Chromium Plating Bath Research Articles

Оptimization of the chrome plating bath operation during the restoration of vehicle parts

Introduction. In the process of chrome plating of car parts, there is a change in the composition of the chrome plating bath, which affects the stability of the ongoing processes – the performance and quality of the chrome coating. Therefore, it is necessary to constantly monitor the chrome plating bath for the presence of foreign elements that can be formed during the operation of the bath during the reaction of the solution with the anode or cathode.Materials and methods. During the research, the necessary equipment was used, which made it possible to determine with sufficient accuracy the content of trivalent chromium and its effect on the electrolysis process – the performance and quality of chrome coatings. A well-known technique was used to determine the quality and performance.Results. When conducting studies of the obtained cold self-regulating chromium plating electrolyte, it was found that trivalent chromium has a significant effect on the stability of the chromium plating bath. The content of which can vary within 2...25 g/l during operation. As a result, it was found that the optimal amount of trivalent chromium is its content in the chromium plating bath from 2 to 15 g/l. With a lower or higher content, the electrolysis performance and the quality of the chrome coating decrease. It was also found that in order to maintain the optimal amount of trivalent chromium and increase the time for stable operation of the chromium bath, it is necessary to observe the ratio of the area of the anode and cathode (the coated surface of the part), the value of which is within 3...4.Discussion and conclusion. As a result of the conducted research, it will make it possible, under certain conditions, to carry out the process of chromium deposition from a cold self-regulating electrolyte, which will allow for stable chromium deposition at high productivity and the necessary quality of the coatings obtained. The main condition is to control and maintain the amount of trivalent chromium in the chromium plating electrolyte in the bath.

Chromium coatings from trivalent chromium plating baths: Characterization and cathodic delamination behaviour

Novel two-layer chromium-based coatings comprised of a first layer containing chromium, oxygen and carbon (Cr-O-C) and an oxygen rich (Cr-O) topcoat were electrodeposited from trivalent chromium electrolyte. The complex structure and composition of the coatings were studied using complementary characterization techniques. The electrodeposited oxide was found to be amorphous and oxygen-deficient. In operando ambient pressure X-ray photoelectron spectroscopy when heating the sample from room temperature to 450 °C and Raman spectroscopy after the heating ascertained the metastable nature of the oxide. The cathodic delamination of a weak model polymer on these samples was studied using in situ scanning Kelvin probe.

Investigation of The Reaction Kinetics of Chromium(III) Ions with Carboxylic Acids In Aqueous Solutions and The Associated Effects on Chromium Deposition

Electroplated chromium is an important industrial coating. Both in the decorative and functional field, research is being carried out to develop trivalent chromium electrolytes. In this work, the interaction between CrIII ions and carboxylic acids (malonic acid, malic acid, oxalic acid and glycolic acid) is investigated. The use of carboxylic acids to improve the current efficiency in trivalent chromium plating baths has been known for a long time. But the thermodynamics and kinetics of the associated complexing reactions are not well understood. It is shown that the complexes form at different rates depending on the acid and its concentration and have a varying influence on chromium deposition. For the development of a technical bath, care must be taken to ensure that the molar ratios between chromium and carboxylic acids can be controlled. This is possible with the HPLC method presented here.

Study on the Electrodeposition of Trivalent Chromium Plating Bath in the Presence of Oxalate Anions

Chromium is not easily electrodeposited from aqueous solutions based on trivalent chromium. Hull cell is employed to determine the optimum bath composition, and several electroplating baths were evaluated. The new bath with oxalate and acetate anions produces very good coatings and our results are valuable for the electroplating community and electrochemists. The baths presented a current efficiency of 37%, high covering power at 8.2 cm, low deposition potential of 7.3 V, and deposition rate of 0.4 μm/min. However, the Hull cell required a high current density (30 A/dm2). After 2 h of the electrodeposition process, the pH values change by 0.2 units. In addition, the baths were analyzed after electrolysis to detect Cr(VI), and this cation was not detected. Our study not only has a technological contribution but also presents a new explanation for the nature of these baths. In the literature, the usual explanation of the performance of these baths is based on the formation of complexes between ligands and Cr(III); however, our novel explanation is based on the high stability of water in the first solvation sphere of Cr(III), and we support our suggestions with several references to chromium solvation studies. The ligand-exchange reaction explanation is replaced by the second sphere hypothesis, that is, our explanation is based on the large stabilization energy of Cr−O bonds in [Cr(H2O)6]3+. Figure 1

Crystalline chromium electroplating with high current efficiency using chloride hydrate melt-based trivalent chromium baths

Chromium (Cr) plating using trivalent chromium has been investigated as a replacement for the highly-toxic hexavalent chromium bath. Herein, we report novel chromium plating baths using hydrate-melts. Hydrate-melts have been investigated in recent years as an electrolyte for aqueous Li-ion batteries with a wide electrochemical window, and can be used as an electroplating bath in which the reduction of protons, i.e., bath decomposition, is suppressed. By using a hydrate-melt for electroplating with trivalent chromium, the increase of local pH during electrolysis is suppressed and generation of the electrochemically-inert oligomer of chromium hydroxide can be avoided. Crystalline chromium electrodeposits were successfully obtained from the hydrate-melt-based aqueous baths, which had not been possible with the conventional trivalent chromium process requiring organic coordination agents. Moreover, a current efficiency greater than 80% was achieved. The hydrate-melt-based aqueous bath, with low material cost, is a promising candidate for industrial trivalent chromium plating.

Characteristic and behavior of an electrodeposited chromium (III) oxide/silicon carbide composite coating under hydrogen plasma environment

Hydrogen permeation barriers play a crucial role in reducing the risk of hydrogen permeation and radioactive leakage during the service of a fusion reactor. In this work, a chromium (III) oxide/silicon carbide (Cr2O3/SiC) composite coating was proposed to improve the hydrogen permeation resistance of ferronickel alloy. At first, the Cr/SiC composite coating was prepared by pulse electrodeposition in a trivalent chromium plating bath containing suspended SiC nanoparticles, and then oxidized it under 500 °C at a pressure of 100 Pa. The surface morphology, phase structure, surface chemical states, thickness, and the integrity of the composite coating were analyzed and compared. In particular, the effects of hydrogen permeation of the composite coatings were investigated. As a result, the composite coating showed huge potential in improving hydrogen permeation resistance, which provides a promising application for fusion reactors.

Hydrogen evolution reaction on Cr–C electrocatalysts electrodeposited from a choline chloride based trivalent chromium plating bath

Hydrogen evolution reaction on Cr–C electrocatalysts electrodeposited from a choline chloride based trivalent chromium plating bath

Trivalent chromium electrodeposition using a deep eutectic solvent

PurposeThis paper aims to investigate the electrolytic deposition of corrosion-resistant chromium coatings from a trivalent chromium plating bath based on deep eutectic solvent, a new generation of room temperature ionic liquids.Design/methodology/approachThe electrolyte contained chromium (III) chloride, choline chloride and the additive of extra water. The surface morphology was estimated by means of SEM technique. The microstructure of as-deposited and annealed coatings was studied using X-ray diffraction method. The kinetics of the chromium electrodeposition and the corrosion electrochemical behavior of the coatings were investigated by cyclic voltammetry technique.FindingsChromium coatings with an amorphous type of microstructure are electroplated from this bath. Some carbon and oxygen are included in deposits obtained. The step-wise mechanism of the electrochemical reduction of Cr(III) ions to Cr(0) is detected. The current efficiency in this system sufficiently exceeds that typical of usual aqueous electrolytes. The coatings fabricated using plating bath based on deep eutectic solvent showed enhanced corrosion resistance in an acidic medium: there is no current peak of active dissolution in polarization curve and the corrosion potential shifts to more positive values as compared with “usual” chromium.Originality/valueThe electrodeposition of chromium coatings from an environmentally acceptable trivalent chromium electrolyte, a deep eutectic solvent containing chloride choline and extra water additive has been investigated for the first time.

The fate of Cr(VI) in contaminated aquifers 65 years after the first spillage of plating solutions: A δ53Cr study at four Central European sites

Chromium isotope systematics and concentrations of dissolved Cr were studied in shallow aquifers at four industrial sites in the Czech Republic, Central Europe. Chromium plating baths and wastewaters started to contaminate groundwater in the late 1940s. Since plating shops at all sites still operate, it was possible to determine the δ53Cr signatures of the plating baths. The mean δ53Cr values of the Cr plating baths, representing contamination sources, were 0.0‰ at Zlate Hory (ZH), 0.5‰ at Loucna nad Desnou (LD), 0.3‰ at Letnany (AV), and 0.1‰ at Velesin (JI). At all sites, groundwater Cr was isotopically heavier, compared to the contamination source, reflecting natural in-situ Cr(VI) reduction to insoluble Cr(III). The magnitude of the average positive isotope shift from the plating bath Cr(VI) to groundwater Craq, mostly residual Cr(VI), was 1.1‰, 1.3‰, 3.3‰ and 3.3‰ at ZH, LD, AV, and JI, respectively. The mean concentration of Craq was 0.43, 0.47, 2.38 and 4.32mgL−1, respectively. AV and JI, the sites with lower residual Craq concentrations in groundwater, had higher δ53Cr values, suggesting higher rates/efficiency of Cr(VI) reduction, and of toxicity removal. Simple Rayleigh models indicated that as much as 60% of Cr(VI) has been removed from the groundwater by spontaneous reduction at AV and JI. At ZH and LD, the same models indicated a 30% Cr removal from the solution. Even if uncertainties in model application and Cr fractionation factors are considered, it appears that natural attenuation at Cr(VI)-polluted sites can improve groundwater quality by tens of percent in a relatively short period of time of several decades.

Characterization of the Cr-C/Si3N4 Composite Coatings Electroplated from a Trivalent Chromium Bath

Cr-C/Si3N4 composite coatings are obtained by electrodeposition under DC conditions from a trivalent chromium plating bath containing suspended Si3N4 nanoparticles. The influences of plating parameters including Si3N4 concentration in the plating bath and current density on the coating composition, deposition rate, morphology, surface roughness, micro-hardness and wear behavior of electrodeposited Cr-C/Si3N4 composite coatings are evaluated and compared with that of electrodeposited Cr-C coating. Our study reveals that Si3N4 particles can be successfully codeposited and uniformed distributed in the electrodeposited Cr-C matrix. The maximum level of incorporation of Si3N4 particles, about 17.22 vol%, is obtained at a bath loading of 5gL−1 and at a current density of 20A dm−2. Due to enhanced dispersion strengthening effect, the incorporation of Si3N4 particles increases the microhardness of the coatings and significantly increases the wear resistance of the coatings.

On the Microthrowing Power of Chromium Plating Baths

On the Microthrowing Power of Chromium Plating Baths

Sample pretreatment for the capillary electrophoretic determination of organic acids in chromium(III) plating baths.

This work deals with the development and optimization of the sample pretreatment and consequent electrophoretic analysis of two modern plating baths containing chromium(III) and either citric acid or oxalic acid. Some model mixtures containing known amounts of components of industrial baths have been prepared to simulate simplified bath matrices. Prior to analysis, a sample pretreatment consisting of the addition of some agents that could release acid from the stable chromium complex was tested. Determination of organic anions was accomplished by indirect UV detection. The best results were achieved by precipitation of chromium(III) hydroxide. The content of oxalate and citrate in real samples was calculated as 96.5% (SD 2.3%) and 97.3% (SD 0.8%), respectively, of the declared amount. Very good robustness of the method and satisfactory repeatability of migration time and peak area were obtained. This simple inexpensive method is suitable for routine determination of citric and oxalic acid in chromium(III)-based plating baths.

710 3価クロムめっき浴における電極反応の調査(OS7-(3),OS7 オーガナイズドセッション《精密/微細加工と評価》)

Our laboratory has been developing a chromium plating bath using trivalent chromium as one of the alternative process. It is, however, difficult to comprehend complex behavior of reaction occurring at the electrodes of the plating bath. So, the purpose of this study is to elucidate the reactions and the change of bath composition during the electro deposition. The authors surveyed the composition of gases generated from the various types of bathes by the electrode reaction with gas chromatography, and evaluated the ratio of electric current used for the gas generation. It became obvious that the ratio greatly depends on the bath composition, especially the ratio becomes very low in the trivalent chromium bath. We have concluded that the lower current efficiency is owing to the reaction that Cl_2 generated at the anode dissolves in the bath again as hypochlorous acid.

Electrodeposition of cobalt–tungsten alloys from alkaline citrate containing bath as alternative for chromium hexavalent replacement

Cobalt–tungsten alloys have been considered as potential materials for various applications. This work investigates the wear and corrosion resistance behaviour of cobalt–tungsten–phosphorus alloys electroplated from alkaline citrate containing baths. The wear rates of the cobalt–tungsten alloy electrodeposits were lower than those of the unalloyed cobalt electrodeposits. The wear rate was also lower than those of chromium plated from hexavalent chromium plating bath. It was also demonstrated that the addition of small quantities of phosphorus into Co–W alloys improved the corrosion resistance of the alloy. In fact, the addition of phosphorus further improved the corrosion of the alloy exposed to immersion test in comparison to cobalt–tungsten. The cobalt–tungsten alloys without having any phosphorus component were subjected to further oxidation of tungsten component followed by dissolution in deionised water during the immersion tests.On a considéré des alliages de cobalt et tungstène comme matériaux potentiels pour diverses applications. Ce travail examine le comportement d’usure et de résistance à la corrosion d’alliages de cobalt, tungstène et phosphore déposés par électrolyse, à partir de bains alcalins contenant du citrate. Les taux d’usures des dépôts de l’alliage de cobalt et tungstène étaient plus faibles que ceux des dépôts non alliés de cobalt. Le taux d’usure était également plus faible que ceux de chrome déposés à partir d’un bain de dépôt électrolytique de chrome hexavalent. On a également démontré que l’addition de petites quantités de phosphore dans les alliages de Co–W améliorait la résistance à la corrosion de l’alliage. En fait, l’addition de phosphore améliorait davantage la corrosion de l’alliage exposé à un essai d’immersion par rapport à l’alliage au cobalt et tungstène. Les alliages de cobalt et tungstène, sans la composante de phosphore, étaient sujets à davantage d’oxydation de la composante de tungstène suivie par la dissolution dans de l’eau déionisée lors des essais d’immersion.

Effect of Cr(III)+Ni(II) solution chemistry on electrodeposition of CrNi alloys from aqueous oxalate and glycine baths

CrNi alloy coatings with various concentrations of Cr and Ni were deposited from trivalent chromium plating baths containing bivalent nickel and glycine or oxalate as a complexing agent. The deposition rate, composition and morphology of CrNi alloy coatings and chemistry of the solutions employed have been studied. It has been found that the substrate surface initially was coated with a layer of Ni, which facilitates the underpotential nucleation of Cr on Ni giving an alloy. The formation of a Ni rich alloy starts at a less negative potential in the oxalate bath as compared to that in the glycine bath. The CrNi alloy coatings are characterised by nodular structures with microcracks and the coatings deposited from the glycine bath have pores and cavities, whereas no pores were detected in the deposits from the oxalate bath. The solution chemistry substantially affects the formation of CrNi alloy. The formation of the Ni(II)–Cr(III) ring structure capable of oligomerisation most probably impedes the electrodeposition making it impossible to obtain a thick CrNi alloy coating in the glycine bath. However, in the oxalate bath, no noticeable effect of Ni(II) ions on the structure of oxalic complexes was revealed. Moreover, active [(H2O)nCr(C2O4)]+ and [(H2O)nCr2(C2O4)]4+ complexes may be restored which allow the prolonging of the lifetime of the oxalate bath.

Chronopotentiometric study of ceramic cation-exchange membranes based on zirconium phosphate in contact with nickel sulfate solutions

In this article, the innovative cation-exchange membranes obtained from ceramic materials are presented. Different microporous ceramic supports were obtained from an initial mixture of alumina and kaolin, to which a varying content of starch was added in order to obtain supports with different pore size distributions. The deposition of zirconium phosphate into the porous supports generates membranes with cation-exchange properties. The fabrication of ion-exchange membranes which could resist aggressive electrolytes such as strong oxidizing spent chromium plating baths or radioactive solutions would allow the application of electrodialysis for the decontamination and regeneration of these industrial effluents. The performance of the manufactured membranes was studied in nickel sulfate solutions by means of chronopotentiometry. An increase of the membrane voltage drop during chronopotentiometric measurements was observed in some membranes, which seems to be a consequence of concentration polarization phenomena resulting from the ionic transfer occurred through the membranes. Current–voltage curves were obtained for the different ceramic membranes, allowing the calculation of their ohmic resistance. The ohmic resistance of the membranes increased when the open porosity (OP) of the samples was incremented up to a value of 50%. For values of OP higher than 50%, the resistance of the membranes decreased significantly with porosity.

Preparation and characterisation of electrodeposited Ni-Cr/Al<SUB align="right">2O<SUB align="right">3 nanocomposite coatings from a trivalent chromium-based bath

Ni-Cr/Al2O3 composite coatings were co-deposited on mild steel substrates by co-electrodeposition of Ni-Cr alloys and Al2O3 nanopowders from a trivalent chromium plating bath. Variations of Cr and Al2O3 nanoparticles in nanocomposite coatings as a function of Al2O3 concentration in electrolyte, cathode current density, stirring rate and temperature of plating bath was investigated. It was found that these parameters strongly affect the weight percentage of Cr and Al2O3 nanoparticles in the coatings. Microstructural characterisation of the coatings was performed by x-ray diffraction (XRD), scanning electron microscopy and energy-dispersive x-ray analysis (EDX). The corrosion behaviour of the nanocomposite coatings was evaluated by charting the Tafel curves of the solution of H2SO4 (5%) at room temperature. The results showed that the amount of Al2O3 nanoparticles in the coating increases with increasing Al2O3 concentration in electrolyte. This also enhances the co-deposition of Ni and Cr. It was also found that the presence of Al2O3 nanoparticles leads to an increase in hardness and corrosion resistance of the coatings. The distribution of Al2O3 nano-particles across the coatings was uniform even in those cases which resulted from baths of higher concentrations of Al2O3.

A comparative research on corrosion behavior of a standard, crack-free and duplex hard chromium coatings

In this study, the single and duplex layers of standard and crack-free hard chromium coatings were prepared by using direct current (DC) and pulse current (PC) electroplating processes on mild steel substrates. The coatings are studied from microstructure, microhardness and corrosion resistance viewpoints. The coating's corrosion resistances have been compared through electrochemical polarization in a 3.5% NaCl solution and standard salt spray test. Before and after corrosion tests microstructural characterization tests were done by optical microscopy (OM) and scanning electron microscopy (SEM). The micro-crack density, in the hard chromium microstructure, could be limited by using the pulse current electrodeposition. Crack-free hard chromium coatings, which are deposited by PC-electroplating, were excellent in terms of corrosion resistance. The thickness ratios in duplex coatings with crack-free sub-layer and hard chromium top coat, were also prepared by PC- and DC-electroplating processes respectively in the standard chromium plating bath. Standard hard chromium coating deposited by DC-electroplating had rust stains on the surfaces and edges. The coatings with crack-free sub-layer coatings exhibited excellent results in corrosion resistance, with no corrosion product on the surfaces and edges of the samples. Their icorr in the 3.5% NaCl solution are lower than the standard Cr-deposited by DC-electroplating. All of the coatings are passivated in both 3.5% NaCl solution and salt spray test environments. In addition, between the duplex layer coatings, the coating with a ratio of a 75% crack-free sub-layer (25% cracked hard top layer) showed the best corrosion resistance.

Preparation and characterization of nanocrystalline Fe–Ni–Cr alloy electrodeposits on Fe substrate

Fe–Ni–Cr alloy layers were prepared by electrodeposition from trivalent chromium plating bath in chloride-sulfate based solution. The influences of bath composition and plating parameters on the alloy electrodeposition process and the properties of deposited alloy were studied. The effects of plating parameters and bath composition such as current density, bath pH, bath temperature, the concentrations of FeSO4 · 7H2O and CrCl3 · 6H2O on the contents of Fe and Cr in Fe–Ni–Cr alloy layer were investigated. Electrodeposited Fe–Ni–Cr alloy layers on Fe substrate were characterized by X-ray diffraction (XRD), Electronic Differential System (EDS) and a CHI600B electrochemistry workstation. The composition of the Fe–Ni–Cr coatings depends on bath composition and plating conditions including pH, current density, and temperature. The internal structure of the alloy is nanocrystalline, the average grain size is 87 nm, and the corrosion resistance of the alloy layers is better than that of pure nickel layers.

Study of Hard Chromium Plating from Trivalent Chromium Electrolyte

Hard chromium deposits were prepared from a trivalent chromium plating bath as an alternative to conventional hexavalent chromium deposits. The influences of bath composition on the trivalent chromium electrodeposition process and deposited coating properties were studied. The effects of plating parameters such as current density, bath pH and plating time on structure and morphology of deposited coatings were investigated. Results show that the hard chromium deposits exhibited amorphous structure with thickness of 50-100μm and acceptable quality for functional coatings. The hard chromium deposits exhibited better wear resistance as well as corrosion resistance than that of hexavalent chromium deposits. The hardness of as-deposited chromium coatings is about 600-700HV. Heat treatment could improve the wear resistance and hardness of the hard chromium deposits. The formation of polynuclear coordination compounds from hydroxyl complex ions at high pH is the main disadvantageous factor for the sustained trivalent chromium plating process.