Pre Oxidation Research Articles

Pre‐oxidized Recycled MgO–Steel Composite Material for Possible Application in Cryolitic Melts

Recycled MgO–C lining bricks and 316L stainless steel are used to manufacture composite material for inert anode samples for aluminum electrolysis cell. The microstructure of the composite material is characterized after preoxidation thermal treatments at 800, 900, and 1000 °C as well as in its sintered state. Preoxidation (PO) process is designed to enhance the material's corrosion resistance in molten cryolite environments by developing robust Fe–Mg–O, Fe–Cr–O‐ containing phases. Analytical techniques including scanning electron microscopy, electron backscatter diffraction, and energy dispersive X‐ray spectrometry are applied to characterize the phase formation, revealing the potential of these composites for use as inert anodes in aluminum electrolysis cells. PO at 800 °C is not sufficient to form adequate protective oxide layers. Whereas, PO at 900 and 1000 °C leads to the formation of protective oxide layers containing Mg–O Fe–O halite‐like solid solutions and (Cr,Fe)3O4 spinel phase. Sample, preoxidized at 1000 °C is sealed in Mg–Fe–O spinel phase.

Study on the oxidized gas production characteristics and spontaneous combustion tendency of pre-oxidized water-soaked coal in lean-oxygen environments.

The oxidation characteristics and spontaneous combustion (SC) tendency of raw long-flame coal (RC), water-soaked 200-day coal (S200), pre-oxidized water-soaked coal at 200°C (O200S200), and pre-oxidized soaked coal at 300°C (O300S200) in an oxygen-poor environment were investigated using a programmed warming system. The results show that pre-oxidation water-soaked treatment (PWT) promotes the coal-oxygen complex reaction and increases the rate of coal oxygen consumption (OCR) and the rate of carbon and oxygen compound production. The rate of CO and CO2 production of the water-soaked (WS) coal increased by 0.329mol·(cm3·s)-1 and 0.922mol·(cm3·s)-1, respectively, compared with that of the original coal sample. PWT reduces the activation energy of coal in the low-temperature oxidation stage (the maximum difference can be up to 110.99kJ/mol) and enhances the oxidizing and heat-releasing capacity. There was a synergistic effect between the pre-oxidation (PO) and WS treatment, and the lowest comprehensive determination index of the SC propensity of coal in O200S200 samples was 831.92 which was 4.72 lower than that of RC samples, presenting a more SC tendency. Low oxygen concentration has an inhibitory effect on the oxidation characteristic parameters of coal, and the apparent activation energy of the low-temperature oxidation stage of pre-oxidized water-soaked coal (PWC) increased to 206.418kJ/mol at 3% oxygen concentration. The lower the oxygen concentration of the anoxic environment, the lower the risk of SC of the coal samples. The results of the study can provide theoretical guidance for the identification and prevention of SC disasters in coal seams with shallow burial and close spacing.

Corrosion behavior of aluminum reinforced austenitic steel in liquid lead bismuth at 550 ℃

The key material issue for the commercialization of advanced lead cooled fast reactors and accelerator driven subcritical systems is the compatibility between structural materials and lead based coolants. Structural steel materials require excellent corrosion resistance in high-temperature liquid lead bismuth eutectic (LBE) alloy. Aluminum forming austenitic steel (AFA steel) has excellent corrosion resistance in extreme environments due to its ability to form an Al<sub>2</sub>O<sub>3</sub> film on its surface. However, excessively high Ni elements are more easily dissolved or oxidized in LBE than Fe and Cr elements. Therefore, this work investigates the effect of reducing Ni element composition (25-Ni steel and 18-Ni steel) on the corrosion resistance of steel in LBE. Surface treatment can protect the substrate from corrosion to some extent, so herein we explore whether it has a protective effect on AFA steel in LBE by generating Al<sub>2</sub>O<sub>3</sub> through high-temperature pre oxidation. The morphology and structure of the oxide layer of AFA steel corroded for 600 h in LBE with saturated dissolved oxygen at 550 ℃ are characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and other technologies. The results indicate that the oxide film formed after corrosion of 18-Ni steel is thinner than that after corrosion of 25-Ni steel. Performing high-temperature pre oxidation is beneficial to forming a protective Al<sub>2</sub>O<sub>3</sub> oxide film on the surface of the sample, thereby reducing the thickness of the oxide layer and improving the material's LBE corrosion resistance. The reduction in thickness of the oxide layer generated after pre oxidation of 18-Ni steel is greater than that of 25-Ni steel, so the anti-corrosion effect of 18-Ni steel after pre oxidation is better than that of 25-Ni steel.

Comparative analysis of synthesis of GO, CoFe2O4 and CoFe2O4 coated GO and its removal efficiency of arsenic present in the solution

A collective process of water purification is designed to reduce or remove the existing water contaminants to make water more applicable. Nanotechnology is considered to be very effective in providing contaminants free water for use. Demand of inexpensive and effective adsorbents is increasing regularly in response to the immeasurable health effects of arsenic exposure through water. The present study covers the procedure of synthesis of Graphene oxide (GO), Cobalt ferrite (CoFe2O4) and CoFe2O4 coated Graphene oxide (GO-CoFe2O4). This study shows that in room temperature at pH of 7, adsorbent dose of 0.4 gm/lit, contact time of 15 min and initial arsenic concentration of 0.2 mg/lit in the solution can be removed with nanoadsorbents with efficiency about 19 % by GO, 79 % by CoFe2O4 and 85 % by GO-CoFe2O4 without considering any other parameters. But efficiency of arsenic adsorption of the prepared nanoadsorbents increased with pre oxidation and increased contact time. Arsenic adsorption efficiency of 40 % using GO, 97 % using CoFe2O4 and 97.5 % using GO-CoFe2O4 has been achieved with pre oxidation and 22 hrs of contact time at pH of 7, adsorbent dose of 0.4 gm/lit, and initial arsenic concentration of 0.2 mg/lit. Based on result obtained, it is established that CoFe2O4 coated GO can be an effective nanoadsorbents for arsenic removal from the solution. This result underlines the need of further study for field application of these nanoadsorbents.

Synthesis of Polytitanocarbosilane and Preparation of Si–C–Ti–B Fibers

Continuous SiC fiber is a kind of high–performance ceramic fiber that combines many advantages, such as high strength, high modulus, high hardness and low density. It has excellent mechanical properties, high–temperature and oxidation resistance, which could be applied as essential reinforcement in advanced ceramic matrix composites (CMCs) in the fields of aerospace and advanced weaponry. Melt–spinnable polytitanocarbosilane (PTCS) is an important precursor, which can be used to prepare continuous SiC fibers through a precursor–derived method. In this work, low–softening–point polycarbosilane (LPCS) and tetrabutyl titanate were used to prepare polytitanocarbosilane with a ceramic yield of 67.5 wt% at 1000 °C. FT–IR, TGA, GPC, 1H NMR, 29Si NMR, and elemental analysis were used to analyze the composition and structure of the PTCS precursor. Finally, Si–C–Ti–B fibers with an average tensile strength of 1.93 GPa were successfully prepared by melt spinning, pre–oxidation, pyrolysis, and high–temperature sintering of the PTCS precursor. The strength retention rates were 71.5% and 79.8% after heat treatment at 1900 °C and 2000 °C under an argon atmosphere for 1 h, respectively. The strength retention rates of Si–C–Ti–B fibers are higher than those of commercial Hi–Nicalon fibers, Tyranno ZMI fibers and Hi–Nicalon S fibers. This work can lay a theoretical foundation and technical support for developing high-performance SiC ceramic fibers containing titanium and their ceramic matrix composites.

Preparation and electrothermal performance of onion-like carbon/carbon nanofibre composite film

An onion-like carbon/carbon nanofibre composite film was prepared by electrospinning. Its precursor application, and the effect of the amount of onion-like carbon additive and carbonization temperature on the physical and chemical properties of onion-like carbon/carbon nanofibre composite film was investigated. The results showed the non-woven fabric obtained by electrospinning solution reagent and the non-woven fabric after pre oxidation can be used to prepare facial mask and adsorb methylene blue (the adsorption rate reaches 83.1%) respectively. The conductivity of the onion-like carbon nanofibre composite film increased with the onion-like carbon content. The electrical conductivity of the composite film with an onion-like carbon content of 20 wt% (1.76 S/cm) was 1.5 times that of pure carbon nanofibres (1.12 S/cm). As the carbonisation temperature increased, the conductivity also increased. The prepared onion-like carbon/carbon nanofibre composite film exhibited an excellent electrothermal conversion performance. When the voltage was 30 V, and the current was 2.79 A, the surface temperature of the onion-like carbon/carbon nanofibre composite film (the carbonisation temperature was 1100 °C, and the content of onion-like carbon was 20 wt%) was as high as 588.4 ℃.

Recovery in oxidation behavior of damaged SiC[sbnd]ZrB2/SiC coating of carbon/carbon composites

Polysiloxane (PSO) was adopted as the matrix of the repair agents, and SiCZrB2 powder was used as the filler, to repair the prefabricated defects on the SiCZrB2/SiC (SZS) coating of carbon/carbon (C/C) composites. The repair agents were brushed on the defect areas and then underwent preoxidation (PR) or heat-treatment (HR) in a vacuum. The effects of different treatment processes on the chemical composition, microstructure of the repair agents, and the oxidation resistance behavior of the repaired coating were investigated. The repaired agents after both processes were pyrolyzed and generated SiOC ceramics, and they were well combined with the original coating. The thermal stability of PSO after preoxidation is poorer than that after heat-treatment, resulting in a weight loss rate of 5.88% after oxidation at 1 500 °C for 270 min, while that of the HR coating is only −0.87%, yet both have been great improvement compared with the unrepaired coating. This work provides an effective and simple approach to repairing damaged coatings for high-temperature applications.

Structural and electronic engineering towards high-efficiency metal-free electrocatalysts for boosting oxygen evolution

Due to low price, easy availability, and high durability, metal-free materials have been considered as one of the most promising substitutes of noble metal-based electrocatalysts for oxygen evolution reaction (OER). However, it is a great challenge and still unfulfilled for carbon-based metal-free catalysts to attain outstanding OER catalytic activities which rival those of their metal counterparts. Herein, we report N, O incorporated carbon sponge (2NOC) as an OER catalyst with excellent catalytic activity and stability. Remarkably, the hierarchical metal-free 2NOC carbon catalyst demonstrates an ultralow overpotential of 186 mV at 10 mA cm−2 (274 mV at 50 mA cm−2), Tafel slope as small as 71 mV dec-1, and current density retention of 96 % at 20 mA cm−2 after 50 h, which is beyond the state-of-the-art metal-free carbon materials and the commercial RuO2. The superior OER performance can be attributed to the all-in-one strategy of structural and electronic engineering. Through a facile and economical carbonization of melamine–formaldehyde sponge wastes after undergoing a controllable pre oxidation process, the constructed 2NOC catalyst possesses optimized N, O incorporation, multiscale pores, and interconnected through-hole inside carbon skeleton, which results in fully exposed active sites. Density functional theory calculations reveal that rational incorporation of N and O can optimize the adsorption of oxygen intermediates and greatly reduce the energy barrier of the rate-determining step (from 2.78 eV to 1.78 eV). Significantly, 2NOC||Pt/C electrolyzer achieves stable overall water-splitting at an applied voltage of only 1.47 V to drive 10 mA cm−2. This work proposes a promisingly sustainable strategy toward low-cost, eco-friendly and practicable electrocatalysts.

Reduced internal oxidation by a rapid carburizing technology enhanced by pre-oxidation for 18CrNiMo7-6 gear steel

Pre-oxidation was adopted as a pretreatment prior to gas carburizing for 18CrNiMo7-6 steel, and its effect on the carburizing efficiency and internal oxidation was evaluated in this research. The results indicated that pre-oxidation could improve the carburizing efficiency and result in much thicker effective case depth than that without PO pretreatment under the same carburizing condition. Meanwhile, the thickness of internal oxidation layer decreases significantly by PO pretreatment. The enhanced carburizing efficiency and decreased internal oxidation tendency could be ascribed to the oxide layer formed on the surface and the higher surface free energy (SFE) by pre-oxidation (PO).

The corrosion of Zr(Fe, Cr)2 and Zr2Fe secondary phase particles in Zircaloy-4 under 350 °C pressurised water conditions

Using Scanning Transmission Electron Microscopy (STEM) coupled with Dual Electron Energy Loss Spectroscopy (DualEELS) and scanned diffraction, the corrosion and incorporation of Secondary Phase Particles (SPPs) in the oxide layer of Zircaloy-4 material has been investigated. This study focuses on mapping the corrosion of Zr2Fe and Zr(Fe, Cr)2 precipitates during the oxidation process and depicting their morphology as the oxidation front advances through the material. It has been found that Zr2Fe SPPs retain the same general shape as in their pre oxidation stage, and transform to a nanocrystalline homogeneous mixed oxide, with a strong crystallographic texture, but hitherto unknown structure. The Zr(Fe, Cr)2 Laves-phase SPPs however, oxidise in a notably more complicated manner. As the α-Zr around an SPP begins to oxidise, the SPP is completely encapsulated by the ZrO2 whilst much of the SPP remains initially unoxidised. But, on oxidation, significant elemental segregation takes place, usually leaving a Cr2O3-rich cap, a nanocrystalline Zr,Cr mixed oxide body and veins of well-crystallised metallic iron. Both forms of SPP have a different expansion on oxidation compared to the Zr, resulting in cracking of the ZrO2.

The effect of oxidation on the tribolayer and sliding wear of a Co-based coating

Abstract The oxide layer formed on the surface of Stellite 1, a CoCrWC alloy, coatings exposed to high temperatures has a major influence on tribological behavior and can reduce friction and wear depending on the characteristics of the oxide. This work investigated the formation and behavior of tribo-oxides on the sliding wear of Stellite 1 coatings at different temperatures. Alumina ball-on-disk wear tests were performed at room temperature, 300, 500 and 700 °C in air with an applied force of 5.0 N, tangential velocity of 0.1 ms − 1 and total sliding distance of 5000 m. Samples were also pre oxidized at the test temperature before wear tests. The tribolayer was characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Raman spectroscopy. Oxidation behavior was evaluated by thermogravimetric analysis and isothermal oxidation tests. Mass change due to oxidation was recorded over five 10 h cycles at 300, 500 and 700 °C. At 700 °C oxide growth is parabolic. The oxide film formed after isothermal wear tests consists of iron oxides and is continuous only at the highest temperature, when it has a favorable impact on wear performance. The increase in temperature favors oxidation and compaction of the debris and contributes to the formation of a protective layer that reduces the wear rate and friction coefficient. Pre oxidation does not affect behavior at intermediate temperatures but at 700 °C causes a significant reduction in friction coefficient and wear.

Effect of Different Treatment on Corrosion Resistance of Sputtered Al Coating on Stainless Steel

AbstractAluminum coating on 1Cr18Ni9Ti stainless steel was prepared by magnetron sputtering method. The specimens were treated with pre-oxidation (PO) or vacuum diffusion annealing (VA). Hot corrosion resistance of the coatings beneath the deposits of Na2SO4 at 1050 °C was investigated. Corrosion products were analyzed by XRD and SEM. Results show that the presence of coating could improve the corrosion resistance of stainless steel. FeAl phase appeared after VA at 600 °C, which enhanced cohesive force between the coating and the substrate, and reduced the oxidation and sulfidation rate. PO treatment can protect the substrate more effectively than VA treatment for metastable Al2O3 formed during PO treatment can be translated to stable Al2O3 more quickly at high temperatures. The corrosion products of the two kinds of specimens with aluminum coating were both composed of Al2O3, a little amount of FeS and Fe2O3 after 24 h corrosion. Al2O3 was formed mainly in the coatings, FeS was mainly distributed in the interface between coating and substrate of the specimens, and a small amount of FeS was distributed in the substrate. Al2O3 film remained intact after 24 h corrosion, and kept its protective effect on the substrate.

A rapid D.C. plasma nitriding technology catalyzed by pre-oxidation for AISI4140 steel

D.C. plasma nitriding (PN) of AISI4140 steel catalyzed by pre-oxidation was investigated primarily. The pre-oxidation was carried out in air prior to plasma nitriding. The results revealed that pre-oxidation had significant catalysis effect on plasma nitriding, the maximum compound layer thickness of 15μm was obtained after nitriding at 500°C for 4h under the optimum pre-oxidation (PO) condition of 300°C and 30min, which was two times thicker than that without pre-oxidation. The possible catalysis mechanism is due to the formation of a uniform nano-iron oxide particle along with some nanocracks and nanopores on the surface, which has the highest SFE.

Effect of pre-oxidation on microcracks in graphite foams

The formation mechanisms of microcracks in graphite foams were investigated by varying the preoxidation temperature of the precursor mesophase pitch. Results indicated that after the mesophase pitch was preoxidized, its quinolineinsoluble component became the dominant fraction, which leads to a decrease in heat stress gradient and as a result, a decrease in the amount, length and width of microcracks.

Application of artificial neural networks to predict chemical desulfurization of Tabas coal

This paper presents a neural network model to predict the effects of operational parameters on the organic and inorganic sulfur removal from coal by sodium butoxide. The coal particle size, leaching temperature and time, sodium butoxide concentration and pre oxidation time by peroxyacetic acid (PAA) were used as inputs to the network. The outputs of the models were organic and inorganic sulfur reduction. Feed-forward artificial neural network with 5-7-10-1 arrangement, were capable to estimate organic and inorganic sulfur reduction, respectively. Simulated values obtained with neural network correspond closely to the experimental results. It was achieved quite satisfactory correlations of R 2 = 1 and 0.96 in training and testing stages for pyritic sulfur and R 2 = 1 and 0.97 in training and testing stages, respectively, for organic sulfur reduction prediction. The proposed neural network model accurately reproduces all the effects of operational variables and can be used in the simulation of Tabas coal desulfurization plant.

Pre concentration and pressure oxidation of Porgera refractory gold ore

The complex mineralogy of the Porgera resource has a pronounced effect on process selection for the recovery of refractory gold and silver. Intimate association of gold with pyrite necessitates a high degree of sulphur preoxidation to achieve acceptable levels of gold recovery. Acid pressure oxidation has been demonstrated to be the only commercially proven process capable of achieving the required level of pyrite oxidation. Gangue mineralization dictates pre concentration of the sulphides to limit the acid consuming capacity and carbon dioxide generation during oxidation. However, the relationship between concentrate sulphur grade and gold recovery to concentrate ultimately governs the optimum degree of sulphide preconcentration. Minipiloting of the pre concentration and oxidation stages of the Porgera flowsheet are described. The influence of these processes on subsequent recovery of precious metals together with the technical and economic necessity of concentrate pretreatment prior to oxidation are discussed.