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Thermal Oxidation (thermal + oxidation)
Selected AbstractsFormation of Nickel Oxide Nanotubes with Uniform Wall Thickness by Low-Temperature Thermal Oxidation Through Understanding the Limiting Effect of Vacancy Diffusion and the Kirkendall PhenomenonADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Yi Ren Abstract In this work, the step-wise oxidation mechanism of nickel (Ni) nanowires is elucidated. Rapid vacancy diffusion plays a significant role at low temperatures in forming heterostructures of nickel oxide (NiO) nanotubes with Ni nanowires. Subsequent investigations of Ni nanowire oxidation at higher temperatures and faster temperature ramp rates show that it is difficult to bypass this rapid vacancy diffusion stage, which affects the formation of the final structure. Therefore, it is unlikely to form solid NiO nanowires or NiO nanotubes with uniform wall thickness through the conventional annealing/oxidation process of Ni nanowires. Instead, a step-wise oxidation process by combining low temperature oxidation with a chemical etching step is utilized to produce for the first time NiO nanotubes with uniform wall thickness from Ni nanowires. [source] Catalytic Effects on Thermal Oxidation of Single-Walled Carbon Nanotubes by Alkali Metal ChloridesCHEMCATCHEM, Issue 4 2010Yuki Kobayashi The walled is not enough: Alkali metal chlorides lower the combustion temperature of single-walled carbon nanotubes by more than 100,K. Unlike ordinary reactions of nanotubes, the oxidation reaction in the presence of these salts is independent of the tube diameter, defects, and the degree of bundling. Furthermore, they produce no additional soot upon combustion. [source] Thermal oxidation of lattice matched InAlN/GaN heterostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2010M. Alomari Abstract In this work we have investigated the thermal oxidation of thin InAlN/GaN heterostructures in their lattice matched configuration (83% Al) in oxygen atmosphere at 800 °C. TEM cross sections revealed a partially crystalline oxide with an initial oxidation rate of 0.37 nm/minute. MOS diodes fabricated using the thermal oxide as a gate dielectric showed an exponential drop in the gate leakage which scales with the square root of oxidation time indicating diffusion limited oxidation through the InAlN barrier. The effect of oxidation on the interfacial InAlN/GaN sheet charge density (NS) is correlated with a reduction of thickness for short oxidation times (up to 4 min) and an abrupt change in the surface potential for longer oxidation times. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Cryogenic condensation: A cost-effective technology for controlling VOC emissionsENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 2 2002Robert J. Davis Cryogenic condensation is an extremely cost-effective technology for controlling emissions of Volatile Organic Compounds (VOCs) from chemical processing facilities under certain conditions. This paper describes the technology and provides the case history of an application in the pharmaceutical industry, in which its cost effectiveness was compared with a range of alternative technologies, including thermal oxidation, catalytic oxidation, flaring, carbon adsorption, and scrubbing. Because the facility already used significant quantities of liquid and gaseous nitrogen for inerting, blanketing, and purging, a very convenient cold source for cryogenic condensation was already present. On a lifetime cost basis, cryogenic condensation was significantly less costly than all other technologies evaluated. [source] Porous Silicon-Based Optical Microsensors for Volatile Organic Analytes: Effect of Surface Chemistry on Stability and SpecificityADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Anne M. Ruminski Abstract Sensing of the volatile organic compounds (VOCs) isopropyl alcohol (IPA) and heptane in air using sub-millimeter porous silicon-based sensor elements is demonstrated in the concentration range 50,800 ppm. The sensor elements are prepared as one-dimensional photonic crystals (rugate filters) by programmed electrochemical etch of p++ silicon, and analyte sensing is achieved by measurement of the wavelength shift of the photonic resonance. The sensors are studied as a function of surface chemistry: ozone oxidation, thermal oxidation, hydrosilylation (1-dodecene), electrochemical methylation, reaction with dicholorodimethylsilane and thermal carbonization with acetylene. The thermally oxidized and the dichlorodimethylsilane-modified materials show the greatest stability under atmospheric conditions. Optical microsensors are prepared by attachment of the porous Si layer to the distal end of optical fibers. The acetylated porous Si microsensor displays a greater response to heptane than to IPA, whereas the other chemical modifications display a greater response to IPA than to heptane. The thermal oxide sensor displays a strong response to water vapor, while the acetylated material shows a relatively weak response. The results suggest that a combination of optical fiber sensors with different surface chemistries can be used to classify VOC analytes. Application of the miniature sensors to the detection of VOC breakthrough in a full-scale activated carbon respirator cartridge simulator is demonstrated. [source] Chitosan Hydrogel-Capped Porous SiO2 as a pH Responsive Nano-Valve for Triggered Release of InsulinADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Jianmin Wu Abstract A pH responsive, chitosan-based hydrogel film is used to cap the pores of a porous SiO2 layer. The porous SiO2 layer is prepared by thermal oxidation of an electrochemically etched Si wafer, and the hydrogel film is prepared by reaction of chitosan with glycidoxypropyltrimethoxysilane (GPTMS). Optical reflectivity spectroscopy and scanning electron microscopy (SEM) confirm that the bio-polymer only partially infiltrates the porous SiO2 film, generating a double layer structure. The optical reflectivity spectrum displays Fabry,Pérot interference fringes characteristic of a double layer, which is characterized using reflective interferometric Fourier transform spectroscopy (RIFTS). Monitoring the position of the RIFTS peak corresponding to the hydrogel layer allows direct, real-time observation of the reversible volume phase transition of the hydrogel upon cycling of pH in the range 6.0,7.4. The swelling ratio and response time are controlled by the relative amount of GPTMS in the hydrogel. The pH-dependent volume phase transition can be used to release insulin trapped in the porous SiO2 layer underneath the hydrogel film. At pH 7.4, the gel in the top layer effectively blocks insulin release, while at pH 6.0 insulin penetrates the swollen hydrogel layer, resulting in a steady release into solution. [source] Insight into the Role of Oxidation in the Thermally Induced Green Band in Fluorene-Based Systems,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2007R. Grisorio Abstract The causes of the spectral instability of poly[9,9-dioctylfluoren-2,7-diyl-co-2,,7,-spiro(cyclohexane-1,9,-fluorene)] during thermal annealing in air, which leads to a green photoluminescence (PL) emission band, are investigated. The Igreen/Iblue ratio evolution (I,=,intensity) is found to be independent of the amount of monoalkylfluorene defects, despite the fact that their presence might be regarded as a trigger for the radical process leading to polymer degradation in the presence of a trace amount of metal catalyst. Furthermore, the absence of a correlation between the degree of oxidation of the material and the Igreen/Iblue ratio indicates that the spatial disposition of fluorenones formed during the thermal degradation of the material, rather than their amount, is to be strictly related to the Igreen/Iblue ratio. The evidenced formation of fluorenone agglomerates, which could be considered the cause for the consistent increase in the Igreen/Iblue ratio during a thermal oxidation of a polyfluorene, confirms that the radical mechanism can also involve dialkylfluorene systems. Finally, the higher resistance to thermal degradation shown by spirocyclohexane fluorene units with respect to dioctylfluorene ones allows the synthesis of new, spectrally stable, fluorene-based copolymers. [source] Accelerated ageing of polypropylene stabilized by phenolic antioxidants under high oxygen pressureJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Emmanuel Richaud Abstract Polypropylene (PP) samples stabilized by a hindered phenol (Irganox 1010) were submitted to thermal ageing at 80°C in air at atmospheric pressure or in pure oxygen at 5.0 MPa pressure. Both the polymer oxidation and the stabilizer consumption were monitored by Infrared spectrometry and thermal analysis. The stabilizer efficiency, as assessed by the ratio induction time/stabilizer concentration is almost constant at atmospheric pressure even when the stabilizer concentration is higher than its solubility limit in PP (0.4% or 24 × 10,3 mol L,1). In contrast, at high pressure, the efficiency decreases almost hyperbolically with the stabilizer concentration when this latter is higher than 6.0 × 10,3 mol L,1. The results indicate the existence of a direct phenol-oxygen reaction negligible at low oxygen pressure but significant at 5.0 MPa pressure. The reality of this reaction has been proved on the basis of a study of the thermal oxidation of a phenol solution in a nonoxidizable solvent. A kinetic model of PP oxidation in which stabilization involves three reactions has been proposed. It simulates correctly the effect of oxygen pressure and stabilizer concentration on carbonyl build-up and stabilizer consumption. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Is thermal oxidation at different temperatures suitable to isolate soil organic carbon fractions with different turnover?JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2010Mirjam Helfrich Abstract Findings of previous studies suggest that there are relations between thermal stability of soil organic matter (SOM), organo-mineral associations, and stability of SOM against microbial decay. We aimed to test whether thermal oxidation at various temperatures (200°C, 225°C, 275°C, 300°C, 400°C, or 500°C) is capable of isolating SOM fractions with increasing stability against microbial degradation. The investigation was carried out on soils (Phaeozem and Luvisol) under different land-use regimes (field, grassland, forest). The stability of the obtained soil organic carbon (SOC) fractions was determined using the natural- 13C approach for continuously maize-cropped soils and radiocarbon dating. In the Luvisol, thermal oxidation with increasing temperatures did not yield residual SOC fractions of increasing microbial stability. Even the SOC fraction resistant to thermal oxidation at 300°C contained considerable amounts of young, maize-derived C. In the Phaeozem, the mean 14C age increased considerably (from 3473 y BP in the mineral-associated SOC fraction to 9116 y BP in the residual SOC fraction after thermal oxidation at 300°C). An increasing proportion of fossil C (calculated based on 14C data) in residual SOC fractions after thermal oxidation with increasing temperatures indicated that this was mainly due to the relative accumulation of thermally stable fossil C. We conclude that thermal oxidation with increasing temperature was not generally suitable to isolate mineral-associated SOC fractions of increasing microbial stability. [source] Metastable alumina formation during oxidation of FeCrAl and its suppression by surface treatmentsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 12 2005E. N'Dah Abstract The influence of various surface treatments of industrial FeCrAl grades was investigated in order to reduce the formation of transition aluminas during thermal oxidation in the 800,950°C temperature range. High temperature gas phase annealing in H2 -H2O mixtures promoted the initial formation of an alpha thin film and no transition alumina formed during subsequent oxidation at lower temperatures, showing very low weight gains compared to non-treated grades. Such a treatment was shown to be efficient for isothermal oxidation in oxygen of laboratory foil specimens but also for cyclic air exposure of fiber mats in near-real operating conditions. Surface modification by application of a slurry TiO2 coating before oxidation was also shown to greatly reduce the amount of transition alumina, observed by X-Ray Diffraction and Laser Induced Optical Spectroscopy. For both treatments, the optimal conditions were determined and the influence on oxidation rate was assessed. [source] Activation energy of thermally grown silicon dioxide layers on silicon substratesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2009G. Gerlach Abstract A detailed numerical consideration is used as basic approach for calculating profiles of activation energy versus oxide thickness for various temperatures between 780 and 930,°C. Results presented here are intentionally not based on models of diffusion and reaction kinetics to avoid introducing correction terms due to the expansion of theory still under discussion. The statistical calculation gives the mean activation energy of 2.01,eV with standard deviation of 0.10,eV, very close to the overall activation energy of 2.05,eV [M. A. Rabie, Y. M. Haddara, and J. Carette, J. Appl. Phys. 98, 074904 (2005)]. More instructive features of the thermal oxidation of silicon have been disclosed directly from measurements of oxide thickness with time [M. A. Hopper, R. A. Clarke, and L. Young, J. Electrochem. Soc. 122, 1216 (1975) and J. Blanc, Philos. Mag. B 55, 685 (1987)]. Graphs of the natural logarithm of the growth rate versus oxide thickness, in the range between 2 and 65,nm, show that the oxide thickness influences the activation energy EA between 1.4 and 2.7,eV. [source] Optical properties of TiO2 thin films prepared by chemical spray pyrolysis from aqueous solutionsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010R. Ayouchi Abstract Titanium dioxide (TiO2) is known to have three different kinds of polymorphous crystalline forms: rutile, anatase, and brookite. The rutile phase is always formed at higher temperatures, while the anatase phase is formed at lower temperatures and transformed into rutile phase above 800 ºC. Various deposition techniques have been developed for depositing TiO2 thin films, including evaporation, sputtering, chemical vapour deposition and thermal oxidation of titanium. Among them, the Chemical Spray Pyrolysis (CSP) technique has many advantages, such as good conformal coverage, the possibility of epitaxial growth and the application to large area deposition. Also, this method is low cost and it is easy to control the deposition growth parameters. In the present work, TiO2 thin films have been deposited on p-Si (001) and fused silica substrates by Chemical Spray Pyrolysis (CSP) method from aqueous solution containing titanium (IV) isopropoxide (Ti[OCH(CH3)2]4. As-deposited thin films show anatase polycrystalline structure, and rutile phase formed for films annealed at 750ºC. SEM images have confirmed a smooth and crack-free surface with low surface roughness. X-ray photoelectron spectroscopy (XPS) combined with 4 keV Ar+ depth profiling has shown that crystallized films correspond to TiO2. Residual carbon coming from the organic precursor solution is only detected at the surface of the film. Thin films deposited on fused silica were highly transparent (more than 85%), with an indirect optical band gap of 3,43 and 3,33 eV for as-deposited and annealed films, respectively, and refractive indexes in the range between 2.01,2.29. Spectroscopic Ellipsometry (SE) also has been used to extract optical parameters. SE data fitted to triple-layer physical model revealed the same tendency to increase refractive index in annealed films. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thermal oxidation of lattice matched InAlN/GaN heterostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2010M. Alomari Abstract In this work we have investigated the thermal oxidation of thin InAlN/GaN heterostructures in their lattice matched configuration (83% Al) in oxygen atmosphere at 800 °C. TEM cross sections revealed a partially crystalline oxide with an initial oxidation rate of 0.37 nm/minute. MOS diodes fabricated using the thermal oxide as a gate dielectric showed an exponential drop in the gate leakage which scales with the square root of oxidation time indicating diffusion limited oxidation through the InAlN barrier. The effect of oxidation on the interfacial InAlN/GaN sheet charge density (NS) is correlated with a reduction of thickness for short oxidation times (up to 4 min) and an abrupt change in the surface potential for longer oxidation times. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Gravimetric method to find internal surface of macroporous silicon membranesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2007A. A. Nechitailov Abstract A simple method to evaluate the internal surface area, porosity, pore diameter and pore density of macroporous silicon membranes has been proposed and tested. The porosity p is obtained from the mass loss under anodizing, and the surface area per unit volume Sv is determined from the mass of SiO2 formed on the pore surface as a result of thermal oxidation. The average pore diameter d and pore density N can be easily calculated from the obtained Sv and p. Experimental verification of d and N was performed by means of SEM and optical microscope images; Sv was checked by BET technique. Surface area and porosity on the resistivity of initial n-Si in the range , = 3,25 Ohm · cm have been studied for the samples with regular and self-organized macropore "lattices". The obtained values are within the limits p = 27,50%, Sv = 2800,6000 cm2/cm3, d = 1.9,6.5 ,m, N = 1.4,10 × 106 cm,2, and in a good agreement with the data of microscopic characterization. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Oxidation treatment on Ni/Au Ohmic contacts to p-type GaNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003Z. Z. Chen Abstract Current,voltage (I,V) characteristics, transmission line method (TLM), and optical transmittance measurements are performed to investigate the effects of thermal oxidation and plasma-induced oxidation treatments on Ni/Au contacts to p-type GaN. Whether oxidation and thermal annealing are performed simultaneously or in succession, the specific contact resistances of Au/Ni/p-GaN are reduced. As to plasma-induced oxidation, neither no-oxidation nor long-time oxidation treatments on Ni/Au layers are suitable for obtaining a low-resistance Ohmic contact. The roles of oxidation are believed to activate the Mg acceptor in p-GaN and to form an oxygenous intermediate semiconductor layer, which may lower the Schottky barrier height between the metal layer and p-GaN. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Sustainable soil remediation by refrigerated condensation at sites with "high-concentration" recalcitrant compounds and NAPL: Two case studiesREMEDIATION, Issue 1 2008Lowell Kessel Remediation of recalcitrant compounds at sites with high concentrations of volatile organic compounds (VOCs) or nonaqueous-phase liquids (NAPLs) can present significant technical and financial (long-term) risk for stakeholders. Until recently, however, sustainability has not been included as a significant factor to be considered in the feasibility and risk evaluation for remediation technologies. The authors present a framework for which sustainability can be incorporated into the remediation selection criteria focusing specifically on off-gas treatment selection for soil vapor extraction (SVE) remediation technology. SVE is generally considered an old and standard approach to in situ remediation of soils at a contaminated site. The focus on off-gas treatment technology selection in this article allows for more in-depth analysis of the feasibility evaluation process and how sustainable practices might influence the process. SVE is more commonly employed for recovery of VOCs from soils than other technologies and generally employs granular activated carbon (GAC), catalytic, or thermal oxidation, or an emerging alternative technology known as cryogenic-compression and condensation combined with regenerative adsorption (C3,Technology). Of particular challenge to the off-gas treatment selection process is the potential variety of chemical constituents and concentrations changing over time. Guidance is available regarding selection of off-gas treatment technology (Air Force Center for Environmental Excellence, 1996; U.S. Environmental Protection Agency, 2006). However, there are common shortcomings of off-gas treatment technology guidance and applications; practitioners have rarely considered sustainability and environmental impact of off-gas treatment technology selection. This evaluation includes consideration of environmental sustainability in the selection of off-gas treatment technologies and a region-specific (Los Angeles, California) cost per pound and time of remediation comparisons between GAC, thermal oxidation, and C3,Technology. © 2008 Wiley Periodicals, Inc. [source] A novel characteristic of porous titanium oxide implantsCLINICAL ORAL IMPLANTS RESEARCH, Issue 6 2007Takashi Sawase Abstract Objective: The anatase form of titanium dioxide (TiO2) is one of the most common crystalline forms of TiO2 and is normally produced by oxidation of titanium via thermal oxidation or anodizing. This crystalline form exhibits photocatalytic activity when it is irradiated with ultraviolet A (UVA) light. The aim of the current study was to analyze the crystal structure of anodic-oxidized TiUnite® implants and to confirm the photocatalytic properties in vitro and in vivo. Material and methods: Cross-sectional observations by transmission electron microscopy were used to determine the surface crystal structure on the TiUnite implant. Subsequently, photocatalytic activity was confirmed by degradation of methylene blue, and hydrophilicity was measured based on the water contact angle. Furthermore, the in vivo effects of the photocatalytic activity of this compound were investigated. Results: An amorphous layer that was about 10 ,m thick was observed on the TiUnite implant surface. In the amorphous layer, the anatase form of the crystalline TiO2 was identified. Photocatalytic activity was clearly demonstrated by the bleaching effect of methylene blue under UVA illumination. The contact angle decreased from 44° to 11° after UVA illumination. Although these data suggest increased hydrophilicity for the TiUnite implant, the bone-to-metal contact at 4 weeks was not influenced. Conclusion: The anodic-oxidized TiUnite implant has inherent photocatalytic activity. UVA illumination increases the surface hydrophilicity of the implant. However, this increase in hydrophilicity does not improve bone apposition to the implant surface at 4 weeks. [source] | ||||||||||||||||