Chromium Deposition Research Articles

“Efficient novel fungal-enriched biochar formulation for hexavalent chromium bioremediation”

Chromium (Cr), a key element in industrial processes such as leather tanning, poses severe environmental hazards, particularly its hexavalent form, Cr(VI), which is highly toxic and prevalent in tannery effluents/sludge. The persistence and toxicity of Cr(VI) necessitate the development of effective remediation strategies to mitigate its environmental impact. This study investigated the potential of Trichoderma yunnanense (NBRICRF_97) and its combination with 0.5% sugarcane bagasse biochar (SBC) for the reduction of Cr(VI). The results demonstrated that T. yunnanense alone achieved a 91.04% reduction of 50 mg L−1 Cr(VI) within 72 h. Combined with 0.5% SBC, the reduction efficiency increased to 99.65% within 48 h. However, the efficiency decreased at higher concentrations (200 mg L−1). The combination also improved fungal growth and increased extracellular ChrR enzyme activity (13.07 U mg−1 protein compared to the control). Total glutathione activity was boosted by 161.07% at 100 mg L−1 Cr(VI). Antioxidant enzymes (SOD, POD, CAT) and proline mitigated oxidative stress and FTIR analysis revealed changes in fungal cell wall functional groups (-OH and -NH) upon Cr(VI) exposure. SEM-EDX confirmed chromium deposition on fungal surfaces. These results underscore the Cr(VI) detoxification capabilities of T. yunnanense and the synergistic benefits of SBC, suggesting a promising bioremediation strategy for Cr(VI)-contaminated environments. The integration of T. yunnanense with SBC offers a sustainable and cost-effective approach for the bioremediation of Cr(VI)-contaminated sites, with potential for implementation in large-scale environmental cleanup efforts.

Features of cavitation wear of chrome electrolytic coatings

Cavitation wear is a pervasive phenomenon on water transport. The parts of ship propulsion system as well as the water-cooled surface of cylinder liners of high-speed ship diesels are subjected to cavitation attack. Bright chromium deposits are used to protect the water-cooled surface of liners. Nevertheless, the effect of cracks appearing in the electrolytic chrome coating upon depositing on the cavitation resistance of coating is still an open relevant problem. The goal of the study is to analyze the kinetics and mechanism of the destruction of the bright chrome electrolytic deposit under cavitation attack. The cavitation resistance of chrome electrolytic coatings after grinding and after polishing was studied. The chrome electrolytic coatings were obtained on the plates (90 × 30 × 7 mm in size) made of cast iron SCh21. The chrome was deposited on one side (90 × 30 mm) of the plate placed vertically by flow anodic jet chrome plating in standard electrolyte (kg/m3): chrome anhydride — 250; sulfuric acid — 2.5; trivalent chrome — no more than 5; trivalent iron ions — no more than 10. The electrolyte was prepared using distilled water of a single distillation. The parameters of depositing: electrolyte temperature is 50°C; the current density amounts to 60 A/dm2. Four samples cut from the same plate were used. The coatings on the first two samples were ground using the abrasive paper number 320. The coatings on the second pair of samples were first ground successively on the abrasive paper of different grit: 320, 500, 800, 1000, and 1200, and then polished on the cloth with GOI paste. The cavitation wear tests were carried out on a magnetostrictive vibratory rig in fresh water, the frequency and amplitude of the rig horn vibration was equal to 22 kHz and 28 μm, respectively. The spacing between the chrome-plated sample surface and the horn butt was 0.5 mm. The wear of the samples was evaluated by periodical weighing during testing. The wear of the ground samples turned to be significantly higher, than that of polished samples. The photographs of the surface after different duration of the cavitation attack show that the initial cracks formed on the coating during chrome plating are the centers of cavitation destruction. To reduce the negative impact of initial cracks on the cavitation resistance of the bright chrome electrolytic coatings deposited on the water-cooled surface of the cylinder liners of diesels it is shown expedient to include polishing in the technological process of depositing chrome coatings.

DLC FILMS ON Ti6Al4V SUBSTRATES OF NANOINDENTATION, SURFACE ROUGHNESS FOR LASER POWDER BED FUSION WAS PERFORMED UTILIZING ORTHOPEDIC IMPLANT MATERIALS

Diamond-like carbon (DLC) films on titanium alloy Ti6Al4V substrates were tested with nanoindentation and surface roughness to look at the hardness and roughness of the coating and substrate systems as well as their mechanical properties. The powdered titanium alloy Ti6Al4V used in the substrate specimen was produced using laser powder bed fusion, an additive manufacturing process. In this study, we investigated the influence of substrates on the nanoindentation and surface roughness of the DLC film layer with an estimated [Formula: see text]m thickness on Ti6Al4V substrates. The findings of the nanoindentation show that the reaction to the impact was more flexible than expected. Maximum load, residual nanoindentation depth, hardness, and modulus may influence mechanical properties. The DLC-film Ti6Al4V substrate materials’ top surface roughness is measured. As a result of the increased load-carrying ability of DLC/Ti6Al4V, Ti6Al4V is a superior choice for substrate materials for DLC films, A DLC coating, measuring [Formula: see text] m in thickness, was applied to a Ti6Al4V substrate utilizing a 5-min chromium deposition process. The biocompatibility of the substrates plays a crucial role in determining the DLC films capacity to prolong the lifespan of bone implants.

ЭЛЕКТРООСАЖДЕНИЕ ХРОМА ИЗ КИСЛЫХ ЭЛЕКТРОЛИТОВ С ДОБАВЛЕНИЕМ ОРГАНИЧЕСКИХ ПОВЕРХНОСТНО-АКТИВНЫХ ВЕЩЕСТВ

The influence of current density on the current efficiency of chromium, the content of organic additives on the microhardness and porosity of chromium deposits, and the thickness of chromium deposits on internal stresses were studied. X-ray studies of the structure of chromium deposits obtained from electrolytes with organic additives were carried out.

Peritectic orthopyroxene entrainment during partial melting of garnet peridotite produced the Bushveld Complex chromite deposits

AbstractOne of the largest chromium deposits on Earth occurs in the Rustenburg Layered Suite (RLS) of the Bushveld Complex as laterally continuous chromitite layers. None of the hypotheses proposed for the origin of the chromitites can explain both the abundance of Cr in the RLS and the unusual enrichment in Cr and V over Ni, relative to typical depleted mantle values. This study investigates the possibility that the layering and chromitite formation are consequences of the entrainment of source components into the magmas that formed the RLS. Thermodynamic modelling results reveal a wedge-shaped domain in pressure-temperature space in the subcratonic mantle within which Cr-bearing orthopyroxene forms as a peritectic product of incongruent melting. Entrainment of this orthopyroxene produces magmas that crystallise peritectic olivine and chromite on ascent, due to the consumption of orthopyroxene by melt. The chromite- and olivine-bearing magmas intrude as sills and can produce chromite and dunite layers by density separation. This model, which interprets the RLS Sr-isotopic composition to reflect prior mantle metasomatism by crustal fluids (ideally ancient and of low volume), readily explains the formation of chromitite layers from relatively thin sills, as well as the very high ratios of Cr and V to other compatible elements relative to typical mantle compositions. The special circumstances required to produce the RLS chromitites do not relate to some oddity of repetitive crustal assimilation or magma compositions that allow chromite-only saturation. Rather, they relate to speed of melting and magma extraction which enabled peritectic orthopyroxene entrainment to the magmas.

Metallization of polypropylene substrates through surface functionalization and physical vapor deposition of chromium coatings

Physical vapor deposition (PVD) of chromium coatings represents an interesting alternative to electroplating to obtain metallized plastic parts for a variety of manufacturing sectors. This process is however hampered by the limited adhesion of the metallic layer on the underlying polymeric substrates. Within this context, PVD metallization of polypropylene substrates has so far been particularly challenging given the low surface energy and poor wettability of this commodity plastics. To address this issue, a comprehensive approach is proposed here to enable the production of PVD-metallized PP substrates with excellent and stable interlayer adhesion. The adhesive properties of the PP substrate are modified by a selective UV-induced photografting process in which vinyl-, glycidyl- or 2-hydroxyethyl methacrylate species are covalently attached to the PP surface, as confirmed by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and surface wettability measurements. Based on the chemistry of the photografted functionality, different resin systems are selected and investigated for use as primers to enable subsequent chromium deposition, including acrylic, epoxy and polyurethane systems. The effect of the photografting process on the adhesion between PP and the primers is systematically assessed by means of pull-off tests, highlighting a significant improvement of the adhesion force after surface functionalization with appropriate grafting agents. Finally, functionalized PP substrates are chromated through PVD, obtaining homogeneous and crack-free chromium surfaces upon judicious selection of suitable primer-grafting agent combinations. This also led to outstanding interlayer adhesion and micromechanical performance. This work provides the first demonstration of chromium-metallization of PP substrates via PVD for metallized plastic components with excellent surface characteristics, and paves the path for the design of mechanically durable and aesthetically-compliant PVD-metallized PP components.

Temporal-spatial characteristics and sources of heavy metals in bulk deposition across China

With the rapid development of industries, agriculture, and urbanization (including transportation and population growth), there has been a significant alteration in the emission and atmospheric deposition of heavy metal pollutants. This has consequently given rise to a range of ecological and environmental health issues. In this study, we conducted a comprehensive two-year investigation on the temporal and spatial distribution characteristics of heavy metals in atmospheric deposition across China based on the Nationwide Nitrogen Deposition Monitoring Network (NNDMN). The atmospheric bulk deposition of Lead (Pb), Arsenic (As), Nickel (Ni), Selenium (Se), Chromium (Cr) and Cadmium (Cd) were 6.32 ± 1.59, 4.49 ± 0.57, 1.31 ± 0.21, 1.05 ± 0.16, 0.60 ± 0.06 and 0.21 ± 0.03 mg m−2 yr−1, respectively, with a large variation among the different regions of China. The order for atmospheric deposition flux was Southwest China > Southeast China > North China > Northeast China > Qinghai-Tibet Plateau and rural area > urban area > background area. The concentrations of heavy metals in bulk deposition exhibit seasonal variation with higher levels observed during winter compared to summer and spring, which are closely associated with anthropogenic activities. The Positive Matrix Factorization (PMF) results indicated that combustion, industrial emissions and traffic are the primary contributors to atmospheric deposition of heavy metals. The single factor pollution index (Pi) of heavy metals is consistently below 1, and the composite pollution index (Ni) is 0.16 across China, indicating that atmospheric heavy metal deposition is at a pollution-free level. The comprehensive potential ecological risk index of heavy metals is 11.8, with Cd exhibiting the highest single factor potential ecological risk index at 7.09, suggesting that more attention should be paid to Cd deposition in China. The present study reveals the spatial-temporal distribution pattern of atmospheric heavy metals deposition in China, identifying regional source characteristics and providing a theoretical foundation and strategies for reducing emissions of atmospheric pollutants.

Research of the Process of Electrochemical Deposition of Chromium in the Presence of a Composite Compound Based on Detonation Diamond-Containing Carbon

The purpose of the study is to develop a method for obtaining high-quality electrochemical chromium coating using a new type of diamond-containing additive that has significant advantages over traditionally used detonation nanodiamonds (DNA) in the form of aqueous suspensions. Detonation diamond-containing carbon (DDC) obtained by detonation of charges from tetryl was used as an additive. DDC contains 63,0 wt. % DNA and 4.4 wt. % non-combustible impurities. We used standard chromium electrolyte: CrO3 - 250 g/l, H2SO4 – 2,5 g/l, DNA – from 0,2 to 5 g/l, traditional methodologies and algorithm of experimentation. The scope of the study is limited to the creation and application of a specific, easy to handle and prepare formulation with DDC. DDC can be added to the standard chromium electrolyte directly or in the form of freshly prepared aqueous suspension, it is environmentally safe. The originality of the work lies in the application of a cheap diamond-containing product obtained directly after the explosion of an individual explosive (tetryl) and providing stability of DDC suspensions. An increase in microhardness of wear-resistant chrome coating by 1,5 times (up to 11 GPa) and hard chrome coating by 1,7 times (up to 13,3 GPa) was achieved. The wear resistance of the obtained coatings increased by 1,9 times. Concentration (per pure detonation nanodiamond (DNA)) from 0,63 to 3,15 g/l in the electrolyte (very low).

Fabrication of nanoscale stencils through focused ion beam milling and dry transfer of silicon-on-nothing membrane with perforations

Nanoscale stencil lithography, providing sub-micrometer resolutions, is being implemented as a reliable patterning technique within the nanotechnology domain. Despite their advantages such as no resist processing, easy manipulation and reusability, patterning using a nanoscale stencil often faces challenges due to the gap between the nanoscale stencil and the substrate. This tends to result in unwanted pattern blurring, typically dimension wider than intended design. To address this issue, we minimize the gap by conformally attaching the nanoscale stencil to the substrate, thereby effectively eliminating a key factor contributing to the blurring effect. The nanoscale stencil is fabricated by forming nanoslits on the 50 nm thick Silicon-on-Nothing (SON) membrane with perforations, using focused ion beam (FIB) milling. The transfer of this stencil onto a substrate enables conformal adhesion due to its 1012 times lower flexural rigidity of the stencil compared to bulk silicon. Upon deposition of chromium and gold through the transferred stencil, a metal pattern array with the full width at half maximum (FWHM) of 43 nm is produced, demonstrating the potential of our approach for fabricating uniform nanoscale patterns with enhanced pattern resolution.

Activation Processes for Electrodeposition on Passive Nickel Surfaces

Electrodeposited layer systems consisting of nickel and chromium are commonly used for decorative applications and to protect components against corrosion. Sometimes, already deposited chromium layers have to stripped again to do rework on technical parts. As a result passive layers can form at the surface of the nickel layer. This often leads to poor adhesion of subsequent layers. To prevent such adhesion problems nickel layers have to be activated to allow subsequent deposition of chromium. The thickness of the passive layers depends on the current density and treatment time during chromium stripping, as well as on the properties of the chromium layer to be removed. In summary, process fluctuations in all steps lead to an impairment of the activation effect and thus to adhesion problems.This work will discuss recent results from a project within the framework of the Central Innovation Program for SMEs (ZIM) of the AiF. The aim of the project is to optimize the electrolyte composition and the individual treatment stages. Furthermore, the focus is on establishing measuring techniques for the various process parameters and developing a process model for the implementation of a controlled activation process in a large-scale plant. To achieve these ambitious goals, different parameter settings such as current density and treatment time were studied during the activation process and the effect of these parameters on the subsequent nickel and chromium deposition was evaluated.

Effect of Pulsed Currents on Oxygen and Carbon Contents of Trivalent Chromium Based Deposits

Hexavalent chromium salts have been identified as toxic for both humans and the environment by Health authorities, which led the authorities to take measures such as the implementation of strict rules, such as the REACH regulation. While some applications may be substituted by other processes, the thick hard chromium plating used for its functional properties in friction and wear lacks of alternatives. Among them, trivalent chromium salts have been extensively studied [1], but this kind of electrolytes presents typical difficulties, leading to more fragile coatings with through-cracks, and a typical increase of hardness up to very high values after annealing. This change in the chromium coating behavior is often attributed to a significant increase in carbon and oxygen contents [2].If temperature as well as current density have shown a great influence on both carbon and oxygen, their effects are reversed, with for example a decrease in oxygen content with temperature (due to a high solubility of hydroxides) accompanied by an increase in carbon content that leads to amorphous deposits. It is however very difficult to reduce both carbon and oxygen. The present work is built on a parallel study carried-out in the IRT M2P project CRONOS 2024, which discover the possibilities to limit the pH increase at the interface by inserting long-time toff during electrodeposition [3].Various parameters (ton times, toff times, peak current density) have been scanned for chromium deposition on a copper tip (to make the oxygen and carbon analysis easier). It has been showed that a possible control of oxygen and carbon is possible, leading to very low values and changes in deposits properties (hardness, behavior after annealing, roughness ...). The best sequence was studied for various temperatures, and the combination of parameters extensively described.Finally, 15CDV6 steel samples were coated and fully characterized.[1] P. Benaben, « An Overview of Hard Chromium Plating Using Trivalent Chromium Solutions », Plating and Surface Finishing, p. 8, 2011.[2] A. Baral et R. Engelken, « Modeling, Optimization, and Comparative Analysis of Trivalent Chromium Electrodeposition from Aqueous Glycine and Formic Acid Baths », J. Electrochem. Soc., vol. 152, no 7, p. C504, 2005, doi: 10.1149/1.1933688.[3] M. Marcelet et al., « Influence of Pulse-Current Parameters on pH Measured By Local Method », Meet. Abstr., vol. MA2019-02, no 21, p. 1046, sept. 2019, doi: 10.1149/MA2019-02/21/1046.

Potential Risk of Significant N2O Emission without Changing NOx Conversion on Commercial V2O5/TiO2 Catalyst under Working Conditions.

Vanadium-based catalysts play a pivotal role in the emission control of industrial NOx via selective catalytic reduction (SCR) technology. However, little attention has been paid to the potential emission of greenhouse gas N2O under complex working conditions. This work reports that a commercial V2O5/TiO2 catalyst may lead to significant N2O emission without greatly changing the outlet NOx concentration after chromium (Cr) deposition. With a Cr loading of 2 wt %, N2O concentration increased from 27.8 to 199.2 ppm at 350 °C with the value of outlet N2O/(N2O+N2) from 2.5% to 19.4%. Experimental results combined with DFT+U calculations suggest that nonselective catalytic reduction (NSCR) is the main route for N2O formation in a wide temperature range of 250 ∼ 400 °C. It is stemmed from the fact that the covalent interaction between Cr and V species on the V2O5/TiO2 surface accelerates the conversion of V4+ + Cr6+ → V5+ + Cr3+, leading to a larger proportion of surface V5+. More importantly, surface V5+ is highly related to the redox property of the V2O5/TiO2 catalyst, which is beneficial to NSCR reaction rather than the standard SCR process. The work suggests that to better inhibit the emission of greenhouse gases during the NH3-SCR process, monitoring N2O emission should be included along with the NOx concentrations, especially in complex flue gases.

Effect of pretreatment on the interfacial bonding strength between modified polyolefin and aluminum foil treated with trivalent chromium chemical conversion: Experimental, quantum chemical calculations and molecular dynamics simulation

Good adhesive strength and joint durability are necessary for aluminum (Al)/polymer laminated film for lithium-ion battery packages. A pretreatment method involving alkaline degreasing followed by acid pickling was employed to treat the Al foil surface to facilitate the deposition of trivalent chromium [Cr(III)] conversion coating on the surface. The adhesive strength between propylene-based elastomer grafted glycidyl methacrylate (GMA-g-PBE) and Cr(III)-converted Al foil pretreated with 0.5 M HF pickling was 51% higher than Cr(III)-converted Al foil without pretreatment. Moreover, the effect of different pretreatments on the interfacial bond strength of GMA-g-PBE/Cr(III)-converted Al foil was studied from macroscopic to microscopic perspectives. The results indicate that the pretreatment of 0.5 M HF pickling results in complete coverage of the Cr(III) compounds and the formation of a thicker Cr(III) conversion coating on the Al foil compared to other pretreatments. A higher content of Cr(III) compounds results in an increased surface free energy of Cr(III)-converted Al foil, improving the wettability of adhesive melt on the substrate and enhancing the adhesion strength. Moreover, quantum chemical calculations and molecular dynamics simulations were used to investigate the interface bonding mechanism, and the results indicate that GMA in the adhesive exhibits a higher binding energy with Cr(III) oxides and hydroxides compared to Al oxides and hydroxides.

Influence of Doped Detonation Nanodiamonds on the Physical and Chemical Properties of Electrochemical Chromium Coatings

Chromium deposition process regularities are analyzed in the standard chromium plating electrolytes, with and without detonation nanodiamonds additives modified with boron, phosphorus (DND-boron, phosphorus-DND) at a temperature of 50º to 55ºC while stirring the solution and without. It was studied by method of recording the partial polarization curves the concentration effect of additives DND-boron (in the range of 2,5 ÷ 10 g/l) on the kinetics of the chromate ion partial and full reducing. It has been shown that increasing the concentration of DND-boron leads to inhibition of the reaction Cr (VI) → Cr (III) and Cr polarization curves shift reaction (VI) → Cr (0) to a negative potential on the magnitude of 40-70 mV. While stirring the electrolyte chromium deposition occurs at more positive potentials than in quiescent electrolyte. Dependence of the electrode potential on the current density logarithm in all cases are linear with a slope close to 120 mV, indicating a limiting step of attaching the first electron. Mechanism of deposition of chrome in the presence of boron-DND does not change. Shiny, smooth, uniform coatings are deposited in electrolytes with DND-boron additives. Increased polarization in the chromium precipitation of electrolytes with DND-boron causes a change in precipitation structure, and as a consequence an increase in microhardness of chrome coatings from 955 kgf/mm2 for pure chromium to 1430 kgf/mm2 for chromium with embedded DND-boron nanodiamond particles. Wear resistance is increased: using DND-TAN - 2-3 times compared to standard chrome plating, using DND-phosphorus - in 3 times in comparison with DND-TAN, and using DCS (Si), doped silicon, wear is not detected (under the test conditions).

Computational Modeling for Cr and S Poisoning Pathways on La0.6Sr0.4Co0.2Fe0.8O3 Surfaces

Perovskite oxygen electrode degradation caused by cation segregation sets the limit of performance and lifetime of solid oxide fuel cells (SOFC) [1][2]. For the state-of-art perovskite oxygen electrode, (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ (LSCF), the commonly known degradation mechanism is through Sr segregation, which can be further poisoned by Cr and as well as by S impurities to form insulating layers, limiting the oxygen evolution reaction (ORR) [3][4]. In order to advance our understanding of Cr and S poisoning pathways on LSCF surfaces, we will combine ab initio density functional theory (DFT) reaction energetics, defect chemistry, and microkinetic modeling to establish a quantitative model to find the deposition reaction on different termination slabs. To predict the reaction mechanism and kinetics of Cr and S poisoning reactions, we will study CrO3 and SO2 molecules deposition pathways on pristine LSCF, and surface-modified (eg. Hf, Zr, Pr, Nd, Ce surface-doped) LSCF slabs. I will correlate adsorption energies with LSCF surface characteristics to explain the origin of the deposition, and use these characteristics to evaluate the effectiveness of the surface infiltration. Ab initio molecular dynamics (AIMD) will be applied at different ensembles to investigate further steps of the reaction, and show how the surface modification will inhibit poisoning reactions. These findings will help to guide the design of better performance and more durable oxygen electrodes for SOFCs.[1] Neagu, D., Tsekouras, G., Miller, D. N., Ménard, H., & Irvine, J. T. (2013). In situ growth of nanoparticles through control of non-stoichiometry. Nature Chemistry, 5(11), 916–923.[2] Lee, K. T., & Wachsman, E. D. (2014). Role of nanostructures on SOFC performance at reduced temperatures. MRS Bulletin, 39(9), 783–791.[3] Jiang, S. P., & Chen, X. (2014). Chromium deposition and poisoning of cathodes of solid oxide fuel cells – a review. International Journal of Hydrogen Energy, 39(1), 505–531.[4] Chen, K., & Jiang, S. P. (2020). Surface segregation in solid oxide cell oxygen electrodes: Phenomena, mitigation strategies and electrochemical properties. Electrochemical Energy Reviews, 3(4), 730–765.

ВІДНОВЛЕННЯ ШТОКІВ СИЛОВИХ ГІДРОЦИЛІНДРІВ АВТОМОБІЛІВ ЛЕКТРОЛІТИЧНИМ ХРОМУВАННЯМ

The quality of the repair of parts of military equipment and the increase of their service life largely depends on how it is organized and in what ways the restoration of malfunctioning or damaged parts is carried out. To restore the full functionality of the damaged parts, it is necessary to return them to their initial dimensions, geometric shape, hardness, corrosion resistance and other properties. One of the progressive methods of restoring the working rods of hydraulic cylinders is the application of electrolytic coatings on their working surface. The purpose of the study is to improve the method of restoration of hydraulic cylinder rods by electrolytic chroming with the aim of intensifying the process, improving operational properties and obtaining electrolytic chromium deposits of uniform thickness on the restored rods. The scientific and practical direction of the work consists in the fact that for the first time the technology of process intensification, improvement of the quality of coatings and obtaining of electrolytic chromium deposits uniform in length with the use of an ejector anode design has been considered. The research methodology is to identify the influence of the chrome plating process parameters on the uniformity, microhardness and microcracking of chrome coatings made of universal (250 г/л – СrO3; 2,5 г/л – H2SO4) та кріолітового (10 г/л – Na3AlF6; 250 г/л – СrO3; 2,5 г/л – H2SO4) of electrolytes by the ejector method. The results of the study are the establishment of the dependence of uniformity, microhardness and microcracking on the parameters of the ejector chromium plating process in standard and cryolite electrolytes and the determination of the optimal temperature and current density for use in restoring the rods of hydraulic cylinders of military equipment. The value of the conducted research is that for the first time an ejector anode is used as a positive electrode, which ensures obtaining high-quality and uniform electrolytic coatings directly in the chrome plating bath. Anode-ejector provides height-adjustable suspension suction of gaseous products of electrolysis and renewal of electrolyte in the interelectrode space due to the ejector effect in the anode tubes when the electrolyte is passed under pressure in the jet tubes. Keywords: stom density, anode-cathode distance, uniformity, cracking, microhardness, electrolyte temperature, anode-ejector.

An investigation of Cr vaporization from SUS430 metallic interconnect and deposition on (La,Sr)MnO3 cathode of intermediate temperature solid oxide fuel cells

In solid oxide fuel cells (SOFCs), chromium deposition and poisoning of metallic interconnect is one of the most important issues in the electrochemical activity and stability of the cathode for the oxygen reduction reaction (ORR). In this paper, the chromium evaporation characteristics, oxide scale growth, and deposition of chromium on the ORR on (La,Sr)MnO3 (LSM) cathode are studied at 700–800 °C for SUS430 alloy interconnect material in the intermediate-temperature solid oxide fuel cells. The chromium vaporization rate is measured using the transpiration technique and the surface morphologies, and cross-sections of oxide scales are examined by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The results indicate that chromium volatilization is correlated with the composition and morphology of the oxide scale, the Cr volatilization process presents two stages according to the structural evolution of the oxide scale. In addition, deposition and poisoning of Cr species released from metallic interconnect on the LSM cathode are studied and the formation of MnCr2O4 phase on the LSM backbone degrades the ORR electrochemical activity, causing the increase of overpotential of the cathode. The results obtained give insight into the mechanism of the Cr poisoning effect in intermediate-temperature.

Specific Morphological Features of the Surface of Chromium Coatings Obtained in Electrolytes with Organic Additives

At the present time, the electrodeposition of chromium metal coatings of sufficient thickness and quality is possible only from chromium plating electrolytes containing chromic acid. The authors investigated the effect of the composition of chromium plating electrolyte on the quality of the resulting metal coating. It has been demonstrated that the introduction of organic additives, of gallic acid in particular, leads to significant changes in the surface of the metal deposit and to a decrease in its hardness. Assumptions have been made about the influence of organic additives on the metal deposition process. The experimental data on the content of gases in the chromium deposits obtained from electrolytes with gallic acid additive and without it have been presented.

Optimizing the parameters of microbial fuel cells using response surface methodology to increase Cr(VI) removal efficiency and power production

Cr(VI) is present naturally as Cr2O72- and its negative charge repels electrons (e-), preventing direct reduction to Cr(III). The Cr(VI) reduction process consumes H+ , suggesting that conventional Cr(VI) reduction techniques a strictly require a low pH, increasing their cost. Therefore, the development of a process that enables Cr(VI) reduction at neutral pH conditions is of interest. In this work, Cu(II) was used as an electron shuttle medium in a microbial fuel cell (MFC). The effects of MFC operating conditions, such as Cu(II)/Cr(VI) ratio, substrate (sodium acetate) concentration and external resistance on the power density (PD) and Cr(VI) removal efficiency were investigated using the response surface methodology (RSM). The maximum Cr(VI) removal efficiency (73%) and power production capacity (30.57 mW/m2) were achieved under pH-neutral conditions with a Cu(II)/Cr(VI) ratio of 1.65, a substrate concentration of 1.36 g/L, and an external resistance of 1360 Ω. The Cr(VI) removal efficiency of the MFC system without added Cu(II) was only 43%, and the power production capacity (15.85 mW/m2) was only half of that under optimal conditions. The removal efficiency of Cu(II) was 100% after seven days. Chromium and copper deposits were observed on the cathode surface, indicating that Cu(II) was deposited on the cathode surface following Cr(VI) removal, eliminating the secondary contamination that is caused by the addition of excess Cu(II). An RSM-optimized MFC system exhibits improved chemical oxygen demand removal, Coulombic efficiency and normalized energy recovery (NER). Its NER is at least 1.5 times higher than that of an unoptimized MFC system, indicating that the MFC most efficiently converts substrates into electrons when the operating conditions are optimized. This work demonstrates that Cu(II) plays a critical role as an electron-shuttle mediator in the removal of Cr(VI). The electron transfer function of Cu(II) increases the efficiency of the reduction that involves Cr(VI), electrons and H+, and eliminates the cost of adding acidic agents, as required in the conventional method in wastewater treatment. The obtained Cu(II)/Cr(VI) ratio is used to determine the maximum amount of Cr(VI) that can be removed by a scaled-up MFC system.

An Estimation of Local Residual Stresses in Amorphous and Crystallized Trivalent Chromium Coatings

Hard chromium coatings have demonstrated their performance for several decades, particularly for their wear and corrosion resistance properties. However, the traditional process using chromium trioxide (CrO3) is very toxic and is intended to disappear in the European Union by 2024, thanks to the REACH regulation. This study aimed to determine the residual stress of amorphous chromium deposits elaborated from baths containing trivalent chromium ions. However, the amorphous structure of these deposits does not allow the determination of residual stresses by conventional means. In this study, we propose adapting a recent method called “FIB-DIC”, which is not limited by the material’s crystalline structure compared to the classical X-ray diffraction (XRD) analysis. The method is based on the measurement of relaxation-induced displacement fields following the ablation of material on a very local scale. The results obtained by the classical (XRD) and the FIB-DIC method on crystallized heat-treated Cr(III) deposits are 296 ± 45 and 377 ± 275 MPa. Then, the FIB-DIC technique allowed us to evaluate a residual stress level of 479 ± 359 MPa for amorphous trivalent chromium coating, which has never been performed before.