Surface Chromium Research Articles

Reusable chromium-coated quartz crystal microbalance for immunosensing

The application of oxidized chromium as a reusable platform for the development of immunosensors is presented. Chromium films were deposited on quartz crystal microbalances to study the affinity interaction between rabbit immunoglobulin G (IgG) and goat anti-rabbit IgG. A covalent approach, based on the silane chemistry, was followed for the grafting of either the rabbit IgG or the anti-rabbit IgG on the silane-modified chromium surface. Next the differences between the deposition of rabbit IgG on immobilized anti-rabbit IgG and the deposition of anti-rabbit IgG on immobilized rabbit IgG were investigated. The chromium layer could be reused between experiments, after the proper removal of the organic layers with piranha etch, obtaining a high repeatability in the steps of the functionalization protocol.

Degradation of Perfluorotrichlorosilane Antisticking Layers: The Impact on Mold Cleaning, Ultraviolet-Nanoimprinting, and Bonded Ultraviolet-Nanoimprint Molds

A reduction of the adhesion between imprint resist and mold is crucial for defect free imprints and is commonly achieved by silane based antisticking layers. Highly stable antisticking layers are required for high throughputs and long imprint mold lifetimes. Hybrid nanoimprint molds avoid the imprint inherent residual polymer layer in UV-assisted nanoimprinting. Such hybrid molds have chemically heterogeneous surfaces of silica and, e.g., chromium oxide regions. The chemical stability of vapor-coated 1H,1H,2H,2H-perfluorodecyltrichlorosilane antisticking layers against acetone, acidic piranha, reactive ion etching and UV-assisted nanoimprinting was investigated. To evaluate the behavior of hybrid mold surfaces, flat silica and antireflective chromium-oxynitride surfaces were used. The antisticking layer on both surfaces was highly chemical resistant against acetone. A continuous antisticking layer degradation with a surface free energy increase of 0.9 mN/m per 10 min piranha treatment and 1.2 mN/m per 10 subsequent UV-assisted imprints was found for silica surfaces. On the chromium surfaces, the antisticking layer quality was much lower than on fused silica and degraded much faster. The surface free energy of silane coated chromium surfaces was increased by 2.3 mN/m after 10 imprints and the antisticking layer was completely degraded after a single 10 min piranha cleaning step. The lower antisticking layer quality on antireflective chromium was attributed to the surface itself. Additionally, the high chemical resistance of the vapor coated silane was used to successfully protect the adhesive joints of cost-efficient, adhesively bonded nanoimprint molds from being degraded by acidic piranha during mold cleaning. This can significantly increase the life-time of such bonded molds.

Degradation of Perfluorotrichlorosilane Antisticking Layers: The Impact on Mold Cleaning, Ultraviolet-Nanoimprinting, and Bonded Ultraviolet-Nanoimprint Molds

A reduction of the adhesion between imprint resist and mold is crucial for defect free imprints and is commonly achieved by silane based antisticking layers. Highly stable antisticking layers are required for high throughputs and long imprint mold lifetimes. Hybrid nanoimprint molds avoid the imprint inherent residual polymer layer in UV-assisted nanoimprinting. Such hybrid molds have chemically heterogeneous surfaces of silica and, e.g., chromium oxide regions. The chemical stability of vapor-coated 1H,1H,2H,2H-perfluorodecyltrichlorosilane antisticking layers against acetone, acidic piranha, reactive ion etching and UV-assisted nanoimprinting was investigated. To evaluate the behavior of hybrid mold surfaces, flat silica and antireflective chromium-oxynitride surfaces were used. The antisticking layer on both surfaces was highly chemical resistant against acetone. A continuous antisticking layer degradation with a surface free energy increase of 0.9 mN/m per 10 min piranha treatment and 1.2 mN/m per 10 subsequent UV-assisted imprints was found for silica surfaces. On the chromium surfaces, the antisticking layer quality was much lower than on fused silica and degraded much faster. The surface free energy of silane coated chromium surfaces was increased by 2.3 mN/m after 10 imprints and the antisticking layer was completely degraded after a single 10 min piranha cleaning step. The lower antisticking layer quality on antireflective chromium was attributed to the surface itself. Additionally, the high chemical resistance of the vapor coated silane was used to successfully protect the adhesive joints of cost-efficient, adhesively bonded nanoimprint molds from being degraded by acidic piranha during mold cleaning. This can significantly increase the life-time of such bonded molds.

Surface layer evolutions of pre-oxidised Fe–30Cr alloy induced by gaseous KCl

This study reports on the evolutions of surface structure and composition of Fe–30Cr alloys that were first oxidised in oxygen atmosphere then followed by an exposure in gaseous KCl environment. After the pre-oxidation treatment at 800°C for 10 h, a continuous, dense and protective chromia scale was produced. During the following exposure in KCl contaminated atmospheres at 650°C, the surface chromia layer was gradually transformed into worm-like potassium chromate textures, which quickly coalesced on the substrate surface along with simultaneous volatility. The protective oxide layer was then severely deteriorated by enhancing cracking, spallation, volatility and porosity. Voluminous iron migrated outward through these defective sites and iron oxide became the dominating reaction products. Both chromate and residual chromia were finally incorporated into the thick and porous iron oxide scale. This process accounts for the major catastrophic destruction of chromia forming materials involving reactions with alkali chloride salts, even at minor amounts.

Aluminium components for marine applications protected against corrosion by organic coating cycles with low environmental impact

Marine propulsion systems, like sterndrive systems, must be protected from corrosion degradation. In particular, in the case of aluminium alloy parts, a protective cycle consisting in a surface pretreatment and an organic coating system are often applied. Traditionally, chromate based pretreatments are often applied on aluminium alloys in aggressive environments for the protective ability of chromate layers, together with the self-healing and adhesion promotion ability. The toxicity of chromium hexavalent is pressed to find new environmentally friendly solutions. In this paper, new results concerning different protective cycles for marine propulsion systems are presented. New surface pretreatments, including zircofluotitanates, chromium(III) treatments and silane layers, were characterised in conjunction with two different organic layers: waterborne paints and powder coatings. All the systems are free from organic solvents and toxic active pigments. By electrochemical measurements and salt spray exposure, it was possible to optimise the protective cycle with low environmental impact for the protection of aluminium components for marine propulsion systems, proving final performance comparable with the traditional systems containing chemicals with high environmental impact.

Micro‐Raman characterization of laser‐induced local thermo‐oxidation of thin chromium films

AbstractMicro‐Raman spectroscopy was applied to the characterization of the chemical composition and topography of protective oxide layers formed under atmospheric conditions on the surface of thin chromium films. Strips of the layers were produced by local thermal heating using focused sub‐picosecond pulsed laser radiation. It is shown that a CrO2 layer is initially formed on the chromium surface at low light exposures. Increasing the exposure results in the transformation of the CrO2 layer to Cr2O3. The influence of the etching conditions on the composition and thickness of the oxide layers is investigated. The topography of the CrO2 and Cr2O3 oxide layers in transverse sections of the strips is demonstrated by the Raman mapping. Copyright © 2011 John Wiley & Sons, Ltd.

Mechanism of Chromium Oxide Formation in Cobalt–Chromium–Molybdenum (F75) Alloys Prepared Using Spark Plasma Sintering

AbstractMetallic implants are known to have higher wear rates compared to ceramic. This causes more wear debris to be produced and results in the release of toxic metal ions to the surrounding areas. The strengthening mechanism in cobalt based cast orthopedic alloys depends upon carbides present in the microstructure, but these cause problems when dislodged between articulating surfaces, accelerating wear by abrasion and fretting. Thus, in order to improve the performance of these implants a novel method of processing the alloys, namely by spark plasma sintering (SPS) of fine powders, has been used as it generates hard oxides and not carbides in the microstructure. The oxide in the SPS processed alloy is identified as chromium oxide formed by a redox reaction between cobalt oxide found on the surface of cobalt particles and chromium. The oxygen associated with the cobalt powder is displaced and combines with the chromium during SPS. This oxide in the microstructure of the alloy can be more beneficial than carbides due to its higher hardness, resulting in lower wear rates and less wear particles. With the oxide in the microstructure, the hardness of the alloy becomes closer to that of ceramics. Also its lower density enables the alloy to be lighter. The chemical stability of the oxide ensures that it remains intact and due its insolubility in water, no carcinogenic or toxic reactions will occur.

Compressive Surface Stress in Magnetic Transition Metals

Because of the increased electron density within the surface layer, metal surfaces are generally expected to have tensile surface stress. Here, using first-principles density functional calculations, we demonstrate that in magnetic 3d metals surface magnetism can alter this commonly accepted picture. We find that the thermodynamically stable surfaces of chromium and manganese possess compressive surface stress. The revealed negative surface stress is shown to be ascribed to the enhanced magnetic moments within the surface layer relative to the bulk values.

Effects of Plasma Nitriding on Low Temperature Salt-Bath Chromizing of W18Cr4V Steel

Effects of plasma nitriding on low temperature salt-bath chromizing of W18Cr4V steel is studied .The chromizing process is investigated by means of optical microscopy(OM), scanning electron microscopy(SEM), X-ray diffraction (XRD). Results show that the specimens are chromized successfully by low temperature salt-bath subjected to plasma nitriding. A chromized layer with average 3.3μm in thickness and 1200HV-1300HV in microhardness is formed on the substrate by chromizing at 610°C for 6h. XRD analysis show that the chromized layer is composed of Cr23C6, CrN, Cr/Fe, (Cr, Fe)7C3 , (Cr, Fe)2N and the surface chromium concentration reaches 77.67%.

Effects of Strong Carbide-Forming Elements on Low Temperature Salt-Bath Chromizing

The microstructure, phase structure, white layer thickness and chromium concentration, microhardness of the chromized layer of T10 steel and 3Cr2W8V steel by low temperature salt-bath chromizing with plasma nitriding are contrasted. The chromizing process is investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD). Results show that the strong carbide-forming elements (Cr, W, V) obstruct the diffusion of chromium and carbon, the white layer thickness and microhardness, surface chromium concentration of the chromized layer are reduced. A chromized layer of T10 steel with average 7.3μm in thickness, 84.47% in surface chromium concentration and 1300HV-1400HV in microhardness is formed on the substrate by chromizing at 610°C for 6h, as compared to the chromized layer of 3Cr2W8V steel with average 3.3μm in thickness, 74.27% in surface chromium concentration and 1200HV-1300HV in microhardness.

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.

Concave and Convex Phases in Ambiguous Figures Showing Colour Shifts. Mach's Figure and the Ambegujas Phenomenon

Two ambiguous figures (Mach's book-figure and the AMBEGUJAS phenomenon) have been studied. They show colour shifts synchronised with the shifts of their alternative phases. The perceived concave phase appeared to have chromatic surface colour, but the perceived convex phase can appear to be in coloured illumination and shadow (film colour). The two perceived reversible shapes of the Mach figure (the book and the tent) and the three perceived alternative shapes of the Mondrians used in the AMBEGUJAS phenomenon (a roof, a ceiling, and a tile) all can appear to have chromatic surface colours in their concave phases but appear to have coloured illumination and shadow in their convex phases.

Chromia-Assisted Decarburization of W-Rich Ni-Based Alloys in Impure Helium at 1273 K (1000 °C)

The microstructure and surface stability of two experimental W-rich Ni-based alloys have been studied at 1273 K (1000 °C) in an impure-He environment containing only CO and CO2 as impurities. The alloy Ni-2.3Al-12Cr-12W contained 0.08 wt pct carbon in solution, whereas the second alloy Ni-2.3Al-3Mo-12Cr-12Co-12W contained M6C carbides at the same carbon level. Both alloys, which were preoxidized with ~2.3 μm Cr2O3 layer, were decarburized completely within 50 hours of exposure to the helium gas mixture at 1273 K (1000 °C) via the following chromia-assisted decarburization reaction: Cr2O3 (s) + 3Calloy (s) → 2Cr (s) + 3CO (g). Microstructural observations, bulk carbon analysis, and microprobe measurements confirmed that the carbon in solid solution reacted with the surface chromium oxide resulting in the simultaneous loss of chromia and carbon. The Cr produced by the decomposition of the Cr2O3 diffused back into the alloy, whereas CO gas was released and detected by a gas chromatograph. Once the alloy carbon content was reduced to negligible levels, subsequent exposure led to the uninterrupted growth of Cr2O3 layer in both alloys. In the preoxidized alloys, chromia-assisted decarburization rates were slower for an alloy containing carbides compared with the alloy with carbon in solid solution only. The formation of Cr2O3 is shown to be the rate-limiting step in the chromia-assisted decarburization reaction. Exposure of as-fabricated alloys to the impure-He environment led to the formation of a thin layer of Al2O3 (<1 μm) between the substrate and surface Cr2O3 oxide that inhibited this decarburization process by acting as a diffusion barrier.

Light alkane dehydrogenation over mesoporous Cr 2O 3/Al 2O 3 catalysts

Light alkane dehydrogenation was investigated over a series of mesoporous Cr 2O 3/Al 2O 3 catalysts containing 2–15 wt.% chromia, synthesized via the supramolecular templating technique. The catalysts were characterized by N 2 adsorption, X-ray diffraction (XRD), Raman, Fourier transform infrared spectroscopy (FTIR), UV–vis (ultra violet visible), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). Depending on chromia loading, chromium was found to be present essentially as two surface species, each possessing one short terminal Cr O bond and polymeric species. UV–vis and XPS studies revealed that the surface chromium occurs in two chemical states as Cr(III) and Cr(VI) species. Investigation of ethane and propane adsorption by in situ diffuse reflectance FTIR spectroscopy (DRIFT) revealed the formation of adsorbed acetaldehyde, acetone, formate and acetate. During the dehydrogenation reaction, acetate/carboxylate and hydrocarbon species were detected. Under otherwise the same conditions, the alkane dehydrogenation activity increased with increasing chromia loading. The activity of regenerated catalysts was found to be lower than the corresponding fresh catalysts, suggesting that the deactivation is partly permanent. Detailed characterization studies of spent and regenerated catalysts indicated that the formation of subsurface Cr(III) species during dehydrogenation may be the reason for the permanently lost activity.

Oxidation Limited Lifetime of Ni‐Base Metal Foams in the Temperature Range 700–900 °C

AbstractINCONEL 625 metal foams produced from alloy powder by the slip‐reaction‐foam‐sinter‐process are tested in respect to cyclic oxidation behavior in air in the temperature range 700–900 °C. The structure of the oxide scales formed on the foam particles is characterized using optical microscopy and SEM/EDX analysis. Main emphasis is put on studying the oxidation limited lifetimes of the foams as function of temperature and foam microstructure. It is shown that mechanical disintegration during long term oxidation at the highest test temperatures is caused by a critical depletion of the Cr content in the alloy as a result of the growth of the initially formed surface chromia layer. This results in chemical breakaway due to accelerated oxide growth of voluminous Ni‐rich oxide on chromium exhausted alloy particles. Lifetime modeling based on calculation of Cr‐depletion in the alloy at the oxide/metal interface of each individual foam particle using the DICTRA software is in good agreement with the experimentally determined values of the time to breakaway.

Tailored Sol-Gel Coatings as Environmentally Friendly Pre-Treatments for Corrosion Protection

Concerning the development of new alternatives for replacement of the toxic chromate surface treatments, the aim of the present study is to design and produce new electrochemically active sol-gel thin films of different composition in the ZrO2-SiO2 system, to act as first chemically active layer for pre-treatments of metallic painted surfaces. For its evaluation, a new methodology combining accelerated test, and global and localised electrochemical impedance spectroscopy (EIS) is proposed. For the localised measurements, a new mini-cell system (MCS) is introduced. An active protection mechanism at the cathodic sites underneath the sol-gel thin film was observed. This inhibitor effect is associated with a self-sealing mechanism by the hydrolysis of Zr4+-ions chemically incorporated in the sol-gel network. After the accelerated test, these Zr4+-ions tend to form links different from Si-O-Zr (i.e. zirconium hydroxides and/or oxides). Such new insoluble compounds plug the pores and defects in the sol-gel coatings increasing the low frequency impedance during immersion in NaCl aqueous solutions.

PEM Fuel Cell Separator with Thermally Nitrided Low Carbon Steel

The separator is one of the most important parts in PEM fuel cells. Stainless steels are widely used as separator for its good mechanical properties and mass production. However, for a good chemical compatibility, stainless steels need to have high chromium content or surface treatment, which makes separator high cost. Low cost of separator is important for commercial use. In this study, conventional low carbon steel is used as base metal of separator. Low carbon steel is low at cost, but has poor chemical properties for separator. For a good corrosion resistance, low carbon steel needs to be surface treated. To make a uniform surface treated layer on low carbon steel, chromium is conventionally electroplated on the steel and thermally nitrided. Surface treated low carbon steel is investigated using microstructure and element analysis tools. Interfacial contact resistance and polarization test is applied for the properties of fuel cell separator. The results show that chromium nitrided layer uniformly formed on low carbon steel. And the surface treated steel showed a good corrosion resistance as a separator.

ADSORPTION OF AN NH3 MOLECULE ON Cr(111) SURFACE BY QCMP 116 PROGRAM

Interactions of an NH3 molecule on chromium (111) surface consists of 20 atoms with three layers has been studied by QCMP 116 (Calzaferri) program, run on IBM PC compatible (Pentium III, 660 MHz). An oncoming NH3 (with the planar molecular plane parallel or perpendicular to surface), at many positions, was optimized three dimensionally by that program. Observing the binding energy of an NH3 on surface (BE (NH3)) and inter atomic distances at the optimized conditions. It's showed that: an oncoming NH3 molecule, with molecular plane parallel to the surface, N atom was oriented to atoms of the first and third layer. One of its NH bond was parallel to the Cr-Cr bond were chemisorbed molecularly with BE(NH3) in range of 0.9797-1.3421 eV/molecule. On the second layer was chemisorbed atomically. However, an oncoming NH3 with molecular plane perpendicular to the surface (with N atom and one of its N-H bond perpendicular to Cr atom) was adsorbed physically with BE(NH3) in a range of 0.4903-0.5614 eV/molecule. Keywords: adsorption, binding energy

Estuarine increase of chromium surface sediments: Distribution, transport and time evolution

Chromium is an estuarine contaminant due to its industrial applications like leather tanning, dyeing or chromium plating. The most common explanation about the presence of this metal is the frequent estuarine spill, particularly in ecosystems like rivers, estuaries and coasts near anthropogenic activities. The purpose of this study is the investigation of the distribution and evolution of chromium in sediments of the surface layer of an estuary, determining directly the total content by electrothermal atomic absorption spectroscopy (ETAAS) using slurries. Results were correlated with the environmental conditions and the chemistry of the metal to have a partial overview of the potential risk of chromium presence in the water column and the biota of the estuary. The pH values, oxidation–reduction potential (ORP), elemental analysis (carbon, nitrogen and hydrogen content), and changes of total chromium with time were analysed. This information was used to establish the environmental conditions where chromium appeared, was transported and was accumulated in the marine sediments collected following a time evolution of two years.

High-resolution spectroscopy (XPS, 1H MAS solid-state NMR) and DFT investigations into Ti-modified Phillips CrO x/SiO 2 catalysts

Ti-modified Phillips catalyst is a most important industrial catalyst widely used in ethylene polymerization, but the mechanism still remains mysterious. In this work, Ti-modified Phillips catalysts were characterized by high-resolution X-ray photoelectron spectroscopy (XPS) and 1H magic-angle-spin solid-state nuclear magnetic resonance ( 1H MAS solid-state NMR) combined with density functional investigations into the effects of Ti-modification on promotion of polymerization activity and regulation of microstructures of the polymer chains. XPS data revealed Ti-modification caused increase in electron-deficiency and photo-stability of the surface chromate species. 1H NMR provided the first direct evidence of surface residual Ti–OH groups. Modeling results rationalized well the effects of Ti-modification on promotion of polymerization activity, extension of molecular weight distribution (MWD) to lower MW region, improvement of the distribution of inserted co-monomer and enhancement of 2,1-insertion in regioselectivity of Phillips catalysts. It was the first time the Ti-modification on Phillips catalysts were theoretically elucidated.