Influence Of Oxidation Temperature Research Articles

Influence of oxidation temperature and time on stresses in thermal barrier coated aerofoil sections

The influence of temperature and time of thermal exposure on the residual stresses developed within a thermal barrier coating (TBC) and the underlying thermally grown oxide (TGO) are investigated. Stress measurements on the TBC and the TGO for specimens with aerofoil geometry features were made at positions of fixed curvature using Raman spectroscopy and photo-stimulated piezoluminescence spectroscopy. The Raman shifts were converted to stress via a factor measured using a diamond anvil cell (DAC). The acquired stresses were shown to be tensile at all positions measured in the as-coated specimens, and change progressively from tensile to compressive with thermal exposure. Residual stresses within the TGO were found to be a function of the ageing temperature and time, substrate geometry and thickness of the TBC. The results are discussed with respect to the long term integrity of the coatings.

Influence of oxidation temperature and time on stresses in thermal barrier coated aerofoil sections

Influence of oxidation temperature and time on stresses in thermal barrier coated aerofoil sections

Structural, optical and electrical properties of N-doped ZnO thin films prepared by thermal oxidation of pulsed filtered cathodic vacuum arc deposited Zn xN y films

In this study, N-doped ZnO thin films were fabricated by oxidation of Zn x N y films. The Zn x N y thin films were deposited on glass substrates by pulsed filtered cathodic vacuum arc deposition (PFCVAD) using metallic zinc wire (99.999%) as a cathode target in pure nitrogen plasma. The influence of oxidation temperature, on the electrical, structural and optical properties of N-doped ZnO films was investigated. P-type conduction was achieved for the N-doped ZnO obtained at 450 °C by oxidation of Zn x N y , with a resistivity of 16.1 Ω cm, hole concentration of 2.03 × 10 16 cm −3 and Hall mobility of 19 cm 2/V s. X-ray photoelectron spectroscopy (XPS) analysis confirmed the incorporation of N into the ZnO films. X-ray diffraction (XRD) pattern showed that the films as-deposited and oxidized at 350 °C were amorphous. However, the oxidized films in air atmosphere at 450–550 °C were polycrystalline without preferential orientation. In room temperature photoluminescence (PL) spectra, an ultraviolet (UV) peak was seen for all the samples. In addition, a broad deep level emission was observed.

Surface morphology and electrical resistance of the oxide film on InSe

Experimental evidence is presented that air oxidation of InSe crystals produces a native oxide layer which possesses not dielectric but conductive properties and is separated from the semiconductor substrate by a potential barrier. The surface resistance of oxide films grown on InSe across and along the C axis has been measured as a function of oxidation time and temperature. The results demonstrate that the surface resistance of the films varies significantly only during the first five minutes of oxidation. Subsequently, the surface resistance remains almost constant at 100–150 Ω/□. The surface morphology of the native oxide on InSe has been studied by atomic force microscopy. The oxide surface is shown to be nanotextured due to nanospikes normal to the substrate surface. The influence of oxidation temperature and time on the dynamics of the surface morphology of the oxide layer (the lateral dimensions, height, and density of nanospikes) is examined.

Influence of oxidation temperature on photoluminescence and electrical properties of amorphous thin film SiC:H:O+Tb

AbstractThe influence of low‐temperature oxidation on chemical composition, luminescent and electrical properties of a‐Si1‐xCx:H thin films fabricated by reactive RF magnetron sputtering has been studied. A strong dependence on RF sputtering power is seen on the electrical and chemical properties. The a‐Si1‐xCx:H films fabricated by low RF power levels followed by low‐temperature oxidation (at 450 °C‐500 °C) display high intensity of PL, good MOSCV characteristic and low leakage current through the dielectric. Increase of oxidation temperature increases precipitation of carbon nano‐inclusions in the materials, that result in reduction of PL intensity and increase of dielectric leakage. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Detoxification of Phenolic Wastewaters by Catalytic Wet Oxidation in Batch and Continuous Mode

Catalytic wet oxidation of simulated olive oil wastewaters has been investigated in batch and trickle-bed reactors. The comparison between two operating reactor systems is presented querying the effect of temperature and pressure. The higher decontamination rates of organic matter were obtained in the batch reactor, which has promoted the complete mineralization of liquid pollutants after 60 min at 200°C and 30 bar. At equivalent operation times, the batch reactor exhibited higher decontamination efficiencies when compared to the continuous flow trickle-bed reactor. Additionally, the effect of pressure on TOC removal became less significant when compared to the influence of oxidation temperature for both reactor configurations.

Influence of Oxidation Temperature and Cr Content on the Adhesion and Microstructure of Scale on Low Cr Steels

Descalability of steels during hot rolling processes is essential in order to maintain the surface quality of steel products, because the remaining scale can be impressed into the steel, producing surface defects. Therefore, a quantitative evaluation of scale adhesion at high temperature is needed in order to find suitable heating conditions for hot rolling processes that promote the formation of scale that easily detach. Round bar shape specimens of low Cr steels were oxidized in a fuel combustion environment, and then compressed at high temperature to detach the scale. The area fraction of the remaining scale was evaluated by image analysis. Under a thick outer oxide scale, a thin continuous inner oxide layer, which consisted of Cr and Si oxides, strongly adhered to the substrate, resulting in poor descalability. On the other hand, if this inner scale changed into a discontinuous layer with a porous FeO layer beneath, the descalability improved. It was found that scales with greater descalability formed on steels containing less Cr and for oxidation at higher temperatures.

Fabrication of TiO 2 film by mechanical coating technique and its photocatalytic activity

In the present study, the composite film was fabricated using mechanical coating technique (MCT) and oxidation process. The microstructure and crystal form of the film were examined. Photocatalytic activity of the film was evaluated by measuring the decomposition rate of methylene blue (MB) solution at room temperature. Influence of oxidation temperature on the microstructure and the photocatalytic activity was discussed. The film has an uneven surface and a composite microstructure with rutile TiO 2 and titanium. The photocatalytic activity goes up and reaches a peak at 723 K with increasing the oxidation temperature.

The influence of oxidation temperature on structural, optical and electrical properties of thermally oxidized bismuth oxide films

Monoclinic bismuth oxide (Bi 2O 3) films have been prepared by thermal oxidation of vacuum evaporated bismuth thin films onto the glass substrates. In order to obtain the single phase Bi 2O 3, the oxidation temperature was varied in the range of 423–573 K by an interval of 50 K. The as-deposited bismuth and oxidized Bi 2O 3 films were characterized for their structural, surface morphological, optical and electrical properties by means of X-ray diffraction, scanning electron microscopy (SEM), optical absorption and electrical resistivity measurements, respectively. The X-ray analyses revealed the formation of polycrystalline mixed phases of Bi 2O 3 (monoclinic, α-Bi 2O 3 and tetragonal, β-Bi 2O 3) at oxidation temperatures up to 523 K, while at an oxidation temperature of 573 K, a single-phase monoclinic α-Bi 2O 3 was formed. From SEM images, it was observed that of as-deposited Bi films consisted of the well-defined isolated crystals of different shapes while after thermal oxidation the smaller dispersed grains were found to be merged to form bigger grains. The changes in the optical properties of Bi 2O 3 films obtained by thermal oxidation at various temperatures were studied from optical absorption spectra. The electrical resistivity measurement depicted semiconducting nature of Bi 2O 3 with high electrical resistivity at room temperature.

Influence of oxidation temperature on the gas permeation and separation properties in a microporous carbon membrane

Of thermosetting polymers, polyphenylene oxide (PPO) is considered as one of the promising alternative polymeric precursors for carbon membrane preparation. In this study, the PPO derived carbon membranes were prepared by carbonization and followed by air-oxidation as post-treatment method to modify the membrane pore structures. The characterization of the pore properties showed that air-oxidation enlarged the pore structure for the postoxidized carbon materials. The permeation results for the post-oxidized carbon membranes showed that the extent of the permeation modification was strongly dependent on the oxidation temperature. In the binary mixture gas systems, the permeation performance of the adsorbing gas species increased due to the surface diffusion mechanism. It is considered in the oxidation effect on the permeation modification that the post-oxidation of the carbon membranes increased gas permeation and separation properties.

Fabrication and characterisation of NiO/ZnO structures

Metal-oxide-semiconductor (MOS) structures were formed on n-ZnO and the electrical properties were compared to Au Schottky barrier diodes (SBDs) on similar ZnO. After evaporating Ni onto either ZnO, Si or glass, the thin films were oxidised to produce transparent, resisitive layers. The structure and composition of these layers were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron microscopy. The electrical properties were investigated by variable temperature current–voltage ( I– V) and four-point probe measurements, whereas the optical properties were investigated by photospectrometry. The influence of oxidation temperature on the resistivity of the nickel oxide layers was used to optimise the processing conditions. NiO layers had a maximum resistivity of approximately 100 Ω cm after oxidation and bandgap of 3.5–3.6 eV at room temperature. The rectifying qualities of the junctions (using Pd gates) were sufficient for DLTS measurements of ZnO in the temperature range 20–390 K.

Influence of oxidation temperature on the microstructure and electrical properties of Ta2O5 on Si

The effect of the oxidation temperature (673–873K) on the microstructural and electrical properties of thermal Ta2O5 thin films on Si has been studied. Auger electron spectroscopy and X-ray photoelectron spectroscopy results revealed that the films are non-stoichiometric in the depth; an interfacial transition layer between tantalum oxide and Si substrate, containing presumably SiO2 was detected. It has been found by X-ray diffraction that the amorphous state of Ta2O5 depends on both the oxidation temperature and the thickness of the films—the combination of high oxidation temperature (>823K) and thickness smaller than 50nm is critical for the appearance of a crystal phase. The Ta2O5 layers crystallize to the monoclinic phase and the temperature of the phase transition is between 773 and 823K for the thinner layers (<50nm) and very close to 873K for the thicker ones. The electrical characterization (current/voltage; capacitance/voltage) reveals that the optimal oxidation temperature for achieving the highest dielectric constant (∼32) and the lowest leakage current (10−8A/cm2 at 1MV/cm applied field) is 873K. The results imply that the poor oxidation related defects are rather the dominant factor in the leakage current than the crystallization effects.

Influence of oxidation temperature, film thickness and substrate on NO 2 sensing of SnO 2 ultra thin films

Thin SnO 2 films of different thickness were fabricated by sputtering of tin followed by thermal oxidation. The oxidation was performed at 600, 700 and 800 °C and silicon and silicon dioxide were chosen as substrates for their compatibility to silicon CMOS technology. Work function measurements were carried out on these films upon exposure to NO 2 in the concentration range 5–100 ppm at a particular temperature under dry and humid conditions using a commercial Kelvin probe measurement set-up. Kelvin probe measures contact potential difference (CPD) resulting from change in work function of a film material on exposure to a gas. The dependence of NO 2 sensitivity of films on oxidation temperature, film thickness and substrate was investigated. The influence of temperature on NO 2 response from 30 to 130 °C was investigated. It has been observed that humidity has negligible effect at 130 °C. It was further observed that response of SnO 2 film on silicon to NO 2 increases with oxidation temperature of the film whereas for the films grown on silicon dioxide the response was parabolic. In the later case, increase in signal was exhibited by the films oxidized up to 700 °C while it was found to decrease for films oxidized at 800 °C. The films of three different thickness (10, 35 and 55 nm) prepared at 800 °C on silicon showed negligible variation in sensitivity. However, sensitivity of the films grown on silicon dioxide is observed to be thickness dependent. The films were characterized using atomic force microscopy (AFM) and Auger electron spectroscopy (AES) to study the surface morphology and depth profile respectively. The observed results are discussed to understand the NO 2 sensing behavior of ultra thin SnO 2 films.

Effect of air oxidation on gas separation properties of adsorption-selective carbon membranes

Molecular sieve carbon membranes (MSCM) obtained by carbonisation of a phenolic resin film can be transformed into adsorption-selective carbon membranes (ASCM) by means of air oxidation at temperatures between 100 and 450°C. ASCM can separate the components of a gas mixture depending on their adsorption properties instead of the size of the gas molecules as occurs for MSCM. In this work ASCM are prepared according to the following steps: (a) deposition of a thin film of a phenolic resin on the inner face of an alumina tube, (b) carbonisation (under vacuum at 700°C) and (c) air oxidation at temperatures above 100°C. The influence of oxidation temperature (between 100 and 475°C) and oxidation time (between 0.5 and 6 h) on the separation characteristics of the prepared carbon membranes is analysed. The membranes show high permeances and selectivities towards the separation of multicomponent gas mixtures formed by hydrocarbons and N 2. As an example, a carbon membrane oxidised at 250°C (0.5 h) shows the following values of permeances (in mol m −2 s −1 Pa −1×10 −10) and selectivities ( α=hydrocarbon/N 2) for the separation of a complex gas mixture formed by 16.3% CH 4, 16.1% C 2H 6, 16.2% C 3H 8, 20% n-C 4H 10 and 31.4% N 2 are: CH 4, 172 ( α=3); C 2H 6, 700 ( α=12); C 3H 6, 1730 ( α=30); n-C 4H 10, 4270 ( α=74).

Influence of feedstock oxidation temperature on stability of paving asphalts

When the oxidation temperature in the production of asphalts is increased, breakdown processes are accelerated, lowering the yield and polarity of the asphalt [1, 2]. Also, because of the high yields of gaseous products and black solar oil, environmental pollution becomes a problem. At the 4th World Petroleum Congress (1955), it was indicated that a temperature of 250~ is optimal for the oxidation of feedstocks to produce asphalt. Since that time, new technologies have been developed for rapid oxidation, yielding highly polar and more chemically inert binders at lower process temperatures. Outstanding properties were demonstrated in [2] for a plastic bitumen obtained by oxidation at a temperature far below 250~ The influence of the oxidation temperature on the thermal and thermooxidative stability of paving asphalt has received very little attention. When asphalt is held in tanks for the preparation of asphaltic concrete mixes for road construction, and during the course of the mixing process itself, the asphalt is exposed to temperatures of 140-160~ During these stages, the asphalt properties undergo their most severe changes. This period is termed the first stage of aging; it can be simulated quite accurately under laboratory conditions. The second stage of aging begins when the asphaltic concrete pavement is laid down, and it continues until the pavement fails (up to 20 years). During this time, the softening point of the asphalt changes (approximately) from 45 ~ to 70~ As a result, the road coating becomes brittle during the winter; it will not sustain dynamic stresses generated by moving vehicles, and is subject to cracking and breakdown. In studying the change of properties of paving asphalt under service conditions, extended observations under natural conditions are necessary [3]. However, hardly any such observations have been made. In the work reported here, aging tests were performed on asphalts obtained by the oxidation of one particular charge stock, from West Siberian crude, in a column-type unit; all oxidations were performed with the same air input rate, but at different temperatures (220-280~ The first stage of aging was evaluated on the basis of property changes due to thermal and thermooxidative action at 160~ The thermal action (this term is somewhat arbitrary) on the asphalt during storage in the hot state in the refinery, in the course of transportation, and upon heating in tanks at the asphaltic concrete plant was simulated by thermostating the test sample at 160_+2~ in a steel cup used for penetration tests (the specific surface area of contact between the test sample and air was 2 cm2/g). Thermooxidative action on the asphalt during the preparation of the asphaltic concrete mix was simulated in tests on a 10-/xm layer of asphalt applied to steel plates (5 x 5 cm), with a 1000 cm2/g specific surface area of contact with air. The penetration and softening point were determined at intervals on samples that had been held in penetration cups in the oven at 160~ the shearing stress at 25~ was determined on plates that were cemented together by a layer of the asphalt (tested in a cohesiometer designed by SoyuzDorNII [State All-Union Scientific-Research Street and Highway Institute]), The charge stock used in preparing the oxidized asphalts had the following physicochemical properties: nominal [Engler] viscosity 26 sec at 80~ chemical group composition (wt. %) paraffins + naphthenes 15; monocyclic, bicyclic, and polycyclic aromatics 10, 29, and 8, respectively; resins 25; asphaltenes 13. With increasing oxidation temperature in the production of the asphalts, the softening point increased at a faster rate (Fig. 1). The results of tests on samples that were practically identical in depth of oxidation at 220 ~ and 280~ (Table 1) confirmed the conclusion stated in [2] that the standard asphalt property indexes (penetration at 25~ softening point, and ductility at 25~ are independent of the oxidation temperature. The low-temperature properties (penetration at 0~ breaking point, and ductility at 0~ are appreciably better for the asphalt obtained at 220~ than for the asphalt obtained at 280~ These two asphalts differ the most significantly in their concentrations of paramagnetic centers.