Chromium Oxide Particles Research Articles

Influence of Tool Pin Profiles on Aluminium Alloy A356 and Ceramic-Based Nanocomposites for Light Weight Structures by Friction Stir Processing

In this research, the main aim is to focus the enhancement of aluminium-based metal matrix composites for improving the attributes of light weight metals, aerospace structures and other tailor blank material properties. By this way, the friction stir processing (FSP) was the suited alternate technique to enhancing the mechanical attributes and superior microstructural amendment in the processed MMCs. Therefore, this study investigates the dispersion of ceramic-based strengthening particles of chromium oxide (Cr2O3) in the aluminium base matrix of A356 alloy. During the processing, the different tool pin sizes having the conical threaded tool pin profiles. Similarly, the tool spinning speed and tool travel speed also varied while in FSP. Before the processing, the A356 alloy was prepared by the grooved surfaces for packing the chromium oxide particles to compose the aluminium metal matrix composites. The tensile strength and hardness was employed to carry out from the friction stir processed A356 alloy with influencing of Cr2O3. The maximum occurred tensile processing parameters are 1500 rpm of spinning speed, 6 mm of tool pin sizes and 90 mm/min of tool travel speed. Similarly, the maximum obtained hardness processing parameter are 2000 rpm of spinning speed, 5 mm of tool pin sizes and 90 mm/min of tool travel speed. A scanning electron microscope was utilized to investigate the dispersed Cr2O3 in the A356 alloy for confirming the refinement grains in the nugget zones of FSPed A356 alloy. The increased grain boundary by the influence of different tool pin sizes was the major reason to produces the better mechanical properties in the processed A356/Cr2O3.

High strength and deformation stability achieved in CrCoNi alloy containing deformable oxides

• The spreading lattice distortion in CrCoNi-O high entropy solution locally relieved the severe interfacial mismatch and led to nanoscale variation of interfacial strain at the matrix-oxide interface. • Dislocations slip transferred from solid solution phase to ceramic phase, enabling the ceramic phase with significant deformability. • The yield strength of the dual-phase samples was twice of the single-phase CrCoNi-O alloy; strong strain hardening was obtained with ultra-high deformation stability, whereas the single-phase CrCoNi-O sample exhibited catastrophic shear localization. Hard secondary phases usually strengthen alloys at the expense of ductility. In this work, we made a dual-phase CrCoNi-O alloy containing a face centered cubic matrix and chromium oxide. On one side, the dispersed chromium oxide nano-particles impeded dislocation movement and increased the strength of the alloy. On another side, the spreading lattice distortion in CrCoNi-O high entropy solution locally relieved the severe interfacial mismatch and led to nanoscale variation of interfacial strain at the matrix-oxide interface, which facilitated dislocations’ transmission from one phase to another. Consequently, unlike the strong but brittle oxide nanoparticles used before, the oxide phase here can afford significant dislocation activities during material's plastic deformation. Comparing the mechanical properties of CrCoNi-O alloys with and without chromium oxide particles, it was found that the yield strength of the dual-phase samples was twice of the single phase CrCoNi-O alloy and strong strain hardening was obtained with ultra-high deformation stability. High density of nanotwins formed in dual-phase samples under high stress, resulting in significant strain hardening according to the well-known twinning-induced plasticity (TWIP) effect. Our results shed light on optimizing the combination of strength and plasticity of compounds by modulating the variation of interfacial strain field based on the spreading lattice distortion.

Enhanced Fe–Cr dispersion on mesoporous silica support using surfactant-assisted melt-infiltration for the water-gas shift reaction in waste-to-hydrogen processes

Iron-chromium/SBA-15 (Fe–Cr/SBA-15) catalysts for high-temperature water-gas shift reactions (HTS) were prepared using the surfactant-assisted melt-infiltration (SAMI) method. The SAMI method was used to synthesize an efficient catalyst that could simultaneously achieve high dispersion and loading (Fe: 40 wt% and Cr/Fe molar ratio: 0.25) without a liquid solution. According to X-ray diffraction (XRD) and transmission electron microscopy analyses, it was observed that the Span60 surfactant enhanced Fe3O4 particle dispersion. N2 adsorption-desorption analysis indicated that the Fe3O4 and chromium oxide particles were thoroughly infiltrated inside the mesopores of the SBA-15 support. XRD and temperature-programmed-reduction analyses revealed that the well-dispersed Fe3O4 acted as active sites for the HTS reaction when Span60 was added to the Fe–Cr catalyst. In other words, the Fe–Cr catalyst synthesized via SAMI exhibited better performance and stability for the HTS reaction than that prepared without the surfactant.

Bionic coating imitating reflection characteristics of plant leaf in solar spectrum waveband for hyperspectral camouflage

Imitating the reflection characteristics of plant leaves in solar spectrum waveband with bionic coatings can effectively counter the hyperspectral detection technology in the vegetation background. Herein, inspired by the formation mechanisms of the reflection characteristics of plant leaves, a bionic coating containing chromium oxide (Cr2O3) particles and a hydrophilic inorganic salt dispersed in a polyvinyl alcohol (PVA) matrix is prepared on metal plates, and a theoretical model was constructed to clarify the bionic mechanisms. Results show that the Cr2O3 particles exhibit absorption characteristics similar to those of chlorophyll and scattering characteristics similar to those of multilayer cells in plant leaves, thereby enabling the bionic coating to imitate the reflection characteristics in the visible and near-infrared waveband. Meanwhile, the hydrophilic inorganic salt can absorb moisture molecules in the air when the bionic coating is placed in natural environments, thereby absorbing incident radiation and imitating the water absorption valleys. Moreover, it was found that there is only non-freezing bound water in the bionic coating with a differential scanning calorimeter, thus the moisture absorption processes associated with the hydrophilic hydroxyl groups in PVA matrix were considered when determining the mass transfer characteristics in a natural environment. In the whole solar spectrum, the bionic coating can significantly suppress the high reflectance of the metal plates when the volume fraction of Cr2O3 particles is 0.81 % and the coating thickness is greater than 0.2 mm. Increasing the surface roughness of the metal plates can further improve the suppressing performance in the range from 800 to 1300 nm, achieving a better similarity of the reflection curves between the bionic coating and the plant leaves. The outstanding imitation performance of the key reflection characteristics of the plant leaves confirms the remarkable application potential of the bionic coating in the field of hyperspectral camouflage.

Highly Selective and Humidity-Resistant Triethylamine Sensors Based on Pt and Cr2O3 Nanoparticles

A triethylamine gas sensor with humidity resistance, high selectivity, and high response is designed. Chromium oxide particles were prepared by heating them in a water bath at 80 °C. Pt/Cr2O3 nanoparticles were obtained by sodium borohydride reduction. The structure morphology of nanoparticles was characterized by some methods. The gas response test results showed that the modification of Pt improved the response value and selectivity of Cr2O3 to triethylamine. It was found that Cr2O3–2Pt nanoparticles had the best performance, and at the optimum operating temperature of 160 °C, its response value reached 200, 68 times that of Cr2O3 (S = 2.95). In addition, the modification of Pt made Cr2O3–2Pt nanoparticles had a wide range of humidity applications. The mechanism of gas response is explained by using the Schottky barrier and hole accumulation layer model of Pt and Cr2O3 contact and energy band theory.

Factors that govern sub-3 nm particle measurements in an Airmodus® PSM and a TSI® DEG–SMPS

Measurements of sub-3 nm particles are technically challenging and characterized with significant uncertainties. This study selected two types of widely used commercial instruments: an Airmodus® Particle Size Magnifier (PSM) and a TSI® diethylene glycol-based Scanning Mobility Particle Sizer (DEG–SMPS), and examined factors that govern their abilities on measurements of sub-3 nm particles. Monodisperse standard particles used in the experiments include positively and negatively charged tungsten oxide particles and nickel–chromium (Ni/Cr) oxide particles, positive and negative ions produced in a soft X-ray neutralizer, and positively charged organic particles including tetraheptylammonium bromide (THABr), tetrabutylammonium bromide (TBABr), and polyethylene glycol (PEG) particles. Our results show that both PSM and DEG–SMPS are subject to the influence of particle composition. Negatively charged tungsten oxide particles were detected at higher efficiencies than positively charged ones, whereas opposite results were observed for Ni/Cr particles and background ions produced in the soft X-ray neutralizer. In addition, the concentration accuracy of PSM and DEG–SMPS are explored after calibration using Ni/Cr particles. The inverted total concentrations by DEG–SMPS are usually underestimated because of the overestimation of penetration efficiency through different modules, whereas the inverted total concentrations by PSM can be either overestimated or underestimated, when the properties of analyte particles are significantly different from the calibration particles. A better understanding on the effects of particle chemical composition and charging state, and their diffusion losses in the instruments will help to diminish the uncertainties in the measurements.Copyright © 2022 American Association for Aerosol Research.

Highly dispersed atomic layer deposited CrOx on SiO2 catalyst with enhanced yield of propylene for CO2 –mediated oxidative dehydrogenation of propane

The increasing worldwide demand for propylene and the necessity of CO2 mitigation attracted the attention of scientists to focus on CO2-oxidative dehydrogenation of propane (CO2-ODHP). In this regard, CrOx/SiO2 catalyst is an important and conventional option. Herein, we studied the atomic layer deposition (ALD) of CrOx on silica to increase the propylene production by increasing the dispersion of the catalyst. For ALD synthesis of CrOx/SiO2 catalyst, Cr(acac)3 and synthetic air were used as metal precursor and oxidant. The catalysts were examined in the CO2-ODHP reaction and their characteristics were compared to their impregnation counterparts using UV–Vis DRS, Raman, XANES, HRTEM and STEM-EDS mapping, H2-TPR, NH3-TPD and TPO. The ALD catalysts have shown up to 2 times higher acidity and enhanced reducibility compared to the impregnation catalysts. The presence of mainly Cr(VI) with a pre-edge peak at 5.994 keV in both series of catalysts was confirmed by XANES. UV–Vis DRS and Raman spectroscopy revealed the higher contents of active polymeric Cr(VI) species in the ALD ones. The dark field HRTEM and STEM-EDS mapping represented higher dispersion of chromium oxide particles in ALD catalysts. In CO2-ODHP, the ALD catalysts showed up to 18 and 15% promotion in propane conversion and propylene yield.

A New Redox Technique for Depositing CrOx on the Surface of Pd(0) Nanoparticles: Catalysts for Selective Phenylacetylene Hydrogenation

A catalyst containing chromium oxide particles on the surface of palladium nanoparticles is synthesized for the first time using a redox technique for reduction with adsorbed hydrogen. The low-temperature reduction of chromium oxide and formation of palladium hydride is reported for the first time in such catalyst. A considerable difference between its catalytic properties in the selective hydrogenation of phenylacetylene and those of the initial palladium catalyst is shown.

Effect of Scratches on Passive Anti-corrosion in Cr-Mn Ferroalloy

To study the scratch effect on the metal corrosion, some special scratches on the Cr-Mn ferroalloy were formed by rubbing a sandpaper on the sample surface. Two environmental cases are considered, that is, a humidity air, and a humidity air bottomed with alkaline–organic solution successively. The micro-surfaces of the samples are observed by Energy dispersive spectrometer, and the elementary contents are analyzed on an area and a line. Special scratches on the surface of Cr-Mn ferroalloy do not accelerate the metal corrosion in a humid organic alkaline environment. On the contrary, it would play a positive role in the sample passive anti-corrosion process. Chromium oxide and manganese oxide particles are produced by the oxidation of metals in a humidity air would gather in the grooves caused by the scratches. The relative study is less reported till now.

ZnCr₂O₄ Inclusions in ZnO Matrix Investigated by Probe-Corrected STEM-EELS.

The ZnCr2O4/ZnO materials system has a wide range of potential applications, for example, as a photocatalytic material for waste-water treatment and gas sensing. In this study, probe-corrected high-resolution scanning transmission electron microscopy and geometric phase analysis were utilized to study the dislocation structure and strain distribution at the interface between zinc oxide (ZnO) and embedded zinc chromium oxide (ZnCr2O4) particles. Ball-milled and dry-pressed ZnO and chromium oxide (α-Cr2O3) powder formed ZnCr2O4 inclusions in ZnO with size ~400 nm, where the interface properties depended on the interface orientation. In particular, sharp interfaces were observed for ZnO [23]/ZnCr2O4 [10] orientations, while ZnO [110]/ZnCr2O4 [112] orientations revealed an interface over several atomic layers, with a high density of dislocations. Further, monochromated electron energy-loss spectroscopy was employed to map the optical band gap of ZnCr2O4 nanoparticles in the ZnO matrix and their interface, where the average band gap of ZnCr2O4 nanoparticles was measured to be 3.84 ± 0.03 eV, in contrast to 3.22 ± 0.01 eV for the ZnO matrix.

Dehydrogenation of Propane with СО2 on Supported CrOx/SiO2 Catalysts

A systematic analysis was performed of the physicochemical properties of amorphous silicas (Acros, Degussa, KSKG) and CrOx/SiO2 catalysts prepared from them with 2, 3, 5, 7, and 10 wt % chromium. The supports and catalysts were characterized by BET, XRD, and UV–Vis diffuse reflectance spectroscopy. In the oxidative dehydrogenation of propane with carbon dioxide, the highest propylene selectivity (95%) was observed for the 5% CrOx/SiO2 (Degussa) sample, and the highest propane conversion (53%) was reported on the 5% CrOx/SiO2 (Acros) catalyst. The structure of chromium oxide particles on the support surface was studied by UV–Vis spectroscopy. The catalytic properties were correlated with the state of chromium.

Microstructural and mechanical properties of α-titanium sintered material via thermal decomposition of additive chromium oxide particles

The pre-mixed pure Ti and Cr2O3 powder was consolidated by spark plasma sintering (SPS) and hot extrusion to fabricate α-titanium (Ti) materials with oxygen (O) and chromium (Cr) elements by powder metallurgy (PM) process. The Cr2O3 particles were completely decomposed during SPS, and then O and Cr atoms were dissolved in α-Ti matrix. Oxygen atoms were remarkably improved the mechanical strength of PM Ti-O-Cr alloys by their solid solution hardening effect. The Cr solution and Ti4Cr precipitates had important roles to obstruct the grains coarsening behavior by the solute drag and Zener pinning effects, respectively. The solid solution strengthening effect by Cr atoms, however, was very limited due to a small Cr solubility of about 0.35 at% in α-Ti phase of Ti-O-Cr alloys. Since Ti4Cr precipitates with 10–20 µm diameters were not so fine, they hardly contributed to the precipitation hardening of Ti-O-Cr alloys.

Hexavalent chromium as a cathodic electron acceptor in a bipolar membrane microbial fuel cell with the simultaneous treatment of electroplating wastewater

Hexavalent chromium wastewater is produced in electroplating processes and the heavy metal industry, highlighting the need for an environmentally friendly treatment and the recovery of chromium. This study compared the performance of microbial fuel cells implemented with a proton exchange membrane (PEM-MFC) and a bipolar membrane (BPM-MFC) using hexavalent chromium from electroplating wastewater as the catholyte. The removal of hexavalent chromium and simultaneous bioelectricity generation were enhanced significantly using a BPM. On the other hand, in the PEM-MFC, the lower pH of the electroplating wastewater (pH 1.8) in the cathodic chamber decreased the anodic pH due to proton diffusion through the PEM, and inhibited the bioelectrochemical reaction. Scanning electron microscopy showed that the reduced chromium particles precipitated on the cathode carbon electrode during the MFC operation. The precipitate was identified as amorphous chromium oxide particles by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy.

Removal studies of Cr2O3 colloidal particles using cationic poly(l-lysine) and its block copolymers with poly(ethylene glycol)

Cr2O3 dispersions are considered to be dangerous for aqueous ecosystems and for this reason it is necessary to develop methods allowing solid particles separation.Structure of the adsorption layer formed at the solid surface determines the colloidal suspension stability. Moreover, in the case of ionic polymers the solution pH considerably affects the chains arrangement. Hence, the influence of cationic poly(l-lysine) and its copolymers adsorption on the chromium(III) oxide (Cr2O3) particles stability was investigated. Although the analyzed substances are characterized by the similar average molecular weight, they exhibit various macromolecular structures resulting from the different PEG and polyamino acid length ratios. The sample's stability was examined by the use of the turbidimetric method enabling the Turbiscan Stability Index (TSI) parameter calculation.As one can see, solid suspensions without the tested polymers are relatively unstable. At pH 4, introduction of the cationic macromolecules causes the increase in the sample stability. This can be explained by the electrostatic repulsion between the totally ionized polymeric chains adsorbed on the adjacent Cr2O3 particles. At pHpzc, changes in the TSI values are related to the different polymer chain arrangements.

A preliminary evaluation of immune stimulation following exposure to metal particles and ions using the mouse popliteal lymph node assay

The objective of this preliminary study was to evaluate the threshold for immune stimulation in mice following local exposure to metal particles and ions representative of normal-functioning cobalt-chromium (CoCr) metal-on-metal (MoM) hip implants. The popliteal lymph node assay (PLNA) was used in this study to assess immune responses in BALB/c mice following treatment with chromium-oxide (Cr2O3) particles, metal salts (CoCl2, CrCl3 and NiCl2), or Cr2O3 particles together with metal salts using single-dose exposures representing approximately 10days (0.000114mg), 19years (0.0800mg), and 40years (0.171mg) of normal implant wear. The immune response elicited following treatment with Cr2O3 particles together with metal salts was also assessed at four additional doses equivalent to approximately 1.5months (0.0005mg), 0.6years (0.0025mg), 2.3years (0.01mg), and 9.3years (0.04mg) of normal implant wear. Mice were injected subcutaneously (50μL) into the right hind foot with the test article, or with the relevant vehicle control. The proliferative response of the draining lymph node cells (LNC) was measured four days after treatment, and stimulation indices (SI) were derived relative to vehicle controls. The PLNA was negative (SI<3) for all Cr2O3 particle doses, and was also negative at the lowest dose of the metal salt mixture, and the lowest four doses of the Cr2O3 particles with metal salt mixture. The PLNA was positive (SI>3) at the highest two doses of the metal salt mixture and the highest three doses of the Cr2O3 particles with the metal salt mixture. The provisional NOAEL and LOAEL values identified in this study for immune activation corresponds to Co and Cr concentrations in the synovial fluid approximately 500 and 2000 times higher than that reported for normal-functioning MoM hip implants, respectively. Overall, these results indicate that normal wear conditions are unlikely to result in immune stimulation in individuals not previously sensitized to metals.

In vitro macrophage response to nanometer‐size chromium oxide particles

An increasing number of studies have reported adverse tissue reactions around metal-on-metal (MM) hip implants. However, the origin and mechanisms of these reactions remain unclear. Moreover, the biological effects of nanometer-size chromium oxide particles, the predominant type of wear particles produced by MM implants, remain mostly unknown. The purpose of this study was to analyze the cytotoxic effects of clinically relevant nanometer-size chromium oxide particles on macrophage response in vitro. J774.A1 macrophages were cultured with either 60 nm or 700 nm commercially available Cr2 O3 particles at different concentrations. Two different particle sizes were analyzed to evaluate potential volume effects. Cell mortality was analyzed by light microscopy, flow cytometry (annexin V-fluorescein isothiocyanate and propidium iodide assay), and using a cell death detection enzyme-linked immunosorbant assay (ELISA). Tumor necrosis factor alpha (TNF-α), monocyte chemotactic protein-1 (MCP-1), and macrophage inflammatory protein-1 alpha (MIP-1α) release was measured by ELISA, and gene expression was analyzed by quantitative real-time PCR. Results showed that, at high concentrations, Cr2 O3 particles of both sizes can be cytotoxic, inducing significant decreases in total cell numbers and increases in necrosis. Results also suggested that these effects were dependent on particle volume. However, TNF-α, MCP-1, and MIP-1α cytokine release and gene expression remained low. Overall, this study demonstrates that nanometer-size particles of Cr2 O3 , a stable form of chromium oxide ceramic, have rather low cytotoxic effects on macrophages. Therefore, these particles may not be the main culprit in the initiation of the inflammatory reaction in MM periprosthetic tissues. However, other parameters (e.g., potential intracellular damage) remain to be investigated.

Synthesis, structure and exchange bias in Cr 2O 3/CrO 2/Cr 2O 5 particles

We report on the synthesis, structure and magnetic properties of a novel exchange bias system with Cr 2O 3/CrO 2/Cr 2O 5 interfaces. Chromium oxide particles with mixed chromium valences were prepared by sintering CrO 3 in air. X-ray diffraction patterns show that CrO 3 lost its oxygen gradually with increasing temperature and time through Cr 3O 8, Cr 2O 5, CrO 2, and finally Cr 2O 3 at temperatures above 760 K. X-ray photoelectron spectra indicate a low CrO 2 content and a binding energy of 579.3 eV for Cr 2 p 3/2 photoelectrons in Cr 2O 5. Chromium dioxide was found to stably coexist with Cr 2O 3 and Cr 2O 5 in the particles. Magnetic measurements show hysteresis loop shifts in the sample, indicating an exchange bias induced by antiferromagnetic Cr 2O 3/Cr 2O 5 in ferromagnetic CrO 2. An exchange bias of 9 mT at 5 K and a coercivity of 26.3 mT were observed in the chromium oxide particles containing CrO 2.

Improvement in the properties of nickel by nano-Cr2O3 incorporation

Abstract Nano-ceramic composite coatings were prepared by the electrodeposition method using sulphamate electrolyte. Nickel was chosen as the metal matrix and nano-Cr2O3 particles were chosen as the reinforcement. The surface morphology and the particle distribution in the coating were analysed using field emission scanning electron microscope (FESEM). The particle content was obtained using energy dispersive X-ray analysis (EDAX). A change in the surface morphology of Ni was seen on the incorporation of Cr2O3 particles. The coatings were characterized for their structure and no change in the diffraction pattern was seen between plain Ni and Ni-Cr2O3 composite. The mechanical property like microhardness and tribological behaviour of the nano-composite coatings was studied and it was observed that the incorporation of Cr2O3 particles enhanced the mechanical properties of Ni matrix. The nano-composites were analysed for their thermal stability and corrosion resistance. An improvement in thermal stability was observed but no change in the corrosion behaviour of Ni was seen on the incorporation of nano chromium oxide particles.

Bimodally grained high-strength Fe fabricated by mechanical alloying and spark plasma sintering

Nanocrystalline iron containing a certain fraction of coarse grains with nanosized oxide dispersoids has been processed by mechanically milling Fe powder and subsequent spark plasma sintering. Sintered samples exhibited a high tensile strength of 2100 MPa with 5% ductility; by optimizing the sintering conditions, it was possible to tune the strength–ductility balance. The optimally sintered material showed a tensile strength of 1500 MPa and 15% elongation. The microstructure consists of nanograined (<100 nm) as well as coarse-grained regions (>1 μm) with uniform dispersion of nanosized chromium oxide particles (∼10 nm). The strength and elongation show strong dependence on the volume fraction of the coarse grains, and the high strength can be attributed to the ultrafine grain size of the nanograined regions and precipitation hardening by the oxide dispersoids. The ductility is considered to be due to the presence of coarse grains.

Early Viridian Pigment Composition CHARACTERIZATION OF A (HYDRATED) CHROMIUM OXIDE BORATE PIGMENT

Pigment analyses on more than 90 paintings dating from between 1885 and 1943 (A. Jawlensky, W. Kandinsky, F. Hodler and C. Amiet) have revealed that the majority of samples with chromium oxide hydrate green contain a spectroscopically conspicuous by-product. With the aim of tracking down the origin of this component, the so-called Guignet green, a variation of viridian produced by calcination, was systematically synthesized under varying conditions. The resulting products were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, energy dispersive spectrometry, electron microprobe microanalysis with wavelength dispersive spectrometry, X-ray diffraction, thermogravimetric analysis, secondary electron and backscattered electron imaging by scanning electron microscopy, polarized light microscopy and colorimetry. The composition of pigment products varies with the calcination conditions. Higher temperatures and/or longer calcination times lead to an insoluble borate matrix incorporating chromium oxide particles. The result is an amorphous chromium oxide borate Cr2O3·(xH2O)–Cr3BO6 polymorph with low water content. Interpreting chromium oxide hydrate green samples within this context, it turns out that calcination conditions in the past were highly variable, leaving behind considerable amounts of borates in the final product. Current data covering more than 60 paintings by Jawlensky suggest that the use of a specific production batch can be resolved in time. Identification of borates in chromium oxide hydrate green samples from paintings may thus provide information about the origin of the paint product used.