Effect Of Cr2O3 Addition Research Articles

Effect of Cr2O3 addition on mechanical and tribological properties of atmospheric plasma-sprayed NiAl-Bi2O3 composite coatings

Existing atmospheric plasma sprayed NiAl-20 wt% Bi2O3 composite coating displays the poor mechanical properties, thus this paper investigated the influence of adding different fractions of Cr2O3 on microstructural alteration and tribological behavior of NiAl-20 wt% Bi2O3 coating at RT, 400 °C and 800 °C. Desirable lubrication of NiAl-Bi2O3-Cr2O3 coating primarily resulted from Bi2O3 by its virtues of soft, low shear stress, and diffusion with temperature stimulus. Instead, Cr2O3 addition improved the wear resistance significantly, which was attributed to the increase of hardness and plastic deformation resistance, especially when 15 wt% Cr2O3 was adopted. The relationship between the Cr2O3 addition and relevant composition migration and mechanical transition on the worn surface at varying temperatures was further researched in this work.

The effect of Cr2O3 additions on sinterability and mechanical properties of liquid-phase sintered SiC ceramics

In this study, the effect of using Cr2O3 with Al2O3 and Y2O3 additives on physical and mechanical properties of SiC-matrix composites was investigated. The samples were sintered at 1900 °C for 1.5 h in argon atmosphere. The phases, microstructure and chemical composition of the samples were studied using X-ray diffraction analysis (XRD), scanning electron microscopy (FESEM) and X-ray diffraction spectroscopy (EDX). The results showed that addition of Cr2O3 nanoparticles up to 5 wt % results in densification improvement of samples. Due to weak interface of SiC grains and grain boundary phase, crack propagation path is mainly grain boundaries. The highest density, elastic modulus, hardness and indentation fracture resistance were respectively 97.45%, 403 GPa, 28.19 GPa and 6.2 Mpa.m1/2, attributed to specimen containing 5 wt % Cr2O3. Microscopic studies showed that, formation of microcracks, crack deflection, crack bridging and crack branching mechanisms are the most important mechanisms in indentation fracture resistance improvement of composites.

Effect of Cr2O3 addition on oxidation induration and reduction swelling behavior of chromium-bearing vanadium titanomagnetite pellets with simulated coke oven gas

The oxidation induration and reduction swelling behavior of chromium-bearing vanadium titanomagnetite pellets (CVTP) with Cr2O3 addition were studied, and the reduction swelling index (RSI) and compressive strength (CS) of the reduced CVTP with simulated coke oven gas (COG) injection were investigated. The results showed that the CS of the CVTP decreases and the porosity of the CVTP increases with increasing amount of Cr2O3 added. The Cr2O3 mainly exists in the form of (Cr, Fe)2O3 solid solution in the CVTP and as Fe-Cr in the reduced CVTP. The CS of the reduced CVTP increases and the RSI of the reduced CVTP decreases with increasing amount of Cr2O3 added. The limited aggregation and diffusion of metallic iron contribute to the formation of dense lamellar crystals, which leads to the slight decrease for reduction swelling behavior of reduced CVTP. This work provides a theoretical and technical basis for the utilization of CVTP and other Cr-bearing ores such as chromite with COG recycling technology.

Evaluation of mechanical properties of Al2O3–Cr2O3 ceramic system prepared in different Cr2O3 ratios for ceramic armour components

The aim of the present study was to introduce Al2O3–Cr2O3 ceramic system as an armour material by evaluating its performance with static mechanical tests. Cr2O3 was used as an additive to the pure Al2O3 owing to the character of substitutional solid solution formation that would provide increases in mechanical properties. The effect of Cr2O3 addition in different volume ratios (0.5, 1, 5 vol%) on the microstructure and the mechanical properties (elastic modulus, equibiaxial flexural strength, hardness, fracture toughness) of Al2O3 were investigated. Densification behavior and grain size of Al2O3 changed with the amount of Cr2O3, the highest relative density and grain size were obtained for 1 vol% Cr2O3 added Al2O3–Cr2O3 system. A 44% increase in flexural strength was achieved by 0.5 vol% Cr2O3 addition and attributed to the localized compressive stresses because of the grain boundary modification of the larger size of the Cr3+ ions. 1 vol % Cr2O3 addition increased the hardness 13% while the effect of Cr2O3 on toughness was negligible. The fragmentation behavior was discussed as a function of the stored energy at failure and total crack surface area. A shorter crack length for a given stored energy was observed for 0.5 vol% Cr2O3 composition compared to other compositions indicating its fragments would be larger in identical impact conditions increasing the erosion of the projectile.

Effect of Cr2O3 addition on the oxidation induration mechanism of Hongge vanadium titanomagnetite pellets

As part of a research project to develop a novel clean smelting process for the comprehensive utilization of Hongge vanadium titanomagnetite (HVTM), in this study, the effect of Cr2O3 addition on the oxidation induration mechanism of HVTM pellets (HVTMPs) was investigated in detail. The results showed that the compressive strength of the HVTMPs was greatly weakened by the Cr2O3 addition, mainly because of a substantial increase in the porosity of the HVTMPs. The Cr2O3 addition marginally affected the phase composition but greatly affected the microstructural changes of the HVTMPs. Increased amounts of Cr2O3 resulted in a decrease in the uniform distribution of the hematite grains and in an increase in the Fe–Cr solid solutions (Fe1.2Cr0.8O3 and Fe0.7Cr1.3O3) embedded in the hematite grains. Moreover, the compact hematite was destroyed by forming a dispersed structure and the hematite recrystallization was hindered during the oxidation induration, which adversely affected the compressive strength. On the basis of these results, a schematic was formulated to describe the oxidation induration mechanism with different amounts of added Cr2O3. This study provides theoretical and technical foundations for the effective production of HVTMPs and a reference for chromium-bearing minerals.

Effect of Cr2O3 addition on corrosion mechanism of refractory castables for waste melting furnaces and concurrent formation of hexavalent chromium

Cr2O3 containing refractories are used as the linings of various waste melting furnaces. Formation of hexavalent chromium (Cr(VI)) has been a major concern despite its admirable corrosion resistance properties. Al2O3-CaO-Cr2O3 refractory castables (0, 4%, 8%, and 12wt% Cr2O3) were fabricated in reducing condition to inhibit Cr(VI) formation while subsequent corrosion tests using waste slag was performed in air atmosphere to simulate the operating conditions. The corrosion mechanism between Cr2O3-containing corundum castables and synthetic waste slag were investigated by XRD and SEM-EDS, whereas concurrent formations of Cr(VI) were assessed effectively by leaching tests. Corrosion of castables (0wt% Cr2O3) occurs via dissolution of Al2O3 and CA6 phases, and formation of Ca2(Al,Mg)(Al,Si)2O7 and (Ca,Na)(Al,Si)2Si2O8, which were significantly restricted by the formation of Al2O3-Cr2O3 (III) solid solution (4%, 8%, and 12wt% Cr2O3). Most of the specimens exhibited less than 5mg/L (EPA limit) of Cr(VI). Only specimen M3 (12wt% Cr2O3) from slag-refractory interface (stage C) leached out 5.41mg/L of Cr(VI) which is above the EPA limit. Specimen M2 (8wt% Cr2O3) exhibits optimum properties in terms of corrosion and Cr(VI) formation.

Effect of Cr2O3 addition on crystallization, microstructure and properties of Li2O–Al2O3–SiO2 glass-ceramics

A new glass-ceramic with high flexural strength and low thermal expansion based on Li2O–Al2O3–SiO2 (LAS) was prepared in this study. The effects of Cr2O3 addition on the crystallization, microstructure, flexural strength, thermal expansion, and electrical properties of LAS system were investigated. The crystallization kinetics based on DSC analysis was calculated using Kissinger and Ozawa methods, which showed that the activation energy E decreases from 158.5 to 149.3 kJ/mol, indicating that Cr2O3 is beneficial to the crystallization of LAS; the crystallization index n varies between 4.46 and 5.09, indicating that the crystallization manner is the volumetric crystallization. XRD analysis was estimated by the whole pattern fitting method, demonstrating that Cr2O3 addition could change the phase contents and promote the crystallinity. The crystallization of CaMgSi2O6 and Cr2O3 with higher CTE not only properly adjusted CTE for matching Si, but also dramatically improved the flexural strength for LAS glass-ceramic. Moreover, we provided a modified formula to calculate CTE of glass-ceramic in the acceptable range. LAS glass-ceramic with 3 wt% Cr2O3 sintered at 800 °C exhibited good properties: σ = 208 MPa, α = 2.64 × 10−6/°C, ε = 8.3, tanδ = 3.6 × 10−3, ρ = 8.82 × 1012 Ω cm, indicating its suitability for LTCC application.

Effects of Cr2O3 addition on property improvement of magnesia-spinel refractories used in RH snorkel

The Ruhrstahl-Heraeus (RH) snorkel is one of the most important parts of the RH furnace, which is the primary facility for producing high-quality steel. The magnesia-spinel refractory is the ideal replacement for the classic magnesia-chrome refractory in the RH snorkel. In this study, the effects of Cr2O3 addition (0–3wt%) on properties of magnesia-spinel refractories were investigated. It was found that the addition of Cr2O3 results in the acceleration of the densification process and a decrease in the cold strength as well as a significant increase in the hot modulus of rupture. Thus, the solid solution formed with the spinel significantly improves the resistance to thermal shocks, with the greatest improvement being observed after the addition of 2wt% Cr2O3.

Effects of Cr2O3 addition on the phase, mechanical properties, and microstructure of zirconia-toughened alumina added with TiO2 (ZTA–TiO2) ceramic composite

Increasing demand for stronger cutting tools has led to the development of several novel composites and other multi-phase ceramics with better properties, particularly high fracture toughness. Cr2O3 is used as new material additive in this study, as it has attracted attention due to the formation of isovalent solid solution when added to Al2O3, contributing to improved fracture toughness. Thus, the aim of this study is to investigate the effects of the addition of Cr2O3 at a concentration of between 0.0wt% to 1.0wt% on the physical properties, microstructural features and phase of a ZTA-TiO2 ceramics composite. The samples were prepared by wet-mixing and uniaxial compaction, then sintered for 1h at 1600°C under pressureless conditions. The sintered samples were then identified in terms of their density, hardness, fracture toughness and crack propagation, and were then subjected to microstructural analysis by XRD and FESEM. It was discovered that with addition of 0.6wt% of Cr2O3 to the composite, an optimum density of 4.0630g/cm3, hardness of 1681HV, and fracture toughness of 7.15MPa.m1/2 were obtained. As a result of this addition, plate-like Al2O3 grains were observed, which caused cracks formed in the composite to spread in an inter-granular manner. This confirmed that the properties of ZTA–TiO2 ceramics composite were augmented by the addition of 0.6wt% Cr2O3.

Effects of Cr2O3addition on microstructure and vacuum flashover performance of glass-ceramics

K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O-MgO-SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -F/Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> glass-ceramics with higher flashover voltage were fabricated by sintering method. The electrical properties were measured, it was found that the flashover voltage was improved obviously with addition of small amount of Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> . The crystalline phases were identified by XRD and the microstructures were observed by SEM and BSE, the results showed that, there were Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> “islands” existed on the surface of ceramics. These “islands” could absorb the secondary electron and form the secondary electron “black hole”. The electric field distribution on surface was also simulated based on BSE and SEM results by ANSYS, it was showed that the Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> “islands” also distorted the surface electrical field. Therefore, the flashover voltage was increased. When adding with 3wt% Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , the hold-off voltage of glass-ceramics reached to 57 kV·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> (improved by 45%).

Microstructures and mechanical properties of (Ti,Cr)Al/Al2O3 composites fabricated by reactive hot pressing from Ti, Al and Cr2O3

Titanium aluminide composites reinforced with in situ formed Al2O3 were fabricated by a reactive hot press method, using Cr2O3, Al and Ti powders as raw materials. The effect of Cr2O3 addition on the microstructures and mechanical properties of the (Ti,Cr)Al/Al2O3 composite was characterized. The results show that the TiAl matrix is refined gradually with increasing the amount of Cr2O3. The Vickers-hardness and densities of the (Ti,Cr)Al/Al2O3 composite increase gradually with increasing Cr2O3 content. When the Cr2O3 content is 4.47wt.%, the compressive strength, flexural strength and fracture toughness of the composite reach the maximum values of 1032MPa, 634MPa and 9.78MPam1/2, which are substantially higher than those of the monolithic TiAl based alloy by about 18%, 78% and 80.5%, respectively. The increase in mechanical properties for the (Ti,Cr)Al/Al2O3 composite is due to the toughening effect arising from the combination of Cr solid solution in TiAl matrix and in situ formed Al2O3.

Effect of Cr2O3 addition on the microstructure and electrical properties of SnO2-based varistor

The effect of Cr2O3 addition on the properties of (Co, Nb)-doped SnO2 varistors were investigated. The samples with different Cr2O3 concentrations were fabricated by the conventional ceramic method and sintered at 1,250, 1,300, 1,350 and 1,400 °C for 2 h. It was found that the nonlinear coefficient present a peak value when 0.05 mol % Cr2O3 was added. The leakage current density decreases with increasing Cr2O3 from 0 to 0.05 mol %, but increases when the concentrations increase from 0.05 to 0.07 mol %. The breakdown electrical field increased from 337 to 866 V/mm with increasing Cr2O3 from 0 to 0.07 mol %. The optimal samples obtained by doping Cr2O3 with 0.05 mol % and sintered at 1,300 °C have the highest nonlinear coefficient value of 27 and lowest leakage current density of 9 μA/cm2.

Microstructure and Mechanical Properties of Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;/Tial &lt;i&gt;In Situ&lt;/i&gt; Composites Doped with Cr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;

Al2O3/TiAl composites were successfully fabricated by hot-press-assisted exothermic dispersion method with elemental powder mixtures of Ti, Al, TiO2 and Cr2O3. The effect of Cr2O3 addition on the microstructures and mechanical properties of Al2O3/TiAl composites has been characterized. The results show that the Rockwell hardness, flexural strength and fracture toughness of the composites increase with increasing Cr2O3 content. When the Cr2O3 content is 3.5 wt %, the flexural strength and the fracture toughness reach the maximum value of 658.7 MPa and 7.2 MPa•m1/2, respectively. The improvement of mechanical properties is firstly associated with a more homogeneous and finer microstructure developed by addition of Cr2O3; secondly, it is related to the increase of the ratio of α2-Ti3Al/γ- TiAl matrix phases.

Effect of the Cr2O3 addition on the electrical conductivity of Li2O:B2O3:SiO2 glass system

The effect of Cr2O3 addition on the variation in electrical conductivity, density, Tg and CTE has been studied in Li2O:B2O3:SiO2 glass system. The results have been explained in the light of the NBOs present in the glass, the electronic contribution to the total conductivity, the size and mass of the Cr3+ ion which is substituted for B2O3 and SiO2 in the glass.

Improved Stability of Mn-Doped WO&lt;sub&gt;3&lt;/sub&gt; Varistor via Doping Cr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;

In this paper, the effect of Cr2O3 addition on the electrical properties and microstructures of WO3-MnO2 ceramics was studied. The samples were fabricated by the conventional solid phase reaction techniques. The current-voltage curves and impedance spectra of sintered samples were measured at room temperature. The samples without Cr2O3 doping exhibit the max nonlinear coefficient α above 8 in current region from 1mA to 10mA and an unstable characteristic of current-voltage curve for repeat measuring cycle, while the samples doped with Cr2O3 display lower nonlinearity with α about 5 and an improved stability of current-voltage curve at the same conditions. The impedance measurements indicate that the influence on electrical properties comes from grain boundary as well as grain. SEM shows the doping of Cr2O3 into WO3-MnO2 ceramics suppresses obviously the growth of WO3, and XRD analysis reveals the coexistence of WO3 phases with some manganese tungstates and chromium tungstates. The problems related to electrical transporting mechanism were discussed simply.

Effect of Cr2O3 addition on the microstructure and electrical properties of Mn-Ni-Co oxides NTC thermistors

The as-sintered Mn 1.1 Ni 1.4 Co 0.5 O 4 crystallized in the solid solution of cubic spinel Mn-Ni-Co oxides, along with a small amount of the cubic spinel Ni-rich oxide phase. On the other hand, the Cr-substituted Mn 1.1 Ni 1.4 Co 0.5-x Cr x O 4 (0.07? x? 0.35) showed a single phase of cubic spinel Mn-Ni-Co-Cr oxides. This indicates that the substituted Cr suppressed the decomposition in the oxides. In addition, the Cr hindered the grain growth during sintering and increased the porosity. The electrical resistivity, the B 25/85 constant, and the activation energy of the Mn 1.1 Ni 1.4 C0 0.5-x Cr x O 4 NTC thermistors increased with increasing Cr content. It is demonstrated that the Cr-substituted Mn 1.1 Ni 1.4 Co 0.5-x Cr x O 4 NTC thermistors provided a variety of electrical properties, depending on the composition.

Effects of Cr2O3 addition on the piezoelectric properties and microstructure of PbZrxTiy(Mg1/3Nb2/3)1−x−yO3 ceramics

Abstract The effects of the addition of Cr 2 O 3 on the piezoelectric properties and microstructure were investigated for the PbZr x Ti y (Mg 1/3 Nb 2/3 ) 1− x − y O 3 (PZTMN) system. The results showed that the Cr 2 O 3 addition was effective in increasing the K p and Q m , which indicated that Cr-doped PZTMN ceramics possessed, simultaneously, the properties of ‘soft’ and ‘hard’ piezoelectrics. Furthermore, the properties were found to become ‘hard’ with an increase of sintering temperature even for the same compositions. Electron spin resonance (ESR) analysis showed that the Cr ion coexisted in both Cr 3+ and Cr 5+ , and that the valence change from Cr 5+ or Cr 6+ to Cr 3+ happened when the sintering temperature was increased. Transmission electron microscopy (TEM) results showed that, with increasing Cr content, the normal stripe-like domain changed to a wavy domain structure due to domain wall pinning by the defect complexes of acceptor impurities and oxygen vacancies.

多元系混合粉の焼結過程および焼結機構 低温焼結ＺｎＯバリスタの電気的性質

By heat-treating the mixture of Bi2O3 and Sb2O3 beforehand and adding the mixture to ZnOwith other metal oxides, ZnO varistors were sintered at tempersture 850-950°C and the electric characteristics were studied. When the content ratio of Bi2O3 and Sb2O3 was 3:1 in the ZnO+Bi2O3+Sb2O3+CoO+MnO+Al2O3, the varistor voltage and α-value became minimum. These values, V1mA/mm and α, increased with increasing amount of Sb2O3 content. The effect of Cr2O3-addition was studied.

Effect of Cr2O3 Addition on Surface Grain Growth of Alumina

Effect of Cr2O3 Addition on Surface Grain Growth of Alumina