Pre-oxidation Temperature Research Articles

Fabrication of 3D-SiC/aluminum alloy interpenetrating composites by DIW and pressureless infiltration

A novel method combining direct ink writing (DIW) and pressureless infiltration is proposed for fabricating 3D-SiC/Al composites. Chopped carbon fiber was added to DIW ink to serve as a pore-forming agent and facilitate pyrolysis to provide infiltration channels during the preoxidation process. The effects of SiC particle size and carbon fiber content on mechanical properties and the infiltration process were investigated. The thickness of the oxide films produced at different preoxidation temperatures was studied using a transmission electron microscope. The interfacial and interpenetrating phase compositions of 3D-SiC/Al were examined using scanning electron microscopy, an energy dispersive spectrometer, and X-ray diffraction. The results showed that carbon fiber can improve the infiltration effect, with SiO2 layers of differing thickness affecting the infiltration process to different degrees. The final sample exhibited good mechanical properties with a bending strength of 330.3 MPa.

Pre-oxidation of lignin precursors for hard carbon anode with boosted lithium-ion storage capacity

Lignin-derived hard carbon (HC) has great potential as energy storage materials. However, it is difficult to obtain desired electrochemical performances by direct carbonization of lignin. Herein, we demonstrate a pre-oxidation strategy to enhance the reversible capacity of hard carbon with lignin as precursor. The pre-oxidation mechanism and its influence on the microstructures of the resulted hard carbon are systematically studied. Based on in-situ FT-IR and 13C NMR spectrum, etc., it is confirmed that three dominant configurations of oxygen-containing functional groups are formed during the process, and the content of the desired carbonyl groups (CO) reaches a maximum value at a pre-oxidation temperature of 200 °C. Meanwhile, the alkyl groups are transformed into peroxides or alcohols, contributing to intermolecular cross-linkage within lignin. As a result, the obtained material with highly random orientation nanotexture gives a much larger d002 and abundant porous structure. Benefiting from these structural merits, the optimized lignin-derived hard carbon enables excellent Li-ion storage performance with a reversible capacity of 584 mA h g−1 at 50 mA g−1. This work provides insights into the rational design of high-performance hard carbon anodes for Li-ion batteries and beyond.

Pre-oxidation of selective-laser-melted titanium dental alloy: effects on surface characteristics and porcelain bonding

The heat treatment of dental alloys prior to porcelain application/veneering has been proposed as a way to ensure sufficient oxide scale and to promote the porcelain’s adherence in porcelain-fused-to-metal (PFM) fixed dental prostheses. The present study investigates the relationship between the bond strength of the dental porcelain to selective-laser-melted (SLM) titanium and the temperature of the titanium’s pre-oxidation. The SLM Ti-6Al-4V substrates were airborne-particle abraded and either left to passivate in air at room temperature (control) or pre-oxidized in a furnace under vacuum conditions (10 kPa) at temperatures of 300, 600, 750, or 800 °C. The surface characteristics were determined using contact profilometry to measure the profile roughness (Ra ), atomic force microscopy for the surface roughness (S a ) and Auger electron spectroscopy for the thickness of the oxide scale. Dental porcelain was applied to the metal substrates and the titanium-ceramic bond was assessed according to the ISO standard 9693-1:2012. The metal-ceramic interfaces were analyzed with scanning electron microscopy and energy-dispersive spectroscopy. The R a and S a values showed a strong positive correlation with the pre-oxidation temperature. The oxide scales covering the titanium surfaces thickened markedly at temperatures of 750 °C and above. However, the bond strength was negatively correlated with the pre-oxidation temperature. Room-temperature passivation in air following the airborne-particle abrasion of the SLM titanium resulted in a titanium-ceramic bond that is well above the ISO 9693-1:2012 recommended minimum value for metal-ceramic systems. Thus, no pre-oxidation of SLM titanium frameworks is necessary prior to the application/firing of porcelain.

Comparative study of conventional and microwave heating of polyacrylonitrile-based fibres

Abstract The effects of the conventional heating method and the microwave heating method on polyacrylonitrile-based fibres in the temperature range of 180–280 °C were investigated. Fourier transform infrared spectroscopy, X-ray wide-angle scattering, Raman spectroscopy, energy-dispersive spectrometer, scanning electron microscopy and bulk density were used to characterise the properties of the samples. Results show that the microwave heating method can shorten the pre-oxidation time, reduce pre-oxidation temperature and reduce the number of surface defects. The pre-oxidised fibres obtained by the microwave heating method exhibit not only good crystallite size but also a smooth surface. Atomic morphology and molecular arrangement are orderly inside the fibre. The FT-IR spectrum shows that the oxidation reaction occurs at 220 °C, and the CI value of PAN fibers stabilised by microwave heating is the larger than the fibers stabilised by conventional heating. XRD analysis shows that fibers stabilised by microwave heating have low stack domains. The SEM and Raman spectra indicate that hydrogen peroxide can improve the surface finish of the fibers and reduce defects. Microwave heating can reduce the pre-oxidation temperature by about 20 °C and shorten the heating time. The economic benefits of using this method are significantly improved.

Influence of pre-oxidation on mechanical properties of single electrospun polyacrylonitrile nanofiber

High performance oxidized polyacrylonitrile (oPAN) nanofibers are highly required for the fabrication of high-performance carbon nanofibers. In this work, single electrospun oPAN nanofibers with different oxidation temperatures were prepared by copolymerization, electrospinning and pre-oxidation. The effect of pre-oxidation temperature on the evolution of chemical structure and mechanical properties were comprehensively investigated by FT-IR, Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and micro-tensile tests. The results indicated that 210 °C was the optimal the pre-oxidation temperature, at which a cyclization degree of 96 % could be achieved. At this temperature, the single oPAN210 electrospun nanofiber showed the best mechanical properties tensile strength, modulus, and toughness of 1690 MPa, 52.3 GPa, and 260 J/g, respectively. This study would guide for the fabrication of high performance electrospun oPAN nanofibers and further the preparation of high-performance electrospun carbon nanofibers.

Thermal Behavior of the Low-temperature Secondary Oxidation of Coal under Different Pre-oxidation Temperatures

ABSTRACT To study the effect of pre-oxidation temperature on the thermal behavior of secondary oxidation of coal, this paper studies samples from a Jurassic coalfield that is susceptible to spontaneous combustion. Under an air atmosphere, pre-oxidized coal samples with different pre-oxidation temperatures (75°C, 115°C, 155°C, 195°C) were prepared by heating at a rate of 0.5°C·min−1. Samples of each, and a raw coal sample, were then heated from 30–300°C at heating rates of 0.2, 0.3, 0.4, and 0.5°C·min−1 in an air atmosphere of 120 mL·min−1. The micro-characteristics of pre-oxidized coal samples were identified by Fourier infrared spectroscopy method. A C80 microcalorimeter was employed to monitor the thermal behavior of low-temperature secondary oxidation of coal. The heat flow curves of raw coal and pre-oxidized coal samples during the heating process show similar trends. Characteristic temperatures determined from the data of samples from different endothermic stages increase with increasing pre-oxidation temperature. The heat absorption of pre-oxidized coal samples in different endothermic stages is significantly lower than that of raw coal, and decreases first and then increases with increasing pre-oxidation temperature. Due to the effect of pre-oxidation, the methyl, hydroxyl and carboxyl groups of pre-oxidized coal samples are obviously lower than that of raw coal. The apparent activation energy of different oxidation stages of the experimental coal samples was calculated with a multi-rate heating method. The secondary oxidation activation energy of coal increases first and then decreases with increasing pre-oxidation temperature. In the rapid endothermic stage and the slow endothermic stage, the activation energy ranges of the coal samples were 68.12–201.46 kJ·mol−1 and 26.21–135.58 kJ·mol−1.

Catalytic Effect of Dimethyl Disulfide on Coke Formation on High-Temperature Alloys: Myth or Reality?

The selection of the reactor material with the lowest coking tendency can result in substantial economic benefits for the steam cracking process. One of the remaining unresolved points of discussion is the determination of the influence of sulfur addition, in particular dimethyl disulfide (DMDS), on various steam cracking reactor alloys with varying Ni-Cr content. To shed some new light on this topic, an extensive thermogravimetric study was performed in a jet-stirred reactor (JSR) setup, evaluating online the coking behavior of four Ni-Cr-Fe alloys under industrially relevant ethane cracking conditions. For each material, the effect of preoxidation/pretreatment with and without the presence of DMDS was evaluated, with an objective to minimize the material coking tendency. The coking rates show that an increased Ni-Cr content of the material improves the coking rates by a factor of 2 or more under the studied process conditions. By continuously feeding DMDS, all non-Al-containing alloys indicate 7 times higher coking rates than the Blank runs, while the carbon oxide(s) formation is suppressed by a factor of 5. In comparison with continuous addition and presulfiding with DMDS, labeled CA + PreS experiments, the AI-containing alloy outperforms itself significantly when preoxidized at 1223 K by 50% in terms of coking rates. The results indicate that Al addition to Ni-Cr-Fe alloys improves their anticoking performance, provided that the preoxidation temperature is higher than for materials without Al. The overall results from coking rates and offline scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analysis for the coked coupons showed an outstanding oxidation homogeneity for the 40/48 Cr-Ni alloy, which was better than that for the Al-containing alloy at lower preoxidation temperatures.

Study on Pre-oxidation of a High-Arsenic and High-Sulfur Refractory Gold Concentrate with Potassium Permanganate and Hydrogen Peroxide

For arsenic-containing refractory gold concentrate, gold recovery by leaching is extremely difficult due to the encapsulation of gold in arsenopyrite and pyrite. In this work, the pre-oxidation of a high-arsenic and high-sulfur refractory gold concentrate in the acidic potassium permanganate or hydrogen peroxide solutions has been investigated. The studied parameters include pre-oxidation time, acidity, pre-oxidation temperature, ethylene glycol addition and oxidant concentration. When potassium permanganate of 0.25 mol/L is used as oxidant, 61.4% of arsenic and 51.8% of iron can be removed, respectively. The results of kinetics analysis indicate that the oxidative dissolution of arsenopyrite during the pre-oxidation process is controlled by the product layer diffusion, with an activation energy of 7.92 kJ/mol. The stability of hydrogen peroxide can be significantly improved by increasing both sulfuric acid concentration and ethylene glycol addition when hydrogen peroxide is used as oxidant. Under optimum conditions, arsenic removal ratio of 57.2% and iron removal ratio of 51.9% have been achieved with hydrogen peroxide of 2.5 mol/L, sulfuric acid of 0.75 mol/L and ethylene glycol of 30 mL/L. The gold extraction of refractory concentrate is only 11.5% in the copper–ammonia–thiosulfate leaching solutions without pre-oxidation. A gold extraction of 71.8% and significant decrease in thiosulfate consumption from 28.2 to 5.7% have been observed for the concentrate after pre-oxidation.

Preparation of a novel nitrogen-containing graphitic mesoporous carbon for the removal of acid red 88

A novel nitrogen-containing graphitic mesoporous carbon was prepared through MnO-templated method using polyacrylonitrile (PAN) as both carbon and nitrogen sources, and MnCO3 as both template and catalyst precursors. The effects of preparation conditions on the physicochemical properties of obtained samples were systematically investigated. The results showed that as the decrease of the weight ratios of PAN and MnO (2:1–1:4), the increase of carbonization temperature (700–900 °C) and pre-oxidation temperature (180–200 °C), the samples had higher specific surface area, mesopores volume and ratios, up to 507 m2/g, 0.824 cm3/g and 96.83%, respectively. Moreover, the prepared samples presented relatively high graphitic degree and nitrogen contents (~2.21%). The adsorption capacity for acid red 88 (AR88) was as high as 309 mg/g, which were dramatically affected by the mesoporous properties and C- and N-containing groups on the surface of prepared carbon. The rich graphic carbon and pyridine-N in mesoporous carbon generated π-π dispersion and electrostatic interaction with AR88, respectively, which jointly were responsible for the adsorption process. The results of the isotherm and kinetic studies indicated that the AR88 adsorption on mesoporous carbon could be well depicted using Langmuir model and pseudo-2nd-order model.

Free-standing cross-linked activated carbon nanofibers with nitrogen functionality for high-performance supercapacitors

Flexible, heteroatoms-rich activated carbon nanofibers with fascinating cross-linked architectures are successfully gained in a facile and controllable way via electrospinning polyacrylonitrile (PAN) /dicyandiamide (DICY) composite nanofibers followed by carbonation and a CO2 activation process. The unique inter-bonded structures and heteroatoms contents could be easily controlled by adjusting the preoxidation temperature applied in the calcining procedure and the addition of DICY. Significantly, the resultant samples display hierarchical pores with micro/meso/macropores, abundant N, O species doped and unique fiber–fiber interconnections, which considerably boost the electrochemical properties. As an electrode material, the activated N-doped cross-linked carbon nanofibers (ANCLCNFs) show a high capacitance of 323 F g−1 with a current density of 0.5 A g−1, excellent rate capacity (230.1 F g−1 at 20 A g−1) and long-term duration (over 95% after 10000 cycles). Furthermore, the symmetrical supercapacitor delivers a maximum energy density of 14.3 Wh kg−1 at a power density of 162.5 W kg−1.

Effects of pre-oxidation temperature on coal secondary spontaneous combustion

Spontaneous combustion of oxidized coal occurs frequently in mining and utilization process, which is influenced by the first oxidation conditions significantly. With a focus on the influence of pre-oxidation temperature on spontaneous combustibility of oxidized coal, oxidized coal samples were prepared by heating at preset temperature of 50 °C, 70 °C, 90 °C, 110 °C and 130 °C. Programmed heating tests on oxidized coal and raw coal samples were carried out in air atmosphere of 120 mL min−1, with the heating rate of 0.3 °C min−1. The gaseous mixture of O2, CO and CO2 at the outlet was identified by gas chromatography to analyze oxidizability and exothermicity of experimental coal samples. The results showed that, with the increasing pre-oxidation temperature, the oxidizability and exothermicity of oxidized coals decreased first and increased later, which were related with change of oxygen consumption rate, emission rate of CO and CO2 gas. The spontaneous combustibility order by pre-oxidation temperatures was 130 °C, raw, 50 °C, 110 °C, 90 °C and 70 °C. Being oxidized at 130 °C could promote coal to self-heat, and being oxidized below 110 °C would inhibit coal self-heating.

Coordination of Pre-oxidation Time and Temperature for a Better Corrosion Resistance to CO2 at 550 °C

Influence of pre-oxidation treatment on the oxidation resistance of F91 to CO2 at 550 °C was investigated. The formation of the thin scale of (Fe, Cr)2O3 corundum-type oxides was achieved by pre-oxidation in air, which significantly improved the oxidation resistance. Nodule nucleation and subsequent growth were analyzed and interpreted. Influences of pre-oxidation temperature and time on the oxidation resistance to CO2 are explained by presenting concepts of insufficient pre-oxidation and excess pre-oxidation. A coordination between pre-oxidation temperature and time is proposed.

Effect of pre-oxidation temperature on the ductility of a zirconium alloy cladding under simulated accident conditions

The ductility of a zirconium alloy cladding tube pre-oxidized at 900, 1000, 1100, and 1200 °C was evaluated after subsequent oxidation at 1000 and 1100 °C by performing ring compression tests. For comparison, ring compression tests were also performed on non-pre-oxidized specimens after oxidation at 1000 and 1100 °C. All the pre-oxidized specimens showed enhanced oxidation resistance during subsequent oxidations, and this effect was stronger for the specimens pre-oxidized at higher temperatures. After subsequent oxidation at 1000 °C for 5130 s, all the pre-oxidized specimens showed higher ductility than the non-pre-oxidized specimen. This was largely due to the enhanced breakaway oxidation resistance by the preformed oxides. In addition, after subsequent oxidation at 1100 °C, the specimens pre-oxidized at 900 and 1000 °C showed higher ductility than the non-pre-oxidized specimens, whereas the specimens pre-oxidized at 1100 and 1200 °C exhibited lower ductility. Even though pre-oxidation at higher temperature was better for enhancing oxidation resistance, pre-oxidation at lower temperature was better for the ductility. To analyze this tendency, oxide thickness and macro-hardness of metal substrates were measured from the specimens which were subsequently oxidized at a same condition. As the pre-oxidation temperature increased, the oxide thickness decreased, and the macro-hardness increased. Considering that macro-hardness is related to the oxygen concentration in the metal substrate, the lower ductility at higher pre-oxidation temperature was due to that the specimens pre-oxidized at higher temperature contained higher concentration of oxygen in the metal substrates.

C@TiO2 /MoO3 Composite Nanofibers with 1T-Phase MoS2 Nanograin Dopant and Stabilized Interfaces as Anodes for Li- and Na-Ion Batteries.

Integrating layered nanostructured MoS2 with a structurally stable TiO2 backbone to construct reciprocal MoS2 /TiO2 -based nanocomposites is an effective strategy. C@TiO2 /MoO3 composite nanofibers doped with 1T-phase MoS2 nanograins were fabricated by partially sulfurizing MoOx /TiO2 precursors. By controlling a suitable preoxidation temperature before severe thermolysis of polyvinylpyrrolidone (PVP), the MoOx /TiO2 precursors formed a polymer-embedded array through coordination of the Mo source and pyrrolidyl groups of PVP. Sulfidation under water/solvent hydrothermal conditions led to partial formation of metallic 1T-phase MoS2 from the MoOx precursor with preoxidation at 200 °C. After carbonization, the TiO2 /MoO3 /MoS2 nanograins were encapsulated in a carbon backbone in a vertical pattern, providing both chemical contact for confined electron transport and sufficient space to adapt to volume changes. The obtained carbon-based platform not only has the advantages of an integral structure, but also exhibited ultrastable specific capacities of 540 and 251 mAh g-1 for Li-ion batteries and Na-ion batteries, respectively, after 100 cycles.

Preparation and Characterization of Wood-based Pre-oxidized Precursors and Activated Carbon Microspheres

Wood-based activated carbon microspheres (WACMs) were successfully prepared from Chinese fir. However, the weak thermal stability of the precursors resulted in melting at high activation temperatures, which led to a lower yield and poor adsorption properties. To promote the thermal stability of the precursors in the process without chemicals, this paper focused on the effects of the pre-oxidation before activation on the thermal stability and chemical structure of the precursors and the pore structure of the activated samples. The results showed that during the pre-oxidation process, the O/C ratio increased noticeably and the intensity of oxygen-containing functional groups, such as carbonyl, carboxyl, and ester groups, were enhanced, which contributed to the improvement of the thermal stability. Moreover, the etching effect of oxygen on the structure of the precursors was verified when the porous structure was enriched by activation. The activated sample pre-treated at pre-oxidation temperature 250 °C had the maximum micropore specific surface area and pore volume. As the temperature was raised to 280 °C, the mesopore specific surface area and pore volume increased, which indicated that the optimization of the pre-oxidation parameters contributed to the formation of the mesopore structure.

Barium (Zinc) Borosilicate Sealing Glass and Joining Interface with YSZ Electrolyte and Crofer22APU Interconnect in SOFCs

This work describes the performance of two glass-ceramic compositions, BaO-SiO2-B2O3 (Barium borosilicate glass: BaBS) and BaO-ZnO-SiO2-B2O3 (Barium zinc borosilicate glass: BaBS−Zn), used for joining YSZ ceramic electrolytes and Crofer22APU metallic interconnects in solid oxide fuel cells (SOFCs) working at 800°C for 50 h. ZnO had a negative effect on the thermal expansion coefficient (TEC) value of the BaBS-Zn glass-ceramic. XRD and SEM results revealed the formation of rod-shaped barium zinc silicate crystalline phases in the BaBS-Zn glass, which was accompanied by cracks and poor adherence at the YSZ/BaBS-Zn joint interface after working at 800°C for 50 h. The formation of cracks parallel to the interface between the Crofer22APU interconnect and the BaBS-Zn glass-ceramic sealant was observed due to the severe TEC mismatch. The BaBS glass–ceramic adhered well to the YSZ electrolyte as well as the pre-oxidized Crofer22APU without cracks. Chromium oxide scale developed between the pre-oxidized Crofer22APU/BaBS glass-ceramic joint interface with increasing the pre-oxidation temperature. This study shows that BaBS glass-ceramic is more effective than BaBS-Zn as a sealant for joining YSZ electrolytes and Crofer22APU metallic interconnects in SOFCs working at 800°C for 50 h.

Thermophysical parameters of coal with various levels of preoxidation

Heat transfer in a coal mass is governed by thermophysical properties such as thermal diffusivity, specific heat capacity, and thermal conductivity. Coal samples were preoxidized at 90, 150, and 200 °C in a temperature-programmed oxidation apparatus, with raw coal acting as the control group. A laser flash method was employed to examine the thermophysical properties of the coal samples and establish a relationship between the thermophysical properties and the coal’s microcrystalline structure/pore structure. The results indicated that thermal diffusivity decreased and specific heat capacity and thermal conductivity raised when the temperature increased. Furthermore, when the preoxidation temperature increased, aromatic microcrystalline structures developed and the specific surface area of the coal samples first decreased and then increased. Moreover, thermal diffusivity and thermal conductivity increased with the elevated preoxidation temperature, and specific heat capacity was the highest at 90 °C. The reason for this was that preoxidation of the coal samples influenced the development of aromatic microcrystalline structures and pore structures, promoting the heat transfer on coal mass.

Microstructural characteristics and different effects of 800–1200 °C preformed oxides on high-temperature steam oxidation of a zirconium alloy cladding

Zr-1Nb-1Sn-0.1Fe nuclear fuel cladding tube was pre-oxidised at five different temperatures (803, 908, 1012, 1112, and 1200 °C), and subsequent oxidation tests were performed at 1012 °C. All the pre-oxidised specimens showed a little or no breakaway oxidation after the subsequent oxidation at 1012 °C for 5130 s, but the non-pre-oxidised specimen showed a severe breakaway oxidation after the subsequent oxidation at 1012 °C for 5130 s. In addition, comparing the weight gains and oxide thicknesses of the pre-oxidised specimens with those of the non-pre-oxidised specimens, all the preformed oxides were effective in enhancing the oxidation resistance, and the preformed oxide formed at higher temperature was more effective. The preformed oxides were examined using electron probe microanalyser and transmission electron microscopy, which showed that the fraction of Zr-Sn type precipitates increased with increasing the pre-oxidation temperature. This phase change of the precipitates may cause the preformed oxide formed at higher temperature to exhibit better oxidation resistance enhancement.

Development and interface characterization of unmatched glass-metal joint

An unmatched glass-metal joint between borosilicate glass and austenitic stainless steel SS 304 was developed for parabolic trough receiver tube application. 40SiO2-54B2O3-4Na2O-2Al2O3 material was used as the glass sealant to join the SS304 metal ring and borosilicate glass tube. The research work reported was carried out with objective of investigating the role of glass sealant, joint design and pre-oxidation conditions on the wettability and adhesion strength of the glass-metal joint. The work also aimed at analysing the types of oxides formed at the glass-metal joint interface. The pre-oxidation behavior of SS304 was studied by varying the pre-oxidation temperature and pre-oxidation time. The oxide formed on the surface of SS304 substrates were examined using x-ray diffraction and energy dispersive x-ray spectroscopy. During the glass-metal sealing process the oxides at the glass-metal interface were characterized using x-ray diffraction and scanning electron microscopy. In-situ wetting behavior of glass sealant 40SiO2-54B2O3-4Na2O-2Al2O3 over austenitic stainless steel SS 304 was examined using the in-house developed image acquisition system. The optimum condition for joining 40SiO2-54B2O3-4Na2O-2Al2O3 glass sealant with SS304 is obtained by pre-oxidizing metal specimen at 700 °C for 3 min, where optimum oxide layer mass gain of 5.8666 × 10−04 g/cm2 and optimum oxide layer thickness of 87.57 μm was achieved. The maximum strength of joint during adhesion test was measured around 2.57 N/mm2 (MPa) corresponding to pre-oxidation temperature of 700 °C and 3 min pre-oxidation time. The FeO and ((SiO2),AlNa(SiO4)) oxide phases were observed at the interface of glass and the metal during joining. During in-situ wettability analysis the contact angle between the glass sealant pallet and SS304 substrate was measured at different temperatures. The contact angle of the glass sealant pallet decreased during heating process and the contact angle increased as the glass sealant pallet cooled from sealing temperature.

Carbon nanofibers prepared by electrospinning accompanied with phase-separation method for supercapacitors: Effect of thermal treatment temperature

Abstract