Chromium Deposition Research Articles

Efficacy of Dietary Chromium (III) Supplementation on Tissue Chromium Deposition in Finishing Pigs

The study was conducted to evaluate the efficacy of different forms of trivalent chromium (Cr) supplementation on tissue chromium deposition in finishing pigs. A total of 96 pigs with an initial average body mass 65.57±1.05 kg were blocked by body mass and randomly assigned to four treatments with three replicates. Pigs were offered one of four diets including a control diet or the control diet supplemented with 200 μg/kg chromium from either chromium chloride (CrCl(3)), chromium picolinate (CrPic) or chromium nanocomposite (CrNano) for 40 days. During the trial, all pigs were given free access to feed and water. After feeding trial, eight pigs from each treatment were slaughtered for samples collection. The results showed that supplemental CrNano increased Cr content in blood, longissimus muscle, heart, liver, kidney, jejunum, and ileum (P<0.05). Supplemental Cr from three sources increased Cr excretion from all feces (P<0.05). Urinary Cr excretion was increased by CrNano or CrPic supplementation significantly. These results suggested that chromium nanocomposite exhibited more effective on tissue Cr deposition in pigs, which indicated higher absorption compared with CrCl(3) and CrPic.

An investigation into the tribological performance of Physical Vapour Deposition (PVD) coatings on high thermal conductivity Cu-alloy substrates and the effect of an intermediate electroless Ni–P layer prior to PVD treatment

The use of high thermal conductivity copper alloys in plastic injection moulds provides the benefit of rapid moulding cycles through effective heat transfer. However, copper alloys are relatively soft and wear rapidly so manufacturers are now developing copper alloys with increased hardness and wear resistance. Their wear resistance can be further improved by the deposition of hard coatings such as electroplated chromium, electroless nickel and Physical Vapour Deposition (PVD) coatings. In this paper, the tribological performance of three proprietary high-strength Cu alloys (Ampcoloy® 940, Ampcoloy® 944 and Ampcoloy® 83) coated with PVD CrN and CrAlN coatings has been evaluated. A medium phosphorous content electroless Ni–P (ENi–P) plated layer was also deposited as a pre-treatment to PVD CrN and CrAlN coatings to increase the load support. The effect of this intermediate ENi–P layer was also evaluated. Surface roughness and instrumented hardness measurements were used to characterise all coated systems in both plated (i.e. with the intermediate ENi–P coating) and standard (i.e. unplated) conditions. Scratch tests were also performed to evaluate the effect of the ENi–P on PVD coating adhesion to Cu alloy substrates. The tribological behaviour of PVD-coated Cu alloy systems was evaluated by pin-on-disc wear tests and ball-on-plate impact tests. Results demonstrate that the ENi–P layer improves the load support for PVD coatings on Cu alloys, thereby improving their tribological performance. However, for PVD-coated Cu alloys in the standard condition, the Cu alloy substrate type plays an important role in the tribological performance of PVD coatings. For instance, PVD CrN coatings were more suited to a certain Cu alloy type whilst CrAlN to the other two types.

Chromium deposition and interfacial interactions of an electrolyte–air electrode-interconnect tri-layer for solid oxide fuel cells

In solid oxide fuel cell operation, electrical current plays an important role in the air electrode interaction with electrolyte and interconnect and long-term cell performance. In this study, (La 0.8Sr 0.2) x MnO 3 (LSM) air electrodes with different stoichiometries ( x = 0.95, 1, and 1.05) are fabricated on the surface of yttria stabilized zirconia (YSZ) and then sandwiched with AISI 441 stainless steel interconnect. The simulated half cells are thermally treated at 800 °C for 500 h under a 200 mA cm −2 current density in dry air. YSZ/LSM interfacial interaction and the reaction of volatile chromium species on the LSM surface are characterized. Different LSM stoichiometry leads to different interfacial reactions and Cr deposition amounts. Mn is a critical species for the Cr deposition under polarization. Excessive Mn in LSM lessens the formation of La-containing phase at the YSZ/LSM interface and accelerates Cr deposition. Deficient Mn in LSM leads to extensive interfacial reaction with YSZ, forming more La-containing phase and inhibiting Cr deposition.

Chromium Deposition on Cobalt-Based Alloys by Pack-Cementation and Behaviour of the Coated Alloys in High Temperature Oxidation

Two TaC-strengthened cobalt-based alloys, with compositions Co-10Cr-0.25C-4.4Ta and Co-10Cr-0.5C-8.7Ta (wt.%) underwent Cr-deposition by pack-cementation, followed by heat-treatment to allow Cr diffusing deeper in their sub-surface. Thereafter they were tested for 50 hours at 1200°C in a thermobalance. These alloys were successfully enriched in chromium, with a maximal content on surface of about 30wt.% and a depth of enrichment of several hundreds of micrometers. This allowed a chromia-forming behavior of the cemented alloys despite the 10wt.%Cr of the bulk. This was especially true for the {C,Ta}-richest alloy the oxidation kinetic of which was wholly parabolic and analogous to a Ni-30Cr alloy known for its good behavior in oxidation at 1200°C. The parabolic constants and chromia-volatilization constants were at the same levels of the Ni-30Cr ones. However, the chromium enrichment step, especially the diffusion heat-treatment following the cementation, causes fragmentation and surface fraction reduction of the tantalum carbides which strengthen the alloy.

Development of Chromium and Aluminum Coatings on Superalloys by Pack-Cementation Technique

Austenitic nickel-iron-chromium based superalloys are materials of choice for high temperature applications as they provide high temperature creep resistance associated with a suitable oxidation behavior in the temperature range of 600-1100°C. However, these properties are not sufficient for applications as Steam Methane Reformer (SMR). As a consequence, aluminum and chromium coatings are developed by the pack-cementation technique to improve their corrosion resistance. The oxidation behavior of the coated samples has been carried out in air at 1050°C. Chromium deposition leads to a layer of bcc chromium-iron solid solution. Oxidation tests indicated that a too high chromium concentration induces a too rapid growth of the chromia layer. In the case of aluminum coatings, a layer of -NiAl is formed at the surface of the alloy. It permits a significant decrease of the oxidation rate.

Hexavalent Chromium Reduction and Accumulation by Acinetobacter AB1 Isolated from Fez Tanneries in Morocco

Hexavalent chromium reduction and accumulation by Acinetobacter AB1 isolated from Fez tanneries effluents were tested. The effects of some environmental factors such as pH, temperature, and exposure time on Cr(VI) reduction and resistance were investigated. We found that this strain was able to resist to concentrations as high as 400mg/l of Cr(VI). Moreover, pH 10 and the temperature 30°C constitute favourable conditions to the growth and reduction of Acinetobacter AB1. Complete reduction of Cr(VI) was observed at low initial Cr(VI) concentrations of 50mg/l after 72h of incubation. Furthermore, Transmission electron microscope (TEM) analysis showed morphological changes in AB1 strain due 48H exposure to 100mg/l chromate concentration and revealed circular electron dense (dark black point) inclusion within the cell cytoplasm suggesting chromium deposition within the cells.

Protection of cobalt-based refractory alloys by chromium deposition on surface: Part II: Behaviour of the coated alloys in oxidation at high temperature

A high chromium content, typically 30 wt.%, is generally considered as necessary for cobalt-based alloys to allow them to resist oxidation by hot gases. Cobalt alloys with a bulk poorer in chromium may become resistant against high temperature oxidation if they are enriched in chromium on surface. The aim of this second part of the work is to expose to air at 1200 °C three low-chromium cobalt-based alloys (Co–10Cr, Co–10Cr–0.25C–4.4Ta and Co–10Cr–0.5C–8.7Ta in wt.%), previously enriched in chromium on surface by pack cementation, in order to examine if the applied cementation treatments are enough to ensure a good behaviour for a long time. The initial surface enrichment in chromium of the Ta-containing alloys, characterized by a maximal content on surface of about 30 wt.% Cr and a depth of enrichment of several hundreds of micrometers, gives them a good resistance to oxidation at 1200 °C, despite the very low-chromium content in the bulk. This is also due to the interdendritic TaC carbides which may facilitate outward diffusion of chromium during oxidation as they facilitated its inward diffusion during cementation. In contrast, the CoCr alloy, enriched in chromium in the same conditions did not display a so good oxidation behaviour.

Electrodeposition of chromium coatings from sulfate–carbamide electrolytes based on Cr(III) compounds

We propose an electrolyte based on chromium sulfate (1 mole/liter Cr(III)) and containing both formic acid and carbamide (urea). This electrolyte enables one to get Cr coatings with a thickness of several micrometers. It is shown that the current yield and deposition rate increase as the current density and pH value increase and temperature decreases. We select the optimal conditions of electrolysis under which bright high-quality chromium deposits are obtained. In this case, the deposition rate of the metal varies from 0.5 to 1.5 μm/min. It is shown that the optimal concentration of both formic acid and carbamide is equal to 0.5 mole/liter. The necessity of using certain surface-active substances to prevent the formation of pitting on the surface of the deposit is demonstrated. Moreover, it is discovered that the microhardness of Cr deposits attains its highest values (950–980kg/mm2) for currents with densities of 30–35 A⋅dm−2 and decreases as the pH value and temperature increase. Electrolysis is realized by using titanium–manganese-dioxide anodes and, hence, it is not necessary to separate the cathodic and anodic spaces.

Residual Stresses and Strength of Hard Chromium Coatings

Experimental and numerical investigations have been performed on the relationships between coating parameters, residual stresses, micro-cracks and the near surface strength of electrochemically deposited hard chromium coatings. The experimental investigations included: X-ray measurements of residual and externally-applied stresses; crack density measurements using microscopy; and load-bearing measurements using ball-on-plate tests. The numerical investigations in combination with analytical conclusions focused on the influence of different crack lengths and densities on the effective elastic modulus of the chromium coating and the stress-enhancing or shielding effect of micro-crack networks respectively. The results show that the residual stresses and crack networks are influenced by the current density used during deposition. Coatings with high tensile residual stresses have low crack densities. This correlation is associated with stress relaxation by formation of micro-cracks and, to a lesser extent, to a direct reduction in residual stresses due to the deposition process. The load bearing capacity is dominated by the crack density and can be significantly increased by shot-peening-induced compressive residual stresses. Thus, optimization of hard chromium deposition parameters for applications needing high surface strength should predominantly focus on minimizing the crack density.

Polyethylene glycol이 3가크롬 전기도금에 미치는 효과

The effect of organic additives, polyethylene glycol (PEG), on the trivalent chromium electroplating was analysed in the view point of current efficiency, solution stability and metallurgical structure. It was measured that PEG-containing trivalent chromium solution had about 10% higher current efficiency than pure solution and controlled the micro-crack density of electrodeposits. PEG exhibited profound effect on the solution stability by reducing the consumption rate of formic acid which acts as a complexant to lower the activation energy required for electrochemical reduction of trivalent chromium ions. It was also revealed that the formation of chromium carbide layer was facilitated in the presence of polyethylene glycol, which meant easier electrochemical codeposition of chromium and carbon, not single chromium deposition. Trivalent chromium layer formed from PEG-containing solution was amorphous with local nano-crystalline particles, which were prominently developed on the entire surface after non-oxidative heat treatment.

Chromium Deposition and Poisoning at Ba0.5Sr0.5Co0.8Fe0.2O3-δ Cathode of Solid Oxide Fuel Cells

Chromium deposition and poisoning at Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) cathodes of solid oxide fuel cells are investigated. BSCF cathode shows an excellent and stable performance in the absence of metallic interconnects. However, in the presence of a chromia-forming metallic interconnect performance of the BSCF cathodes degrades quickly. Chromium deposition was observed on the BSCF cathode surface after 1200 min polarization at 900 and 800°C. The Cr2O3/SrO and Cr2O3/BaCO3 oxide couple study indicates that SrCrO4, BaCrO4, and BaCr2O4 start to form at temperatures above 500°C. The results indicate that BSCF cathode is not chromium-tolerant despite its superior activity for the O2 reduction reaction.

The corrosion and wear resistances of magnesium alloy (LZ91) electroplated with copper and followed by 1 μm-thick chromium deposits

The Mg-Li-Zn alloy, LZ91, is a potential material for industrial application owing to its high specific strength. However, the LZ91 has so high chemical reactivity that it is easily corroded in air and an aqueous environment. In this study, an eco-friendly electrodeposition method was proposed to obtain a protective Cr/Cu coating on the LZ91 substrate. That is, the LZ91 surface electroplated a Cu undercoat in an alkaline Cu-plating bath and followed by decorative 1 μm-thick Cr electroplating in a plating bath with trivalent chromium ions. After electroplating, some of the Cr/Cu-deposited specimens were heated with a reduction flame for 0.5 s to increase the hardness of Cr-deposit. The wear resistance of as-plated and flame-hardened Cr/Cu-coated LZ91 specimens was estimated with ball-on-plate wear tester by using a steel-ball counterpart. Whereas, their corrosion resistance was evaluated in a 0.1 M H 2SO 4 solution before and after wear test. Experimental results show that a Cu deposit could be uniformly electroplated on the LZ91 surface by using our proposed electroplating method. The corrosion resistance of LZ91 was markedly improved after decorative 1 μm-thick Cr electroplating. After wear test, the steel counterpart was ground obviously with either as-plated or flame-hardened Cr/Cu-coated LZ91 specimen. According to the results of electrochemical corrosion test, some parts of the Cr deposit were peeled off from worn flame-hardened Cr/Cu LZ91 surface. This reduces its corrosion resistance significantly. On the other hand, the corrosion resistance of as-plated Cr/Cu LZ91 was not changed after wear test. That is, an as-plated Cr/Cu-coated LZ91 specimen could have good corrosion and wear resistance.

Chromium nitride films formed by ion beam assisted deposition at low nitrogen ion energies in comparison to high energies

In ion beam assisted deposition (IBAD), apart from the relative ion irradiation intensity, which is the arrival ratio of impinging ions to deposited atoms (I/A-ratio), the kinetic ion energy E k plays a dominant role. The energy deposited into the growing film by the ions, given by the I/A-ratio and E k, influences the features of the film, such as the phase composition and microstructure, including crystallographic orientation. The influence of the kinetic nitrogen ion energy on chromium nitride films was investigated. Chromium was evaporated and condensed onto silicon wafers at ambient temperature. The growing film was concurrently bombarded with nitrogen ions at 1 kV acceleration voltage. The films were deposited with different chromium deposition rates. They were analyzed for their phase composition by X-ray diffraction, and for the elemental depth profile with secondary ion mass spectrometry. The results are compared with findings from earlier experiments with a high ion energy. It turns out that different ion energies yield different phase compositions of Cr/Cr 2N/CrN, different preferential crystal orientations and different nitrogen distributions in depth.

Simulation for Aberration of Chromium Atomic Beam Focusing and Deposition

The image distortion which comes from aberration is analyzed and the effects on focal line features are also discussed, which are resulted from the spherical aberration, chromatic aberration and beam spread. The simulation results have show that source imperfection, especially the transverse velocity spread, plays a critical role in broadening the feature width.

Control of the optical properties of silicon and chromium mixed oxides deposited by reactive magnetron sputtering

The development of mixed-oxide thin films allows obtaining materials with better properties than those of the different binary oxides, which makes them suitable for a great number of applications in different fields, such as tribology, optics or microelectronics. In this paper we investigate the deposition of mixed chromium and silicon oxides deposited by reactive magnetron sputtering with a view to use them as optical coatings with an adjustable refractive index. These films have been characterized by means of Rutherford backscattering spectrometry, Auger electron spectroscopy, X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy and spectroscopic ellipsometry so as to determine how the deposition conditions influence the characteristics of the material. We have found that the deposition parameter whose influence determines the properties of the films to a greater extent is the amount of oxygen in the reactive sputtering gas.

Protection of cobalt-based refractory alloys by chromium deposition on surface: Part I: Sub-surface enrichment in chromium by pack-cementation and diffusion

The feasibility of surface chromium enrichment by pack-cementation was assessed for different low chromium-containing cobalt alloys, in order to improve their resistance against high temperature oxidation. A binary Co–10Cr alloy, two ternary Co–10Cr–0.5C and Co–10Cr–1.0C alloys and two TaC-containing Co–10Cr-based alloys were elaborated by foundry for the study. 7.5h-long and 15h-long cementations at 1050°C, followed or not by a 75h-long heat treatment at 1200°C were performed on these alloys. Microstructure examinations performed using a Scanning Electron Microscope and concentration profiles using Electron Probe Micro Analysis–Wavelength Dispersion Spectrometry were realized in order to analyze the level of Cr-enrichment of the sub-surface region, with as studied criteria: the nature of the external Cr-enriched zone, the maximal chromium content on surface and the depth of chromium enrichment. The Cr-enrichment of the sub-surface succeeded for the Co–10Cr alloy and for the two tantalum-containing alloys, with the formation of an external metallic zone containing around 30wt.% Cr. In contrast the chromium carbides-containing alloys were effectively enriched in chromium in surface but in the form of a continuous chromium carbide layer which can induce other problems such as spallation and then possible fast oxidation of the denuded alloy. Finally it appeared that only the carbon-free alloys, and the alloys reinforced by carbides more stable than chromium carbides, are potentially able to be successful enriched in chromium in their sub-surface by pack-cementation.

Effect of Strontium Content on Chromium Deposition and Poisoning in Ba1−xSrxCo0.8Fe0.2O3−δ (0.3 ≤ x ≤ 0.7) Cathodes of Solid Oxide Fuel Cells

The effect of strontium content on Cr deposition and poisoning in barium strontium cobalt ferrite electrodes, Ba1−xSrxCo0.8Fe0.2O3−δ (BSCF, 0.3 ≤ x ≤ 0.7), was investigated at 900°C for 20 h with a cathodic polarization of 200 mA cm−2. In contrast to the superb and stable electrochemical performance of the BSCF electrodes without interconnects, electrode polarization resistance and overpotential (RE and η) were found to increase for the O2 reduction reaction on BSCF electrodes in the presence of Fe-Cr metallic interconnects. Most important, the increase in RE and η values, ΔRE and Δη measured after polarized at 200 mA cm−2 for 20 h, increased significantly as the Sr content of the BSCF electrodes was increased, indicating that the Sr content in BSCF electrodes is a governing factor in Cr poisoning. Scanning electron microscopy (SEM) analysis of the BSCF electrodes after the Cr poisoning test at 900°C for 20 h revealed the presence of Cr deposits on the cathode surface. The magnitude of Cr deposits on the electrode surface under the rib of the interconnect is significantly higher than that under the channel of the interconnect. The results in this study indicate that Sr and/or Ba segregation plays an important role in the Cr deposition and poisoning for the O2 reduction on BSCF cathodes, which is closely related to the Ba/Sr ratio of the cathode.

Fabrication of Anti-reflection Structure using Photo-curable Polymer

Antireflection (AR) structure is the most promising nano-scale application for AR film such as flat panel display, mobile phone display and so on. Ultraviolet nanoimprint lithography (UV-NIL) is a potentially powerful tool for such a nanofabrication, thus, we have been established the fabrication method of AR structure film using photo-curable polymer and UV-NIL. The AR structure mold was fabricated by oxygen ion beam irradiation to glassy carbon (GC) surface. This process can obtain large area and uniform AR structure surface easily. The AR structured surface has strong adhesive force, thus, release layer is important. The developed release method is chromium deposition and succeeding fluorinate silnane coupling agent. This release layer enables to transfer during UV-NIL. First, AR structures were replicated on PET film and reflection property was measured. However, interface between AR structured polymer and PET generates interface reflection. To reduce the interface reflection, we have been developed the fabrication method of self-support photo-curable polymer with AR structures. The method is utilizing polyvinyl alcohol (PVA) instead of PET film. PVA is water-soluble material, thus, after the AR structure replication by UV-NIL, PVA was removed by dipping water. The fabricated self-support film is 0.5 % reflectivity at visible light wavelength.

Role of carbon in the chromium deposit electroplated from a trivalent chromium-based bath

Precipitation of fine chromium carbides have been considered to be the hardening mechanism of the anneal-hardened Cr–C deposit for a long time. However, according to this study, precipitation of carbon-based membranes may serve the hardening mechanism for annealed Cr–C deposit. The carbon-based membranes could be extracted from as-plated and annealed Cr–C deposits by etching in a solution of 33vol.% HNO3+67vol.% HCl. The structure of carbon-based membrane transforms from an amorphous carbon to a crystalline diamond-like structure with increasing the annealing temperatures. This leads to obvious increase in the hardness of annealed Cr–C deposits. Based on this mechanism, a hardened surface on Cr–C deposited steel specimens could be achieved by using reduction-flame heating for a short period (~1s).

Effects of chromium poisoning on the long-term oxygen exchange kinetics of the solid oxide fuel cell cathode materials La 0.6Sr 0.4CoO 3 and Nd 2NiO 4

The influence of chromium poisoning on the long-term stability of the oxygen exchange kinetics of the promising IT-SOFC cathode materials La 0.6Sr 0.4CoO 3−δ (LSC) and Nd 2NiO 4+δ (NDN) is investigated in-situ by dc-conductivity relaxation experiments. The as-prepared LSC and NDN samples show high chemical oxygen surface exchange coefficients k chem. After the deposition of a 10 nm thick Cr-layer onto the surface, k chem of LSC decreases to 50% of the initial value. Additional chromium deposition of 20 nm on LSC leads to a further decrease of k chem to 27% of the initial value. In contrast, the effect of a 10 nm thick Cr-layer on k chem of NDN is negligible. Even with additional 20 nm of chromium and a total testing time of 1750 h, the nickelate retains a k chem of 60% of the initial value. X-ray photoelectron spectroscopy (XPS) of the degraded. LSC shows a significantly altered surface cation composition with Sr-enrichment down to 30 nm depth while XPS analysis of the degraded NDN reveals a thin surface zone of approximately 30 nm containing nickel and chromium. In contrast to LSC, the changes in the surface composition of NDN due to Cr-poisoning ultimately had only a minor influence on the surface exchange properties.