Addition Of Cr2O3 Research Articles

Toughening Mechanism of CaAl12O19 in Red Mud–Al2O3 Composite Ceramics

The utilization of red mud in the production of ceramic products represents an efficient approach for harnessing red mud resources. Composite ceramics were prepared from Al2O3, red mud, and Cr2O3 by atmospheric pressure sintering, and the phase composition and microscopic morphology of the composite ceramics were investigated by XRD, SEM, and EDS. The flexural strength and fracture toughness of composite ceramics were measured by three-point bending and SENB methods. The results showed that the composite ceramics sintered at 1500 °C with the addition of 1.5 wt.% Cr2O3 had a flexural strength of 297.03 MPa, a hardness of 17.44 GPa, and a densification of 97.75% and fracture toughness of 6.57 MPa·m1/2. The addition of Cr2O3 helps to improve the low strength of red mud composite ceramic samples. The CaAl12O19 phase can form a similar “endo-crystalline” structure with Al2O3 grains, which changes the fracture mode of the ceramics and thus significantly improves the fracture toughness. The wettability tests conducted on Cu and RM–Al2O3 composite ceramic materials revealed that the composites exhibited non-wetting behavior towards Cu at elevated temperatures, while no interfacial reactions or elemental diffusion were observed. Composites have higher surface energy than Al2O3 ceramic at high temperatures. The present study provides a crucial foundation for enhancing the comprehensive utilization value of red mud and the application of red mud ceramics in the field of electronic packaging.

Enhancing UV light sensitivity of PVP polymer by doping chromium trioxide via the electrospun solutions

Herein, chromium trioxide (Cr2O3) doped Polyvinylpyrrolidone(PVP) nanofibers with high crystallinity and UV light sensitivity are successfully grown onto the glass substrates by electrospun deposition at room temperature. The effect of Cr2O3 concentration on the morphology, structure, and photoluminescence properties of the as-fabricated PVP nanofibers is examined. With the increase in doping concentration of Cr2O3 (i.e., 1, 2 and 3 %), the direct band gap of PVP nanofibers is reduced to 4.05, 4.01, and 3.85 eV, respectively. XRD and FE-SEM results manifest that the crystallinity and diameter of the nanofibers are dependent upon Cr2O3 concentration, i.e., the mean diameter decreases from 600 to 200 nm. Photoluminescence spectra indicate higher UV emission upon the addition of Cr2O3, with greater emission near the band edge for thinner nanofibers. A possible mechanism for the formation of PVP/Cr2O3 nanofibers is addressed in detail. Furthermore, it is found that the sensitivity of the as-fabricated PVP/Cr2O3 detector to UV-light emission strongly depends on Cr2O3 concentration, i.e., good responsivity (2.257 A/W) and specific detectives (9.8 × 1012 cm Hz1/2/W) at a Cr2O3 concentration of 2 % are achieved at a wavelength of 454.1 nm, besides recording the lowest rise and fall times.

Mathematical modeling and flow thermodynamics study of borosilicate glass melt after external addition of Cr2O3

This article uses a high-temperature sintering imaging instrument to test the flowability of borosilicate glass melt doped with Cr2O3, and establishes a mathematical model for high-temperature glass melt spreading. Discuss the glass melt from a thermodynamic perspective by combining model interpretation with experimental characterization. The results indicate that the thermodynamic judgment formula for high-temperature flow spreading of borosilicate glass is: Q≥ρ[A0exp(−T/k0)+S0]−M·δ[A0exp(−T/k0)+S0]1/2. To improve the high-temperature flow ability of borosilicate glass, it is necessary to increase the spreading activation energy Q. On the other hand, it is necessary to reduce the spreading coefficients A0、 k0 and S0. As a refractory metal oxide and active oxide, Cr2O3 plays a role in reducing the spreading coefficient of glass systems.

Preparation of CaO-MgO-Al2O3-SiO2 glass-ceramic with a high content of Cr2O3 using the spark plasma sintering (SPS)

2, 6, or 10 wt% of Cr2O3 was added into the CaO-MgO-Al2O3-SiO2 precursor glasses (PG), aiming to investigate the effects of high contents of Cr2O3 on the crystallization behavior and mechanical properties of glass-ceramics (GCs). The PGs were milled into powder and then sintered by spark plasma sintering (SPS) technology at 750∼850 °C under the pressure of 10 MPa. It was found that Cr2O3 induced the precipitation of spinel nuclei in the PGs, which served as the heterogeneous nucleation sites for the augite crystals. Augite and spinel were the main phases of the GCs, and the crystallinity increased by increasing the Cr2O3 addition amount and sintering temperature. The GC prepared at 850 °C with 6 wt% Cr2O3 addition showed excellent bending strength, with Vickers hardness, and fracture toughness of 214 MPa, 8.2 GPa, and 1.3 MPa·m1/2, respectively.

The lattice contraction of UO2 from Cr doping as determined via high resolution synchrotron X-ray powder diffraction

High resolution synchrotron powder X-ray diffraction analysis of Cr-doped UO2 samples with additions of Cr2O3 as 0, 500, 1000, 1500, 2500 to 3500 ppm prepared under sintering conditions of -420 kJ/mol and 1700 °C is reported. The lattice dependence from Cr doping is established through the Rietveld refinement method where the rate of linear lattice parameter contraction from Cr doping, Δacr, was found to be considerably smaller and more subtle than previously described. This investigation highlights the need for high resolution and precise specimen preparation when measuring and interpreting subtle changes to nuclear material crystal structures due to trace doping.

Mechanical Properties of ZTA-Cr2O3 Ceramic Composites Prepared with Nano and Micron Sized of Cr2O3 Powder on Different Ratios

In this study, the effect of Cr2O3 addition in different powder sizes on the densification and mechanical properties (elastic modulus, hardness and flexural strength) of ZTA composites were investigated. Nano and micron sized of Cr2O3 powder were added to the ZTA composite separately in different weight ratios (0.3, 0.6, 1%) and uniaxially dry pressing right after pressureless sintering at 1650°C/2 h in the air used as processing procedure. The relative density values of all the composites were close to each other for the Cr2O3 containing composites. A slight decrease in both densification and elastic modulus was observed with the addition of Cr2O3 due to the evaporation problem. Also, the addition of Cr2O3 did not have a serious effect on the hardness of the ZTA composites. The main effect of Cr2O3 addition on ZTA composites was seen for flexural strength. Compared to the ZTA, a nearly 7% increase in strength was obtained for 0.6%Cr2O3 containing composite prepared with micron sized Cr2O3 powder due to the generated compressive stresses in the grain boundary caused by solid solution formation.

Effects of Ni/MoS2, Ag and Cr2O3 on the Microstructure and Mechanical Performance of a CoCrFeNi High-Entropy Alloy over a Wide Temperature Range

In the field of aerospace, core components require excellent wear resistance, lubrication and mechanical properties over a wide temperature range. In this study, three groups of CoCrFeNi high-entropy alloy (HEA)-based self-lubricating composites were designed with the addition of Ag, Ni/MoS2 and Cr2O3 using discharge-plasma-sintering technology. Their microstructure, phase composition, mechanical properties, friction and wear properties were analyzed. The results showed that, with the addition of Ag, the hardness and yield stress of HEA-Ni/MoS2-Ag were reduced by 36 HV and 24 MPa, respectively, while the plastic strain was increased by 2%. With the addition of Cr2O3, the hardness (382 HV) and yield stress (430 MPa) of HEA-Ni/MoS2-Ag-Cr2O3 reached their highest values, but the plastic strain reached its lowest value. HEA-Ni/MoS2-Ag-Cr2O3 had the smallest friction coefficient in which the friction coefficient at 800 °C was only 0.42. Additionally, it had a small wear rate of 3.2 × 10−6 mm3/Nm over a wide temperature range. At lower temperatures, Ni/MoS2 and Ag were conducive to lubrication, and the wear resistance was improved by the presence of Cr2O3. At high temperatures, a nickel oxide phase and a variety of silver molybdate phases were formed via a tribochemical reaction, which was vital to the high-temperature tribological properties.

Effect of chromium on the spatial distribution of sulfur during pyrolysis of coal with high organic sulfur

The selective removal of stable sulfur-configuration makes high-sulfur coking coal reserves available in coking process. However, stable organic sulfur is difficult to remove effectively and is easily immobilized by secondary reactions in the volatile phase migration pathway. In this work, Cr commonly found in steelmaking wastewater was used as additive for the desulfurization of high organic sulfur coking coal, and its effect on spatial distribution and conversion of sulfur forms during the high-temperature coking process was studied by sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy. The results show that the chromium additives effectively promote sulfur removal during pyrolysis. In the vertical direction, the addition of Cr2O3 captures sulfur radicals to form sulfide and promotes the breaking of sulfoxide OS bonds at the bottom of the coke. Furthermore, in the horizontal direction, the addition of CrCl3 by impregnation generates sulfide by combining with sulfur radicals after breaking down thiophenic CS bonds and promotes the breaking of sulfoxide O-S bonds. This results in a significant decrease of the desulfurization rate as the escape of volatiles from the bottom to top and from inside to outside of the coke. The results not only provide guidance for selective sulfur removal of coal during pyrolysis with high-sulfur coking coal but also for the conversion of polluting steelmaking wastewater into available resources.

The effect of different transition metal oxides on the characterization and photoluminescence properties of borosilicate glass ceramics containing nanosized anatase type-TiO2

In this study, crystallization of anatase type-TiO2 was achieved in the traditional borosilicate glasses (Na2O.B2O3.SiO2) for the first time. The effect of the TiO2 /Na2O ratio was studied to optimize the selected glass composition, also the effect of adding a definite amount of different transition metal oxides (TMO) was studied. The glasses were prepared via the conventional melt-quenching method. According to DSC results, heat treatment at 650 °C /10hrs was applied to convert the glasses into glass ceramics. XRD detected the crystallization of anatase, rutile, and cristobalite. A sample with a lower value of TiO2 /Na2O revealed a higher degree of crystallization of anatase than that with a higher value. Both Cr2O3 and NiO additions enhanced the crystallization of cristobalite; while additions of CoO, Fe2O3, V2O5, MnO, CuO or ZnO significantly enhanced the crystallization of anatase in the same order. The morphology of glass ceramic was observed by TEM and SEM, which revealed crystal size < 50 nm. The optical band gap was estimated from UV-Visible absorption spectra, it depicted a wide range of values (4.4–2.1 eV). PL spectra revealed emission colors varied from purple to blue color according to TMO and TiO2 /Na2O ratio. The obtained materials can be utilized as electron transport layers for perovskite solar cells.

Equilibrium Phase Relationships of CaO-SiO2-TiO2 System with 5 wt% Cr2O3 Addition for Titania-Bearing Slag Recycling

Equilibrium Phase Relationships of CaO-SiO2-TiO2 System with 5 wt% Cr2O3 Addition for Titania-Bearing Slag Recycling

Mechanical properties and microstructure of Cr2O3 reinforced 3Al2O3·2SiO2 composite refractories

Chromium-containing refractories have excellent high-temperature corrosion resistance. In this work, Cr2O3 reinforced Al2O3–SiO2 composite refractories were prepared by reaction sintering process. The microstructure, phase composition, mechanical properties and strengthening mechanism of the Cr2O3 reinforced Al2O3–SiO2 composite refractories were investigated. The results show that when the Cr2O3 content is 10–20 wt%, the composites are mainly composed of Cr-mullite (Al3.94Cr0.50Si1.56O10.44), (Al, Cr)2O3, and a small amount of SiO2 phase. When the Cr2O3 content exceeds 20%, the composite refractories mainly consist of (Al, Cr)2O3 and SiO2 phases. The appropriate amount of Cr2O3 can effectively enhance the mechanical properties and compactness of the Cr2O3 reinforced Al2O3–SiO2 composites. This is mainly due to the formation of Cr doped mullite and SiO2 phases, which reduces the sintering temperature of mullite ceramics and improves its density and mechanical properties. The highest hardness (27.03 GPa), flexural strength (213.21 MPa) and compressive strength (528 MPa) values are observed at a Cr2O3 content of 20 wt%. However, excessive addition of Cr2O3 will deteriorate the mechanical properties of the composites. The formation of a large amount of (Al, Cr)2O3 solid solution phase will increase the porosity of the composites, and reduce the compactness and sintering properties of the composites.

Influence of ZnO on the structural, optical, ligand field and antibacterial characteristics of sodium borosilicate glasses containing minor Cr2O3 additions

In this work, the structural, optical, ligand field, and antibacterial properties of Cr2O3, ZnO and Na2O borosilicate glasses were studied. A glass system of the compositions 70B2O3−14.8 SiO2-(15-x)Na2O-0.2Cr2O3-xZnO, where x = 0, 3, 5 and 7 mol% was prepared via melt-quenching technique. In this study, X-ray diffraction (XRD) spectra were used to check the amorphous state of the prepared glass specimens. Infrared (IR) spectra were used to study the internal structure of the formed units and groups within the glass matrix. Moreover, the optical absorbance spectra were used to study the optical parameters, such as optical band gap and ligand field parameters. Furthermore, the antibacterial activities of the glass samples were investigated against different antibiofilm activities, for example, Staphylococcus aureus and Escherichia coli. The optical studies showed that Eg values increased from 3.06 to 3.62 with further ZnO doping. Furthermore, values increased and B values decreased with the increase in ZnO content. The 10Dq increased values reflect the increased interactions between the Cr3+ cations and their environments, such as oxygen anions. Further, the decreased values of B refer to the tendency of the bonds of Cr3+ cations and their environments toward the covalent nature. On the other hand, the results showed that the investigated glasses are promising materials owing to high antibacterial activity on a large scale (food covering, wound curing, and surface coatings), especially the glass sample that contains the highest concentrations of ZnO. Furthermore, it demonstrated antioxidant activity using DPPH and H2O2 free radical scavenging activities.

Crystallization of Sodium Borosilicate Glass with the Addition of Cr2O3

Crystallization of Sodium Borosilicate Glass with the Addition of Cr2O3

Crystallization of Sodium Borosilicate Glass with the Addition of Cr2O3

Glass composition of 6Na2O 22B2O3·70SiO2·2Cr2O3 is studied by scanning electron microscopy, X‑ray powder diffractometry (XRPD), and differential thermal analysis, depending on the duration of heat treatment at a temperature of 550°C. It is established that during heat treatment for 24–96 h, a phase separation structure with interpenetrating phases is formed in the studied glass, and a crystalline phase of eskolaite—Cr2O3 is also formed. With the maximum heat treatment duration of 96 h, cristobalite is formed in the bulk of the glass, which is accompanied by a decrease in the glass transition temperature of the low-viscosity phase. In this case, the intensity of eskolaite peaks decreases. Cr2O3 and SiO2 crystallize apparently due to the substance of the low-viscosity phase.

Corrosion mechanism of magnesia-chrome refractory bricks with FetO-SiO2-Cr2O3 copper converter slag

The paper investigates the effect of Cr2O3 on the resistance of magnesia-chrome refractory bricks to copper converter slag. The static crucible method was employed to carry out the slag resistance experiment. The corrosion of magnesia-chrome refractory bricks under the action of FetO-SiO2-xCr2O3 (x = 0–5 wt%) slag at 1300 °C was discussed. The microstructure of the corroded sample was analyzed by XRD and SEM-EDS to elucidate the corrosion mechanisms of magnesia-chrome refractory bricks with FetO-SiO2-Cr2O3 slag. The results indicated that the permeability index of the slag-resistant samples gradually decreased with increasing Cr2O3 content in the FetO-SiO2-Cr2O3 slag. Combined with SEM and XRD characterization, the MgO in the refractory reacted with FeO and SiO2 in the molten slag, leading to dissolution and reaction corrosion of the refractories. Meanwhile, forming a (Mg, Fe)O solid solution layer in corroded samples can prevent further chemical reactions and high-temperature dissolution between the FetO-SiO2-Cr2O3 slag and refractories. With the addition of Cr2O3 in the FetO-SiO2-Cr2O3 slag, the corrosion effect of slag on refractories was weakened, and the (Mg, Fe)O solid solution layer became thinner. The magnesia-chrome refractory bricks showed excellent slag resistance when the Cr2O3 content in the copper converter slag was 5 wt%.

Enhanced electrical properties of Cr2O3 addition NBT‐based high‐temperature piezoelectric ceramics

AbstractOwing to industrial and technological developments, there has been an increasing demand for piezoelectric ceramics that can function at temperatures of 500°C or higher. Na0.5Bi4.5Ti4O15 (NBT) with its high Curie temperature (TC) of 650°C is a typical bismuth layer–structured ferroelectric. However, its relatively low piezoelectric coefficient (d33 ∼ 16 pC/N) hinders its potential application at high temperatures. In this study, compositions of Ca0.05(Na0.5Bi0.5)0.95Bi4Ti4O15 with different additions of Cr2O3 (CNBT–Cr100x) were designed based on previous studies on Ca2+‐doped NBT piezoceramics, and the effects of the addition on the structural and electrical properties were investigated. The d33 value of CNBT–Cr20 was as high as 29 pC/N, almost twice higher than that of pure NBT ceramics. This increase was investigated in depth using X‐ray diffraction refinement and piezoelectric force microscopy in terms of intrinsic and extrinsic contributions. The Ps values of CNBT and CNBT–Cr20 were almost equal. The density of the domain walls of CNBT–Cr20 was significantly higher than that of CNBT, indicating that the increase of d33 of CNBT–Cr20 is mainly due to the increase in the extrinsic contribution. The CNBT–Cr20 ceramic exhibited excellent properties with a high TC of 655°C, a high d33 of 29 pC/N, and a resistivity high than 106 Ω cm at 500°C, demonstrating its potential for applications at high temperatures such as 500°C.

Influence of Cr2O3 doping on the electrical characteristics of novel ZnO-Cr2O3-based varistor ceramics

Novel ZnO-Cr2O3-based varistors can overcome the problems related to the volatile, high-cost and toxic components of conventional ZnO-Bi2O3-, ZnO-Pr6O11-, and ZnO-V2O5-based varistors. The influence of the varistor former with different doping levels, i.e., the Cr2O3, on the microstructure and electrical properties was examined and the optimal amount of Cr2O3 doping to enhance the electrical performance of ZnO-Cr2O3-based varistor ceramics was determined. The results showed that about 0.1 mol.% of Cr2O3 is optimal for the formation of the electrostatic double Schottky barriers with increased height at the grain boundaries (GBs) and thus an enhanced I-V nonlinearity (i.e., a coefficient of nonlinearity α = 73) and a lower leakage current (IL < 0.2 μA/cm2) in ZnO-Cr2O3-based varistor ceramics with an Eb of 383 V/mm. For larger additions of Cr2O3, a Ca3(CrO4)2 phase forms, which decreases the barrier height and leads to a lowering of α and an increase in IL.

Formation of electric spark WC-Co coatings with modifying Cr2O3 additives

Tungsten carbide coatings are widely used on steels due to their high hardness and wear resistance, but they have low high-temperature oxidation resistance and therefore need to be modified with oxidation resistance compounds. Electrode materials based on WC-8 %Co with addition of 1, 3 and 6 wt.% Cr2O3 were prepared by powder metallurgy for the deposition of electric spark coatings on steel 1035. An increase in the content of Cr2O3 in electrodes led to a rise in the thickness of the coatings from 18.2 to 28.3 µm. The tungsten semicarbide phase dominated in the structure of the coatings. The concentration of chromium in the coatings is a function of it in the electrodes. Polarization tests of coated samples showed an increase in the corrosion potential and a decrease in the corrosion current density with an increase of Cr2O3 concentration in WC-Co electrodes. The Cr2O3 additions into the WC-8 %Co electrode allow increasing the oxidation resistance of coatings at a temperature of 700°C. The coating microhardness increased monotonically from 9.6 to 13 GPa, the friction coefficient decreased from 0.7 to 0.58, and wear rate decreased with increasing Cr2O3 content. Electric spark deposition of the WC-8 %Co electrode with addition of Cr2O3 on steel 1035 allows increasing its wear resistance up to 14 times.

Impact of Cr doping on the performance of Ni/Al2O3 catalyst through methane decomposition into COx-free hydrogen and carbon nanomaterials

The co-production of clean hydrogen and nanostructured carbon materials via methane decomposition is a desirable alternative route for energy savings and environmental considerations. In the current study, Al2O3 supported monometallic 50%Ni and bimetallic 40%Ni-10%Cr catalysts were prepared and evaluated for this reaction. The as-prepared catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), and N2 physisorption, and Raman spectroscopy. Meanwhile, the spent catalysts were characterized by XDR, SEM, and Raman spectroscopy. According to XRD, TPR, and SEM results, the incorporation of Cr2O3 into the Ni/Al2O3 catalyst improved metal dispersion and reduction behavior compared to the un-promoted catalyst. As a result, the Ni-Cr/Al2O3 catalyst exhibited exceptional activity in terms of hydrogen yield throughout the whole reaction periods. Furthermore, the Cr2O3 inclusion enhanced catalyst stability by preventing the aggregation of active metal sites during the decomposition process. In contrast, the presence of agglomerated NiO particles on the surface of the Al2O3 support was the primary cause of deteriorating the activity of Ni/Al2O3 catalyst over a long reaction period. Both catalysts produced 79 % hydrogen at the start of the reaction (10 min), but by the end of the reaction (180 min), the hydrogen yield was 57 % and 76 % for Ni/Al2O3 and Ni-Cr/Al2O3 catalysts, respectively. In addition, the addition of Cr2O3 raised the accumulated carbon yield from 9.2 to 13.5 gC/gNi for both catalysts, respectively. SEM images showed that thin carbon nanotubes were deposited on the Ni-Cr/Al2O3 catalyst, whereas large-diameter carbon nanotubes were grown on the Ni/Al2O3 catalyst.

Synthesis of new Cr2O3/Fe2O3/glass composites from industrial wastes; from undesired to advanced optical products

For the tendency toward cleaner production and safe conversion of undesired toxic wastes to highly priced advanced products, this work introduces new ceramics/glass composites of Cr2O3/Fe2O3/lead silicate glass (LSG) from industrial LSG wastes. Both chromia Cr2O3 and hematite Fe2O3 ceramics are added equally to the LSG wastes with different percentages (10, 20, and 30 wt.%) via the pressureless sintering method. The competitiveness of this work is dependent on the conversion of undesired waste materials into advanced/smart optical materials with a low cost and an environmentally friendly method. Hence, the influence of both Cr2O3 and Fe2O3 additions on the behavior and the different characteristics of the lead silicate wastes are comprehensively investigated. Evaluation of the final ceramics/glass composites was achieved through their phase composition, microstructure, optical, and magnetic characteristics. The results verified that the insertion of both chromia and hematite together into the glass waste had a key role in improving its morphological properties and optical and magnetic behaviors. Composite with 30% of Cr2O3/Fe2O3 gave the highest optical absorbance of 90%, the lowest and best band gap energy of 1.68 ev, and the highest refractive index of 2.85. Also, it recorded the best magnetic behavior with the highest saturation magnetization of 139.700 × 10−2A m2 kg−1 and the best coercivity of 190.0 Oe. These findings confirmed the successful clean conversion of the hazardous lead silicate waste into advanced products with promising optoelectronic characteristics.Graphical abstract