Cr2O3 Composites Research Articles

Improving magnetic properties of Fe–Si–Cr-based soft magnetic composites through precise adjustment of salt dosage based on interface engineering

Herein, the composite powder with a core–shell heterostructure (Fe–Si–Cr magnetic particles as the core and ZnSO4 as the shell) was synthesized using hydrothermal method, and Fe–Si–Cr-based soft magnetic composites (SMCs) with an insulation layer of ZnO·SiO2·Cr2O3 (ZSC) composites were successfully prepared via powder heat treatment and cold pressing. The formation mechanism of the ZSC composite insulation layer was thoroughly investigated, and the impact of varying amounts of ZnSO4 on the Fe-Si-Cr/ZSC SMCs’ microstructure and magnetic properties was analyzed. ZnSO4 released oxygen during thermal decomposition and oxidation reaction occurred at the core–shell heterogeneous interface, forming ZSC composite insulation layer. The incorporation of ZnSO4 significantly influenced the homogeneity and thickness of the composite insulation layer, effectively modulating the magnetic properties of Fe–Si–Cr/ZSC SMCs. This SMCs had the best magnetic properties after the addition of 2 wt% ZnSO4. Under 10 mT and 300 kHz, the relative permeability was 37.7, with a total loss of 248.8 kW/m3 The method proposed in this study is beneficial for facilitating the advancement of SMCs towards high frequency and further optimizing its performance.

Effect of particle size on microstructure and properties of Cu–Cr2O3 composites prepared by supercritical water in situ oxidation

In this paper, three kinds of Cu–Cr2O3 composites with different particle sizes were prepared from Cu-0.67 wt%Cr atomized alloy powder by supercritical water liquid phase in-situ oxidation (SW-LIO) through reduction and spark discharge plasma sintering (SPS). The structure and properties of the composites were systematically analyzed by X-ray diffractometer (XRD), scanning electron microscope (SEM), energy spectrometer, transmission electron microscope, electron backscattering diffraction, universal material testing machine, microhardness tester, eddy current conductometer, friction and wear testing machine, etc. The results show that Cr2O3 particles are evenly distributed in Cu matrix composites. The hardness of composites improved by 19% as the particle size decreased, while the tensile strength and electrical conductivity first increased as the particle size is refined. Meanwhile, the deformation behavior research is carried out, and the mechanical properties and electrical conductivity of composites are enhanced as the deformation amount increases.

X-ray absorption spectroscopy study of the electronic and structural properties of hexavalent chromium adsorbed by volcanic ashes

X-ray absorption spectroscopy (XAS) was used to characterize the volcanic ash (VA) materials as a low-cost and natural environmental adsorbent for the sorption of Cr (VI). The batch adsorption method was employed to synthesize the sample of chromium (VI) sorbed by VA. The results showed that the Cr-VA material is in the chromium oxidation state (III) and can be described as a composition of Cr2O3 (47.9%), FeCr2O4 (45.2%), and Na2Cr2O7 (6.9%). The promotion of the 1s Cr core electron implies the electronic transitions 1s to 3d(t2g) and 1s to 3d(eg). The first and second shells in the Cr-VA material were coordinated with the oxygen and chromium atoms in a distorted geometrical arrangement. The adsorption mechanism was associated with the chemical reduction of Cr (VI) to Cr (III) via an ion-exchange process. The XAS technique significantly contributes to the characterization of environmental VA, which can be proposed as an economical and alternative adsorbent for the sorption of Cr from contaminated wastewater.

Microstructure, phase evolution, mechanical properties and slag corrosion resistance of ZrO2 reinforced Al2O3–Cr2O3 composites

Al2O3–Cr2O3 refractories have excellent slag corrosion resistance and can adapt to the oxidation/reduction atmosphere in the smelting reduction ironmaking furnace. Improving the corrosion resistance of chrome corundum refractories is of great significance for extending the life length of industrial kilns and decreasing carbon emissions. In this work, the influences of ZrO2 content on the phase evolution, microstructure, physicochemical properties, mechanical properties and slag corrosion resistance of the ZrO2 reinforced Al2O3–Cr2O3 composite refractories were investigated. The results show that the ZrO2 reinforced Al2O3–Cr2O3 composites are primarily composed of (Al, Cr)2O3 solid solution and m-ZrO2. The compressive strength, flexural strength and hardness of the composite refractories can be improved by adding 2.5 wt% ZrO2. However, adding more ZrO2 will reduce its mechanical properties. This is due to ZrO2 excessive content will augement the porosity of the composite refractories, and the phase transformation of ZrO2 will also lead to the formation of microcracks during the cooling process. It is worth noting that higher ZrO2 content improves the thermal shock resistance of the composites, which is primarily put down to the microcrack toughening mechanism of ZrO2. The corrosion tests show that the thicknesses of the corrosion and infiltration layers of composite refractories are significantly decreased accompanied by ZrO2 content increase. This is because the formation of high melting point CaZr4O9 reduces the CaO content and slag alkalinity, and inhibits the dissolution of Al2O3 into the slag to a certain extent. Therefore, the slag corrosion/penetration resistance of the of the composites are obviously improved with the increase of ZrO2 addition.

Strontium-doped chromium oxide for RhB reduction and antibacterial activity with evidence of molecular docking analysis.

The emergence of multi-drug resistance (MDR) in aquatic pathogens and the presence of cationic dyes are the leading causes of water contamination on a global scale. In this context, nanotechnology holds immense promise for utilizing various nanomaterials with catalytic and antibacterial properties. This study aimed to evaluate the catalytic and bactericidal potential of undoped and Sr-doped Cr2O3 nanostructures (NSs) synthesized through the co-precipitation method. In addition, the morphological, optical, and structural properties of the resultant NSs were also examined. The optical bandgap energy of Cr2O3 has been substantially reduced by Sr doping, as confirmed through extracted values from absorption spectra recorded by UV-Vis studies. The field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) micrographs illustrate that the composition of Cr2O3 primarily consisted of agglomerated, irregularly shaped NSs with a morphology resembling nanoflakes. Moreover, the presence of Sr in the lattice of Cr2O3 increased the roughness of the resulting NSs. The catalytic activity of synthesized NSs was analyzed by their reduction ability of Rhodamine B (RhB) dye in the dark under different pH conditions. Their antibacterial activity was evaluated against MDR Escherichia coli (E. coli). Sr doping increased antibacterial efficiency against MDR E. coli, as indicated by inhibition zone measurements of 10.15 and 11.75mm at low and high doses, respectively. Furthermore, a molecular docking analysis was conducted to determine the binding interaction pattern between NSs and active sites in the target cell protein. The findings corroborated antimicrobial test results indicating that Sr-Cr2O3 is the most effective inhibitor of FabH and DHFR enzymes.

Spherical TiO2 /Cr2O3 Composites Synthesized Using Ion-Exchange Resins as a Template

Two samples of TiO2 /Cr2O3 composites were synthesized as spherical grains by stepwise thermal treatment of ion-exchange resins, which were preliminarily saturated with chromium cations Cr3+ and dichromate anions Cr2O7 2– and covered with a film-forming solution of titania. The modes of calcination were based on thermal analysis and determined by the type of ion-exchange resin chosen as a template. The obtained composites consist mostly of the α-Cr2O3 phase, while the content of the TiO2 phase does not exceed 4 %. The composites retain the spherical grain shape of the initial ion-exchange resins with the size from 370 to 660 μm. Grains of the sample based on cationite, which adsorbs Cr3+ ions, have a pore structure with swells and voids. Grains of the sample based on anionite have fractures and cracks over the entire surface due to nonuniform distribution of adsorbed Cr2O72– anions in the initial anionite. The composites exhibit the catalytic activity in the complete oxidation of p-xylene. The sample based on cationite is more active. This may be related to a smaller accessible specific surface area of titania in the anionite-based sample due to formation of the Ti3+ solid solution in α-Cr2O3.

Microstructure and corrosion behavior of Al2O3–Cr2O3 composites with various Cr2O3 content in Al2O3–SiO2–CaO–FeO slag

The corrosion of refractory materials by high-temperature slag has caused severe technical challenges and economic losses to the metallurgical industry. In this study, the microstructure and mechanical properties of Al2O3–Cr2O3 composites were investigated. The static crucible method was used to investigate the corrosion and infiltration behavior of a typical smelting reduction ironmaking slag for the Al2O3–Cr2O3 refractory. Corrosion test results indicate that the corrosion region of Cr2O3–Al2O3 composites is mainly composed of a corrosion and infiltration layer, and the thickness of the corrosion layer decreases significantly with increasing Cr2O3 content in the sample, whereas the thickness of the infiltration layer increases gradually. The dissolution of Al2O3 into the slag is the main reason for the severe erosion of Al2O3–Cr2O3 composites with a low Cr2O3 content. Increasing the amount of Cr2O3 can significantly improve the slag corrosion resistance of Cr2O3–Al2O3 composites, however will have a negative effect on the slag infiltration resistance, which is mainly owing to the increase in porosity of the composite refractory. The formation of the (Al, Cr)2O3 solid solution effectively inhibited the dissolution of alumina in the slag. In addition, excessive Cr2O3 content can also consume Al2O3 in the slag and form an (Al, Cr)2O3 solid solution, which improves the slag corrosion resistance of the aluminum chromium composite refractory.

Fabrication of superhydrophobic bilayer composite coating for roof cooling and cleaning

Building energy consumption is an important part of energy consumption. Cooling materials can be applied to reduce building energy consumption. In this study, chromium trioxide (Cr2O3) and titanium dioxide (TiO2) were introduced into low-density polyethylene (LDPE) matrix to prepare the solar-infrared reflective layers, then styrene–butadiene-styrene triblock copolymer (SBS) and surface functionalized nano-silicon dioxide (SiO2) superhydrophobic coating was constructed on the surface forming bilayer composites applying for building roof. It was found that SBS/SiO2 coating had higher roughness, which provoked a soaring contact angle of about 160° realizing superhydrophobic surfaces. Withal, the contact angle was invariant nearly 160° after dropping the solution of calcium chloride (pH = 6), acid (pH = 2), and alkali (pH = 13) on the surface, which engendered chemical stability and anti-pollution property. Subsequently, the emissivity of LDPE and 10 wt% Cr2O3 composites coated with SBS/SiO2 coating (LDPE/Cr-10/S) as well LDPE and 10 wt% TiO2 composites coated with SBS/SiO2 coating (LDPE/Ti-10/S) were increased to 83% and 83.9% along with high near-infrared reflectance was 47% and 63.1% separately. Simultaneously, when the initial temperature was 24 °C for 1 h under strong light irradiation in indoors, the final temperature of glass was 69 °C while the finished temperature of LDPE/Cr-10/S and LDPE/Ti-10/S were reduced to 30.5 °C and 25.8 °C respectively, showing the excellent cooling property.

Influence of thermal shock behavior on microstructure and mechanical properties of IN718 superalloy

The influence of thermal shock behavior between 960 °C and room temperature on microstructure and tensile properties of IN718 alloy after three heat treatments was investigated in this paper. The experiments show that protective and dense oxide films with the composition of Cr2O3, Ti0.95Nb0.95O4 and (Cr, Fe)2O3 are formed on the surface of alloys. The average oxide films increased with the thermal shock cycle. The thermal shock behavior changed the distribution and quantities of δ phases, which have significantly reduced the strength and increased the elongation of IN718 alloy. The decrease of strength was mainly determined by the dissolution of strengthening phase and grain coarsening. High standard treatment alloy shows the best thermal shock resistance since the strength decreased smallest after thermal shock.

Structural Characterization of NiO/Cr2O3Composites and Hydrothermal Synthesis, Properties Gas Sensing

Pure Cr2O3 and NiO/Cr2O3 nanocomposite were luckily synthesized by simple hydrothermal technique. X-ray films diffraction (XRD), Filed Emission scanning electron microscopy (FESEM), Energy dispersive X-ray spectroscopy (EDS), were used to research the crystalline structures, surface morphologies and nanostructures, and element components and their valences of the as-synthesized samples. Moreover, gas sensors based on the synthesized pure Cr2O3 and NiO/ Cr2O3 composites were fabricated and their sensing behavior, to NH3.Gas sensing experiments reference that the NiO/ Cr2O3 composites showed much higher gas response and lower working temperature than those of pure Cr2O3. These results assure that the as-synthesized NiO/ Cr2O3 composites a favorable NH3 sensing material

Synthesis and characterization of Ag-8 %wt Cr2O3 composites prepared by different densification processes

A novel Ag-8 %wt Cr2O3 composite prepared via powder metallurgy route. Silver and chromium oxides were used as starting powders. The powder mixtures were mechanically milled by a SPEX high energy mill for 5 h. Based on the thermogravimetric analysis (TGA) and X-Ray Diffraction (XRD) results, the milled powders were calcined in an argon atmosphere at 550?C. During calcination, the silver oxide decomposed into silver. The results showed that the Heckel equation was the preferred one for description the cold compressibility of the powders. The calcined powders were consolidated by Press-Sinter-Repress (PSR), Press-Sinter-Repress-Anneal (PSRA) and Spark Plasma Sintering (SPS) processes. The Field Emission Scanning Electron Microscope (FESEM) investigations showed a nearly dense microstructure of the sintered samples. However, the hardness of the pressed-sintered-repressed samples was 81 Vickers which was the highest among the processed specimen. Furthermore, the flexural strength of the PSR and SPS processed samples were 231 and 255 MPa, respectively which were too higher than that of the annealed specimens. The results confirmed the effect of microstructural parameters such as Cr2O3 particle size and processing route on the mechanical properties of the sintered composites.

Design and synthesis of Cr2O3@C@G composites with yolk-shell structure for Li+ storage

Cr2O3 is of high theoretical capacity for lithium-ion (Li+) storage. However, its cyclic stability is very poor due to the large volume change during lithiation/delithiation. In addition, the low conductivity of Cr2O3 blocked the fast transfer of electrons, resulting in an inferior rate capacity. In this study, we design yolk-shell Cr2O3 composites using carbon/Cr2O3 as core and graphene as shell to improve the conductivity of electrode materials and provide spaces for the volume change of Cr2O3. Therefore, this composites (Cr2O3@C@G) exhibit a higher specific capacity and stable cyclic performance achieved the remarkable reversible capacity of 648 mA hg−1 after 120 cycles at 0.1 A g−1, even a capacity of 347 mA hg−1 is obtained after 600 cycles at 1 A g−1. Due to the space between carbon sphere and graphene, they not only effectively alleviate the volume expansion of Cr2O3, but also enhance the electrochemical properties of the composites. Eventually the electronic conductivity and Li+ diffusion rate more pleasantly during cycling due to the excellent structural characteristics.

Synthesis of Fe2O3–NiO–Cr2O3 composites from NiFe-layered double hydroxide for degrading methylene blue under visible light

To develop a low-cost and highly efficient photocatalyst under the visible illumination, Ni3Fe–CO3–LDH (referred to hereafter as NiFe-layered double hydroxide or NiFe–LDH) was used as a precursor to synthesize Fe2O3–NiO–Cr2O3 composite. The NiFe–LDH was prepared by co-precipitation and then it was exchanged with dichromate. After calcining at 600°C, the Fe2O3–NiO–Cr2O3 composite was obtained. The composites' absorption edge intensely extended up to ca. 700nm covering the full visible light spectrum and showed high catalytic activity at natural pH under the visible light illumination. A very high methylene blue degradation of 91.2% was achieved with the aid of H2O2 in 120min with no detectable Cr in solution.

Analysis of DC and AC properties of a humidity sensor based on polyaniline–chromium oxide composites

Polyaniline–Chromia (PANI–Cr2O3) composites were synthesized by in situ polymerization. The prepared composites were characterized by scanning electron microscopy, X-ray diffraction and Fourier transforms infrared spectroscopy. The structural studies confirm the polymerization of aniline over Cr2O3 particles which results into strong interaction between PANI and Cr2O3 particles. Direct current conductivity of composites increases with increase in temperature. Among all composites, 30 wt% shows high conductivity. The humidity sensing mechanism of the PANI–Cr2O3 composites is studied and change in its resistance with respect to percentage relative humidity ranging from 20 to 95 % is recorded. The humidity sensing studies shows that the change in the resistance is due to the uncurling of polymer chains by the absorption of water vapor which leads to increase in conduction paths. The results indicate better humidity sensing response by the addition of Cr2O3 particles to PANI, among all the composites, 30 wt% composite shows higher sensitivity.

The ferromagnetic–antiferromagnetic properties of Ni–Cr2O3composite hollow spheres prepared by an in situ reduction method

Considerable efforts have been exerted on the facile synthesis of magnetic composite materials because of their unique properties and potential applications. Especially for ferromagnetic–antiferromagnetic systems, the magnetic exchange bias effect is essential for the development of magneto-electronic switching devices and magnetic storage media. In this research, a facile ethylene glycol in situ reduction strategy has been successfully employed in the preparation of Ni–Cr2O3 composite hollow spheres. X-Ray powder diffraction was used to determine the phase composition. Scanning electron microscopy and transmission electron microscopy was employed to characterize the morphologies of the as-prepared samples. Experiments proved that the volume ratio of ethylene glycol to water played a determinative role in the final morphology of the products. The magnetization vs. temperature results revealed a spin-glass-like behavior with blocking temperature of about 150 K for the as-prepared Ni–Cr2O3 composites. Induced by the coupling between ferromagnetic Ni and antiferromagnetic Cr2O3, a small exchange bias effect could be observed in the magnetic hysteresis loops. At lower temperature, a larger exchange bias field and coercivity are obtained. A high surface area of 145.1 m2 g−1 was obtained for the prepared porous hollow spheres.

Carbon-coated graphene–Cr2O3 composites with enhanced electrochemical performances for Li-ion batteries

Graphene-based Cr2O3 composites are prepared and exhibit better electrochemical properties than free Cr2O3 particles without the graphene. The synthesis procedure consists of the direct growth of CrOOH on the surface of graphene and the subsequent thermal decomposition of CrOOH to Cr2O3. Moreover, the electrochemical properties of graphene-based Cr2O3 are further improved through carbon coating, and two strategies are developed. Interestingly, the carbon layers pyrolyzed from glucose on CrOOH can separate the particles on the graphene and limit their growth, while those on Cr2O3 merely cover the particles and cannot prevent particle aggregation. Consequently, compared to the latter carbon-coated composite, the former shows further improved electrochemical behavior.

Investigation of the properties of ferromagnetic ZnO:Cr2O3 nanocomposites

Present work focuses on the structural, optical and magnetic properties of ZnO:Cr2O3 nanocomposites. ZnO nanoparticles were synthesized and the structure was confirmed using powder x-ray diffraction. ZnO nanoparticles was grown in the hexagonal wurtzite structure with the preferential orientation along (101) plane. ZnO:Cr2O3 composites have been synthesized by doping different concentration of Cr2O3 (1, 3 and 5wt%) into ZnO. The incorporation of Cr2O3 was confirmed using Fourier transformed infrared spectroscopy. UV–visible absorption spectra have been observed and interpreted for the determination of optical constants of ZnO:Cr2O3 composites. The optical constants like optical band gap, refractive index were determined and the effect of Cr2O3 on these constants was investigated. Relation between optical band gap and the refractive index were obtained. Magnetic studies using vibrating sample magnetometer reveal the ferromagnetism at 150K in the composites with 3 and 5wt% of Cr2O3.

Preparation and Application of High Near-Infrared Reflective Green Pigment for Ceramic Tile Roofs

Complex inorganic green pigments having a high near-infrared (NIR) solar reflectance were synthesized. Chromium oxide (Cr2O3) was used as the host component with mixtures of TiO2, Al2O3, and V2O5 as the guest components. TiO2, Al2O3, and V2O5 were mixed into 39 different compositions. It was found that a sample, denoted by S9, with the composition of Cr2O3, TiO2, Al2O3, and V2O5 are 80, 4, 14, and 2 wt%, respectively, gives a maximum NIR solar reflectance of 82.8% compared with 69.6% of a commercially available cool pigment powder. The comparison study on the effectiveness of the synthesized pigment and a commercial pigment on ceramic glaze and sprayed on ceramic tile roofs show that the new powder has given a better result by keeping the tested room about 2°C cooler. It can be concluded that the new formulated green pigment is a highly thermal effective as an NIR reflective roof coating.

Synthesis of V-Ti-Cr alloys by aluminothermy co-reduction of its oxides

Synthesis of V-Ti-Cr solid solution alloy by co-reduction of V2O5, Cr2O3 and TiO2 with aluminium in an open bomb reactor was investigated. The reduction of V2O5 and Cr2O3 was highly exothermic while reduction of TiO2 was not sufficiently exothermic for self-sustaining reaction. A range of composition of V2O5, Cr2O3 and TiO2 mixture was chosen to make overall process sufficiently exothermic to sustain the reaction in a controlled manner. After the co-reduction, V-Ti-Cr-Al solid solution was obtained. As-obtained solid solution was refined by electron beam melting (EB) to remove the aluminium and residual oxygen. EB melted V-Ti-Cr thus obtained contains substantially less amount of aluminium (~0.081%.) Throughout the synthesis process the prepared products were analyzed using scanning electron microscope (SEM), energy dispersive X-ray fluorescence (EDAX), chemical analysis, gravimetric analysis and X-ray diffraction.

Preparation and using of high near-infrared reflective green pigments on ceramic glaze

Complex inorganic green pigments having a high near infrared solar reflectance have been synthesized. Cr2O3 is the host component and mixtures of TiO2, Al2O3, and V2O5 were used as the guest components. TiO2, Al2O3 and V2O5 were mixed into 39 different compositions. It was found that a sample, denoted by S9, with a composition of Cr2O3, TiO2, Al2O3 and V2O5 of 80, 4, 14 and 2 wt% respectively, gives a maximum near infrared solar reflectance of 82.8%. The S9 pigment powder was then prepared as a reflective coating material with different amounts of pigment powder from 4–8 g in 100 g of ceramic glaze. The prepared materials were sprayed on the clay tiles for reflectance measurements. It was found that 6 g of S9 pigment powder mixed with 100 g of ceramic glaze gives the highest near-infrared reflectance value of 74.5%. The newly synthesized pigment is a suitable ceramic roof coating for its high reflectance performance and the durability performing once the ceramic roof installed on house.