control of the mass flux.At equilibrium conditions, i.e. in the bulk of the electrolyte with pH2.3, Cr(III) mainly exists in the form of [Cr(HCOO)(H2O)5]2+. A deposition mechanism is proposed based on a fast, stepwise deprotonation of the water ligands in the Cr(III)-complex ion induced by a surface pH increase due to the hydrogen evolution reaction, which is controlled via the applied current density. Three different regimes can be defined related to the current density and mass flux.At low current densities no deposit is formed on the electrode, because soluble [Cr(HCOO)(OH)(H2O)4]+ is formed at the electrode (regime I). Above a certain threshold value of the current density Cr(HCOO)(OH)2(H2O)3 is deposited on the electrode (regime II). A part of the Cr(III) of the deposit is reduced to Cr-metal and formate is broken down leading to the formation of Cr-carbide. The amount and composition of the deposit in regime II strongly depend on the applied current density, mass flux and electrolysis time. At high current densities, a further shift of the acid-base equilibrium to [Cr(HCOO)(OH)3(H2O)2]− results in a deposit on the electrode that is mainly composed of Cr-oxide (regime III). In stark contrast to regime II, the amount and composition of the deposit in regime III are almost invariant of the applied current density, mass flux and electrolysis time.

Аноди для гальванічних ванн тривалентного хрому

Electrochemical behavior of different anode materials in electrolytes containing trivalent chromium salts was investigated. Some of electrodes (Ti/MnO 2 , platinized titanium, materials based on Ebonex ® ) were shown to be n-type semiconductors. Semiconducting properties of electrodes affects their electrochemical behavior.It was shown that choice of an appropriate anode for a trivalent chromium electroplating bath should be based on compromise between its selectivity and service life. It was found that current efficiency of Сr(VI)-species strongly depends on the nature of anode material. Dimensionally stable anode based on mixture of titanium oxides and ruthenium oxides, PbO 2 , Ti/MnO 2 anodes are characterized by low rates of Cr(VI)-species generation. Nevertheless these materials are not stable in the electrolyte media that limits their application for hard chromium electrodeposition. Composite materials based on platinized titanium or platinized Ebonex ® are recommend as anodes for carbamide-containing electrolytes since they characterized by good service life and admissible values of current efficiency of Сr(VI)-species.

Kinetics and mechanism of chromium electrodeposition from methanesulfonate solutions of Cr(III) salts

Kinetics and mechanism of the chromium electrodeposition process in methanesulfonate and sulfate solutions of Cr(III) ions have been investigated. The electroreduction of Cr(III) complex ions is shown to proceed stepwise with the formation of relatively stable intermediates—Cr(II) compounds. Chromium is established to be deposited via the discharge of Cr(II) hydroxocomplexes in these electrochemical systems. Some differences in electrodeposition behavior of methanesulfonate and sulfate trivalent chromium electrolytes are associated with the differences in their buffering capacity.

The use of trivalent chromium bath to obtain a solar selective black chromium coating

Abstract Black chromium coatings were electrodeposited from a trivalent chromium bath using a ZnO additive as a second main component. Black chromium was electrodeposited on steel and copper plates and substrates plated with bright nickel prior to black chromium electrodeposition. The black chromium coatings were characterized by XRD and SEM. The XRD data suggest that the phase structure of black chromium may be defined as a zinc solid solution in chromium or a chromium solid solution in zinc depending on the chromium/zinc ratio in the deposit. The role of substrate finish was evaluated through the corrosion resistance and reflectance of black chromium. According to corrosion tests the samples plated with bright nickel prior to black chromium deposition have shown the highest corrosion resistance. The electrodeposited black chromium possesses good optical properties for the absorption of solar energy. The absorption coefficient of black chromium was found to be over 0.99 for the samples obtained without the Ni undercoat and below 0.99 for those obtained with the use of Ni undercoat. However, the use of nickel undercoat before black chromium plating is recommended because it remarkably improves the corrosion resistance of samples.

Electrochemical mechanism of trivalent chromium reduction in 1-butyl-3-methylimidazolium bromide ionic liquid

The electrodeposition and electrocrystallization behaviour of chromium reduction in 1-butyl-3-methylimidazolium bromide ([BMIM]Br) ionic liquid on a glassy carbon (GC) electrode is investigated. These results from cyclic voltammetry and linear sweep voltammetry show that the reduction of trivalent chromium (Cr3+) occurs by a two-step process, Cr3+ to Cr2+ and Cr2+ to Cr0, respectively, the first step is an irreversible process with a diffusion coefficient of Cr3+ in solution of 2.3×10−6 cm2 s−1 at 358K, and the two-step reduction reaction has been identified by chronopotentiometry. The electrodeposits are characterized by SEM, EDS and XRD. XRD pattern of the electrodeposited layer reveals the characteristic peak of crystal Cr. Chronoamperometry results provide direct evidence that chromium electrodeposition in [BMIM]Br takes place through an instantaneous nucleation and diffusion-controlled three-dimensional growth mechanism.

Formation of chromium hydride in chromium being electrodeposited alloyed with hydrogen

The aim of the work was experimental verification of validity of the recently discovered phenomenon of phase formation through a stage of liquid state in metals being electrodeposited. The idea of the work was based on the known fact, that during crystallization of liquid phase of a transitional metal (e.g. chromium) alloyed in significant concentration with non-metal of minor atomic radius (e.g. hydrogen) intermediate phases with simple crystal lattices (e.g. hydrides) appear. Therefore, if in electrodeposited chromium alloyed with hydrogen the chromium hydride will be detected, this result will indicate validity of the phenomenon of phase formation through a stage of liquid state in metals being electrodeposited. To find the variants of chromium alloying with hydrogen during its electrodeposition the method for estimation of the degree of hydrogen saturation of metals being electrodeposited was developed. Electrodeposition of chromium was accomplished in such conditions where the volume of hydrogen being formed on the cathode was 62700 times higher than the volume of chromium being formed, which indicated alloying of chromium during its electrodeposition with hydrogen in significant concentration. On the basis of the accomplished experiments the formation of chromium hydride during electrodeposition of chromium alloyed with hydrogen was found. The conclusion, that existence of intermediate phases in electrodeposited metals is a result of crystallization of liquid metallic phase being formed during electrochemical deposition of metals, was made. The obtained result proves the validity of the phenomenon of phase formation through a stage of liquid state in metals being electrodeposited.

Speciation, physical and electrolytic properties of eutectic mixtures based on CrCl3·6H2O and urea

The electrodeposition of chromium is a technologically vital process, which is principally carried out using aqueous chromic acid. In the current study, it is shown that eutectic mixtures of urea and hydrated chromium(III) chloride provide a liquid which reduces the toxicological issues associated with the current aqueous Cr(VI) electroplating solution. Using EXAFS, mass spectrometry and UV-Vis spectroscopy, it is shown that chromium is present predominantly as a cationic species. Conductivities are higher than for most comparable ionic liquids. It is shown that the electrodeposition of chromium is electrochemically reversible, with a current efficiency much higher than in aqueous electrolytes. Surface tension and density measurements indicate that hole theory is a valid model to describe transport properties in these liquids. Bulk Cr deposits are not macrocrystalline but they are generally crack-free. The deposits have a hardness of 600 ± 10 Vickers and, as such, are comparable to deposits from aqueous systems.

Evolutionary support vector regression algorithm applied to the prediction of the thickness of the chromium layer in a hard chromium plating process

The hard chromium plating process aims at creating a coating of hard and wear-resistant chromium with a thickness of some microns directly on the metal part, without the insertion of copper or nickel layers. It is one of the most difficult electroplating processes due to the influence of the hydrogen evolution that occurs on the cathode surface simultaneously to the chromium deposition. Chromium plating is characterized by high levels of hardness and resistance to wear and it is thanks to these properties that they can be applied in a huge range of sectors. Resistance to corrosion of a hard chromium plate depends on the thickness of the coating, adherence and micro-fissures of the latter. This micro-fissured structure is what provides the optimal hardness of the layers. The electro-deposited chromium layer is not uniformly distributed: there are zones such as sharp edges or points where deposits are highly accentuated, while deposits are virtually nonexistent in holes or in the undercuts. The hard chromium plating process is one of the most effective ways of protecting the base material in a hostile environment or improving surface properties of the base material. However, in the electroplating industry, electro-platers are faced with many problems and often achieve undesirable results on chromium-plated materials. Problems such as matt deposition, milky white chromium deposition, rough or sandy chromium deposition and insufficient thickness or hardness are the most common problems faced in the electroplating industry. Finally, it must be remarked that defects in the coating locally lower the corrosion resistance of the layer and that the decomposition of chromium hydrides causes the formation of a network of cracks in the coating. This innovative research work uses an evolutionary support vector regression algorithm for the prediction of the thickness of the chromium layer in a hard chromium plating process. Evolutionary support vector machines (ESVMs) is a novel technique that assimilates the learning engine of the state-of-the-art support vector machines (SVMs) but evolves the coefficients of the decision function by means of evolutionary algorithms (EAs). In this sense, the current research is focused on the estimation of the hyper-parameters required for the support vector machines technique for regression (SVR), by means of evolutionary strategies. The results are briefly compared with those obtained by authors in a previous paper, where a model based on an artificial neural network was tuned using the design of experiments (DOE).