High-temperature Treatment In Air Research Articles

Research of the Thermal Effect on the Fe-Cr-Al Alloy Foil in the Initial State and with the Supported Secondary Carrier

Iron and chromium based alloys have found wide application in various fields of science and technology. A primary carrier based on Fe-Cr-Al alloy is used in block catalysts for high-temperature hydrocarbon conversion, in production of block metal catalysts for neutralization of toxic gases released during operation of internal combustion engines, as well as those present in smoke emissions from enterprises. The influence of thermal action on Fe-Cr-Al alloy foil and stability of the secondary carrier on its surface was studied. The elemental composition of the surface layer of Fe-Cr-Al alloy foil does not remain constant during heating and depends on the thermal treatment mode. Some of the elements come to surface and the elemental composition of the surface layer can differ significantly from that observed in the bulk of the foil sample. This implies the possibility of changing the adhesive and adsorption properties of the foil surface, as well as the need to take this fact into account when supporting a secondary carrier and active phase to the foil. An applied technique of phosphating and supporting a secondary carrier at the foil surface makes it possible to obtain a sufficiently stable coating. There is no shedding of the secondary carrier from the foil surface during high-temperature treatment in air.

Gentle hydrotreatment of shale oil in fixed bed over Ni-Mo/Al2O3 for upgrading

Catalyst Ni-Mo/Al2O3 was applied to gentle hydrotreatment of shale oil in a fixed bed. It shows that 84.6% of sulfur was removed from the shale oil with a yield of upgraded oil high as 96.2% under the optimal catalytic hydrodesulfurization (HDS) conditions as at a liquid hourly space velocity (LHSV) of 4 h−1, a temperature of 380 °C, a H2/oil volume ratio of 600:1, and a pressure of 4 MPa. The upgraded shale oil met the quality requirement of national standard Marine fuel oil (GB17411-2015, China) requiring sulfur contents below 0.5 wt%. With the HDS the shale oil also got obvious improvement on its heating value and viscosity. The catalyst used for upgrading was always deactivated owing to coke deposition but an in-situ high-temperature treatment in air effectively removed the coke on the surface of the catalyst to enable its high activity after a re-sulfidation operation. In order to provide low-cost hydrogen for industrial upgrading processes that implement shale oil upgrading, a conceptual process was finally proposed through coupling a high-pressure operation methanol reforming unit and the tested high-pressure HDS upgrading reactor.

High-Temperature Oxidation of Heavy Boron-Doped Diamond Electrodes: Microstructural and Electrochemical Performance Modification.

In this work, we reveal in detail the effects of high-temperature treatment in air at 600 °C on the microstructure as well as the physico-chemical and electrochemical properties of boron-doped diamond (BDD) electrodes. The thermal treatment of freshly grown BDD electrodes was applied, resulting in permanent structural modifications of surface depending on the exposure time. High temperature affects material corrosion, inducing crystal defects. The oxidized BDD surfaces were studied by means of cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM), revealing a significant decrease in the electrode activity and local heterogeneity of areas owing to various standard rate constants. This effect was correlated with a resultant increase of surface resistance heterogeneity by scanning spreading resistance microscopy (SSRM). The X-ray photoelectron spectroscopy (XPS) confirmed the rate and heterogeneity of the oxidation process, revealing hydroxyl species to be dominant on the electrode surface. Morphological tests using scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that prolonged durations of high-temperature treatment lead not only to surface oxidation but also to irreversible structural defects in the form of etch pits. Our results show that even subsequent electrode rehydrogenation in plasma is not sufficient to reverse this surface oxidation in terms of electrochemical and physico-chemical properties, and the nature of high-temperature corrosion of BDD electrodes should be considered irreversible.

Oxygen Surface Exchange Kinetics of Pr2(Ni,Co)O4+δ Thin-Film Model Electrodes

Dense thin-film microelectrodes of the first-order Ruddlesden-Popper phases Pr2NiO4+δ (PNO) and Pr2Ni0.9Co0.1O4+δ (PNCO) were prepared by pulsed laser deposition and photolithographic patterning on yttria-stabilized zirconia (YSZ) substrates. The thin-films were characterized by X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy, inductively coupled plasma optical emission spectroscopy, energy dispersive X-ray spectroscopy and electron energy loss spectroscopy. Investigation of the phase stability of PNO and its reactivity with YSZ was performed by X-ray diffraction analyses after high-temperature treatment in air. Resistive and capacitive contributions of the individual processes occurring at the microelectrodes were determined by means of electrochemical impedance spectroscopy at various temperatures (550 ≤ T/°C ≤ 850) and oxygen partial pressures (1 × 10−3 ≤ pO2/bar ≤ 1). Oxygen surface exchange coefficients kq and kchem were calculated from the surface resistances and chemical capacitances of the thin-film electrodes. Comparing kq-values of PNO and PNCO shows that substitution of Ni with 10% of Co increases the oxygen surface exchange rates, especially at lower oxygen partial pressures.

The interplay of Au nanoparticles and ZnO nanorods for oxygen-promoted, base-free, complete formaldehyde reforming into H2 and CO2

Au nanoparticles on ZnO nanorods is a sustainable catalyst for oxygen-promoted, base-free, complete formaldehyde reforming into H2 and CO2 at low temperatures. The strong metal-support interaction (SMSI) between Au and ZnO is suggested to be responsible for this catalytic feature partially due to the presence of surface cationic Au+ species formed during high temperature treatment in air. in-situ EPR and resonance Raman analysis show that a two-electron reduction pathway is involved to produce hydrogen peroxide as the active species and CH bond cleavage is the rate-determining step.

Synthesis of alumina aerogels from AlCl3·6H2O with an aid of acetoacetic-grafted polyvinyl alcohol

Alumina aerogels are prepared from the cheap AlCl3·6H2O precursor by the sol-gel method using acetoacetic-grafted polyvinyl alcohol (acac-PVA) as a template and dispersing agent, and propylene oxide as a gelation initiator. The acac-PVA has a high dispersing ability for Al3+ ion through complexation interaction and increases the content of AlCl3·6H2O in sols to as high as 37 wt%, leading to the formation of wet gels without precipitate and crack, and little shrinkage. As-prepared alumina aerogels have high density, high mechanical strength, high mesoporosity, and high-surface area. The shrinkage in supercritical drying processes is greatly reduced. The specific surface area increases and pore size decreases with increasing the content of the acac-PVA in sols. The acac-PVA also acts as a template that provides nucleation sites for boehmite AlOOH particles and inhibits their growth. An excess content of the acac-PVA isolates secondary particles, weakens the interaction between them, and therefore decreases the Young’s modulus. Coarsening is not alleviated obviously after removal of the acac-PVA by high-temperature treatment in air, and the fine primary particles grow into nanorods with diameters of 10–20 nm and lengths of 30–70 nm.

Microscale evaluation of laser cladded Inconel 625 exposed at high temperature in air

Ni-based superalloys offer resistance to high-temperature oxidation in different industrial sectors. These alloys can also be deposited as coatings onto metallic substrates by means of different techniques. In this work, a diode laser with carefully selected process parameters was used to generate Inconel 625 coatings onto ferritic and stainless steel substrates. The coatings obtained were exposed to high-temperature treatment in air and different exposition times were studied. The evolution of the coatings microstructure was analysed and depth-sensing indentation tests were performed to measure the evolution of elastic modulus and hardness with the exposition time. Finally, mechanical properties and microstructural changes were correlated. The results revealed that the average mechanical properties and the microstructure of the coatings were not affected by the steel used as the substrate. The treatment at 520°C increased the amount of carbides and brought to the appearance of Laves phases. The treatment at 800°C promoted the formation of mainly δ and Laves phases. These microstructural evolutions involved changes in the values of the mechanical properties of the coatings, which could control their response under operating conditions.

In situ X-ray investigation of coatings based on titanium nitride upon high-temperature oxidation in air

Multicomponent nanocrystalline coatings synthesized by the plasma-assisted vacuum arc method at high-temperatures are studied in situ by the X-ray diffraction method using synchrotron radiation. The main features of these coatings are superhardness (39–45 GPa) and nanocrystalline structure (5–20 nm). Analysis of the results of structural and phase investigations and the physical and mechanical characteristics after high-temperature treatment in air is presented.

Thermochemical Transformations of Phenolformaldehyde Fibers

Thermochemical transformations of phenolformaldehyde fibers (PFF) obtained from novolac resin were investigated during high-temperature treatment in air and an inert medium. Thermal transformations of the polymer were characterized by thermogravimetry, IR spectroscopy, and chemical analysis. The principal features of the thermochemical transformations of PFF were found and included a region of extensive thermal decomposition accompanied by the formation of an intermediate thermally stable product. A carbonized product could be produced in 65-70% yield of the initial fiber mass.

A novel method to control atomic defects in graphene sheets, by selective surface reactions

Behaviors of atomic defects in graphene sheets in air at high temperature are studied. Results indicate that the number of defects in graphene sheets decreases after high temperature treatment in air. Mechanism for the behaviors are studied by molecular simulations and interpreted as follows. Charge distributions of atoms in graphene sheets are relatively uniform due to large conjugated π bond, but atomic defects in the graphene sheets change the uniform charge distributions. The change of charge distributions makes these defect-regions have higher chemical activities, thus these defect-regions are easy to be eroded selectively by O2 in air, which makes the number of them decrease. Thus, high temperature treatment in air can be used as a novel method to control atomic defects in graphene sheets. However, in order to obtain the graphene sheets after reactions, two problems should be dealt with: one is sufficient contact between air and graphene sheets during reaction; the other is transfer and enrichment of graphene sheets after reaction. Our method dealt with the two problems.

Study of Densification Process and Microstructure for Highly Dense Doped MgB2 Bulk Samples

In order to give a contribution in the subject of MgB2 processing technique to obtain low cost high density bulk samples with improved superconducting properties, studies on dilatometry and on the microstructures of in situ and ex situ MgB2 bulk samples prepared in the presence of carbon compounds are presented in this paper. The ex situ densification was performed by isostatic pressure followed by high temperature treatment in air, which promoted high density samples compared to the common magnesium diboride in situ samples. It was observed that each carbon compound addition (hydrocarbon—C8H18, SiC and silicon oil—SiC2H6O), corresponds to one microstructure, which can be noticed even after the ex situ process for sintering the pellets. Among the compounds, the SiC showed to present the most irregular structure for the in situ samples. However, this microstructure showed to change completely and reaches higher density (90 %) very rapidly when heat treated in the ex situ process. The X ray diffraction (XRD) analyses also revealed that the presence of spurious phases—like Mg2Si, Mg3B2O6, MgO and others—for the ex situ samples treated in air at high temperature.

Temperature-Induced Irreversible Change of ZnO Optical Energy Gap

It is generally recognized that the change of ZnO optical properties due to high-temperature treatment is reversible. However, herein, it is reported that high-temperature treatment in air caused an irreversible decrease in ZnO optical energy gap (Eg). The irreversible decrease in Eg was enhanced with increasing treatment temperature. Furthermore, it was found that the irreversible decrease in Eg can be attributed to the enlargement of ZnO crystal particles.

Characterization of dispersed indium species obtained by thermal treatment of In–NH 4-zeolites and their impact on the SCR of NO x

Indium species dispersed on zeolites by high temperature treatment in air of indium-impregnated NH 4-zeolites were characterized and related to the catalytic behavior of the solids in the selective catalytic reduction of NO x . NO-TPD, H 2-TPR and CO-TPR experimental results show that higher temperatures increase the fraction of dispersed InO + and In x O y phases. These species can oxidize nitric oxide to NO 2 and are in greater amounts on the mordenite framework. X-ray indium mapping and TEM observations show a heterogeneous distribution of In 2O 3 particles in solids with higher indium content. These oxides have smaller crystal size and a larger interaction in the framework of ZSM5. TGA–SDTA results point out that the thermal treatment simultaneously produces a solid-state indium exchange and a zeolite dehydroxylation, the exchange level being higher at larger indium contents. The catalytic behavior of the In–zeolites studied can be explained in terms of the type and proportion of indium species present according to the indium loading, thermal treatment and type of zeolite framework. For both zeolites, a higher temperature treatment extends the NO x conversion windows because there are larger amounts of active InO +. But the maximum deNO x activity is lower for In–mordenite due to the larger amounts of In x O y in this zeolite. This non-selective phase increases the methane conversion level. When the indium content is higher, the deNO x activity further increases, in line with a larger fraction of active InO + species. Besides, the catalytic activity of the solids does not decrease despite the excess of indium in these samples under the form of In 2O 3 crystals.

Sputtered YSZ based protective thin films for SOFCs

Protective Zr(Y)O2–δ based films, deposited using magnetron sputtering, onto apatite type ceramics, were appraised for potential applications in solid oxide fuel cells with silicate based solid electrolytes, where performance may suffer from surface decomposition processes in reducing atmospheres. While as prepared Zr(Y)O2–δ films without copper additive were already crystallised and single phase, fresh Cu containing Zr(Y)O2–δ are essentially amorphous, requiring high temperature treatment in air for crystallisation. Deposition rate of 0·50–0·75 μm h–1 at sputtering power of 300 W was achieved. Surface morphology studies using atomic force microscope revealed typical film structures with small (<50 nm) grains. The hardness of films decreases from 15·8 to 8·4 GPa with increasing copper content. Polarisation studies of electrochemical cell with cermet anodes, applied over protective films, suggested that electrochemical reaction is essentially governed by oxygen anion transfer from zirconia phase and/or hydrogen oxidation in vicinity of zirconia film surface. Copper incorporation into Zr(Y)O2–δ film leads to higher anode resistivity.

Synthesis and structure of nanocrystalline La0.50Ba0.50MnO3

Nanocrystalline manganite La0.50Ba0.50MnO3 was synthesized by the soft-chemical method. For this purpose, the sol-gel method was modified and improved. A trihydric saturated alcohol, e.g., glycerol, was suggested as a new organic matrix. The crystal structure of the composite was studied by X-ray powder diffraction at room temperature. A La0.50Ba0.50MnO3 powder annealed in air at T = 500°C is characterized by a perovskite-like cubic structure with the unit-cell parameter a = 3.869 A. The chemical composition of the sample was studied by electron-probe X-ray microanalysis. The La: Ba: Mn cation ratio in the material was 1: 1: 2. The surface topography was examined with a scanning electron microscope. The crystallite size was ∼30 nm. The dependence of the crystal structure and the surface topology on the annealing temperature was studied. The high-temperature treatment in air resulted in the growth of larger, micrometer-size, crystallites.

Effect of FePO 4 coating on electrochemical and safety performance of LiCoO 2 as cathode material for Li-ion batteries

LiCoO 2 was surface modified by a coprecipitation method followed by a high-temperature treatment in air. FePO 4-coated LiCoO 2 was characterized with various techniques such as X-ray diffraction (XRD), auger electron spectroscopy (AES), field emission scanning electron microscope (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), electrochemical impedance spectroscopy (EIS), 3 C overcharge and hot-box safety experiments. For the 14500R-type cell, under a high charge cutoff voltage of 4.3 and 4.4 V, 3 wt.% FePO 4-coated LiCoO 2 exhibits good electrochemical properties with initial discharge specific capacities of 146 and 155 mAh g −1 and capacity retention ratios of 88.7 and 82.5% after 400 cycles, respectively. Moreover, the anti-overcharge and thermal safety performance of LiCoO 2 is greatly enhanced. These improvements are attributed to the FePO 4 coating layer that hinders interaction between LiCoO 2 and electrolyte and stabilizes the structure of LiCoO 2. The FePO 4-coated LiCoO 2 could be a high performance cathode material for lithium-ion battery.

One-dimensional α-MnO 2: Trapping chemistry of tunnel structures, structural stability, and magnetic transitions

Highly crystalline one-dimensional (1D) α-MnO 2 nanostructures were synthesized by a hydrothermal method. All samples were characterized by X-ray diffraction, transmission electron microscope, thermogravimetric and differential scanning calorimeter, and infrared spectroscopy. During the formation reactions, the tunnel structure of 1D α-MnO 2 was simultaneously modified by NH 4 + species and water molecules. The amount of NH 4 + species that were trapped in the tunnels is almost independent on the reaction temperature, while the total water content increased with the reaction temperature. The average diameter of α-MnO 2 nanorods increased from 9.2 to 16.5 nm when the reaction temperature increased from 140 to 220 °C. 1D α-MnO 2 was destabilized by a subsequent high-temperature treatment in air, which is accompanied by a structural transformation to 1D Mn 2O 3 of a cubic structure. At low temperatures, all 1D α-MnO 2 nanorods showed two magnetic transitions that were characterized by a decreased Néel temperature with rod diameter reduction. According to the effective magnetic moments experimentally measured, Mn ions presented in the nanorods were determined to be in a mixed valency of high spin state Mn 4+/Mn 3+.

Thermal Treatment and Light Illumination Effects in EPR Spectra of KTaO3:Cu

In order to understand the manner of incorporation of oxygen vacancies into perovskite structure oxides, KTaO3 crystals containing Cu2+ impurity ions were investigated following thermal treatments in atmosphere of H2, air, and vacuum. The results of thermal treatments were controlled by EPR. The influence of light illumination on copper centres in these crystals was studied also. The thermal treatment and light illumination effects in EPR spectra of Cu impurity centres are studied for the incipient perovskite-like ferroelectric KTaO3 single crystals. It was found that thermal treatment at ∼950°C in hydrogen atmosphere and in vacuum strongly depresses EPR signal of both types of Cu2+(1) and Cu2+(2) axial centres substituting Ta5+ in the B-sublattice positions. Subsequent high-temperature treatment in air restores EPR signals of Cu2+ centres, but changes the ratio between Cu2+(1) and Cu2+(2) centres concentration. These effects, together with UV light illumination effects observed for T < 80 K, are connected with the possibility of the Cu2+ ←→ Cu+ thermal and photo-induced transformations of the Cu impurity centres.

Electrochemical evaluation and modification of commercial lithium cobalt oxide powders

As the cathode materials for rechargeable lithium batteries, five commercial lithium cobalt oxide powders have been investigated for a comparative study. The X-ray diffraction analysis indicates that all these powders exhibit the α-NaFeO2 layered structure. The size distribution and morphology were analyzed by particle sedimentation method and scanning electron microscopy (SEM). Their electrochemical properties including cycleability and especially 3.6 V plateau efficiency, a recently required control parameter, are compared. Two kinds of modifications, i.e. Li2CO3 coating and high-temperature treatment, have been applied to improve the electrochemical performance of one of these five powders. After the high-temperature treatment in air, cobalt oxidation-state becomes higher and Li(LixCo1−x)O2 is formed. Both of the two modified means can significantly improve the 3.6 V-plateau efficiency through suppressing the cell impedance rise during cycling. A general discussion on the factors influencing the plateau efficiency is also given.

Structural and surface property changes of macadamia nut-shell char upon activation and high temperature treatment

Structural and surface property changes of macadamia nut-shell (MNS) char upon activation and high temperature treatment (HTT) were studied by high-resolution nitrogen adsorption, diffuse reflectance infra-red Fourier transform spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed desorption. It is found that activation of MNS char can be divided into the low extent activation which may involve the reactions of internal oxygen-containing groups and leads to the formation of comparatively uniform micropores, and the high extent activation which induces reactions between carbon and activating gas and produces a large amount of micropores. The surface functional groups (SFGs) basically increase with the increase of activation extent, but high extent activation preferentially increases the amount of –C–O and –CO. HTT in air for a short time at a high temperature (1173 K) greatly increases the micropore volume and the amounts of SFGs. By appropriately choosing the activation and HTT conditions, it is possible to control both the textural structure and the type and amounts of SFG.