Finite Element Analysis of Large Size Chromium Oxide Green Bodies During Firing

To prevent dense chromium oxide covers from cracking during firing,such as internal cracking,surface cracking and fracture,the firing process of dense chromium oxide products was simulated,and the performance parameters at several specific temperatures before and after densification of chromium oxide green bodies were tested.The temperature difference and the stress difference of chromium oxide green bodies were calculated by Finite Element Software at heating and cooling rates of 10,20,30 and 40℃·h^(-1),respectively.The results show that large temperature difference and thermal stress difference are the main causes of internal cracking,surface cracking and fracture of the brick.Suitable heating rates reduce or avoid internal cracking of the brick.When the heating rate is 30℃·h^(-1) below 1450℃and 10℃·h^(-1) above 1450℃,the temperature difference and the thermal stress difference in the brick are below 4℃and 4 MPa,respectively,and there is no internal crack in the brick after firing.The initial cooling stage is the key stage that causes cracking or fracture of bricks.When the cooling rate is 20℃·h^(-1) above 1450℃,the thermal stress difference in the brick is less than 4 MPa,which can significantly reduce the surface cracks and fracture of the brick.

Reduction of chromium oxides in stainless steel dust

The recovery of metal oxides from stainless steel dust using C（graphite）, SiFe, and Al as reductants was investigated under various conditions. The apparent distribution ratio of Cr（L Cr ′^m/s ） in the recovered metal and residual slag phases was defined as the major performance metric. The results show that the recovery ratio of metals increases as the ratio of CaO ：SiO2 by mass in the residual slag increases to 1.17. The residual content of metals in the slag decreases as the Al2O3 content of the slag is increased from approximately 8wt% to 10wt%. The recovery ratio of Cr increases with increasing L Cr ′^ m/s , and a linear relationship between L Cr ′^m/s and the activity coefficient ratio of CrO in the slag and the recovered metal phase is observed. The combination of C and SiFe or Al as the reducing agents reveals that Si is the more effective coreductant.

Preparation and Characterization of Plasma-Sprayed Ultrafine Chromium Oxide Coatings

Ultrafine chromium oxide coatings were prepared by plasma spraying with ultrafine feedstock. Processing parameters of plasma spraying were optimized. Optical microscope （OM） was used to observe the microstructure of the ultrafine chromium oxide coatings. Scanning electron microscopy （SEM） was used to observe the morphology and particle size of ultrafine powder feedstock as well as to examine the microstructure of the chromium oxide coating. In addition, hardness and bonding strength of the ultrafine chromium oxide coatings were measured. The results showed that the optimized plasma spraying parameters were suitable for ultrafine chromium oxide coating and the properties and microstructure of the optimized ultrafine chromium oxide coating were superior compared to conventional chromium oxide wear resistant coatings.

Effect of Atmosphere on Sintering Behavior of Chromium Oxide Materials

The chromium oxide materials were prepared using Cr2O3 micropowder as main starting material, TiO2 micropowder as sintering aid, polyvinyl alcohol as binder, by a series of processes such as slurrying, spraying granulation, machine moulding and cold isostatic pressing, and firing at 1 500 ℃ for 3 h in air （ oxygen partial pressure was 2. 1× 10^4 Pa ）, industrial nitrogen （ oxygen partial pressure was 1×10^3 Pa ） , pure nitrogen （ oxygen partial pressure was 10 Pa） , high purity nitrogen （ oxygen partial pressure was 0.1 Pa ） , and carbon cake embedded atmosphere （ oxygen partial pressure wtas 2.3×10-12 Pa ）. Effects of oxygen partial pressures on the sintering behavior of Cr2 O3 materials were investiga- ted. The results show that （ 1 ） for 3 wt% TiO2-doped specimeas, there is a substantial dependence of sintering on oxygen partial pressure （0. 1 Pa - 2. 1 ×10^4 Pa ） , and the bulk density increases and apparent porosity decreases with oxygen partial pressure decreasing; （2） even if the oxygen partial pressure is 0. 1 Pa, the specimen without TiO2 cannot reach densification sintering; （3） under very low oxygen partial pressure of carbon embedded atmosphere, Cr2O3 materials containing TiO2 or not can attain denzification.

Use of Chromium Oxide and Alkane Indicator Methods for Determination of Feed Intake for Grazing Sheep

This experiment was carried out to determine feed intake and digestibility of grazing sheep on pasture. A total of 14 animals randomly divided into two groups with seven animals each group were used in the experiment. Digestibility of pastures was determined using two types of markers-alkane （C32-C36） and chromium oxide. Dry matter intake （DMI） was 717.22 g/d based on chromium oxide method in the experiment, while according to alkane method, DMI was 965.93 g/d and 1,051.07 g/d for C32 and C36, respectively. In conclusion, pastures met 74%-81% of crude protein （CP） and 57%-61% of energy requirements of lambs grazing on Yuzuncu Yil University pasture, who are mid-quality and 4-7 month-old with a 275 g/d expected daily gain. It was calculated that when 628-693 g/d of barley is given, both CP and metabolizable energy （ME） requirements of animals can be met.

Efect of chromium oxide as active site over TiO_2-PILC for selective catalytic oxidation of NO

This study introduced TiO2-pillared clays （TiO2-PILC） as a support for the catalytic oxidation of NO and analyzed the performance of chromium oxides as the active site of the oxidation process. Cr-based catalysts were prepared by a wet impregnation method. It was found that the 10 wt.% chromium doping on the support achieved the best catalytic activity. At 350℃, the NO conversion was 61% under conditions of GHSV = 23600 hr^-l. The BET data showed that the support particles had a mesoporous structure. Hz-TPR showed that Cr（10）TiP （10 wt.% Cr doping on TiO2-PILC） clearly exhibited a smooth single peak. EPR and XPS were used to elucidate the oxidation process. During the NO ＋ O2 adsorption, the intensity of evolution of superoxide ions （O2^-） increased. The content of Cr^3＋ on the surface of the used catalyst was 40.37%, but when the used catalyst continued adsorbing NO, the Cr^3＋ increased to 50.28%. Additionally, Oα/Oβ increased markedly through the oxidation process. The NO conversion decreased when SO2 was added into the system, but when the SO2 was removed, the catalytic activity recovered almost up to the initial level. FT-IR spectra did not show a distinct characteristic peak of SO4^2-.

Preparation of hexagonal and amorphous chromium oxyhydroxides by facile hydrolysis of K_xCrO_y

The hydrolysis process and mechanisms of unique as-prepared KCrO2 and K3 CrO4 were systematically investigated. The characterization results of XRD, IR and SEM show that the hydrolysis reaction can be realized at a low reaction temperature of 80 ℃ and a reaction time of 24 h. Moreover, the greyish-green α-CrOOH with a hexagonal plate-like morphology and a large size of 10 μm is formed via the hydrolysis of the single-phase hexagonal KCrO2, while the green sol-gel of amorphous Cr(OH)3 with a lumpy aggregate morphology is generated through the hydrolysis of a cubic K3 CrO4. It is a facile and rapid method to synthesize pure-phase chromium oxyhydroxide via the above hydrolysis.

Preparation of Chromium Oxide Coatings on Aluminum Borate Whiskers by a Hydrothermal Deposition Process

Aluminum borate whiskers (9Al 2O 3·2B 2O 3) can be used to reinforce aluminum alloys to produce light and strong composites. However, the adverse interfacial reactions between the whiskers and the aluminum alloys inhibit their practical uses; therefore, a protective coating is needed on whiskers. In this work, aluminum borate whiskers were coated with chromium coating deposits in a hydrothermal solution containing CrCl 3, Na 2C 4H 4O 6, NaPH 2O 2, and H 3BO 3. The presence of the impurity P in the hydrothermal deposits can be avoided by reducing the amount of NaPH 2O 2 in the coating solution. Thermodynamic analysis was used to discuss the behavior of ions in the coating process. The subsequent heating of the hydrothermal products in air at 800 ℃ yielded smooth Cr 2O 3 films with a thickness of 0.060.07 μm.

Influence of Target-Substrate Distance and Sputtering Power on Chromium Oxide Films Prepared by Medium-Frequency Magnetron Sputtering

Chromium oxide films were deposited on Si（100） substrates by medium-frequency（MF） unbalanced magnetron sputtering at different target-substrate distances DTS（60,100,120 mm） and sputtering power（2.8,5.6,11.2 kW）,respectively.The structure,surface morphologies,and microhardness of the chromium oxide films were examined by X-ray diffraction（XRD）,atomic force microscopy（AFM）,and microhardness tester.The results indicate that elevated MF sputtering power can improve the crystallization of the films;The DTS value affects the structure of the films by changing the preferential orientation from CrO3（221） to Cr2O3（116）;The microhardness of the chromium oxide films is found to increase with the sputtering power.For preparing the Cr2O3-dominated films with comparatively high-performance,the optimized condition is the target-substrate distance of 100 mm and MF sputtering power of 11.2 kW.

Bimetallic CoNi single atoms supported on three-dimensionally ordered mesoporous chromia:highly active catalysts for n-hexane combustion

Developing the alternative supported noble metal catalysts with low cost,high catalytic efficiency,and good resistance toward carbon dioxide and water vapor is critically demanded for the oxidative removal of volatile organic compounds(VOCs).In this work,we prepared the mesoporous chromia-supported bimetallic Co and Ni single-atom(Co_(1)Ni_(1)/meso-Cr_(2)O_(3))and bimetallic Co and Ni nanoparticle(Co_(NP)Ni_(NP)/mesoCr_(2)O_(3))catalysts adopting the one-pot polyvinyl pyrrolidone(PVP)-and polyvinyl alcohol(PVA)-protecting approaches,respectively.The results indicate that the Co_(1)Ni_(1)/meso-Cr_(2)O_(3)catalyst exhibited the best catalytic activity for n-hexane(C_(6)H_(14))combustion(T_(50%)and T_(90%)were 239 and 263℃ at a space velocity of 40,000 mL g^(-1)h^(-1);apparent activation energy and specific reaction rate at 260℃ were 54.7 kJ mol^(-1)and 4.3×10^(-7)mol g^(-1)_(cat)s^(-1),respectively),which was associated with its higher(Cr^(5+)+Cr^(6+))amount,large n-hexane adsorption capacity,and good lattice oxygen mobility that could enhance the deep oxidation of n-hexane,in which Ni_(1) was beneficial for the enhancements in surface lattice oxygen mobility and low-temperature reducibility,while Co_(1) preferred to generate higher contents of the high-valence states of chromium and surface oxygen species as well as adsorption and activation of n-hexane.n-Hexane combustion takes place via the Mars van Krevelen(MvK)mechanism,and its reaction pathways are as follows:n-hexane→olefins or 3-hexyl hydroperoxide→3-hexanone,2-hexanone or 2,5-dimethyltetrahydrofuran→2-methyloxirane or 2-ethyl-oxetane→acrylic acid→CO_x→CO_(2)and H_(2)O.

Direct electrolytic preparation of chromium metal in CaCl_2-NaCl eutectic salt

The electro-reduction of chromium oxide（Cr2O3） was investigated in an equimolar mixture of CaCl2-NaCl molten salt at 800℃ for developing a more efficient process for chromium preparation. Cyclic voltammetry and potentiostatic electrolysis were used to study the electro-reduction of the Cr2O3-loaded metallic cavity electrode. In addition, a number of parameters affecting the rate and extent of Cr2O3 electrolysis were considered to better understand the electrolysis process. The results demonstrate that CaCl2-NaCl molten salt is applicable for preparing Cr directly from Cr2O3 and the electrolysis parameters exert great influence on the cathode product. Under optimal experimental conditions, nodular Cr with an oxygen content of 0.5%（mass fraction） was obtained without any chromium carbides detected by XRD. Furthermore, the relatively high solubility of CaO and quite rapid crystal growth result in the formation of large platelet CaCr2O4, and the addition of NaCl to CaCl2 results in several variations on the electrolysis process and the product morphology from pure CaCl2 molten salt.

Effects of lanthanum ion-implantation on microstructure of oxide film formed on Co-Cr alloy

Isothermal and cyclic oxidizing behavior of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1000 ℃ in the air by thermal-gravimetric analysis （TGA）. Scanning electronic microscopy （SEM） and transmission electronic microscopy （TEM） were used to examine the morphology and structure of oxide film after oxidation. Secondary ion mass spectrum （SIMS） method was used to examine the binding energy change of chromium caused by La-doping and its influence on the formation of Cr2O3 film. laser Raman spectrum was used to examine the stress changes within the oxide film. It was found that lanthanum implantation remarkably reduced isothermal oxidizing rate of Co-40Cr and improved anti-cracking and anti-spalling properties of Cr2O3 oxide film. The reasons for the improvement were mainly that the implanted lanthanum reduced the grain size and internal stress of Cr2O3 oxide and increased high temperature plasticity of the oxide film. Lanthanum mainly existed on the outer surface of Cr2O3 oxide film in the form of fine La2O3 and LaCrO3 spinel particles.

Roles of Ceria on Base Metal Oxide Catalysts——NO+CO Reaction

A microreactor system was used to study the catalytic reaction of NO+CO→1/2 N_2+CO_2 over Cu,Fe, Mn,Cr,and Ce oxides supported on alumina,and the effect of adding Ce in supported Cu-M-O(M=Mn,Fe and Cr) catalysts on their catalytic activities for the topic reaction and the concentration of N_2O produced.It was found that the catalytic activity order of the single-element oxide is:CuO>Fe_2O_3≈Cr_2O_3> MnO_2>CeO_2>NiO.Cu-Mn-O is more active than CuO,and Cu-Fe-O is more active than Cu-Mn-O and Cu-Cr-O for NO+CO reaction.This study shows that the addition of Ce in supported Cu-M-O can promote their catalytic activities Jot the topic reaction,which makes the reaction of 2NO+CO→N_2O+CO_2 fast,and N_2O is an intermediate compound produced during NO+CO reaction.

Environmental toxicity assessment of chromium (III) oxide nanoparticles using a phytotoxic, cytotoxic, and genotoxic approach

Chromium(III)oxide nanoparticles(NPs)have a wide range of industrial applications,particularly in the production of lithium-ion batteries;however,the toxicity of these NPs has not been studied extensively.The phytotoxicity and genotoxicity of chromium(III)oxide NPs have not been assessed,and only one study reported their cytotoxicity,underscoring the need to perform comprehensive toxicity studies on these NPs.Here,we showed that chromium(III)oxide NPs had no effect on germination rates,and only decreased root elongation in L.sativa as determined by root elongation and biomass studies.Chromium(III)oxide NPs had no phytotoxic effects under environmental realistic conditions,whereas they had cytotoxic effects against HK-2 and Raw 264.7 cells in vitro.However,the cytotoxicity of chromium(III)oxide NPs did not occur under environmentally realistic conditions.The genotoxicity of chromium(III)oxide NPs was not significant in HK-2 cells,suggesting that the potential environmental cytotoxicity of chromium(III)oxide NPs is limited.This study proposes comprehensive phytotoxicity,cytotoxicity,and genotoxicity testing tools that would be easy,safe,and effective for evaluating the toxicity of NPs.This integrated testing system could be an accurate and stable method for evaluating the toxicity of other nanomaterials.

Preparation and Properties of Ultra-fine Chromium Carbonization of High Performance Mechanical Activation

The preparation of hydroxyl chromium oxide by hydrogen reduction of disodium chromate and particulate hydroxyl mechanical activation features were studied. Then with self-made hydroxyl chromium as the raw material, a direct reduction and carburization process was used to prepare ultra-fine chromium carbonization. Through SEM and XRD, the high performance mechanical activation, key coefficients, microstructure, hardness and wear-resisting property were investigated. The results reveal that suitable mechanical activation and carbon reducing carbonization temperature, carbonization time, carbon content are beneficial to obtaining ultra-fine chromium carbonization. Typically, when the time of high performance grinding is 5 min, the carbon reducing temperature is 1100 ℃, the carbon reducing time is 1h, the carbon content is 28%, and finally the particle size of chromium carbide powder is 1 μm. Under this condition of preparation of ultra-fine chromium carbide, both the hardness and wear resistance are better than those in the industrialization of chromium carbide coating.

CrOx supported on high-silica HZSM-5 for propane dehydrogenation

Industrial propane dehydrogenation(PDH)catalysts generally suffer from low catalytic stability due to the coke formation onto the catalyst surface to cover the active sites.The exploitation of an efficient catalyst with both high catalytic selectivity and long-term stability toward PDH is of great importance but challenging to make.Herein CrOx supported on high-silica HZSM-5 with a SiO2/Al2O3 ratio of 260(Cr/Z-5(260)is synthesized by a simple wet impregnation method,which exhibits high catalytic activity,good selectivity and excellent stability for PDH.At a weight hourly space velocity(WHSV)of 0.59 h-1,a propylene formation rate of 4.1 mmol g-1cath-1(~32.6% propane conversion and ~94.2% propylene selectivity)can be maintained over the 5%Cr/Z-5(260)catalyst after 50 h time on stream,which is much better than commercial Cr/Al2O3(Catofin process,catalyst life is several hours)at the same reaction conditions.With increasing the WHSV to 5.9 h-1,a high propylene formation rate of 27.9 mmol gcat-1h-1can be obtained over the 5%Cr/Z-5(260)catalyst after 50 h time on stream,demonstrating a very promising PDH catalyst.Characterization results and Na+doping experiments reveal that the Cr species combined with Br?nsted acid sites in Cr/HZSM-5 catalysts are responsible for the high catalytic performance.In particular,the Br?nsted acid sites in HZSM-5 zeolite could increase the propane adsorption and enhance the C–H bond activation.Furthermore,the high surface area and well-defined pores of HZSM-5 zeolite can provide a special environment for the dispersion and stabilization of Cr species,thus guaranteeing high catalytic activity and stability.

Preparation of Cr_2O_3 precursors by hydrothermal reduction in the abundant Na_2CO_3 and Na_2CrO_4 solution

Precursors of chromium oxide （p-Cr203） were prepared by reducing hexavalent chromium in the presence of sodium carbonate solution under hydrothermal conditions. Methanal was used as the reductant, and carbon dioxide was the acidulating agent. The influences of reaction temperature, initial pressure of carbon dioxide, isothermal time and methanal coefficient on Cr（VI） reduction were investigated. Ex- perimental results showed that Cr（VI） was reduced to Cr（III） with a yield of 99%. Chemical titration, thermogravimetry （TG）, X-ray diffrac- tion （XRD） analysis, and scanning electron microscopy （SEM） were used to characterize the p-Cr203 and Cr203. The series of p-Cr203 were found to be multiphase even if they presented different colors, from gray green to lavender. After these p-Cr203 samples were calcined, the product of rhombohedral Cr203 with a purity of 99.5wt% was obtained.

Oxidative Dehydrogenation of Ethylbenzene over ZSM-5 Type Chromosilicates in the Presence of CO2

In this work, ZSM-5 type chromosilicate samples as K[Cr]ZSM-5(KCS) and Na[Cr]ZSM-5(NCS) were prepared by hydrothermal method and their catalytic properties were investigated for the oxidative dehydrogenation of ethylbenzene in the presence of CO2 as an oxidant using a fixed-bed stainless steel reactor. The prepared samples were characterized by their morphology (SEM), structural parameters (XRD), and textural parameters (BET). The performance of these catalysts was evaluated in terms of conversion, styrene yield, and selectivity. The KCSBW catalyst (potassium chromosilicate before washing with distilled water) afforded the highest styrene yield, 56.19%, with the selectivity of 96.05% in the presence of CO2 because of the coexistence of potassium ion and Cr2O3 in its structure and their synergistic effect. The influence of the presence of Cr2O3 and sodium or potassium ion on the catalytic activity of the chromosilicate samples in the catalytic EB dehydrogenation process was discussed in detail. Moreover, according to the results, the catalytic activity of the chromosilicate samples (CS) in EB dehydrogenation was increased by decreasing the surface area.

Layer-Structured Ti Doped O3-Na1-xCr1-xTixO2（x=0,0.03,0.05）with Excellent Electrochemical Performance as Cathode Materials for Sodium Ion Batteries

Layer-structured O3 type cathode materials Na1-xCr1-xTixO2(x=0,0.03,0.05)are fabri-cated by a thermo-polymerization method.The structures and morphologies are characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM)respectively.It has been found that the appropriate Ti doping effectively leads to the formation of uniform morphology.As a cathode,the x=0.03 sample delivers a quite high discharge capacity of 110 mAh/g at 32 C in the voltage range from 2.0 V to 3.6 V(vs.Na/Na+)and with a capac-ity retention of 96%after 100 cycles at 0.2 C.The Na//Na0:97Cr0.97Ti0.03O2 cell exhibits very high coulombic efficiency(above 96%).All these results suggest that Na0:97Cr0.97Ti0.03O2 is very promising for high-rate sodium ion batteries.

Surface Mapping of Resistive Switching CrOx Thin Films

In this work, we investigated resistive switching behavior of CrOx thin films grown by using sputtering technique. Conventional I-V measurements obtained from Ag/CrOx/Pt/Ti/SiO2/Si structures depict the bipolar switching behavior, which is controlled by formation/dissolution processes of Ag conducting filaments through electrochemical redox reaction under external electric field driven. Conductive atomic force microscopy (C-AFM) technique provides the valuable mapping images of existing Ag filaments at low resistance state as well as the characteristics of filament distributions and diameters. This study also reveals that where the higher amplitude of topography is, the easier possibility of forming conducting filament paths is on CrOx surface films.