Chromium Oxide Layer Research Articles

Formation of a Calcium Phosphate Layer with Immobilized Cobalt Chromite Nanoparticles on Cobalt−Chromium Alloy by a Laser-Assisted Biomimetic Process

The biocompatibility and osteoconductivity of metallic biomaterials can be achieved by calcium phosphate (CaP) coating. We recently developed a laser-assisted biomimetic (LAB) process for rapid and area-specific CaP coating on several materials. In the present study, the LAB process was applied to cobalt–chromium (Co−Cr) alloy, a metallic biomaterial widely used in orthopedic and dental applications. The LAB process was conducted by irradiation of unfocused pulsed laser light onto the substrate immersed in supersaturated CaP solution. The LAB-processed substrate formed CaP on the irradiated surface within only 5 min and was coated with a micron-thick CaP layer within 30 min by the effects of laser-induced surface modification and heating. Ultrastructural analysis with transmission electron microscopy revealed that the resultant CaP layer was integrated with the underlying substrate through two intermediate layers, an upper chromium oxide layer and a lower Co-rich (Cr-deficient) alloy layer. The CaP layer was loaded with a large number of cobalt chromite (CoCr2O4) nanoparticles. The results obtained offer new insights into the mechanism of CaP coating in the LAB process and future applications of LAB-processed Co−Cr alloys.

Ba0.5Sr0.5Co0.8Fe0.2O3−δ-Sm0.2Ce0.8O1.9 carbonate perovskite coating on ferritic stainless steel interconnect for low temperature solid oxide fuel cells

Ferritic stainless steel interconnect at a high temperature and a prolonged operating time is exposed to severe conditions, such as the overgrowth of chromium oxide layer on an interconnect and cathode chromium poisoning due to chromium oxide migration. In this study, a protective Ba0.5Sr0.5Co0.8Fe0.2O3−δ-Sm0.2Ce0.8O1.9 carbonate (BSCF-SDCC) perovskite coating was developed on SUS 430 stainless steel through electrophoretic deposition and subsequently sintering to overcome these problems. BSCF-SDCC coating layer was sintered from 550 °C to 750 °C and examined in terms of its crystalline phase, carbonate bonding and microstructure. Area specific resistance (ASR) was tested at each sintering temperature of BSCF-SDCC coating by using a two-probe DC technique during oxidation at 600 °C. Afterwards, the microstructure was analyzed to ensure the endurance of coating characteristics and determine chromium diffusion during oxidation. Carbonate bonding in BSCF-SDCC decreased when sintering temperature increased. The microstructure of the BSCF-SDCC coating sintered at 550°C-650 °C was uniform and dense, but a crack was observed in the coating sintered at 700 °C and 750 °C. The crystalline phase of BSCF-SDCC was verified except the coating sintered at 750 °C, indicating the secondary phase formation of BaCO3. After 500 h of oxidation, the BSCF-SDCC coating sintered at 550°C-650 °C was achieved below the required 0.1 Ωcm2, whereas the coating sintered at 600 °C exhibited the lowest ASR of 0.073 Ωcm2. The coating microstructure remained dense, compact and uniform after thermal oxidation. Therefore, a protective BSCF-SDCC coating for interconnects was successfully developed at low temperatures (400°C-600 °C).

Ion transport mechanisms in the passive film formed on 304L stainless steel studied by ToF-SIMS with 18O isotopic tracer

The ion transport in the pre-formed passive film on 304L stainless steel surface has been investigated by in situ ToF-SIMS with isotopic tracer. The passive film, formed electrochemically in sulfuric acid, has a bilayer structure with outer iron oxide and inner chromium oxide layers. Further exposure of the passive film to 18O2 gas (isotopic tracer) at 300 °C reveals that outward cation diffusion is the governing ion transport mechanism for the oxide growth. The parabolic rate constant for the oxide growth was determined. The cation diffusion coefficient is found to be markedly higher than the oxygen diffusion coefficient.

Effect of Ligand-Complex Interactions on the Electrodeposition of Mixed Chromium Metal-Carbide-Oxides from Trivalent Chromium Electrolytes

Electrolytic chromium coated steel (ECCS) is packaging steel coated with a thin layer of chromium with an outer layer of chromium oxide. This coating system provides corrosion protection in addition to good adhesion properties due the outer oxide layer. The coating for ECCS is deposited via a hexavalent chromium electrolyte which has been found to be an environmental and health hazard and is therefore subject to restrictions under REACH legislation. A new coating process based on trivalent chromium chemistry has therefore been developed.According to prior studies, coatings comparable in terms of corrosion resistance to those achieved with the traditional Cr(VI)-based process have been produced with this process [1]–[4]. However, at present there is limited understanding of the mechanism and kinetics of electrodeposition from trivalent chromium based electrolytes. This knowledge is key to optimize the process design for industrial plating lines. In the present study, we investigate the effect of the chemistry of the Cr(III) complex – as determined by the relative concentration of the formate complexing agent and temperature – on the electrodeposition of mixed chromium metal-carbide-oxide coatings on low carbon steel in a rotating cylinder electrode (RCE) setup.In this study, low carbon steel samples are electroplated in an aqueous Cr(III) based electrolyte bath with a deposition time of 0.8 s with applied current densities ranging from 20 to 90 A dm-2. The pH of the electrolyte is maintained at 2.6. A rotation speed of 776 RPM is used. SEM and XPS analysis is also performed to determine the effect of the above parameters on the microstructure and composition of the deposits. The amount of Cr deposited is determined using XRF measurements. Relative chromium metal, oxide and carbide contents are determined via XPS analysis. UV-Vis spectra of each of the electrolytes are also measured.Optical surface analysis shows that of the three regimes distinguishable as a function of current density [2], homogeneous, bright coatings are deposited in regime II (Figure 1). The current range over which acceptable coatings are deposited is significantly wider with higher relative ligand concentrations. Lower applied currents are required with lower bath temperatures. Increasing the chromium ion concentration (at a fixed relative ligand concentration) results in increased Cr metal deposition and an associated decrease in the carbide content of the coating. At higher bath temperatures, carbide formation is favoured. Results also indicate a threshold ligand-to-complex ratio at ~2.0 [HCOO-]/[Cr3+] above which a bright, homogeneous coating is deposited. This threshold corresponds with UV/Vis results which indicate the formation of a new complex species in the electrolyte at that ratio (Figure 2). Figure 1

Bio-Based Coatings for Food Metal Packaging Inspired in Biopolyester Plant Cutin.

Metals used for food canning such as aluminum (Al), chromium-coated tin-free steel (TFS) and electrochemically tin-plated steel (ETP) were coated with a 2–3-µm-thick layer of polyaleuritate, the polyester resulting from the self-esterification of naturally-occurring 9,10,16-trihydroxyhexadecanoic (aleuritic) acid. The kinetic of the esterification was studied by FTIR spectroscopy; additionally, the catalytic activity of the surface layer of chromium oxide on TFS and, in particular, of tin oxide on ETP, was established. The texture, gloss and wettability of coatings were characterized by AFM, UV-Vis total reflectance and static water contact angle (WCA) measurements. The resistance of the coatings to solvents was also determined and related to the fraction of unreacted polyhydroxyacid. The occurrence of an oxidative diol cleavage reaction upon preparation in air induced a structural modification of the polyaleuritate layer and conferred upon it thermal stability and resistance to solvents. The promoting effect of the tin oxide layer in such an oxidative cleavage process fosters the potential of this methodology for the design of effective long-chain polyhydroxyester coatings on ETP.

Graphene as interface modifier in ITO and ITO-Cr electrodes

We explore graphene as interface modifier for electrodes in optoelectronic organic devices by measuring the electrical properties of ITO/graphene and ITO/Cr/graphene. For this purpose, exfoliated graphene (EG) was electrochemically synthesized and deposited by spray-pyrolysis. The built-in voltage (Vbi) values were 450 mV for the ITO/CuPc/Al reference, 750 mV for ITO/Cr/graphene/CuPc/Al and 1000 mV for ITO/graphene/CuPc/Al device structures. From these results, we estimate the work functions as 3.20 eV, 3.45 eV and 4.75 eV for ITO/EG, ITO/Cr/EG and ITO. To understand how the work function changes, we carried out first-principles calculations based on density-functional theory (DFT) where Cr work function (~4.2 eV) is not modified by the deposition of pristine graphene; however there is a substantial increase (from 4.2 eV to 5.2 eV), upon deposition of graphene oxide (GO), resulting from a complete transfer of O atoms from the GO sheet to the Cr surface forming a thin layer of chromium oxide.

Oxidation studies on nickel-base superalloy 617 OCC

Nickel-base superalloy 617 OCC has been indigenously developed for potential use in Advanced Ultra-Super Critical (USC) Power Plants. Hot corrosion is one of the serious issues associated with superheater and reheater tubes in the boiler part of the USC power plant. To understand the high temperature corrosion processes coming into play, it is useful to have a good understanding of the oxidation behavior of the alloy at the same temperature in ambient air environment. The present study reports, how the Alloy 617 OCC behaves in laboratory air environment at 700 °C. Studies were carried out at intervals of 500 h for a cumulative exposure time of 5000 h. Thermogravimetry, XRD of the corroded surface, SEM/EDAX analysis of corroded surface and cross-sectional surface were carried out after each of the 10 exposure times. Thermogravimetry revealed that there was essentially no weight change of the test specimen over the entire exposure time range. XRD revealed that chromium oxide is essentially the only corrosion product. SEM/EDAX and XRD of the corroded surface showed the progressive increase in the extent of chromium oxide formation on the surface. A well-developed chromium-depleted region was seen below the chromium oxide layer in the X-ray mapping studies. The present research showed that considerable levels of nickel and cobalt occur above the chromium oxide layer at the surface. There is evidence that metallic agglomerates form above the chromium oxide layer. Titanium present in the superalloy gets preferentially oxidized and gets into the chromium oxide layer at the surface. Preferential surface oxidation of aluminum was also noticed. There was evidence for internal oxidation of aluminium at long exposure times. The above findings will be presented and discussed, bringing out the oxidation mechanisms coming into play for 617 OCC at 700 °C.

Investigation of oxidation and electrical behavior of AISI 430 steel coated with Mn–Co–CeO2 composite

Ferritic stainless steels, under the working conditions of solid oxide fuel cells, form a chromium oxide layer. This layer has a low electrical conductivity and consequently reduces the efficiency of these energy converters. An action to improve the properties of the connecting plates is to use a conductive and protective layer of coating. In this study, AISI 430 stainless steel was coated with Mn–Co–CeO2 through electroplating technique. To evaluate the oxidation behavior, isothermal and cyclic oxidation tests were used at 800 °C. Area specific resistance (ASR) of uncoated and coated specimens was also compared as a function of time during oxidation at 800 °C. Coating microstructure and oxidized samples were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) device. In isothermal oxidation, uncoated samples had more weight gain than the Mn–Co–CeO2 coated samples. The coating layer improved oxidation resistance by limiting the diffusion of chromium cation and oxygen anion. The cyclic oxidation results showed that the Mn–Co–CeO2 coated samples had a very good resistance to cracking and spallation. Also, the results of ASR showed that formation of MnCo2O4 and MnFe2O4 spinels and also the presence of CeO2 resulted in reduction of area specific resistance. ASR for samples coated with Mn–Co–CeO2 and uncoated samples was 12.4 mΩ.cm2 and 38.7 mΩ.cm2, respectively after 200 h of oxidation at 800 °C.

High temperature oxidation performance of Ni-Cr-Ti and Ni-5Al coatings

In the present investigation, the Ni-Cr-Ti and Ni-5Al coatings have been successfully deposited on T22 and T91 steels and achieved coating thickness of 250–300 µm using wire arc spray process. The coated samples were exposed to high temperature air oxidation environment under cyclic condition for 50 cycles at 900 °C, where the uncoated and coated samples were heated for one hour followed by 20 min cooling in air. The oxidation kinetics of bare and coated boiler steels have been established with the aid of weight change measurements. The surface and cross sectional analysis of coated samples before and after oxidation has been carried out using SEM/EDS and XRD analysis. It has been found from the results that the coated samples have shown high oxidation resistance in comparison to bare steels. Ni-Cr-Ti and Ni-5Al coated T91 steel offered highest oxidation resistance than the coated T22 steels, based upon weight change data. This may due to combined effect of highest hardness and presence of strong chromium oxide layer to combat oxidation.

A typical super-heater tube leakage and high temperature corrosion mechanism investigation in a 260 t/h circulated fluidized boiler

Aiming to explore the high temperature corrosion mechanism in a 260 t/h circulated fluidized boiler, a section of bursting super-heater tube was cut down and the scanning electron microscope relevant characterization analysis was conducted. Results show that the major compositions in the corrosion products are iron oxide such as Fe2O3, Fe3O4 and FeCr2O4 rather than sulfide, occupying a rough 70% mass ratio. The corrosion type is not typical H2S corrosion but salt corrosion. The sodium sulfate and sodium chloride are both found covered on the super-heater tube surface, but the sodium sulfate is the major corrosion culprit. Line scan results show that the layered structure of two oxidation layers are obviously observed. The chromium is enriched in the inner layer with a depth of 572 μm while the iron is full of the whole oxidation layer with a 1017 μm depth. The chromium oxide layer is compact and can diminish the corrosion rate. The iron oxide layer is loose and porous and can supply the transfer path to the oxygen medium. To alleviate the high temperature corrosion, thermal spay coatings, aluminized steel tube, coal quality control etc. these measures are suggested and put forward.

The Ability of PVD Chromium (III) Oxide Films to Inhibit the Corrosion-Driven Cathodic Delamination of Organic Coatings from the Surface of Mild Steel

This paper describes a systematic study into the role of metallic chromium and chromium (III) oxide films of varying thickness in slowing or preventing the corrosion-driven cathodic disbondment of an organic overcoat applied to chromium/oxide coated steel. A graded wedge of chromium metal or chromium (III) oxide is applied to a steel substrate using physical vapour deposition (PVD) in conjunction with a stepping motor driven sliding shutter arrangement. An overcoat of electrically insulating polyvinyl butyral (PVB) lacquer is then applied and this acts as model organic coating. Corrosion is initiated from an artificially created coating defect, penetrating to the steel substrate, though the introduction of an aqueous sodium chloride electrolyte. Scanning Kelvin probe (SKP) potentiometry is then used to follow the resulting kinetics of PVB coating delamination in air at high relative humidity. The variation in layer thickness across the PVD wedge allows for a high-throughput investigation of the effect of the layer thickness for both metallic chromium and chromium (III) oxide on the rate of corrosion driven cathodic coating delamination, as shown schematically in the figure below. Varying chromium metal layer thickness between 100 nm and 1000 nm produced very little change in the rate of PVB film delamination and the delamination kinetics remained parabolic throughout. Parabollic kinetics are consistent with rate limitation by the mass transport of (sodium) cations through electrolyte layer forming beneath the delaminated coating. Conversely, increasing the thickness of chromium (III) oxide from 10nm to 200 nm (applied over a 500 nm metallic chromium layer), resulted in a significant decrease in rates of PVB delamination. At chromium oxide layer thicknesses ≥ 120 nm delamination kinetics became linear (zero order with respect to time). Linear kinetics are consistent with rate limitation by cathodic electron transfer to oxygen across the chromium (III) oxide layer. For chromium (III) oxide thicknesses of 200 nm PVB delamination was prevented over the entire 48 hour experimental time period. This level of inhibition is comparable to the protection provided by electroplated hexavalent chromium/ hydrated chromium oxide (ECCS) material used in packaging steel products. These finding indicate the ability of PVD to produce corrosion resistant coatings of controlled thickness and composition and provides relevant information regarding the likely relative importance of metallic metal and chromium (III) oxide in potential alternatives to coatings produced using hexavalent chromium. Figure I. Schematic representation of: a) the process by which a wedge of chromium metal or chromium (III) oxide is formed using a sliding shutter mechanism and b) how the PVB overcoated wedge sample is oriented with respect to the cathodic delamination cell. Figure 1

Visualization and characterization of localized outgassing position on surface-treated specimens: Chromium oxide layer on stainless steel

Abstract Hydrogen outgassing from a metal surface and a coated metal surface was visualized by two-dimensional mapping of hydrogen ions desorbed upon scanning electron beam irradiation. The samples used were stainless steel covered with a dense chromium oxide layer, and a reference surface of stainless steel. The coating layer was made by using the segregation phenomenon of the metal. Outgassing of hydrogen was detected from the holelike defects on the treated surface. However, hydrogen was not released from all the holelike defects seen in the SEM image. The outgassing positions were positions without chromium, but not all areas without chromium and/or oxygen coincided with outgassing positions.

A comparative study on microstructure and properties of Ti(C,N)-based cermets with the various Cr doping methods

In this work, the effects of chromium doping methods on the microstructures and properties of Ti(C,N)-based cermets were investigated systematically. The results showed that the existence state of Cr element in the cermet was influenced by the different doping methods. The additive pure Cr powders might cause the appearance of Cr particles and solutions in the binder phase of cermets. However, with the addition of NiCr powders, the Cr element might distribute in the binder phase of cermet. The Cr3C2 addition could make Cr element disperse in the rim and binder phase. Moreover, the Cr atoms dissolved into binder phase might have the solid solution strengthening effect on the binder phase, which increased the hardness of cermets. The Cr element in binder phase could improve the oxidation resistance of cermets owing to the existence of chromium oxide layer in the internal oxidation region. Furthermore, the diffusion process of Mo atoms to the surface during oxidation was prevented by the dissolved Cr element in the binder phase, which led to the increased bonding strength between oxidation layer and unoxidized substrate. In addition, a larger amount NiCr powder addition had the excellent reinforcing effect on the corrosion resistance of cermets due to the appearance of stable chromium oxide film on the binder phase.

Solving an ancient chrome-plating mystery

In 1974, a Chinese farmer found fragments of a crushed terra-cotta warrior while digging a well. That find led archaeologists to unearth over 6,000 terra-cotta figures guarding the tomb of Emperor Qin. And all those warriors needed weapons—weapons that have remained remarkably well preserved for over 2,000 years. Previous analysis found layers of chromium oxide on the blades and spears of the warriors, leading many to suggest that ancient Chinese manufacturers used a form of chrome plating to protect the bronze weaponry. New research suggests a different source (Sci. Rep. 2019, DOI: 10.1038/s41598-019-40613-7). Researchers at University College London and the Emperor Qin Shihuang’s Mausoleum Site Museum found that the chromium is mainly located where the metal would have connected to handles, shafts, fittings, and fasteners. Further analysis revealed that the lacquer on those parts was the source of the chromium. The exceptional preservation, the researchers say, is due to the

Sublimation of advanced tungsten alloys under DEMO relevant accidental conditions

Tungsten (W) is deemed as the main candidate for the first wall armor material of future fusion power plants such as DEMO. Advantages of W include a high melting point, low erosion yield, low tritium retention, and a high thermal conductivity. One issue concerning W is the oxidation resistance in case of a loss-of-coolant accident with simultaneous air ingress. The major challenge in such a scenario is to suppress the sublimation which is responsible for a release of radioactivity. This work studies an alloy containing tungsten (W), 12 weight % chromium (Cr), and 0.6 weight % yttrium (Y) in DEMO-relevant conditions: a temperature in the range of 1100 K to 1473 K in humid air. The sublimation rates are measured for the first time in humid air. Tungsten oxide sublimates at a rate of 1.4 × 10−4 mg cm−2 s−1 at 1273 K in humid air. At the same conditions the alloy suppresses sublimation by more than one order of magnitude as compared to that of pure W. This suppression is achieved due to the formation of a protective chromium oxide layer on the surface of the sample. Details about the protection mechanisms are presented and discussed. Testing is performed for up to 10 days.

Influence of Boron Addition on the Microstructure and the Corrosion Resistance of CoCrMo Alloy

Cobalt-based alloys are extensively used in orthopedic applications for joint replacements due to their wear and corrosion resistance. Corrosion, however, is often associated with fatigue failure in these orthopedic devices. In this study, the effect of boron addition on the corrosion behavior of CoCrMo alloys was studied using linear polarization resistance, potentiodynamic polarization curves, electrochemical impedance spectroscopy, and cyclic voltammetry. The samples were analyzed under as-cast and heat treatment conditions after 21 days of immersion in phosphate-buffered saline (PBS) solution at 37 °C. The boron addition increased the particle content, while the heat treatment promoted enlargement and even distribution of the precipitates throughout the structure. The corrosion resistance was improved by both boron and heat treatments. The best performance was observed for a heat-treated alloy having a very small amount of boron, which had an increased resistance to corrosive attack. Such behavior was attributed to the homogenized microstructure achieved by boron and heat treatment that helped to form a stable passive layer of chromium oxide which endured the 21 days of immersion.

Corrosion Behavior of Mechanically Alloyed SUS304L with Zirconium Addition in High-Temperature Water

A mechanically alloyed austenitic stainless steel (MA304LZ) was produced from pre-alloyed SUS304L powder with a small amount of zirconium addition. Coupon-type specimens of MA304LZ and SUS304L steels were subjected to hot water at 300 ℃/25 MPa and supercritical pressurized water (SCW) at 500 ℃/25 MPa for 1000 hr. MA304LZ is significantly less susceptible to corrosion weight gain in SCW than SUS304L which follows the parabolic rule between weight gain and elapsing time. The reduction of weight gain in MA304LZ can be attributed to much smaller grains which enhance chromium diffusion through grain boundaries and consequently accelerate the formation of a protective chromium oxide layer.

Surface oxidation effect on deuterium permeation in reduced activation ferritic/martensitic steel F82H for DEMO application

Fuel loss and environmental contamination by tritium permeation through structural materials are critical issues for the establishment of a fusion DEMO reactor. In this study, the effectivity of a chromium oxide layer formed on reduced activation ferritic/martensitic steel F82H as a tritium permeation barrier and its stability under simulated solid/liquid breeder blanket conditions have been investigated. A uniform 100-nm-thick chromium oxide layer was formed by heat treatment at 710 °C for 5 min in 50% argon-50% hydrogen mixed gas with the flow rate of 200 standard cubic centimeter per minute. After exposure to simulated solid breeder blanket conditions, an iron oxide layer and a spinel-type iron-chromium oxide layer formed. In the case of a liquid breeder blanket condition, the chromium oxide layer partly lost at 500 °C for 100 h. The chromium oxide-formed sample decreased deuterium permeation flux by a factor of up to 150. The permeation reduction efficiency deteriorated after exposure to a solid breeder blanket condition due to a change of the chromium oxide layer. However, the chromium oxide formation would play a role to reduce hydrogen isotope permeation even after reduction of the oxide layers.

Enhancement of Hot Corrosion Resistance of Modified 9Cr-1Mo Steel Through Surface Nanostructuring and Pre-oxidation

Nanosize grains of ~ 65 nm were developed with large misorientation angles of grain boundaries in surface region of normalized and tempered modified 9Cr-1Mo steel by ultrasonic shot peening (USSP) with hard steel balls of 3 mm diameter. The surface roughness and the depth of nanostructured surface region were found to increase with the duration of USSP from 0.5 to 5 min. Hot corrosion tests were performed for the Un-USSP and the samples USSPed for the durations of 0.25 and 1.5 min and also for the samples subjected to USSP and subsequently pre-oxidation at 600 °C for 4 h. The hot corrosion resistance at 600 °C under 100% NaCl coating was significantly improved by USSP for 1.5 min and subsequent pre-oxidation at 600 °C for 4 h. The results are discussed in terms of the formation of more uniform and effective protective iron–chromium oxide layer on the USSPed surface from the subsequent pre-oxidation treatment, prior to hot corrosion of the specimens under 100% NaCl coating at 600 °C.

Low Outgas Surface Treatment of Stainless Steel 316L Using Segregated Chromium Oxide Layer

Low Outgas Surface Treatment of Stainless Steel 316L Using Segregated Chromium Oxide Layer