Different Forms Of Carbon Research Articles

Carbon cycling from mangrove litter to the adjacent Hooghly estuary, India – A modelling study

Abstract Carbon cycle has a fundamental role in changing climate of the earth. Recent models of the estuary-atmosphere system demonstrate the potentially great importance of estuarine environment to the regulation of atmospheric carbon dioxide. Carbon, the key element of life is available in organic and inorganic forms as different compounds in air, water and soil. Our study site, Hooghly - Matla estuarine system receives a large load of nutrients throughout the year. This is mainly due to high litterfall from the adjacent luxuriant mangroves and yield of huge suspended sediment carried along with the river Ganges which is flowing through the western part of the Sundarban mangrove ecosystem.Keeping in view the crucial role of carbon, a seven compartment model has been proposed to study the dynamics of carbon in this estuarine system. Different forms of carbon present in soil (as soil organic carbon (SOC), soil inorganic carbon (SIC)) and in water (as dissolved inorganic carbon (DIC), dissolved carbon dioxide (DCO2), dissolved bicarbonate (DBC), dissolved organic carbon (DOC) and particulate organic carbon (POC)) are taken as state variables. Litter biomass, dissolved oxygen, primary productivity, community respiration, temperature of water, pH of water, pH of soil, air-water exchange of carbon dioxide and conversion rates among different forms of carbon are considered as graph time functions. The data used in the present model are collected for over two years from our field works and experiments. Other sensitive rate parameters which are not possible to collect from survey or experiment, calibrated following standard procedure. Sensitivity analysis is performed along with calibration. Model simulation results are validated with observed data. Results show seasonal variations of litterfall and which is the main source of SOC pool and ultimately transported to the estuary. Other than litterfall, death of organisms in soil and water enriches the SOC and POC respectively. pH of water is governing factor and depending on this factor, DIC is converted to DCO2 and DBC, which are taken up by phytoplankton during photosynthesis. Mineralization rate of SOC to SIC and uptake rate of DCO2 and DBC are the sensitive parameters.

Age and source of different forms of carbon released from boreal peatland streams during spring snowmelt in E. Finland

Isotopic data are increasingly being used to quantify and understand the processes that control the release of carbon (C) from northern peatlands. We used δ13C and 14C measurements to investigate the source and age of different forms of aquatic C (DOC, POC and evasion CO2) released from 2 contrasting (undrained v drained) forested peatland catchments at the end of the winter snowmelt period in boreal E Finland. The δ13CVPDB values of DOC (range −28.3 to −28.8 ‰) were generally more 13C depleted than evasion CO2 (range −22.7 to −31.5 ‰) and showed no clear differences between the pre-flood, flood and post-flood periods. Both forms of C had evidence of bomb-14C (i.e. >100%modern), indicating that they contained substantial quantities of C fixed since the mid AD 1950s. However, DOC was 14C enriched compared to evasion CO2, with 14C concentrations suggesting that, on average, DOC-C was ~5–6 years younger than evasion CO2–C, with the most recently fixed C being released when temperatures were highest. POC was significantly depleted in 14C with conventional (uncalibrated) radiocarbon ages of 805–1135 BP. In contrast to other studies, the isotopic compositions of DOC and evasion CO2 were very similar, suggesting a predominantly single and consistent C source (decomposition of soil organic matter; SOM) during the snowmelt period. Whilst we found no evidence to suggest that old (pre-bomb) C was being released at the end of the winter period, the drained site was associated with more 14C depleted and 13C enriched evasion CO2, suggesting a closer link to the atmospheric CO2 pool. Our isotopic data suggest that the various forms of C released to the aquatic system from these forested Finnish peatlands are closely related, largely unaffected by drainage and (at least in the case of evasion CO2 and DOC) indicate strong connectivity between C cycling in the soil–plant–water system.

Structural stability of stepped nickel surfaces

The structural stability of stepped Ni(755) and Ni(771) surfaces in the temperature range 20–500°C and during adsorption of oxygen and different forms of carbon has been studied using scanning tunneling microscopy and low-energy electron diffraction. A phase transition from the structure with double steps at room temperature to the structure with single steps at a temperature above 350°C has been observed on the clean Ni(755) surface. This transition disappears after oxygen adsorption at a temperature above 350dgC. In this case, the structure on the Ni(755) surface with single steps is stabilized in contrast to Ni(771), which tends to faceting during oxygen adsorption. It has been shown that fullerenes C60 form an array of one-dimensional chains at the upper boundaries of steps of the substrate, when they are adsorbed on the Ni(755) surface.

Thermal behavior of carbon nanotubes decorated with gold nanoparticles

Three different forms of carbon, i.e., multi-walled carbon nanotubes (CNTs), single-walled CNTs, and soot, were decorated with gold nanoparticles by a new method. In this method C10H8− ions transfer electrons to the CNTs or soot. These electrons on the carbon surface can then reduce Au3+ species to form supported Au nanoparticles with a narrow particle size distribution. Thermogravimetric/differential thermal analyses (TG/DTA), XRD, Raman, and TEM show that naphthalene molecules remain trapped inside the Au nanoparticles and can only be removed by treatment at ca. 300 °C. Remarkable effect of the Au nanoparticles on the oxidation of carbon by O2 is also observed by TG/DTA, i.e., on-set oxidation temperature and activation energy (Ea). It is shown that as the Au particle size decreases from 25 to 2 nm a linear decrease of the oxidation temperature is observed. Au particles larger than 25 nm do not produce any significant effect on carbon oxidation. These results are discussed in terms of spillover catalytic effect where Au nanoparticles activate O2 molecules to produce active oxygen species which oxidize the different carbon supports.

Wavelet analysis of soil variation at nanometre- to micrometre-scales: an example of organic carbon content in a micro-aggregate

This paper demonstrates the potential of wavelet analysis to investigate fine-scale spatial variation in soil without statistical assumptions that are generally implausible. We analysed the optical densities of different forms of carbon which were measured at intervals of 50 nm along a 16-µm transect on a soil micro-aggregate using near-edge X-ray fine-structure spectroscopy (NEXAFS). We found different patterns of scale-dependent variation between the carbon forms, which could be represented by pair-wise wavelet correlations at the different scales, and by principal components analysis of all the correlations at each scale. These results represent only one small soil micro-aggregate and are not presented as general findings about soil carbon, but they do indicate that fine-scale variation of soil carbon can be complex in ways that the wavelet analysis can accommodate but alternative spatial statistics such as variograms cannot. Among the patterns of variation that the analysis could identify were scale-dependent correlations of the different forms of carbon. In some cases, positive correlations were found at coarser scales and negative at the finest scales, suggesting a multi-scale pattern in which contrasting forms of carbon are deposited in common clumps but at finer scales either one or the other form dominates. Aromatic and carboxylic carbon varied jointly in this way. Other forms of carbon, such as carboxylic and aliphatic carbon, were strongly correlated at the finest scales but not the coarser scales. We found evidence for changes in the variance and correlation of forms of carbon along the transect, indicating that the spatial distribution of carbon at these fine scales may be very complex in ways that are inconsistent with the assumptions of geostatistics. This quantitative analysis of the spatial patterns of different soil components at micro-scales offers a basis for formulating and testing specific hypotheses on replicated samples.

Chemical characterisation by WD‐XRF and XRD of silicon carbide‐based grinding tools

AbstractThis paper addresses the chemical characterisation of silicon carbide‐based grinding tools. These are among the most widely used grinding tools in the ceramic sector, and instruments are required that enable the grinding tool quality to be controlled, despite the considerable complexity involved in determining grinding tool chemical composition. They contain components of quite different nature, ranging from the silicon carbide abrasive to the resin binder. To develop the analysis method, grinding tools containing silicon carbide with different grain sizes were selected from different tile polishing stages. To develop the grinding tool characterisation method, the different measurement process steps were studied, from sample preparation, in which different milling methods (each appropriate for the relevant type of test) were used, to the optimisation of the determination of grinding tool components by spectroscopic and elemental analyses. For each technique, different particle sizes were used according to their needs. For elemental analysis, a sample below 150 µm was used, while for the rest of the determinations a sample below 60 µm was used. After milling, the crystalline phases were characterised by X‐ray powder diffraction and quantified using the Rietvel method. The different forms of carbon (organic carbon from the resin, inorganic carbon from the carbonates and carbon from the silicon carbide) were analysed using a series of elemental analyses. The other elements (Si, Al, Fe, Ca, Mg, Na, K, Ti, Mn, P and Cl) were determined by wavelength‐dispersive X‐ray fluorescence spectrometry, preparing the sample in the form of pressed pellets and fused beads. The chemical characterisation method developed was validated with mixtures of reference materials, as there are no reference materials of grinding tools available. This method can be used for quality control of silicon carbide‐based grinding tools. Copyright © 2010 John Wiley & Sons, Ltd.

Improvement of DMFC Electrode Kinetics by Using Nanohorns Catalyst Support

One of the factors limiting direct methanol fuel cells (DMFC) performance is the slow kinetics of methanol oxidation at the anode. The importance of the catalyst support for fuel cells has been recognized and different forms of carbon have been suggested. Single wall nanohorns (SWNH) are a new class of carbon with a similar graphitic structure of carbon nanotubes. They are self-assembling materials that produce aggregates of about 100 nm. In the present study, the comparison of the performance of a DMFC equipped with electrocatalysts supported on a commercial carbon black and on SWNH was carried out. The SWNH were synthesized by the arc discharge method in air. The deposition of the Pt and Pt/Ru catalysts on the carbon supports was accomplished by using ethylene glycol as reducing agent. The synthesized catalyst nanoparticles have a very small diameter size (ca. 2.5 nm) and they are uniformly distributed on both carbon supports. The supported electrode catalysts were tested in a DMFC and results indicate that employing SWNH is very promising showing catalytic activities 60 % higher.

Sistema RTP: uma técnica poderosa para o monitoramento da formação de nanotubos de carbono durante o processo por deposição de vapor químico

In this work, a TPR (Temperature Programmed Reduction) system is used as a powerful tool to monitor carbon nanotubes production during CVD (Chemical Vapour Deposition), The experiments were carried out using catalyst precursors based on Fe-Mo supported on Al2O3 and methane as carbon source. As methane reacts on the Fe metal surface, carbon is deposited and H2 is produced. TPR is very sensitive to the presence of H2 and affords information on the temperature where catalyst is active to form different forms of carbon, the reaction kinetics, the catalyst deactivation and carbon yields.

Raman and electron microscopy analysis of carbon nanotubes exposed to high power laser irradiance

High power laser radiometry requires efficient and damage-resistant detectors. The current study explores the evolving nature of carbon nanotube coatings for such detectors upon their exposure to incrementally increasing laser power levels. Electron microscopy images along with the D-band to G-band intensity ratios from the Raman spectra from eight irradiance levels are used to evaluate changes before and after the exposure. Electron microscopy images of the exposed multiwalled carbon nanotubes revealed the formation of intermittent pockets of moundlike structures at high power densities exceeding 11 kW/cm2. Raman spectroscopy measurements also demonstrated higher values for the ratio of the D-band intensity to that of the G-band, suggesting the possible transformation of nanotubes into structurally different forms of carbon. Exposure to a sample of single-walled nanotubes did not demonstrate the evolution of structural changes, which could be due in part to the higher irradiance levels relative to the damage threshold, employed in the experiment.

Deactivation phenomena during catalytic wet air oxidation (CWAO) of phenol over platinum catalysts supported on ceria and ceria–zirconia mixed oxides

Catalytic wet air oxidation (CWAO) of aqueous solution of phenol was carried out with pure oxygen at 160°C in a stirred batch reactor on platinum supported oxide catalysts (Pt/CeO2c calcined at 650 and 800°C and Pt/CexZr1−xO2 with x=0.90, 0.75 and 0.50). The catalysts were characterized before (BET, FT-IR spectroscopy, hydrogen chemisorptions, oxygen storage capacity (OSC)) and after reaction (TPO, elementary analysis, GC–MS and DTA–TGA). The results demonstrate a poisoning of the catalysts during CWAO reaction due to the formation of different forms of carbon deposit on the materials: carbonates and polymeric carbon species. This poisoning phenomenon is limited by the introduction of 50% of zirconium into ceria lattice for the catalysts presenting the lowest surface area. Polymeric deposits play a major role in the catalyst deactivation.

The Influence of Source Material Composition on Morphology and Optical Properties of ZnO Nanostructures

We investigated the influence of the composition of the source materials on the morphology and optical properties of ZnO nanostructures. The source materials consisted of a mixture of ZnO and carbon, or ZnO, carbon, and another metal oxide (In2O3, MnO2, or V2O5). The addition of a different metal oxide to the source materials is a commonly used method to achieve doping and/or alteration of the morphology of ZnO nanostructures. For each metal oxide additive, we investigated the influence of different forms of carbon (graphite, carbon nanofibers, and single wall carbon nanotubes). Obtained nanostructures were studied using scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, selected area electron diffraction, and photoluminescence. The morphology and the optical properties of the obtained nanostructures were strongly dependent on the source material composition. Possible reasons for observed differences are discussed.

The effect of monomer and electrolyte concentrations during synthesis on the actuation of PPy(CF 3SO 3) films in aqueous electrolytes

Free-standing films of polypyrrole, PPy(CF 3SO 3), were electropolymerised galvanostatically from propylene carbonate solutions containing tetrabutylammonium trifluoromethanesulfonate of a range of pyrrole or electrolyte concentrations. The electrochemomechanical deformation (ECMD), measured in situ during cyclic voltammetry experiments, was found to increase when a higher concentration of pyrrole monomer or CF 3SO 3 electrolyte was used during the polymerisation. X-ray photoelectron spectroscopy was used to estimate the presence of different forms of carbon in the PPy(CF 3SO 3) films, including the α and β carbons of the pyrrole ring, the ‘disordered carbon’ and carbonyl carbon. These XPS results were correlated with the strains observed in ECMD measurements and the doping level estimated from N1s XPS spectra. The morphology of the films obtained for different growth conditions was also investigated by means of SEM.

Carbon in Particulate Matter in the air

Carbon in Particulate Matter in the AirCarbon (Latin carbo) in elemental form appears as diamond, graphite, fullerene, and black amorphous carbon. Black amorphous carbon can be found in atmospheric aerosols and its main forms are elemental (EC), organic (OC), and carbonate (CC) carbon. Atmospheric carbon particles are transmitted through more than 70 sources of air pollutants. Elemental carbon is the primary pollutant, which results from incomplete combustion of fossil and biomass fuels. It also appears as soot, in sediment, soil, and ice core. Many quantitative determinations of elemental carbon are based on its chemical inertness, thermal stability, and visual features. Organic carbon includes organic compounds such as polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), polychlorinated dibenzo-p-dioxins and furans, polybrominated diphenylethers, and other organic pollutants are the products of combustion and formation of secondary organic aerosols.The aim of this paper was to describe different forms of carbon in the atmosphere, how they affect people, climate, and the atmosphere, and to give an overview of different methods for their determination.

Polishing of polycrystalline diamond by the technique of dynamic friction, part 3: Mechanism exploration through debris analysis

This paper investigates the mechanisms of material removal in dynamic friction polishing of polycrystalline diamond composites through the analysis of polishing-produced debris. The specimens used were PCD compacts composed of diamond and silicon carbide. In order to uncover the debris’ structure, high-resolution transmission electron microscopy (HRTEM), electron diffraction and electron energy loss spectroscopy (EELS) were used. Additionally, the density and the sp 2 to sp 3 ratio in the hybridized carbon materials of the debris were estimated from the EELS spectra. It was found that the debris were mainly of amorphous structure and consisted of different forms of carbon, silicon oxide/carbide, iron oxides, etc. The results show that during polishing, the diamond has transformed to non-diamond carbon, and silicon carbide to amorphous silicon carbide/oxide.

Gold Electrocrystallization from a Spent Thiosulfate-Sulfite Electrolyte

Although there are several electrolytes in the market for gold electrodeposition, a thiosulfate-sulfite mixed ligand bath has been recently developed specially for microelectronics applications. The main driver for the development of this electrolyte is long-term sustainability. At the end of a gold electrodeposition process, the spent electrolyte can contain a significant amount of gold in solution. This study has been initiated to study the feasibility of gold recovery from a used thiosulfate-sulfite electrolyte. In our work, we have used glassy carbon and graphite as electrodes. The two different forms of carbon were chosen due to the difference in their structures. It was found that at the early stages of the reduction process, the deposition of gold on glassy carbon exhibits an instantaneous nucleation. At longer times, the deposition follows the classical progressive nucleation phenomenon. Deposition of gold on graphite does not follow the classical nucleation phenomenon. Particle sizes and density can be controlled by varying the deposition potentials and time. This work is expected to elucidate information on the electrochemical behavior of a spent electrolyte at carbon electrodes, as well as studying their microstructural properties, which is likely to govern the utility of recovered gold.

Raman spectroscopy of diamond and doped diamond.

The optimization of diamond films as valuable engineering materials for a wide variety of applications has required the development of robust methods for their characterization. Of the many methods used, Raman microscopy is perhaps the most valuable because it provides readily distinguishable signatures of each of the different forms of carbon (e.g. diamond, graphite, buckyballs). In addition it is non-destructive, requires little or no specimen preparation, is performed in air and can produce spatially resolved maps of the different forms of carbon within a specimen. This article begins by reviewing the strengths (and some of the pitfalls) of the Raman technique for the analysis of diamond and diamond films and surveys some of the latest developments (for example, surface-enhanced Raman and ultraviolet Raman spectroscopy) which hold the promise of providing a more profound understanding of the outstanding properties of these materials. The remainder of the article is devoted to the uses of Raman spectroscopy in diamond science and technology. Topics covered include using Raman spectroscopy to assess stress, crystalline perfection, phase purity, crystallite size, point defects and doping in diamond and diamond films.

The route to fullernoid oxides.

Tetrahedral oxides, like silicates and aluminates, have attracted great interest due to their potential for numerous applications in various fields ranging from catalysis, ion exchange and molecular sieves, to thermo- and photoluminescence. In spite of their tetrahedral character, no effort has been made to date for establishing structural relationships between these tetrahedral oxides with different forms of carbon, for example, fullerenes. Here, we report for the first time an oxide that exhibits a three-dimensional framework of AlO4 tetrahedra forming huge 'Al84' spheres, similar to those of the D2d isomer of the C84 fullerenes. These Al84 spheres, displayed in a face-centred-cubic lattice, are easily identified by high-resolution electron microscopy. We also show that this Sr33Bi24+delta Al48O141+3 delta/2 aluminate exhibits an onion-skin-like subnanostructure of its Bi/Sr/O species located inside the Al84 spheres. The role of the original pseudo-spheric anion [Bi16O52-n empty square box n]-with n vacancies (empty square box)-in the stabilization of such a structure is discussed. This structure seems to be promising for the generation of a large family of fullerene-type (fullerenoid) oxides with various properties.

Release of gaseous and particulate carbonaceous compounds from biomass burning during the SAFARI 2000 dry season field campaign

Source strengths to the atmosphere for different forms of carbon (CO2, CO, CH4, nonmethane hydrocarbons (NMHC), and PM2.5) produced by biomass burning were calculated during the Southern African Regional Science Initiative (SAFARI 2000) intensive study period (August and September 2000) for Africa south of the equator. For a given pixel burned, these calculations are a product of the aboveground biomass before a fire, the proportion of biomass that is burned by the fire, and the emission factor for a given carbon compound based on the combustion efficiency. The total emission for the region is the summation of such calculations for all the burned pixels. Products used for these calculations are a prototype satellite‐based burned area based on the SPOT‐VGT‐S1 satellite product, a fuel load map produced by a simulation model developed and applied to southern Africa at 1 km2 resolution, information from fire experiments from our own research in southern Africa to compute combustion completeness, and emission factors published for the region. Over August and September 2000, 31,067 fires detected by the SPOT satellite are calculated to have emitted 96.9 × 1012 g CO2, 4.6 × 1012 g CO, and lesser amounts of CH4, NMHC, and PM2.5. These calculations are in the range of previous estimates of the emissions of these compounds for southern Africa. Along with documenting the estimates of the emissions during the SAFARI 2000 campaign, regional emission estimates are very strongly controlled by the burned area of fires due to a correlation between the cumulative distribution of percent burned area and the cumulative distribution of percent emissions.

Infrared Space ObservatoryLong Wavelength Spectrometer Observations of C+and O0Lines in Absorption toward Sagittarius B2

High spectral resolution Fabry-Pérot observations of the [O I] 63.2 and 145.5 μm and [C II] 157.7 μm fine-structure lines are presented for the center of the Sagittarius B2 complex (Sgr B2). The data were obtained with the Long Wavelength Spectrometer on board the Infrared Space Observatory (ISO). Both the [O I] 63.2 μm and the [C II] 157.7 μm lines are detected in absorption. The upper state level of atomic oxygen at 145.5 μm is in emission. Whereas the [O I] 63.2 μm line is seen in absorption over the entire wavelength range -200 to 100 km s-1, the [C II] 157.7 μm line displays a more complex profile: absorption occurs at velocities less than 20 km s-1, and emission comes from the Sgr B2 complex at velocities greater than 20 km s-1. Using observations of the CO isotopes and of the H I lines, absorption components can be associated with many clouds along the Sgr B2 line of sight. From these data, we were able to disentangle three different layers that contain atomic oxygen. These layers, as predicted by photodissociation region models, are characterized by different forms of carbon in the gas phase, i.e., the C+ external layer, the C+ to C0 transition, and the CO internal layer. We derive lower limits for the column densities of atomic carbon and oxygen of the order of ~1018 cm-2 and 3 × 1019 cm-2, respectively. An O0/CO ratio of around 2.5 is computed in the internal cores of the clouds lying along the line of sight, which means that ~70% of gaseous oxygen is in the atomic form and not locked into CO. The fact that the [C II] 157.7 μm line is detected in absorption implies that the main cooling line of the interstellar medium can be optically thick, especially in the direction of large star-forming complexes or in the nuclei of galaxies. This could partially account for the deficiency in the [C II] 157.7 μm line that recently has been found toward infrared-bright galaxies in ISO data.

Formation of nitrogen-substituted carbon cluster anions by gas-feed Cs-sputtering from different forms of carbon

We have investigated the mechanism of formation of Cn - and CnN- cluster anions during Cs+-ion sputtering from surfaces of different crystallographic forms of carbon (polycrystalline graphite, amorphous C and C60), in the presence of high purity N2 or NO2 gas. The normalised yields of sputter-ejected CnN- (n? 10) cluster anions display an oscillatory dependence on n: the odd n clusters being more abundant than the even n ones. Significantly, CnN- clusters produced from the three different forms of C, show similar oscillatory variations with n. Moreover, the CnN- yields follow a single power law decline as a function of cluster size for all three surfaces sputtered, and over a wide range of operating conditions. This strongly indicates that the intrinsic structure of the ion-induced surface does not play a significant role in the formation of sputtered cluster anions. The observed abundance patterns of Cn - and CnN- clusters also suggest that mono-nitrogen substitution of the carbon clusters does not allow the chain to ring transformation to occur up to n = 10.