Oxidation Of Carbonaceous Materials Research Articles

Flash‐sintering behavior of the composites of 3YSZ and graphene oxide

AbstractFlash sintering is a novel technique that involves the sintering of green bodies in few seconds at relatively very low furnace temperature as compared to what is required to sinter them conventionally. In the present work, we flash‐sintered composites of 3 mol.% yttria‐stabilized zirconia (3YSZ) and graphene oxide (GO). The main aim of this work was to see if the decomposition or oxidation of carbonaceous materials can be prevented by the high heating rates during flash sintering and if composites of 3YSZ and GO can be processed in air. 3YSZ with 5, 10, and 20 wt.% of GO were prepared and subjected to constant heating rate flash‐sintering experiments where electric field was applied across the sample right from room temperature. A DC electric field of 100 V/cm was applied and the current density was set to 100 mA/mm2. It was observed that GO decomposed from the surface of the samples; however, in the core of samples, GO was retained but was reduced to graphite. Grain size of the 3YSZ phase increased with increase in the GO content, whereas the hardness decreased. It was observed that the composites containing carbonaceous reinforcements need to be flash sintered in inert atmosphere to realize their full potential.

Rapid and controllable perforation of carbon nanotubes by microwave radiation

This study presents a new controlled approach to deep perforation of millimeter-long carbon nanotube arrays (CNTAs) by fast oxidative cutting. The approach is based on decorating CNTAs with silver (Ag) nanoparticles, followed by heating Ag-decorated CNTAs with microwave radiation (2.48 GHz, 300 W). The perforation was evaluated using different techniques such as transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller method. The results of the oxidation of carbonaceous materials indicated that the relative amount of oxygen functional groups increased without total oxidation of carbon up to ~ 60 s. After 60 s, the amount of functional groups decreased as the total oxidation started suddenly. Afterwards, at around 120 and 420 s, the oxidation of Ag-decorated CNTAs reached the point of total perforation and total cutting, respectively. Though carbon decomposition terminated at around 420 s, the total pore volume and surface area increased continuously. This was attributed to the steady growth of Ag nanoparticles located between CNTAs.

Fatigue behavior of 2D C/SiC composites modified with Si-B-C ceramic in static air

In order to investigate fatigue behavior of 2D C/SiC composites modified with Si-B-C ceramic, different kinds of modified specimens were fabricated and fatigued at desired temperatures in static air. Fatigue lifetime and load-displacement hysteresis loop of C/(SiC-SiBC)m modified with Si-B-C matrix and SBS-C/SiC modified with Si-B-C coating were analyzed after fatigue respectively. Results show that Si-B-C ceramic can improve obviously fatigue lifetime of C/SiC composites in static air. Meanwhile, fatigue lifetime of sample modified with Si-B-C coating is superior to that of Si-B-C matrix. Quantity and formation rate of borosilicate glass formed from Si-B-C ceramic directly affect crack-healing and fatigue lifetime of specimens. Oxidation damage dominates for the specimens, and damage caused by fatigue stress accelerates the oxidation damage during fatigue process. The damage is controlled by oxidation of carbonaceous material under 1000°C, and oxidant diffusion from borosilicate glass above 1000°C.

Direct Numerical Simulation of combustion near a carbonaceous surface in a quiescent flow

In this work, unsteady gasification and oxidation of carbonaceous materials with gas-phase combustion under oxy-combustion conditions is studied. An original analytical solution is derived to validate the numerical species boundary condition for the heterogeneous surface reactions with frozen gas-phase. Direct Numerical Simulations accounting for multi-species diffusion and detailed chemistry with both species and energy boundary conditions taking into account the Stefan flux were subsequently performed to study combustion near a carbonaceous wall. Transition from gasification to solid carbon oxidation and gas-phase ignition is evidenced. The competition between homogeneous and heterogeneous reactions is discussed based on the analysis of the time-dependent surface and gas-phase species consumption and production rates. Transient histories of surface species as well as spatial profiles of gas-phase species, heat release and temperature are presented for two identified structures of gas-phase CO/O2 reaction zone. In order to quantify the error induced by the Hirschfelder &Curtiss approximation for the multi-species diffusion and to evaluate the importance of the Dufour and Soret terms, a library dedicated to the computation of complex diffusion phenomena has been used to rebuild a priori, species and Soret fluxes for mass diffusion as well as Fourier, species and Dufour diffusion heat fluxes. Eventually, characteristic times of gas and surface reactions and those corresponding to the switch between the two structures of the gas-phase reaction zone are obtained over a wide range of initial O2/CO2 concentrations.

Thermochemical analysis of Palm Oil Wastes as fuel for Biomass Gasification

The production of palm oil in Malaysia generates large quantities of solid waste annually. A small fraction is currently utilized for steam and electricity production in palm oil mills. However, a large fraction is openly combusted or incinerated resulting in increased greenhouse gas (GHG) emissions. Gasification is considered to be a promising technology for converting bio waste into clean energy. It involves the partial oxidation of carbonaceous materials into gaseous products at high temperatures. This study is aimed at evaluating the thermal and physical properties of EFB, Shell and Fibre palm oil waste as gasification fuel. This is vital for the design, optimization and operation of biomass gasifiers. Consequently, the heating value (HHV), specific heat (c), combustion rate (CR), combustion heat (Q) of the wastes were determined. The results showed that the c, CR, Q displayed an increasing trend in the order EFB, Shell and Fibre. Furthermore, c, CR, Qwere significantly influenced by the organic and mineral content of the fuels. The results for heating value were EFB 17.97 MJ/kg, Fibre 18.71 MJ/kg and Shell 19.07 MJ/kg.

Correlation between phase composition and activity of complex oxide catalysts

Correlation between the catalytic activity in oxidation of carbonaceous materials and a change in the phase composition of the La1−xCsxVO4±y and Ce1−xPrxO2−d catalysts was studied. The activity values obtained by iso- and polythermal methods are close.

Heterogeneous CO2 Evolution from Oxidation of Aromatic Carbon-Based Materials

Carbon dioxide is one of the main gaseous products in oxidation of carbonaceous materials via both homogeneous and heterogeneous reactions. However, the mechanisms of heterogeneous CO(2) evolution during oxidation of aromatic carbon-based materials are not known in detail. Using density functional theory, a new oxidation mechanism of aromatic hydrocarbons with atomic oxygen was suggested to consist of four main steps, namely, (1) adsorption of oxygen atom, (2) insertion of O atom into the ring, (3) rearrangement to form a five-membered ring and four-membered ring lactone group, and (4) desorption of CO(2). Using naphthoxy radical as a model system, the proposed reaction pathway can explain how some of the experimentally observed CO(2) is formed.

Lithogeochemistry of orogenic gold deposits in Victoria, SE Australia: a preliminary assessment for undercover exploration

It is probable that the most fruitful exploration strategy for discovery of new orogenic gold deposits in Victoria, SE Australia, will be to focus on areas buried by post-mineralization cover rocks. There are several possible approaches in the absence of robust predictive models and detailed subsurface data with which to apply them. This paper focusses on the detection of primary hydrothermal alteration envelopes and presents new data on the mineralogical and bulk-chemical expression of alteration in weathered outcrop around the deposits of Bendigo, Fosterville and Stawell. Little useful information was gleaned from visual inspection of weathered bedrock but short-wave infrared (SWIR) spectra could be used as vectors to gold ore. Key parameters are the depth of 1920 nm SWIR peak indicating white-mica crystallinity and the ratio of kaolinite to white mica. Observed mineralogical trends are consistent with those from studies of unweathered samples from underground openings and drillcore and from surface samples elsewhere in Victoria. Weathering appears to have resulted in relatively minor changes to rock mineralogy, mainly breakdown of hydrothermal pyrite to poorly crystalline and crystalline iron oxides and oxidation of carbonaceous material. Bulk analysis after total digest reveals that proximity to gold ore is reliably indicated by extreme enrichment in Au, As and K. Several other elements are anomalous but not at every deposit. Use of a partial leach targetting poorly crystalline and crystalline iron oxides appears to offer significant advantages over total digestion as it generates diagnostic anomalies for elements such as Co, Cu, Mn, Ni, Pb and Sr, some of which are not noticeably anomalous in the total digest data. Our preliminary data suggest that drilling through unmineralized cover and sampling weathered bedrock beneath could be a viable exploration method, providing that secondary dispersion at the unconformity has not substantially modified the primary hydrothermal dispersion. This is currently under investigation.

A Preliminary Mass Balance Model of Primary Productivity and Dissolved Oxygen in the Mississippi River Plume/Inner Gulf Shelf Region

A deterministic, mass balance model for phytoplankton, nutrients, and dissolved oxygen was applied to the Mississippi River Plume/Inner Gulf Shelf (MRP/IGS) region. The model was calibrated to a comprehensive set of field data collected during July 1990 at over 200 sampling stations in the northern Gulf of Mexico. The spatial domain of the model is represented by a three-dimensional, 21-segment water-column grid extending from the Mississippi River Delta west to the Louisiana-Texas border, and from the shoreline seaward to the 30–60 m bathymetric contours. Diagnostic analyses and numerical experiments were conducted with the calibrated model to better understand the environmental processes controlling primary productivity and dissolved oxygen dynamics in the MRP/IGS region. Underwater light attenuation appears relatively more important than nutrient limitation in controlling rates of primary productivity. Chemical-biological processes appear relatively more important than advective-dispersive transport processes in controlling bottom-water dissolved oxygen dynamics. Oxidation of carbonaceous material in the water column, phytoplankton respiration, and sediment oxygen demand all appear to contribute significantly to total oxygen depletion rates in bottom waters. The estimated contribution of sediment oxygen demand to total oxygen-depletion rates in bottom waters ranges from 22% to 30%. Primary productivity appears to be an important source of dissolved oxygen to bottom waters in the region of the Atchafalaya River discharge and further west along the Louisiana Inner Shelf. Dissolved oxygen concentrations appear very sensitive to changes in underwater light attenuation due to strong coupling between dissolved oxygen and primary productivity in bottom waters. The Louisiana Inner Shelf in the area of the Atchafalaya River discharge and further west to the Texas border appears to be characterized by significantly different light attenuation-depth-primary productivity relationships than the area immediately west of the Mississippi Delta. Nutrient remineralization in the water column appears to contribute significantly to maintaining chlorophyll concentrations on the Louisiana Inner Shelf.

三波川変成作用から見た沈みこみ帯の進化

Evolution of pressure-temperature paths and fluid compositions during the Sanbagawa prograde metamorphism was reviewed on the basis of chemical characteristics and zonal structures of sodic pyroxene, amphibole, garnet and phengite. Zonal structures of sodic pyroxene, garnet and phengite imply that (1) dP/dT of prograde P-T paths of individual rocks decreased with increasing metamorphic grade and (2) dP/dT just before metamorphic climax might have been negative in some high-grade rocks. Changes of amphibole composition indicate that the prograde P-T path recorded in the higher-grade rocks was situated on the higher-temperature side of that of the lower-grade rocks and on the lower-pressure side of the metamorphic field gradient (1.4-1.8kbar/100°C). The systematic change of prograde P-T path implies an increasing dP/dT during continuous subduction by continuous cooling of the surrounding mantle. These features can be interpreted as documenting prograde metamorphism within a young subduction zone that has a non-steady-state geotherm. Xco2 [=CO2/(CO2+H2O)] value of metamorphic fluid seems to increase with increasing metamorphic grade, and reaches>0.2 in some higher-grade rocks. The increasing Xco2 might have been promoted by oxidation of carbonaceous material caused by mechanical mixing of metapelites and Fe2O3-rich metabasites. Differences in petrological and age data between the Sanbagawa high-grade rocks and pebbles of high-grade in the Eocene Kuma Group in central Shikoku were also briefly reviewed to discuss evolution of subduction zone in the southwest Japan of Jurassic-Cretaceous age.

Growth and dinitrogen fixation by azospirillum, species grown under various growth conditions

AbstractThe effect of strain specificity, various culturing conditions, and incubation periods on the growth and efficiency of dinitrogen fixation by A. lipoferum and A. brasilense, grown in semisolid N2 malate medium was investigated.The properties of the particular strain markedly affected the proliferation as well as the nitrogen gains of Azospirillum in either growth condition. In A. lipoferum strain 1244 and A. brasilense strrain 1771 the multiplication rates were much higher, the counts reaching 7 × 106 and 9 × 106 cells/ml after 15 days in case of 50/300 ml growth condition, associated with high nitrogen gains reaching 99.8 and 114.3 mgl−1, while in A. lipoferum strain 8670 and A. brasilense strain 5677 the counts were 6 × 105 and 2 × 106 cells/ml after both the same period and growth condition, associated with low nitrogen gains, reaching 62.5 and 69.6 mgl−1, i. e., the amounts of nitrogen fixed is usually linked to cell proliferation. The microbial activity in both nitrogen fixation and oxidation of carbonaceous material is directly reflected on the efficiency of dinitrogen fixation. In all treatments the efficiency of N2‐fixation generally increased markedly with time. In A. lipoferum strains 1244 and 8670 the efficiency of N2‐fixation was 118.5 and 107.4 in case of 50/100 ml growth condition after 20 days, while in A. brasilense strains 1771 and 5677 the corresponding figures were 126.5 and 115.4. The response of the available oxygen was linked to the growth conditions, accordingly, the efficiency of N2‐fixation increased by 4.4% & 8.8% in case of A. lipoferum strains 1244 and 8670, and 11.0% & 9.8% in case of A. brasilense strains 1771 and 5677 as a result of increasing the surface area: depth ratio by altering the volume of medium in the experimental flasks.

Factors Influencing Growth (Count and Yield) and Nitrogen Fixation by Azotobacters: I. Properties of Particular Strains

Summary The effect of strain specificity on the growth and efficiency of nitrogen fixation by Azotobacter chroococcum and Azotobacter vinelandii , grown in nitrogen-free liquid medium under shaking and static culture conditions, was investigated. The properties of the particular strain markedly affected the proliferation of Azotobacter in either culture condition. In A. chroococcum (strains 1 and 2) and A. vinelandii (strains A and B) multiplication rates were much higher, the counts reaching 21 – 36 × 10 9 and 18–32 × 10 9 cells/ml after 10 days, associated with high yields, ranging from 264 – 420 and from 220 – 260 mg dry wt. organisms/100 ml, while in A. chroococcum (strains 3 and 4) and A. vinelandii (strains C and D) the counts were 6–11 × 10 9 and 5 – 9 × 10 9 cells/ml after the same period, associated with low yields, ranging from 135 – 172 and from 120 – 165 mg dry wt. organisms/100 ml. There is a considerable variation in the amount of nitrogen gains and the oxidation of carbonaceous material between the different strains under either condition of cultivation, which is directly reflected on the efficiency of nitrogen fixation. The studied strains comprised two groups with a high and a low rate of fixation, the former of these fixed 14 – 20 mg N/g glucose consumed and the latter 10 – 14 mg N/g glucose consumed.

The insoluble matter of coal tar. VI. Oxidation of free carbon

AbstractWork on the oxidation of carbonaceous materials with alkaline potassium permanganate is briefly outlined and the experimental step‐wise oxidation of free carbon is described. The course of reaction as interpreted from these results is indicated. Bulk oxidation of free carbon and the nature of the products are reported. In the steam‐volatile fraction, formic, acetic and butyric acids have been identified. The water‐soluble non‐volatile acids and their methyl esters have been fractionated. Oxalic, succinic, phthalic, terephthalic and mellitic acids have been identified in the oxidation products. The major portion of the acids, however, was found to be more complex, probably having polynuclear structures.Oxidation of C1 and C2 shows that C3 is more highly condensed than C2 and resembles graphite and coke in its properties.

The mechanism of the oxidation of carbonaceous materials at low temperatures

The mechanism of the oxidation of carbonaceous materials at low temperatures