Showing papers on "Wet oxidation published in 1997"
TL;DR: In this article, the chemistry, microstructure, and processing of buried oxides converted from AlGaAs layers using wet oxidation was reviewed and the influence of gas flow, gas composition, temperature, Al-content, and layer thickness on the oxidation rate was characterized.
Abstract: We review the chemistry, microstructure, and processing of buried oxides converted from AlGaAs layers using wet oxidation Hydrogen is shown to have a central role in the oxidation reaction as the oxidizing agent and to reduce the intermediate predict As/sub 2/O/sub 3/ to As The stable oxide is amorphous (Al/sub x/Ga/sub 1-x/)/sub 2/O/sub 3/ which has no defects along the oxide/semiconductor interfaces but can exhibit strain at the oxide terminus due to volume shrinkage The influence of gas flow, gas composition, temperature, Al-content, and layer thickness on the oxidation rate are characterized to establish a reproducible process Linear oxidation rates with Arrhenius activation energies which strongly depend upon AlAs mole fraction are found The latter produces strong oxidation selectivity between AlGaAs layers with slightly differing Al-content Oxidation selectivity to thickness is also shown for layer thickness <60 nm Differences between the properties of buried oxides converted from AlGaAs and AlAs layers and the impact on selectively oxidized vertical cavity laser lifetime are reported
310 citations
TL;DR: In this article, it was shown that the activity of ruthenium is particle size dependent: the smaller the sizes, the lower the activation energy, while the larger the size of the particles, the higher the activity.
156 citations
TL;DR: In this paper, the authors studied the kinetics of WO of formic acid in the absence and presence of a cupric sulfate as catalyst in the temperature range 150−240 °C and oxygen partial pressure range 0.345−1.380 MPa.
Abstract: Oxidation of lower molecular weight carboxylic acids such as formic, acetic, glyoxalic, and oxalic acids is often the rate-controlling step during wet oxidation (WO) of an aqueous waste stream exhibiting very high chemical oxygen demand (COD). The kinetics of WO of formic acid was studied in the absence and presence of a cupric sulfate as catalyst in the temperature range 150−240 °C and oxygen partial pressure range 0.345−1.380 MPa. Wet oxidation of acetic acid was carried out in the presence of cupric sulfate in the temperature range 215−235 °C. Homogeneous copper sulfate was found to be a very good catalyst for oxidation of formic acid and acetic acid.
82 citations
TL;DR: Wet air oxidation is presented as a technique for removal of organic pollutants found in waste water streams The oxidation of phenol has been achieved at moderate temperatures (T=473 K) and pressures (30 MPa total pressure) with up to 95% destruction in less than 30 minutes.
79 citations
TL;DR: In this paper, an original approach to the treatment of phenolic aqueous wastes using H 2 O 2 with Fe-ZSM-5 as a heterogeneous catalyst was presented.
77 citations
TL;DR: In this article, a Pt/TiO2 catalyst was used for wet oxidation of phenol by air or oxygen over a batch reactor in the temperature range 150-200°C, pressure range 34-82 atm, and a catalyst loading range of 0-4 g catalyst L−1.
66 citations
TL;DR: In this article, rates of low carbon steel oxidation in various nitrogen-based atmospheres of O2, CO2, and H2O in the temperature range 800 °C to 1150 °C were analyzed.
Abstract: The article describes rates of oxidation of low carbon steel in various nitrogen-based atmospheres of O2, CO2, and H2O in the temperature range 800 °C to 1150 °C. In characterizing the oxidation process, the weight gains of the samples per unit surface area vs time data were analyzed. Reaction rates during oxidation in the binary atmospheres of CO2-N2 and H2O-N2 followed a linear rate law and were found to be proportional to the partial pressures of CO2 or H2O. These rates were controlled by rate of reactions at the oxide surface and were highly dependent on oxidation temperature. The activation energies of the phase boundary reactions obtained were approximately 274 and 264 kJ/mole, for oxidation in CO2 and H2O atmospheres, respectively. Oxidation in gases containing free oxygen showed that the main oxidizing agent was the free oxygen and that additions of CO2 and H2O had little effect on the magnitude of the initial oxidation rates. Experiments for oxidation in multicomponent gases showed that the overall oxidation rates were the additions of rates resulting from oxidation with the individual gaseous species O2, CO2, and H2O. Oxidation in these atmospheres exhibited an initial linear rate law which gradually transformed into a parabolic. Examination of scale microstructure after 1 hour of oxidation showed that, for oxidation in carbon dioxide and water vapor atmospheres, only wustite was present, while in atmospheres containing free oxygen, all three iron oxides, wustite, magnetite, and hematite, were present.
64 citations
TL;DR: In this paper, three important processes dominate the wet thermal oxidation of AlGaAs on GaAs: formation and elimination of crystalline and amorphous elemental As, and crystallization of the amorphized oxide film.
Abstract: Three important processes dominate the wet thermal oxidation of AlxGa1−xAs on GaAs: (1) oxidation of Al and Ga in the AlxGa1−xAs alloy to form an amorphous oxide, (2) formation and elimination of crystalline and amorphous elemental As and of amorphous As2O3, and (3) crystallization of the amorphous oxide film. Residual As can lead to strong Fermi-level pinning at the oxidized AlGaAs/GaAs interface, up to a 100-fold increase in leakage current, and a 30% increase in the dielectric constant of the oxide layer. Thermodynamically favored interfacial As may impose a fundamental limitation on the use of AlGaAs wet oxidation in metal-insulatorsemiconductor devices in the GaAs material system.
61 citations
TL;DR: The results obtained during the treatment of nitrogenous compounds like aniline, nitrophenol, beta-alanine and ammonia are discussed, and several parallel pathways are considered for the transformation of organic nitrogen, amongst which is an interaction with the catalyst surface.
59 citations
TL;DR: In this paper, the treatment of dyeing and printing wastewater from the textile industry by oxidation was studied, and experiments were conducted using various catalysts including metal salts, metal oxides, and porous alumina supported metals.
55 citations
TL;DR: In this article, the authors explain the transition between the linear and parabolic time dependence of the wet oxidation of buried AlGaAs layers and explain the near-total suppression of wet oxidation by O2 is attributed to the suppression of volatile product formation through consumption of atomic hydrogen by reaction with O2 to form H2O in preference to the hydrogen reduction of As2O3.
Abstract: Wet oxidation of AlGaAs to form Al2O3 by the reduction of H+ from water to H produces intermediate As2O3. Reduction of As2O3 by H to elemental As enables the escape of arsenic from the oxidized film. Further reduction of As to AsH3 can provide another volatile As species. Formation of intermediate As is problematic for the use of wet oxidation in metal-insulator-semiconductor applications. The kinetic balance between As2O3 formation and As escape can explain the transition between the linear and parabolic time dependence of the wet oxidation of buried AlGaAs layers. The near-total suppression of wet oxidation by O2 is attributed to the suppression of volatile product formation through consumption of atomic hydrogen by reaction with O2 to form H2O in preference to the hydrogen reduction of As2O3.
TL;DR: Since DON originating froin phytoplankton constitutes an important resource for some organisms, processrs other than direct active excretion must be the main ones leading to significant release of these biodegradable compounds and might explain the high levels of DON release sometimes observed during experimental studies or in the natural environment.
Abstract: The release of DON in diatom (Phaeodactylum tr~cornutum) and Chlorophycea (Dunallella tertjollecla) batch cultures was examined by both the wet oxidation procedure and the newly improved 15N tracer technique for simultaneous isotope-ratio analysis of inorganic and organic forms of nitrogen. Cultures were conducted under different initial nitrate/phosphate ratios and under light and nutrient stressed conditions. Experimental results remalned lower than previous and recent evaluations and showed that less than 10% of the nitrate uptake was released or excreted as DON. Rates of DON release were around 10.4 to 13.3 nmol N 1.' h-' Taking into account potential stressinduced DON losses, results tend to confirm that these products were not artefactual and had resulted from phytoplankton excretion. These values of DON reledbe enabled us to completely or nearly completely balance the nltrogen budgets in our experiments. However, since DON originating froin phytoplankton constitutes an important resource for some organisms, processrs other than direct active excretion (such as g]-azing, cell death or virus infections) must be the main ones leading to significant release of these biodegradable compounds and might explain the high levels of DON release sometimes observed during experimental studies or in the natural environment
TL;DR: In this article, the intrinsic kinetics of the oxidation of formic acid over a 1% Pt/C catalyst have been performed, at oxygen concentrations in water varying from 0.6 to 2.8 mol m−3 and at formic acids concentrations varying from 30 to 400 molm−3.
Abstract: A study of the intrinsic kinetics of the oxidation of formic acid over a 1% Pt/C catalyst has been performed, at oxygen concentrations in water varying from 0.6 to 2.8 mol m−3 and at formic acid concentrations varying from 30 to 400 mol m−3. Experiments were performed in a continuous-flow stirred slurry reactor. To avoid mass transfer limitation of oxygen, a temperature interval from 282 to 293 K and a total pressure in the reactor of 0.6 MPa has been used. The pH interval of the experiments ranged from 1.1 to 13.0. Single response non-linear regression has been used to fit the parameters for a kinetic model. The proposed model can predict the steady-state disappearance rate of formic acid, as a function of the oxygen concentration, the formic acid concentration, the temperature and of the pH. Electrochemical experiments have been carried out for a better understanding of the pH effect on the formic acid oxidation.
TL;DR: Water-soluble salts of polyoxometalate (POM) anions can be used as catalysts for selective, effluent-free oxygen delignification (bleaching) of unbleached kraft wood-pulps as discussed by the authors.
Abstract: Water-soluble salts of polyoxometalate (POM) anions can be used as (net) catalysts for selective, effluent-free oxygen delignification (bleaching) of unbleached kraft wood-pulps. Essential to this process is the use of the POM anions as catalysts for the wet oxidation of the lignin removed from the pulp fibers. In anaerobic bleaching, a 0.5 M solution of {alpha}-Na{sub 5}[PV{sub 2}Mo{sub 10}O{sub 40}] (POM{sub ox}) is combined with wood pulp and the mixture heated to 125 C. This treatment dissolves certain organic compounds (some lignin and polysaccharide fragments) with a combined chemical oxygen demand (COD) of 1,500--2,000 mg of O{sub 2}L. Before the solution can be used again for bleaching, the POM anions (POM{sub red}) must be reoxidized and the dissolved organic compounds removed. Here, a second function of the POM anions is realized. They are used under mild conditions (150 C, 0.7 MPa of O{sub 2}) to catalyze the wet air oxidation of the dissolved organic compounds. After several cycles of anaerobic bleaching and wet oxidation, a steady-state condition in COD (at ca. 550 mg of O{sub 2}/L) is achieved.
TL;DR: In this article, a combination of an oxidative and a separative step was used to achieve a higher selectivity of the overall process toward partial oxidation in polyethylene glycol.
Abstract: Wet oxidation and nanofiltration are employed in an integrated system for the treatment of bioresistant industrial wastewaters. The partial oxidation products formed during a brief period of pretreatment in a low pressure WO reactor are separated by nanofiltration, and larger molecules are recycled into the reactor where they undergo further oxidation. Experiments were carried out with polyethylene glycol as a model compound in aqueous solution, representing polymer manufacture wastewater. The results demonstrate that by using a combination of an oxidative and a separative step, a higher selectivity of the overall process toward partial oxidation can be achieved. The permeate leaving the filtration step is mainly composed of short chain organic acids which could be readily biodegraded in a subsequent biological treatment, or discharged if concentrations are low.
TL;DR: In this article, the effect of molecular weight on the aerobic biodegradability of polyethylene glycol (PEG) was assessed by performing shake flasks experiments with various PEGs in a molecular weight range from 200 to 35000.
Abstract: The treatment of a model wastewater containing polyethylene glycol (PEG) of molecular weight 10000 in an integrated wet air oxidation–aerobic oxidation process was investigated. Partial wet air oxidation under mild operating conditions was capable of converting the original polymer to lower molecular weight compounds, such as oligomers and short-chain organic acids. The effect of molecular weight on the aerobic biodegradability of polyethylene glycol was assessed by performing shake flasks experiments with various polyethylene glycols in a molecular weight range from 200–35000 and it was found that biodegradability generally decreased with increasing molecular weight. Aqueous solutions of PEG 10000 were subjected to continuous wet air oxidation at a temperature of 423 K and a residence time of 30 min and the oxidised effluents were then subjected to subsequent continuous aerobic oxidation at residence times varying between 0·5 and 4 days. Simultaneously, continuous aerobic oxidation experiments on solutions of PEG 10000 were performed and used to compare the efficiency of the integrated treatment process with that of the direct biological treatment. Partial pretreatment by wet air oxidation under mild operating conditions resulted in effluents whose biodegradation rates were significantly higher than those of the original, unoxidised wastewater, as assessed by total organic carbon (TOC) removal rates. The original wastewater was practically non-biodegradable at a 0·5-day residence time with direct biological treatment, while an 80% TOC removal was achieved when biological treatment was coupled with a preceding wet air oxidation step. Conversely, with a 4-day residence time for the direct biological treatment the original wastewater was only partially degradable with 60–70% TOC removal recorded; with the integrated treatment process at a 4-day residence time in the bioreactor the overall TOC removal was greater than 90%. © 1997 SCI
TL;DR: In this paper, aqueous solutions of phenol were oxidized in a batch reactor at temperatures between 150 and 300 “C and pressures from 100 to 200 bar, with an activation energy of 34.4 kJ mol- ‘.
TL;DR: In this paper, the partial wet air oxidation of aqueous solutions of p-coumaric acid and polyethylene glycol, two model organic pollutants typically found in wastewaters of agricultural origin and polymer-manufacturing respectively, has been investigated at temperatures from 373 K to 513 K and oxygen partial pressures from 0.2 MPa to 3 MPa.
TL;DR: In this article, phenol degradation studies were conducted using continuous flow packed bed microreactors configured to minimize the deviation from plug flow, and reaction rate constants for the disappearance of phenol were determined using a pseudo first order plug flow kinetic model over the temperature range between 35-65°C.
Journal Article•
TL;DR: In this article, the basic subcritical wet oxidation process and the two main modifications (supercritical and catalytic oxidation) are briefly presented and design considerations of the processes and the oxidation kinetics which directly affects the reactor volume and process economics are also discusssed.
Abstract: The basic, subcritical wet oxidation process and the two main modifications (supercritical and catalytic oxidation) are briefly presented. Some design considerations of the processes and the oxidation kinetics which directly affects the reactor volume and process economics are also discusssed.
TL;DR: In this article, the orientation dependence of the thermal oxidation rates in 6H-SiC was investigated and the wet oxidation was performed in steam and in the temperature range of 1000 to 1200 °C.
Abstract: The orientation dependence of the thermal oxidation rates in 6H-SiC has been investigated. The wet oxidation was performed in steam and in the temperature range of 1000 to 1200 °C. The linear rate sharply changes at an off-angle around 30° from the {0001}-face. This large anisotropy in oxidation rate will cause a difficulty in controlling the bird's beak length in LOCOS. The activation energy of the linear rate gradually increases from C-face to Si-face. The situation is quite different from silicon in which the orientation dependence of the activation energy is explained by the steric hindrance.
TL;DR: In this paper, a mathematical model of oxidation of SixGe1−x alloys is presented, where the growth of SiO2 is simulated in conjunction with the determination of silicon distribution in SixGe 1−x using numerical methods.
Abstract: A mathematical model of oxidation of SixGe1−x alloys is presented. The growth of SiO2 is simulated in conjunction with the determination of silicon distribution in SixGe1−x using numerical methods. The main feature of the model is the assumption of simultaneous oxidation of germanium and silicon when exposing the SixGe1−x to an oxidizing atmosphere. In accordance with thermodynamics, the GeO2 formed is subsequently reduced by the (free) silicon available at the interface between the growing SiO2 and the remaining SixGe1−x through a reduction reaction. Thus, the enhanced oxidation of silicon in the presence of germanium is modeled as a result of the rapid oxidation of germanium followed by the quick reduction of GeO2 by silicon. The growth of a mixed oxide in the form of either (Si,Ge)O2 or SiO2–GeO2 only occurs when the supply of silicon to the SiO2/SixGe1−x interface is insufficient. A comparison is made between simulation and experiment for wet oxidation (in pyrogenic steam) of polycrystalline SixGe1−x ...
01 Jan 1997
TL;DR: In this article, the effects of the mixer speed, operating pressure, initial pH of wastewater and temperature on the pollutant (chemical oxygen demand or COD) removal were investigated to determine their respective effect on the COD removal.
TL;DR: In this article, partial wet air oxidation of aqueous solutions of polyethylene glycol, a model organic pollutant typically found in wastewaters of polymer-manufacturing, has been investigated at temperatures from 383 K to 513 K and oxygen partial pressures from 2 MPa to 3 MPa.
TL;DR: In this article, the wet oxidation kinetics of AlAs layers of interest in vertical cavity surface emitting laser (VCSEL) fabrication are investigated in detail, and the process is modeled as a diffusion-reaction process.
Abstract: The wet oxidation kinetics of AlAs layers of interest in vertical cavity surface emitting laser (VCSEL) fabrication are investigated in detail. The process is modeled as a diffusion-reaction process. For oxidation over a long time interval, variation of the oxidation rate with the variation of the radius of the etched mesa of the VCSEL is observed. A theory has been developed to obtain the rate equation of the oxidation process and the dependence of the oxidation rate on the size of the VCSEL is explained.
TL;DR: In this article, the thickness of barrier layers between layers of Al0.94Ga0.06As and Al 0.98Ga 0.02As was determined to determine the concentration of additional oxidizing species in the barrier layer.
Abstract: Selective wet oxidation of AlGaAs layers can be used to form embedded optical elements, such as buried lenses and current control apertures in vertical cavity structures. Oxidation rates of buried Al0.94Ga0.06As layers were controlled by varying the thickness of GaAs barrier layers between layers of Al0.94Ga0.06As and Al0.98Ga0.02As. This phenomenon can be attributed to the superposition of a vertical oxidation component due to species diffusing through the barrier layer and a constant lateral oxidation component. The magnitude of the vertical component is controlled by the GaAs barrier thickness, which determines the concentration of additional oxidizing species in the Al0.94Ga0.06As layer.
TL;DR: In this article, a semi-batch wet oxidation of / p -coumaric acid, a biorecalcitrant polyphenolic compound typically found in olive processing and wine-distillery wastewaters, using a CuO.ZnO-Al 2 O 3 catalyst in slurry form at temperatures from 373 K to 403 K, oxygen partial pressures from 2.3 to 32.3 bar, catalyst concentrations from 0.088 to 4.4gl 1 and particle size from 38-250 /μm, has been investigated.
Abstract: The semi-batch wet oxidation of / p -coumaric acid, a biorecalcitrant polyphenolic compound typically found in olive processing and wine-distillery wastewaters, using a CuO.ZnO-Al 2 O 3 catalyst in slurry form at temperatures from 373 K to 403 K, oxygen partial pressures from 2.3 to 32.3 bar, catalyst concentrations from 0.088 to 4.4gl –1 and particle size from 38–250 /μm, has been investigated. The catalyst was found to be capable of increasing the rate of p -coumaric acid oxidation by as much as 20 times that of the uncatalysed reaction, at 403 K. The rate of p -coumaric acid oxidation was found to be first order with respect to its concentration and proportional to oxygen partial pressure to the power of 0.65 over the range of operating conditions where oxygen partial pressure exerts a significant effect (2.3 to 17.3 bar). With the particle sizes used, there were no intraparticle diffusional limitations.
TL;DR: In this paper, the treatment of high-strength desizing wastewater obtained from a textile dyeing and finishing plant by wet air oxidation (WAO) is studied. Experiments were conducted to investigate the effects of the...
Abstract: Treatment of high-strength desizing wastewater obtained from a textile dyeing and finishing plant by wet air oxidation (WAO) is studied. Experiments were conducted to investigate the effects of the...
Patent•
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30 Apr 1997
TL;DR: In this paper, a process for treating a sulfide-containing alkaline aqueous effluent, which includes subjecting it to a wet air oxidation treatment which oxidizes sulfide ions to environmentally acceptable sulfur acid ions, is described.
Abstract: The invention provides a process for treating a sulfide-containing alkaline aqueous effluent, which includes subjecting it to a wet air oxidation treatment which oxidizes sulfide ions to environmentally acceptable sulfur acid ions, the oxidation being carried out in two or more chambers connected in series, flow of effluent between the chambers being effected at least primarily by gravity such that the pressures in the respective chambers can be maintained at substantially the same value.