Thermal Oxidation In Air Research Articles

Low-temperature NO2 sensor based on γ-In2Se3/In2O3 nanoflower heterojunction

The γ-In2Se3/In2O3 nanoflower-like heterojunctions were synthesized by solvothermal treatment followed by thermal oxidation in Air. The nanoflower-like γ-In2Se3/In2O3-based chemiresistive-type sensor showed a significantly enhanced response to NO2 at an operating temperature of 170°C. The sensor achieves a response of 2.69–0.2 ppm NO2 at 170°C. The sensor exhibits remarkable selectivity to several possible interferents such as carbon monoxide, ammonia, formaldehyde, acetone, methanol, and toluene, and good stability at 170°C. The nanoflower structure increases the specific surface area and introduces more active sites, which improves the sensitivity of the sensor to NO2. The heterojunction formed between γ-In2Se3 and In2O3 improves the charge carrier transfer between NO2 gas molecules and sensing materials, thereby increasing the response of the sensor to NO2. Density functional theory was used to elucidate this sensing mechanism, and it was found that improved sensing performance is mainly due to heterojunction formation, which increases the adsorption energy of nitrogen dioxide molecules on a sensing material surface and facilitates charge transfer between molecules.

Plasma assisted remediation of SiC surfaces

This paper describes a three-step process to remediate surface and sub-surface defects on chemo-mechanically polished SiC surfaces. In this process, a CF4-based inductively coupled plasma with reactive ion etch was used to remove material to a depth, which is unaffected by surface and subsurface polishing damage. This produced a planarized but carbon-rich fluorinated surface. This surface was then exposed to a 2 min rapid thermal oxidation in air at 1000 °C to oxidize and volatilize the excess carbon and fluorinated species, respectively. The resulting surface oxide was then stripped using a dilute hydrofluoric acid in water solution. This process, referred to as plasma assisted remediation, reproducibly yielded planarized, stoichiometric surfaces with low levels of carbon and oxygen contamination suitable for subsequent device fabrication. In the supporting studies described here, 4H- and 6H-SiC(0001) surfaces were remediated and characterized by x-ray photoelectron spectroscopy and atomic force microscopy at each stage of the process. Experimental studies under ion-rich and radical-dominant conditions are also reported which provide greater insight into the underlying chemistry and physics of the process.

Effect of prolonged annealing on the morphology and optical properties of ZnO films produced by magnetron sputtering

The effect of annealing time on the structural and optical properties of ZnO films, which are formed from Zn films obtained by magnetron sputtering followed by oxidation in air, is described. Thermal oxidation in air was carried out for 7 and 24 hours, respectively, in a programmable muffle furnace at T = 750°C. A change in the structure of the film surface depending on the annealing time of the Zn film and the substrate material was found, which manifests itself in the optical properties of the films.

Thermal oxidation of MoS2 into defective crystalline MoO3 with enhanced Li-ion storage kinetics

Thermal oxidation in air of molybdenum disulfide (MoS2) into layer structured molybdenum trioxide (α-MoO3) is investigated using a combination of thermal analysis, electron microscopy, Raman, X-ray diffraction and photoelectron spectroscopy. The phase evolutions occurred during the thermal process is characterized by the surface oxidation of MoS2, followed by the bulk oxidation to form α-MoO3 and the formation of Mo17O47 at higher temperatures. The single-phase MoO3 formed at optimum temperature condition is found to possess crystalline defects and considerably greater values of Li-ion storage cycling and rate performances in comparison with samples prepared at alternative temperatures and also the initial MoS2. This sample (P-MoO3-820) exhibits a charge capacity of 628 mA h g−1 after 250 cycles (100 mA g−1) with a Li+ diffusion coefficient of 2.3 × 10-13 cm2 s−1, substantially greater than that of initial MoS2 (8.1 ×10−16 cm2 s−1). The electrochemical performance of P-MoO3-820 in full-cell configuration against a commercial LiFePO4 cathode is evaluated and a specific capacity of 100 mAh g−1 after 500 cycles is recorded. This article, for the first time, discusses the thermal oxidation in air of MoS2 as a simple and relatively clean approach to fabricate defective crystalline MoO3 with enhanced Li-ion storage kinetics.

Silver nanoparticles decorated ZnO–CuO core–shell nanowire arrays with low water adhesion and high antibacterial activity

Nanostructured surfaces based on silver nanoparticles decorated ZnO–CuO core–shell nanowire arrays, which can assure protection against various environmental factors such as water and bacteria were developed by combining dry preparation techniques namely thermal oxidation in air, radio frequency (RF) magnetron sputtering and thermal vacuum evaporation. Thus, high-aspect-ratio ZnO nanowire arrays were grown directly on zinc foils by thermal oxidation in air. Further ZnO nanowires were coated with a CuO layer by RF magnetron sputtering, the obtained ZnO–CuO core–shell nanowires being decorated with Ag nanoparticles by thermal vacuum evaporation. The prepared samples were comprehensively assessed from morphological, compositional, structural, optical, surface chemistry, wetting and antibacterial activity point of view. The wettability studies show that native Zn foil and ZnO nanowire arrays grown on it are featured by a high water droplet adhesion while ZnO–CuO core–shell nanowire arrays (before and after decoration with Ag nanoparticles) reveal a low water droplet adhesion. The antibacterial tests carried on Escherichia coli (a Gram-negative bacterium) and Staphylococcus aureus (a Gram-positive bacterium) emphasize that the nanostructured surfaces based on nanowire arrays present excellent antibacterial activity against both type of bacteria. This study proves that functional surfaces obtained by relatively simple and highly reproducible preparation techniques that can be easily scaled to large area are very attractive in the field of water repellent coatings with enhanced antibacterial function.

Multi–length scale characterization of point defects in thermally oxidized, proton irradiated iron oxides

A key for the success of safe nuclear power generation system is to consider structural materials that are economical, meet mechanical property needs, possess good corrosion resistance, and are radiation tolerant. Nevertheless, fundamental insights that elucidate the details of radiation damage on materials corrosion performance are lacking. This includes the behavior of surface oxides which often regulate corrosion. For example, it is unclear how non-equilibrium point defects, oxide structure, mass transport in oxides, and subsequent oxidation behavior are altered by the radiation. In this work, some of the effects of proton irradiation on the attributes of point defects, iron oxide microstructures, and the physical nature of the oxidation product were correlated with corrosion behavior. Iron oxides, fabricated by thermal oxidation in air at 400°C and 800°C for 1 h, were subjected to 200 keV, 0.03 dpa (displacements per atom) of proton irradiation, and subjected to corrosion reactivity assessment using AC and DC electrochemical methods. Experimental methods that target materials information at different length scales, such as positron annihilation spectroscopy (atomistic), transmission electron microscopy (mesoscopic), and electrochemical methods (macroscopic), were coupled to shed light on the impact of radiation-induced defect modifications and structural changes in oxides on corrosion reactivity which ultimately affects durability in harsh environments.

Growth of titania and tin oxide from Ti2SnC via rapid thermal oxidation in air for lithium‐ion battery application

AbstractHerein, we report the synthesis of TiO2–SnO2–C/carbide hybrid electrode materials for Li‐ion batteries (LIBs) via two different methods of controlled oxidation of layered Ti2SnC. The material was partially oxidized in an open‐air furnace (OAF) or using a rapid thermal annealing (RTA) approach to obtain the desired TiO2–SnO2–C/carbide hybrid material; the carbide phase encompassed both residual Ti2SnC and TiC as a reaction product. We tested the oxidized materials as an anode in a half cell to investigate their electrochemical performance in LIBs. Analysis of the various oxidation conditions indicated the highest initial lithiation capacity of 838 mAh/g at 100 mA/g for the sample oxidized in the OAF at 700°C for 1 h. Still, the delithiation capacity dropped to 427 mAh/g and faded over cycling. Long‐term cycling demonstrated that the RTA sample treated at 800°C for 30 s was the most efficient, as it demonstrated a reversible capacity of around 270 mAh/g after 150 cycles, as well as a specific capacity of about 150 mAh/g under high cycling rate (2000 mA/g). Given the materials’ promising performance, this processing method could likely be applied to many other members of the MAX family, with a wide range of energy storage applications.

Catalytic thermo-oxidation of carbon matrix in the nanocomposite electrode material for supercapacitors preparation process

The study of thermal oxidation in air of carbon matrix in the presence of nanosized particles of filler - cobalt oxide Co3O4, as well as mixed oxides NiCo2O4 and ZnxCo1-xOy was carried out. The particles of transition metal oxides were created by thermal decomposition of precursor compounds (azides and hydroxides). It is shown that vigorous oxidation in the air of the porous carbon matrix starts after the formation of Co3O4 at temperatures above 300 ° C. The intensity of oxidation is directly proportional to the filler concentration in the carbon-transition metal oxide composite system. Carbon matrices based on multilayer carbon tubes show higher resistance to oxidation processes.

Antibacterial Properties of TiO<sub>2</sub> Layers Formed by Au-Sputtering and Thermal Oxidation of Titanium under Visible Light

To prevent infection in dental implants using photocatalytic activity under visible-light irradiation, the fabrication of Au-added TiO2 layers on Ti substrates and their antibacterial properties were studied. Pure Au and Ti–(60, 40) mol%Au alloy films with thicknesses of 10–47 nm were sputtered onto Ti, followed by thermal oxidation in air at 873 K for 1.8 ks to form TiO2 layers. The antibacterial properties against Escherichia coli, cytotoxicity, and bonding strength to Ti substrates were evaluated. The highest antibacterial activity under visible-light irradiation was obtained when the sputtered film was pure Au and its thickness was 38 nm. Compared with as-polished commercially pure Ti, the number of viable mouse osteoblast-like cells and human gingival fibroblasts on Au-added TiO2 layers increased after placement in the dark but decreased after visible-light irradiation. The best antibacterial property-bonding strength balance was achieved when the Ti–40 mol%Au sputtered film with a thickness of 42 nm was formed on Ti. To the best of our knowledge, this study is the first to report the formation of TiO2 layers with antibacterial activity under visible-light irradiation by combining Au-sputtering and thermal oxidation of Ti.

Air-thermal oxidation of diamond nanopowders obtained by the methods of mechanical grinding and detonation synthesis

In this work, using the methods of X-ray phase analysis, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy, the features of the impact of annealing in air within the temperature range of t = 200÷÷550 °C on the morphology, elemental and phase composition, chemical state and structure of primary particles of nanopowders obtained by grinding natural diamond and the method of detonation synthesis are studied. It is shown that heat treatment in air at given values of temperature and heating time does not affect the elemental composition and atomic structure of primary particles of nanopowders obtained both by the methods of detonation synthesis (DND) and natural diamond grinding (PND). Using XPS, Raman spectroscopy, and transmission electron microscopy, it has been found that annealing in air within the temperature range of 400–550 °C results in the effective removal of amorphous and graphite-like carbon atoms in the sp2- and sp3-states from diamond nanopowders by oxidation with atmospheric oxygen. In the original DND nanopowder, containing about 33.2 % of non-diamond carbon atoms of the total number of carbon atoms, after annealing for 5 h at a temperature of 550 °C, the relative number of nondiamond carbon atoms in the sp2-state decreased to ~21.4 %. In this case, the increase in the relative number of carbon atoms in the sp3-state (in the lattice of the diamond core) and in the composition of oxygen-containing functional groups ranged from ~39.8 % to ~46.5 % and from ~27 % to ~32.1 %, respectively. In the PND nanopowder, which prior to annealing contains about 10.6 % of non-diamond carbon atoms in the sp2-state of the total number of carbon atoms, after annealing under the same conditions as the DND nanopowder, their relative number decreased to 7.1 %. The relative number of carbon atoms in the sp3-state increased from 72.9 % to 82.1 %, and the proportion of carbon atoms in the composition of oxygen-containing functional groups also slightly increased from 10.2 % to 10.8 %. It is demonstrated that the annealing of PND and DND nanopowders in air leads to a change in their color, they become lighter as a result of oxidation of non-diamond carbon by atmospheric oxygen. The maximum effect is observed at a temperature of 550 °C and an annealing time of 5 h. In this case, the weight loss of PND and DND nanopowders after annealing was 5.37 % and 21.09 %, respectively. The significant weight loss of DND nanopowder compared to PND is primarily caused by the high content of non-diamond carbon in the initial state and the high surface energy of primary particles due to their small size.

Bi to β-Bi2O3 thin films transformation by thermal oxidation in air at low temperature

Bismuth oxidation by thermal treatment has been studied by several groups, however, low temperature (well below melting) oxidation is rarely reported in the literature. In this work, we focused on the straightforward phase transition from bismuth to the β-Bi2O3 phase, by gradually heating the bismuth film. This is proved that by carrying out the oxidation process at the low temperature 175 °C (as compared to the melting temperature 271 °C) it is possible to turn pristine bismuth into β-Bi2O3. In order to achieve this transformation, the thermal treatment was span for up to 10 h, finding that at 6 h the initially opaque bismuth film becomes optically translucid, meaning that the bismuth oxide beta phase is reaching downwards to the substrate. For 8 and 10 h of thermal treatment the bismuth film is clearly fully oxidized. The bismuth to β-Bi2O3 transformation was characterized by using Raman micro-spectroscopy, UV–Vis Spectroscopy, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Our results demonstrated a feasible, simple and reliable method for the synthesis of β-Bi2O3, at well below melting temperature.

Study of the optical response of oxidized porous silicon structures by thermal oxidation in air

Study of the optical response of oxidized porous silicon structures by thermal oxidation in air

Self-connected CuO–ZnO radial core–shell heterojunction nanowire arrays grown on interdigitated electrodes for visible-light photodetectors

An original photodetector system based on self-connected CuO–ZnO radial core–shell heterojunction nanowire arrays grown on metallic interdigitated electrodes, operating as visible-light photodetector was developed by combining simple preparation approaches. Metallic interdigitated electrodes were fabricated on Si/SiO2 substrates using a conventional photolithography process. Subsequently, a Cu layer was electrodeposited on top of the metallic interdigitated electrodes. The CuO nanowire arrays (core) were obtained by thermal oxidation in air of the Cu layer. Afterwards, a ZnO thin film (shell) was deposited by RF magnetron sputtering covering the surface of the CuO nanowires. The morphological, structural, compositional, optical, electrical and photoelectrical properties of the CuO nanowire arrays and CuO–ZnO core–shell nanowire arrays grown on metallic interdigitated electrodes were investigated. The performances of the devices were evaluated by assessing the figures of merit of the photodetectors based on self-connected CuO–ZnO core–shell heterojunction nanowire arrays grown on the metallic interdigitated electrodes. The radial p–n heterojunction formed between CuO and ZnO generates a type II band alignment that favors an efficient charge separation of photogenerated electron–hole pairs at the CuO–ZnO interface, suppressing their recombination and consequently enhancing the photoresponse and the photoresponsivity of the photodetectors. The electrical connections in the fabricated photodetector devices are made without any additional complex and time-consuming lithographic step through a self-connecting approach for CuO–ZnO core–shell heterojunction nanowire arrays grown directly onto the Ti/Pt metallic interdigitated electrodes. Therefore, the present study provides an accessible path for employing low dimensional complex structures in functional optoelectronic devices such as photodetectors.

A facile and green strategy to synthesize N/P co-doped bio-char as VOCs adsorbent: Through efficient biogas slurry treatment and struvite transform

Controllable introduction of active sites on bio-char is certified as an available method to resolve a bottleneck issue of conversion of various greenrenewable bio-char into valuable materials. In this work, the bio-char was modified by air thermal oxidation after the formation of struvite via the facile impregnation in the biogas slurry. The structural and elemental properties of the surface of modified bio-char were analyzed by SEM, BET, XRD, and XPS. XPS analysis of the nitrogen and phosphorus valence states on the carbon surface shows that the N/P elements of struvite were synergically converted into N/P functional groups via air thermal oxidation. Then the modified bio-char was used as VOCs-acetone adsorber and the result shows that the acetone adsorption capacity was 4.8 times higher than that of bio-char. The density functional theory (DFT) proves that the binding force of C-O-P and acetone (-16.882 kcal) is stronger than that of C-P-O and acetone (−7.779 kcal). The results certified that air thermal oxidation coupling eutrophic element recycling is a promising approach for the preparation of N/P co-doped bio-char as value-add materials for improving acetone adsorption performance.

Ionic liquid modified boron nitride nanosheets for interface engineering of epoxy resin nanocomposites: Improving thermal stability, flame retardancy, and smoke suppression

Hexagonal boron nitride (h-BN) is more challenging to exfoliate into fewer layers than graphene due to the ionic bond between B and N atoms (lip-lip interaction) from adjacent layers. In this paper, boron nitride was exfoliated and hydroxylated by thermal oxidation in air. Hydroxylated boron nitride nanosheets (BNO) were modified by ionic liquids and added to epoxy resin to prepare epoxy matrix nanocomposites (EP/BNO@IL). The SEM results of EP/BNO@IL nanocomposites suggested that the introduction of ionic liquids enhanced the interfacial interaction between boron nitride nanosheets and epoxy resin (EP). Thermogravimetric (TG) results showed that introducing 2 wt% BNO@IL nanosheets improved the thermal stability of EP. In addition, cone calorimeter test (CCT) results showed that BNO@IL nanosheets enormously improved the fire safety performance of the epoxy resin. The peak heat release rate, total heat release, peak smoke release rate, and total smoke release of epoxy resin nanocomposites with 2 wt% BNO@IL nanosheets decreased significantly. In this work, the realization of ionic liquid modified boron nitride nanosheets (BNO@IL) provides new possibilities for improving the fire safety performance of EP.

The exceptional oxidation of Ti6Al4V alloy with a pre-deposited silver layer

For the first time, we discovered the exceptional oxidation phenomenon on Ti6Al4V alloy. A thin layer of silver was pre-deposited via PVD on a Ti6Al4V alloy surface before ceramic conversion treatment (CCT) based on thermal oxidation in air at 620 °C. The pre-deposited silver particles accelerated the oxidation of the Ti6Al4V alloy by up to 50 times, and also helped to produce a thick compact surface oxide layer with a larger surface area compared to a non-silver pre-treated surface. However, silver had a less profound effect on the oxidation of other titanium alloys that didn’t contain vanadium, additionally the silver particles tended to agglomerate on their surfaces, particularly for commercially pure titanium (CPTi). Systematic work examining the impact of vanadium found that vanadium together with silver played a critical role in activating oxygen and promoting its diffusion in the oxide layer, thus dramatically accelerating the oxidation of the vanadium-containing titanium alloys with a pre-deposited Ag layer in CCT. SEM/EDX, TEM, XRD and XPS analyses on the surface phase constituents and microstructure helped to explicate the rapid oxidation mechanism of pre-deposited silver on Ti6Al4V surfaces, and thus provide a new insight into modifying the titanium alloys surface efficiently.

The Novel Nano Porous Spinel Films Prepared by One-Step Air-Thermal Oxidation Method for Solar Selective Absorber Applications

The Novel Nano Porous Spinel Films Prepared by One-Step Air-Thermal Oxidation Method for Solar Selective Absorber Applications

A study of oxide layer growth on the surface of aluminium alloys with Ti, Zr, Hf during heating in air

The growth of surface oxide films on binary aluminium alloys with transition metal (TM) Ti, Zr and Hf additives at temperatures 600 and 620° С in air was studied using the single-wave ellipsometry method (wavelength 0.6328 µm). It was shown that the annealing temperature affects the growth rate and extinction coefficient of surface oxide films for alloys having ∼5 at.% and ∼18 at.% TM in aluminium. Alloys with hafnium demonstrated the most active growth of oxide films during heating. A considerable increase in the extinction coefficients of oxide films was observed during oxidation of Al ∼18 at.% TM alloys. The optical properties of alloys (substrates) were found to correlate with their chemical composition. The aluminium alloys with 6 and 18.5 at.% Ti retain their resistance to thermal oxidation in air at the indicated temperatures.

On the growth of copper oxide nanowires by thermal oxidation near the threshold temperature at atmospheric pressure

This study focuses on the growth of copper oxide nanowires networks (CuO NWs) close to the onset temperature, found to be 310 ℃. The NWs were obtained by thermal oxidation in air of polycrystalline copper foils on hot plate. The investigated oxide layers with the NWs network on their surface grown between 200 ℃ and 440 ℃, were characterized by: SEM-EDX, STEM-EDX, XRD, and micro-Raman techniques. The accurate determination of copper content in self-exfoliated oxide sheets is above the stoichiometric concentration. XRD reveals nano-crystallites of 20–40 nm, in Cu2O phase of thick oxide sheets located close to the oxide-substrate interface. Statistical data on the average length of the NWs versus annealing time indicates unexpected early saturation in between 10 and 40 min at 320–340 ℃. A semi-empirical model proofs quantitatively that the emerging delays of the NWs relative to the start of copper oxidation determine the plateau of the average length versus time. The excess concentration of copper found in the cuprous oxide layer is cautioned to accompany the early saturation effect having critical restrictions regarding the oxidation time and temperature. This study sustains the development of control and monitoring methods, applied to the growth of CuO NWs.

Abatement of Polycyclic Aromatic Hydrocarbon Residues in Biochars by Thermal Oxidation

Biochars often contain residues of polycyclic aromatic hydrocarbons (PAHs) that can pose risks to exposed organisms and ultimately to human health. This study shows that thermal oxidation of an anoxically produced (500 °C) softwood biochar using brief post-pyrolysis thermal oxidation in air caused a substantial decline in solvent-extractable PAHs (up to 85% of Tot-PAH) and a sharp decrease (up to 82%) in the EPA Relative Potency Factor. Optimum conditions were 400 °C for 20 min. An alternative approach of including 1% O₂ in the nitrogen flow stream during pyrolysis was less effective. PAH loss is attributed to combustion processes as opposed to outgassing. Oxidation of PAHs occurs in the gas and adsorbed phases and is promoted by pore reaming of biochar micropores and mesopores during thermal oxidation, which facilitates diffusive exchange of O₂, reactive oxygen species, and PAH molecules. Oxidation also may be promoted by self-heating of the biochar body, which increases the local temperature. The results indicate that a short post-pyrolysis thermal oxidation step can reduce the risks associated with PAH residues in biochar.