Min Of Oxidation Research Articles

Tuning the Surface Characteristic of Al-Si Alloys and Its Impacts on the Formation of Micro Arc Oxidation Layers

Aluminum Silicon (Al-Si) alloys are the most important among cast alloys and have widespread application. The β-Si phase is detrimental to the growth of micro arc oxidation (MAO) layers on Al-Si alloys. In this paper, the β-Si in the skin layer of different Al-Si alloys was removed by an acid etching pretreatment. Then, the impacts of different etching condition on their MAO process were investigated. Results show that, as etching time was prolonged, the Si content on the surface of Al-12 Si was decreased greatly (less than 0.5 wt.%), and the average size of pores left on the sample surface was increased gradually. This then led to the occurrence of some bigger and more drastic discharge sparks at the earlier oxidation stage. The corresponding layers had a higher ratio of Al2O3 and better corrosion resistance after 30 min of oxidation. Moreover, a 60 s etching pretreatment benefitted and boosted the growth rate and energy efficiency of layers on the Al-9 Si, Al-12 Si and Al-15 Si alloys. Such pretreatment was believed to be applicable to restrain the negative effects of Si on the MAO of different Al-Si alloys.

Surface formation of plasma-electrolytic cobalt-containing coatings on piston alloys of aluminum

Based on the review of functional coatings on piston alloys of aluminum, a conclusion was made on the feasibility of using oxide coatings to increase the strength and durability of parts of the piston group of internal combustion engines. It is shown that the synthesis of the oxide layer on alloys of the Al-Si system (silumins) can be carried out by plasma electrolyte treatment in alkaline electrolytes with the addition of salts of dopant metals, in particular cobalt. This will allow to obtain coatings that have activity in the processes of catalytic combustion of fuel. It is proposed to form cobalt-containing oxide coatings on piston alloys by plasma-electrolytic oxidation in the electrolyte of 0.4 mol/dm3 K4P2O7, 0,1 mol/dm3 CoSO4 at current densities of 3–5 A/dm2 in the “decreasing power” mode. It is established that under these conditions during 15 min of oxidation on high-silicon alloys AL30 and AK21 an oxide layer with a content of up to 4.7 at.% Co is formed. The presence of up to 6.4 at.% of phosphorus in the synthesized coating will increase the heat resistance of the oxidized surface. At the same time, the silicon content in the surface layers decreases 4–5 times compared to the source material. It is shown that the morphology and phase composition of the coating changes with the incorporation of the additive component into its composition. The inclusion of cobalt occurs in the form of thermodynamically stable oxide Co3O4 (CoO·Co2O3), which crystallizes in the spinel crystal cell. This, along with a high degree of surface development is a prerequisite for improving the functional properties of the obtained oxide layers. The developed method was used for applying a cobalt-containing coating on the surface of a piston made of alloy AL30. It is established that in order to obtain a uniform oxide layer, certain technological parameters should be observed. The predicted use of a piston coated with cobalt-containing oxide coating will reduce the amount of toxic substances with exhaust gases and hourly fuel consumption, which is promising for intracylinder catalysis.

Silver deposition optimization process on ultrananocrystalline diamond applied to nitrate reduction

ABSTRACT Nitrate is a serious contaminant of ground and surface water, which cause high concern in the field of health and environmental protection. In this work, a ternary composite of silver/boron-doped ultrananocrystalline diamond/reticulated vitreous carbon (Ag/B-UNCD/RVC) was prepared and its electrocatalytic activity for nitrate reduction was examined. B-UNCD films were grown by hot filament chemical vapour deposition technique on RVC after a substrate seeding process improvement using 4 nm diamond powder. Compared to conventional 0.25 µm diamond seeding, this new procedure allowed uniform RVC coverage avoiding its etching process during diamond growth, in addition to obtaining more reproductive electrodes. In order to improve the catalytic effect of B-UNCD/RVC electrodes for nitrate reduction, silver deposition was performed on B-UNCD surface after oxidation for 10, 20 and 30 min in 0.5 mol L-1 H2SO4 solution using a potential of 2 V vs. Ag/AgCl. The most oxidized diamond film (30 min of oxidation) presented the highest silver deposit and particle adhesion. Thus the electrochemical response to nitrate of B-UNCD/RVC oxidized for 30 min was compared to that of RVC and B-UNCD/RVC electrodes showing the important Ag influence in the catalytic process.

Novel Cu(II)-EDTA Decomplexation by Discharge Plasma Oxidation and Coupled Cu Removal by Alkaline Precipitation: Underneath Mechanisms.

Strong complexation between heavy metals and organic complexing agents makes the heavy metals difficult to be removed by classical chemical precipitation. In this study, a novel decomplexation method was developed using discharge plasma oxidation, which was followed by alkaline precipitation to treat water containing heavy metal-organic complex, that is, Cu-ethylenediaminetetraacetic acid (Cu-EDTA). The decomplexation efficiency of Cu complex reached up to nearly 100% after 60 min's oxidation by discharge plasma, which was accompanied by 82.1% of total organic carbon removal and energy efficiency of 0.62 g kWh-1. Presence of free Cu2+ favored Cu-EDTA decomplexation, whereas the presence of excessive EDTA depressed this process. Cu-EDTA decomplexation was mainly driven by the produced 1O2, O2•-, O3, and •OH by discharge plasma. Cu-EDTA decomplexation process was characterized by UV-vis, ATR-FTIR, total organic carbon, and three-dimensional fluorescence diagnosis. The main intermediates including Cu-EDDA, Cu-IDA, Cu-NTA, small organic acids, NH4+, and NO3- were identified, accompanied by Cu2+ releasing. The followed precipitation process removed 78.1% of Cu2+, and Cu-associated precipitates included CuCO3, Cu2CO3(OH)2, CuO, and Cu(OH)2. A possible pathway of Cu complex decomplexation and Cu2+ removal in such a system was proposed.

Adhesion Force Measurements: Graphite Cluster Interacting with VHTR Steel

Graphite dust is generated in the reactor core during normal operation of very high temperature reactors (VHTRs). This dust is transported throughout the reactor circuit and plates-out at different locations. The resuspension of graphite dust is believed to be a major contributor to the nuclear source term. The adhesion force is an important parameter governing the resuspension of the dust. The present study employed an atomic force microscope to measure the adhesive force between a reactor-grade graphite cluster “particle” and VHTR structural materials including Inconel 617 and Hastelloy X in an air glove box. Results for a reactor-grade graphite (MLRF-1 from SGL Carbon Ltd.) cluster particle interacting with Inconel 617 and Hastelloy X samples are reported under four different surface conditions including as received, and after 5, 10, and 15 min of oxidation. These forces were also predicted using the Johnson-Kendall-Roberts theoretical model with the estimate of the work of adhesion. The measured values depend on oxidation times but are in general a factor of about 20 lower than the predicted values. With surface roughness taken into account, the predicted values differ from the measured values by factors of 2 and 4 at the maximum for Hastelloy X and Inconel 617, respectively.

Ozone-Based Technologies for Parabens Removal from Water: Toxicity Assessment

ABSTRACTOzone was tested for the detoxification of a mixture of five parabens. A combined O3/H2O2 process was optimized leading to up to 50% of COD removal in 15 min, while less than 50 min were needed to achieve total degradation. The toxic effect of the raw mixture and after 15 min of treatment by O3/H2O2 was evaluated using V. fischeri and C. fluminea and it was observed a strong detoxification after 15 min of oxidation. Moreover, while the raw effluent promoted the formation of reactive oxygen species in Wistar rat brain slices, no changes were observed after the O3/H2O2 treatment.

Initial Oxidation Behavior of Ferritic Stainless Steel with Sputtered Mn–Cu Coating

Initial oxidation behavior of SUS 430 steel with a sputtered Mn–Cu coating was investigated in air at 800 °C. It was found that Mn was preferrentially oxidized upon thermal exposure from 2 to 10 min. The surface scale mainly consisted of MnO inner layer and Mn3O4 outer layer, although a small amount of Fe was observable in the scale. In addition, CuO developed on the outer surface of the scale after 10 min of oxidation. However, the scale formed on the coated steel upon oxidation for 20–300 min was obviously different from that upon oxidation for 2–10 min. It was composed of a tri-layer containing a top layer of CuO, a middle layer of (Mn,Cu)3O4 with some Fe, and an inner layer of Cr-rich oxide from the outer surface to the interface between scale and steel. With increasing oxidation time, furthermore, the top layer of CuO thickened first and then became thin. The oxidation mechanism was discussed.

Optimization of ultrasound-assisted oxidative desulfurization of high sulfur kerosene using response surface methodology (RSM)

An experimental investigation was conducted on the ultrasound-assisted oxidative desulfurization of non-hydrotreated kerosene. The influences of various operating parameters including oxidant-to-sulfur molar ratio (n o/n s), formic acid-to-sulfur molar ratio (n acid/n s), the ultrasound power per fuel oil volume, sonication time, and temperature on the sulfur removal of kerosene have been investigated. Response surface methodology based on Box–Behnken design has been employed. 95.46 % sulfur removal of kerosene has been achieved in the sonication time of 10.5 min under the optimal oxidation conditions (i.e., n o/n s = 15.02, n acid/n s = 107.8, and the ultrasound power per fuel oil volume of 7.6 W/mL) followed by liquid–liquid extraction. More than 90 % sulfur removal of kerosene has been achieved in about 3.5 min of sonication followed by the liquid–liquid extraction. 70.2 % sulfur removal of kerosene has been achieved in the same operating conditions after 3.5 min of oxidation followed by the liquid–liquid extraction in the absence of ultrasound irradiation. The effects of the number of extraction stages on the desulfurization and recovery of kerosene have been also investigated.

Thermal oxidation of cholesterol: Preliminary evaluation of 2-methyl-6-heptanone and 3-methylbutanal as volatile oxidation markers

Cholesterol oxidation in food and model systems is usually monitored by evaluating cholesterol oxidation products, but the analysis is time-consuming and expensive. Therefore, the determination of volatile compounds deriving from cholesterol thermoxidation could be valuable to identify other possible oxidation markers. Cholesterol alone and in the presence of a triacylglycerol mixture (tripalmitin, tristearin, and triolein) were thermoxidized at 170°C for 15min. In both model systems, the total volatile compounds increased three times when oxidation time rose from 5 to 15min. The main classes of volatile compounds were aldehydes, ketones, alcohols and hydrocarbons, displaying a similar behavior in both systems. After 5min of oxidation, 2-methyl-6-heptanone was the main volatile compound, followed by 3-methylpentane, 2,3-dimethyl-1-pentene and 3-methylbutanal. To verify if 2-methyl-6-heptanone could be used as volatile marker of cholesterol oxidation, data were compared with the total cholesterol oxidation products content of each system. A significant correlation between total cholesterol oxidation products content and 2-methyl-6-heptanone amount was found when cholesterol was oxidized alone (r2=0.994) and in presence of triacylglycerols (r2=0.998). When egg yolk was thermoxidized at 80°C for 6h, 3-methylbutanal was the volatile compound that better explained the oxidative trend in this food system, showing a significant correlation with cholesterol oxidation rate (r=0.91). In conclusion, 2-methyl-6-heptanone and 3-methylbutanal could represent an easy and cheaper strategy for monitoring cholesterol oxidation in model systems and food samples, respectively; however, a deeper investigation on the amount and type of volatile compounds generated from cholesterol oxidation according to the food matrix, should be carried out.

Formation of two-dimensional ZnO nanosheets by rapid thermal oxidation in oxygenated environment.

Crystalline 2-D (dimensional) ZnO nanosheets were formed by rapid thermal oxidation of etched Zn foil in oxygen at 300 degrees C and 400 degrees C. Short oxidation time was varied from 10, 20 and 30 min. The morphologies and optical properties of the ZnO nanosheets evolved with the oxidation temperature and time. At 300 degrees C, ZnO nanosheets with thickness ranging from 32 nm to 80 nm were obtained while at 400 degrees C, the thickness of the nanosheets increased from 88 nm to approximately 200 nm after 10 and 30 min of oxidation, respectively. The surface roughness of the ZnO nanosheets and grain size increased with oxidation time and temperature. Photoluminescence of the oxidized samples shows ultraviolet (UV) and visible emissions indicating good crystallinity of ZnO which was further confirmed by high-resolution transmission electron microscope observation of ZnO wurtzite interplanar spacing. Photocatalytic activity of ZnO was also investigated by using degradation of methyl orange (MO) and all the samples exhibit photocatalytic activity. The sample oxidized at 400 degrees C for 10 min show better MO degradation after 2 h of exposure due to higher surface area and better crystallinity of the ZnO nanosheets obtained.

Novel and Precise Method to Isolate, Identify, and Quantify Volatile Compounds in Headspace of Pear Juice Enriched with α-Cyclodextrin

The combination headspace solid phase micro-extraction + gas chromatography–mass spectrometry + gas chromatography with flame ionization detector was successfully used in quantitative determination of the instrumental odor of pear juice. Esters, aldehydes, alcohols, and terpenes were the major chemical families of the pear juice odor. Twenty-six were identified and quantified, with propyl acetate, hexyl acetate, 2-methyl-1-butanol, and butyl acetate being the major compounds. α-Cyclodextrins (CD) significantly improved the color of pear juice, leading to higher values of L* and lower of scores of a*, b*, and ΔE*. However, α-CD also reduced the total concentration of volatiles in the headspace of the juice by creating inclusion complexes with volatiles; after 40 min of oxidation, total volatiles were 8.2 and 3.4 mg L−1 in control and α-CD-treated juices, respectively. But in summary, the global quality (joint consideration of the main sensory attributes) was improved by the addition of α-CD (6.9 compared to 5.2).

Oxidation Behavior at 1600 °C of Si‐SiC‐ZrB2 Composites Produced by Si Reactive Infiltration

Si–SiC–ZrB2 are produced by the reactive infiltration with molten silicon in porous SiC–C–ZrB2 preforms. It is observed that oxidized Si–SiC–ZrB2 ceramics present a layered structure composed of an outer layer of silica and a borosilicate glass intermediate layer with ZrO2 particles and the unoxidized bulk material. The graphs show that the passivation is very effective already after 5 min of oxidation. The thermograms do not vary significantly when the oxidation times are increased.

Influence of Chromium Alloying on the Cyclic Oxidation Behavior of Nanocrystalline (MoxCr1−x)5Si3 Films at 800 °C in Air

In order to investigate the influence of the chromium content on the oxidation performance of the chromium-alloyed Mo5Si3, five kinds of sputter-deposited nanocrystalline (MoxCr1−x)5Si3 (x = 1, 0.78, 0.75, 0.64, 0.57) films have been prepared on Ti−6A1−4 V alloy substrates by double-cathode glow discharge. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy have been used to characterize the nanocrystalline (MoxCr1−x)5Si3 (x = 1, 0.78, 0.75, 0.64, 0.57) films. The as-deposited films were free of crack having metallurgical bonding with a substrate and consisted of an outer (MoxCr1−x)5Si3 layer and an inner diffusion layer. The inner diffusion layer could be divided into a β-phase layer with high Mo content (>10 wt %) and an α′′/α′ layer with low Mo content (<10 wt %). During the cyclic oxidation test at 800 °C in air, for the monolithic nanocrystalline Mo5Si3 film, local spallation of the oxide scale took place by internal stresses after 5 min of oxidation, and severe spal...

Charge Retention in Single Silicon Nanocrystal Layers

ABSTRACTSilicon (Si) nanocrystals formed by controlled thermal crystallization of amorphous silicon dioxide (a-SiO2)/amorphous silicon (a-Si)/amorphous silicon dioxide (a-SiO2) layers hold considerable promise for application in non-volatile memory products and optoelectronic devices. The size of the nanocrystals is fixed by the thickness of the Si layer and strong quantum confinement is provided in the vertical (growth) direction by the insulating a-SiO2 layers. However, the extent of quantum confinement in the lateral dimensions remains to be established. Electron energy loss spectroscopy (EELS) measurements performed within a scanning transmission electron microscope (STEM) indicate that the nanocrystals are laterally isolated by approximately 2nm of a-SiO2. The confinement potential provided by this barrier is insufficient to localize carriers within a nanocrystal for prolonged durations and can permit quantum mechanical tunneling via wave function overlap between adjacent nanocrystals. Charge leakage kinetics within a sheet of Si nanocrystals was studied using electric force microscopy. Approximately 750 electrons were injected within a 100nm radius circular patch with an atomic force microscope cantilever. The entire charge dissipated from this area in 70min via lateral conduction routes. With a goal of localizing the injected charge and enhancing its retention time, the samples were subjected to relatively low temperature dry oxidation at 750°C. After 20 min of oxidation, retention times above 400 minutes were observed.

High-temperature surface oxidation of low-carbon rimming steel

Phase composition and macrostructure of the surface oxide films formed during the oxidation of hot-rolled low-carbon rimming steel in air at 600°C have been investigated by standard and grazing incidence x-ray diffraction. The oxidation kinetics have been analysed by the weight change method. It has been revealed that the oxide film consists of layers of FeO, Fe 3 O 4 and Fe 2 O 3 . The latter two phases have been observed after 2 min of oxidation, whereas the first one appears only after 6 min of annealing in air at 600°C. The oxidation kinetics obeys a logarithmic law during the whole investigated time interval of annealing.

The kinetic of the oxidation of InSn48.

The oxidation of InSn48 has been investigated at partial pressures between 10(-8) Pa and 10(+4) Pa over a temperature range from 22 ( degrees )C to 250 ( degrees )C with different analytical methods. The oxide film contains a mixture of several oxides, although indium oxide forms preferentially. Below the melting point a logarithmic growth, and above this, a parabolic growth of the oxide film has been observed. The oxide film formed in air at 250 ( degrees )C does not become thicker than 50 nm in the first 5 min of oxidation.

Oxidation of In‐48Sn

The oxidation of In‐48Sn was investigated at partial pressures between 10−8 and 10+4 Pa over the temperature range from 22 to 250°C with different analytical methods. The oxide film contains a mixture of several oxides, although indium oxide forms preferentially. The measurements show at the surface an excess of indium compared to the eutectic composition. Below the melting point, a logarithmic growth, and above this point, a parabolic growth of the oxide film was observed. The oxide film formed in air at 250°C does not exceed about 50 nm in the first 5 min of oxidation.

Synthesis and applications of reactive carbohydrates. IV. Reactive finishes based on CMC and oxidized CMC copolymers

Carboxymethyl cellulose (CMC) and persulfate-oxidized CMC samples were assessed for acidic and reducing properties before and after graft copolymerization with acrylamide using K2S2O8 as initiator. The acidic properties were expressed as milliequivalents of carboxyl groups/100 g CMC while the copper number was taken as a measure for the reducing properties. Results obtained signify that increasing the duration of persulfate oxidation from 15 to 60 min causes a significant enhancement in the carboxyl content of CMC particularly during the first 50 min of oxidation. The same holds true for the copper number, but no further significant enhancement could be observed after 30 min. The copolymerization reaction decreases substantially the acidic and reducing groups of the CMC substrates examined. The results showed also that oxidation of CMC increases its susceptibility toward grafting: The higher the extent of oxidation, the higher the extent of grafting. Methylolation of the polyacrylamide–CMC graft copolymers results in reactive finishes. The latter were applied either alone or together with etherified methylolated melamine to cotton fabric samples according to the conventional pad–dry–cure method. The treated samples withstand severe washing, suggesting the occurrence of chemical bonding between the methylolated CMC products and cotton.

Primary stage of Fe-Cr-C alloy oxidation at 1100°C

The oxidation of Fe-Cr-C alloys containing 13% Cr and carbon ranging from 0.15 to 1.63% was studied at 1100°C for 3 hr. It was found that the oxidation rate increased with increasing carbon content in the alloys. The measured time variation of CO2 evolution showed that, during the first period of oxidation (0–40 min), a compact surface layer of FeO formed, which prohibited the free transfer of CO2 into the streaming oxidation atmosphere. The measurable CO2 evolution started between 40 and 50 min, and the most rapid evolution occurred in the interval t=60–90 min of oxidation. This effect corresponds well to scale-layer damage and to the maximum O2 absorption. The measurements carried out by the combined thermobalance-Chromatograph equipment were supplemented by metallographic investigation of the oxide layers. The results enabled us to interpret the primary stage of the oxidation of Fe-Cr-C alloys and to discuss the relations between the cation diffusivities in the individual oxide sublayers, i.e., in wustite, magnetite, and hematite.

Preferential oxidation of carbon during the initial stage of oxidation of an Fe-0.8%C alloy at 400�C

The preferential oxidation of carbon in an Fe-0.8%C alloy during the first 60 min of oxidation in air at 400°C was studied by a thermogravimetric method and by measuring the quantity of evolved carbon oxides. The morphology of the external oxide surface depended on the type of exposed phase—a rosettelike oxide grows over ferrite, whereas the oxide surface over cementite is relatively smooth. A possible mechanism for the preferential oxidation of carbon and its subsequent cessation is proposed.