Chromium Oxide Powder Research Articles

Synthesis, Characterization of Chromium Oxide Powders and Coatings

The chromium oxide powders are transformed into plasma sprayable particles by using synthetic polymers for agglomeration. In order to carry out the agglomeration process, spray drying technique was employed. This research work highlights the significance of the process variables that control the synthesis of plasma spray powder and consequently, the properties that were suited for plasma spray coating. Energy Dispersive Spectroscopy (EDS) was used to characterize the elemental composition, while scanning electron microscopy (SEM) was used to analyse the morphology and powder grain sizes and X-ray diffraction (XRD) was used to identify the phase structure. And for the development of coatings on the substrates, Atmospheric plasma spray (APS) technique was used. The plasma sprayable powders were created with the intention of investigating for use as corrosion-resistant coatings.

In Situ Reactive Formation of Mixed Oxides in Additively Manufactured Cobalt Alloy.

Oxide-dispersion-strengthened (ODS) alloys have long been considered for high temperature turbine, spacecraft, and nuclear reactor components due to their high temperature strength and radiation resistance. Conventional synthesis approaches of ODS alloys involve ball milling of powders and consolidation. In this work, a process-synergistic approach is used to introduce oxide particles during laser powder bed fusion (LPBF). Chromium (III) oxide (Cr2O3) powders are blended with a cobalt-based alloy, Mar-M 509, and exposed to laser irradiation, resulting in reduction-oxidation reactions involving metal (Ta, Ti, Zr) ions from the metal matrix to form mixed oxides of increased thermodynamic stability. A microstructure analysis indicates the formation of nanoscale spherical mixed oxide particles as well as large agglomerates with internal cracks. Chemical analyses confirm the presence of Ta, Ti, and Zr in agglomerated oxides, but primarily Zr in the nanoscale oxides. Mechanical testing reveals that agglomerate particle cracking is detrimental to tensile ductility compared to the base alloy, suggesting the need for improved processing methods to break up oxide particle clusters and promote their uniform dispersion during laser exposure.

Microstructural evolution and wear properties of chromium carbide coating formed by thermo-reactive diffusion (TRD) process on a cold-work tool steel

In the current study, the possibility of forming a chromium carbide layer on the surface of an AISI W1 cold work tool steel was investigated. The coatings were fabricated through a thermo-reactive diffusion (TRD) treatment by the molten salt bath at 800, 900, and 1000 °C for 4, 5, and 6 h using chromium oxide powder. The structural and mechanical properties of the coatings formed at the different conditions (temperature and immersion time) were compared together. For this purpose, the coating layers were characterized by field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectrometer (EDS) as well as X-ray diffraction (XRD) method. Moreover, the hardness and friction coefficient (COF) of the coated samples were examined through micro-indentation and ball-on disk tests, respectively. It was determined that at 800 °C, just chromium carbide nuclei are formed, and the temperature is insufficient to produce a complete chromium carbide layer on the substrate. XRD results of the coating produced at this temperature showed that the main phase is Fe–Cr solid solution. However, compact, adherent, uniform, and crack-free chromium carbide coatings with thickness ranging from 5.14 to 18.06μm were successfully obtained on the substrate at 900 and 1000 °C, mainly consisting of Cr7C3, Cr23C6, and Cr3C2. The XRD results showed that the possibility of forming chromium carbide phases increases with increasing temperature and immersion time. The hardness of the coatings was in the range 771 to 1600 HV, depending on the process condition. The results demonstrated that increasing the temperature and immersion time of the TRD process increases the thickness and hardness of coatings, resulting in low friction coefficient values and improvement in the wear resistance up to 6 times compared to the untreated AISI W1 sample.

Digesta retention time and recovery rates of ants and termites in Chinese pangolins (Manis pentadactyla).

Pangolins are myrmecophagous mammals whose biology and ecology remain poorly studied. Termite mandibles and ant head capsules are the two primary remains found in pangolin feces. Determining the retention time of insect cuticles is important for understanding the digestive physiology of pangolins, while determining the recovery rate of termites and ants in feces is required to estimate the number of these prey items that are consumed by pangolins. In this study, the authors conducted feeding trials with captive Chinese pangolins (Manis pentadactyla). Sixty grams of the fungus-growing termite Odontotermes formosanus (18,816 individuals) and 15-20 g of the yellow crazy ant Anoplolepis gracilipes (14,400-19,200 individuals) were fed to each pangolin. After feeding, pangolin feces were collected daily for 1 week. The authors also assessed the accuracy of using chromium (III) oxide powder (Cr2 O3 ) as a proxy for determining gut passage time, as has been done in previous studies. The results showed that remaining termite mandibles and ant head capsules in feces peaked at 66 and 90 hr after feeding and their recovery rates were 0.35 ± 0.10 and 0.65 ± 0.04, respectively. In both feeding trials, the retention time of Cr2 O3 was much shorter than that of the termite mandibles and ant head capsules, indicating that Cr2 O3 is not an appropriate indicator for estimating food retention time of myrmecophagous animals. Our results revealed that the ant head capsules were preserved better in feces compared with the termite mandibles, suggesting that termites may be considerably underestimated in the feces of wild pangolins.

Adverse Effect of Europium Doping on Magneto-Optical Properties of Cr2O3

The article describes in detail the effect of doping Europium (Eu) on magnetic and optical properties of Cr2O3. Undoped and Eu (1–5 mol%) doped Cr2O3 samples were synthesized using solid state synthesis method. The structural, magnetic and optical properties of undoped and Europium (Eu) doped chromium oxide powder were studied by X-ray diffractometer (XRD), vibrating sample magnetometer (VSM) and photoluminescence (PL) measurements. The X-ray diffraction pattern confirms the polycrystalline nature of undoped and Europium (Eu) doped chromium oxide powder. The magnetic measurements revealed decline in magnetism with increasing Eu concentration. With increasing Eu concentration, the visible luminescence of Cr2O3 improved. The study highlighted that Eu as a dopant is not suitable for improving the magnetic properties of Cr2O3.

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.

Chromium silicide-based composites fabricated via solid-state reactions: Phase development, oxidation behavior and electrical properties at high-temperatures

The chromium silicide-based electroconductive composites were fabricated by solid-state sintering of chromium silicide and chromium oxide powders at 1370 °C in argon. The final densified composites were composed of various solid solution and silicide phases (e.g. Cr3Si, Cr5Si3) and silica, depending on the starting silicide/oxide volume ratio ranging from 0.67 to 9.0. Major phases were found to be homogeneously distributed within the metastable (cristobalite) and/or amorphous silica grain boundary phase. The controlled oxidation experiments revealed excellent oxidation resistance at 50°-870 °C, where low-level oxidation was observed. The composites all displayed a metallic-type electrical conductivity due to the presence of the Cr3Si, Cr5Si3 and CrSi as the major conductive silicide phases. Their electrical conductivities ranged from 42.1 to 213.7 S/cm at 1000 °C. High-temperature annealing of the composites resulted in phase and microstructural changes, which further improved their high-temperature oxidation resistance and electrical transport properties.

Effect of Carbon Nanotubes on Properties of Ceramics Based Composite Coatings

In the present work, 2% and 6% carbon nanotubes (CNT) were reinforced in chromium oxide powder and were deposited on T22 steel using high velocity oxy-fuel spraying process. The effect of CNT reinforcement on hardness and porosity was investigated. The hardness was observed to be highest for coating reinforced with 6%CNT and hardness was found to increase with decrease in porosity. The coating microstructure and elements were characterised using field emission scanning electron microscopy (FE-SEM) with energy dispersive spectroscope (EDS), Elemental point analysis and X-ray mapping analysis. The constituents of the coating were identified using X-ray diffractometer. It was found that the CNT were uniformly distributed throughout Cr2O3matrix. The CNT were found to be chemically inert during the spraying process.

Effect of arc\u2013current and spray distance on elastic modulus and fracture toughness of plasma-sprayed chromium oxide coatings

In this experimental study, chromium oxide powder was sprayed on a low-carbon steel substrate using the atmospheric plasma spray process. The current and standoff distances (SODs) were varied to study their effect on the fracture toughness of the coatings. Theoretically, as the arc current increases, the melting of the ceramic oxide should increase and this in turn should lead to the formation of a dense coating. However, it was observed that if the arc power is too high and because the particle size of the powder is small (approximately 30 μm), the particles tend to fly away from the plasma core. Similarly, an appropriate SOD should provide the particles with more melting time, thus resulting in a dense coating. On the other hand, a larger SOD leads to the solidification of the molten particles before the droplets can reach the substrate. All these effects may lead to substantial variation in the fracture toughness of the coating. The present paper attempts to correlate the plasma spraying parameters and microstructure of the coating with the fracture toughness and other primary coating properties.

A comparative study on solid particle erosion behavior of plasma sprayed Cr2O3 coatings on 410 grade steel

In the present investigation chromium oxide (Cr2O3) powder particles were used to deposit on 410 martensitic steel. Ni-Cr was used as bond coat. Erosion studies were directed on uncoated and also plasma sprayed steel examples at room temperature. The Erosion analyses were done utilizing an air-jet erosion test rig at a speed of 30 m/s by varying stand-off distance as per ASTM G-76. The stand-off distance considered were 10mm, 20mm, 30mm & 40mm. Silica sand particles of size 312μm was used as erodent. The surface morphologies were characterized using Scanning electron microscope (SEM) and presence of coating material was confirmed using energy dispersive X-ray analyzer (EDS). Vickers micro harness test was performed on surface of coated and un-coated substrates. It was observed that Cr2O3 Coated specimen exhibits better Erosion resistance when contrasted with uncoated substrates because of its enhanced property like micro hardness.

Plasma transferred arc surface modification of atmospheric plasma sprayed ceramic coatings

In this study, a 90MnCrV8 steel surface was coated with aluminum oxide and chromium oxide powders through the Atmospheric plasma spray (APS) and Plasma transferred arc (PTA) methods. The effects of PTA surface melting on the microstructure, hardness, and wear behavior were investigated. The microstructures of plasma-sprayed and modified layers were characterized by Optical microscopy (OM), Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDS). The dry-sliding wear properties of the samples were determined through the ball-on-disk wear test method. Voids, cracks, and nonhomogeneous regions were observed in the microstructure of the APS ceramic-coated surface. These microstructure defects were eliminated by the PTA welding process. The microhardness of the samples was increased. Significant reductions in wear rate were observed after the PTA surface modification. The wear resistance of ceramic coatings increased 7 to 12 times compared to that of the substrate material.

Characterization of Physical, Thermal and Structural Properties of Chromium (VI) Oxide Powder: Impact of Bio Field Treatment

Chromium (VI) oxide (CrO3) has gained extensive attention due to its versatile physical and chemical properties. The objective of the present study was to evaluate the impact of biofield treatment on physical, thermal and structural properties of CrO3 powder. In this study, CrO3 powder was divided into two parts i.e. control and treatment. Control part was remained as untreated and treated part received Mr. Trivedi’s biofield treatment. Subsequently, control and treated CrO3 samples were characterized using Thermo gravimetric analysis-differential thermal analysis (TGA-DTA), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). DTA showed that the melting point of treated CrO3 was increased up to 212.65°C (T3) as compared to 201.43°C in control. In addition, the latent heat of fusion was reduced upto 51.70% in treated CrO3 as compared to control. TGA showed the maximum thermal decomposition temperature (Tmax) around 330°C, was increased upto 340.12°C in treated CrO3 sample. XRD data revealed that lattice parameter and unit cell volume of treated CrO3 samples were reduced by 0.25 and 0.92% respectively, whereas density was increased by 0.93% in treated CrO3 sample as compared to control. The crystallite size of treated CrO3 was increased from 46.77 nm (control) to 60.13 nm after biofield treatment. FT-IR spectra showed the absorption peaks corresponding to Cr=O at 906 and 944 cm-1 in control, which were increased to 919 and 949 cm¬1 in treated CrO3 after biofield treatment. Overall, these results suggest that biofield treatment has substantially altered the physical, thermal and structural properties of CrO3 powder.

Characterization of Physical, Thermal and Structural Properties of Chromium (VI) Oxide Powder: Impact of Biofield Treatment

Characterization of Physical, Thermal and Structural Properties of Chromium (VI) Oxide Powder: Impact of Biofield Treatment

Characterization of Physical, Thermal and Structural Properties of Chromium (VI) Oxide Powder: Impact of Biofield Treatment

Characterization of Physical, Thermal and Structural Properties of Chromium (VI) Oxide Powder: Impact of Biofield Treatment

Ca3(PO4)2 biomaterial: A non toxic template to prepare highly porous Cr2O3

There is great interest in finding efficient templates. Here we report that Cr2O3 powders with enhanced surface properties were synthesized by a calcination of chromium nitrate salt that used Ca3(PO4)2 calcium phosphate nanopowder as a biotemplate reactant. We used various amounts of template in order to modulate the surface properties of the chromium oxide powder, which was characterized by different techniques. Improved surface properties (SBET=49.59m2/g, Vp=0.18cm3/g) for the Cr2O3 powder were obtained with a Cr2O3/Ca3(PO4)2 weight ratio of 1. This calcium-based biotemplate is clearly an alternative to other conventional templates used for preparing large surface materials. The template is non-toxic and readily removable, which are real advantages.

The Hydrogen Evolution Reaction on Ni Electrode Material Modified with Molybdenum(IV) Oxide and Chromium(III) Oxide Powders

The Ni+MoO2and Ni+Cr2O3composite coatings were prepared by the electrodeposition under the galvanostatic conditions (jdep= -200 mA cm-2) from the nickel bath containing powder of MoO2or Cr2O3. Studies of hydrogen evolution reaction (HER) in 5 M KOH solution at room temperature were conducted using steady-state polarization and electrochemical impedance spectroscopy (EIS) methods. It was ascertained that the HER rate is higher for the Ni+MoO2composite electrode in comparison with the Ni+Cr2O3composite electrode due to the presence of Mo in the nickel matrix.

Characterization of Physical, Thermal and Structural Properties of Chromium (VI) Oxide Powder: Impact of Biofield Treatment

Chromium (VI) oxide (CrO3) has gained extensive attention due to its versatile physical and chemical properties. The objective of the present study was to evaluate the impact of biofield treatment on physical, thermal and structural properties of CrO3 powder. In this study, CrO3 powder was divided into two parts i.e. control and treatment. Control part was remained as untreated and treated part received Mr. Trivedi’s biofield treatment. Subsequently, control and treated CrO3 samples were characterized using Thermo gravimetric analysis-differential thermal analysis (TGA-DTA), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). DTA showed that the melting point of treated CrO3 was increased upto 212.65°C (T3) as compared to 201.43°C in control. In addition, the latent heat of fusion was reduced upto 51.70% in treated CrO3 as compared to control. TGA showed the maximum thermal decomposition temperature (Tmax) around 330°C, was increased upto 340.12°C in treated CrO3 sample. XRD data revealed that lattice parameter and unit cell volume of treated CrO3 samples were reduced by 0.25 and 0.92% respectively, whereas density was increased by 0.93% in treated CrO3 sample as compared to control. The crystallite size of treated CrO3 was increased from 46.77 nm (control) to 60.13 nm after biofield treatment. FT-IR spectra showed the absorption peaks corresponding to Cr=O at 906 and 944 cm-1 in control, which were increased to 919 and 949 cm¬1 in treated CrO3 after biofield treatment. Overall, these results suggest that biofield treatment has substantially altered the physical, thermal and structural properties of CrO3 powder.

Effect of protective release coatings on the basis of superdispersersed zirconium oxide powder on the formation of gas defects in bronze casting

This paper investigates the use of nanopowders in the composition of foundry coatings when casting leaded tin bronzes. Influence of the composition of the applied protective coating on surface finish is studied. The effects of the coatings of the following compositions are compared: non-stick coating (a mixture of low-dispersed chromium oxide powder and heat-treated vegetable oil); non-stick lubricant ASPF-2/RgU on the basis of low- dispersed graphite powder and heat-treated vegetable oil; patent #2297300 (a mixture of superdispersed zirconium dioxide powder with industrial oil). It is demonstrated that application of foundry coatings containing superdispersed metal oxide powders with low thermal conductivity makes it possible to significantly reduce irregularities and eliminate gas porosity on the surface of tin-leaded bronze castings.

Chromium oxide dissolution in steels via short pulse laser processing

Changes of microstructure, chemical and phase compositions in thin surface layers of low carbon steel saturated by chromium oxide have been studied by TEM, XPS and XRD methods. Ultrafine chromium oxide powder was spread on a steel surface and subjected to laser processing with nanosecond pulses. It was found that such conditions of processing as overheating of small volume of metal, high temperature gradient, rapid solidification and laser-induced plasma formation lead to dissolution of chromium oxide in the metal matrix. As a result of laser processing the surface layers contain chromium oxide, chrome-spinel FeO $$\cdot $$ Cr $$_{2}$$ O $$_{3}$$ and chromium in metal state dispersed in alpha and gamma iron. The processing technique allows to obtain surface layers whose chemical composition might be equivalent to the composition of stainless steels.

In-Situ Synthesis of Alumina Reinforced (Fe,Cr)3Al Intermetallic Matrix Nanocomposite

In this study, a mixture of chromium oxide, elemental iron, and aluminum powders was subjected to high energy ball milling to produce Al2O3 reinforced (Fe,Cr)3Al matrix nanocomposite. The structural changes of powder particles during milling were investigated by X-ray diffractometry. Cross-sectional microstructure of powder particles after different milling times was observed by scanning electron microscopy using back scatter mode. The change in morphology of powder particles was followed by scanning electron microscopy observations. The transmission electron microscopy was used to confirm the development of nano-sized structure in the final product. The changes in phase composition, structure and morphology of powder particles suggested that during milling, Al gradually reacts with Cr2O3 leading to the formation of metallic Cr and Al2O3 phases and concurrently, the reduced Cr and remaining Al diffuse into the Fe lattice and as a result, a Fe(Al,Cr) solid solution forms. This structure was transformed to (Fe,Cr)3Al intermetallic compound at longer milling times.