Surface Concentrations Of Iron Research Articles

Porous carbonaceous materials simultaneously dispersing N, Fe and Co as bifunctional catalysts for the ORR and OER: electrochemical performance in a prototype of a Zn-air battery.

Infiltration of the mesoporous structure of SBA-15 silica as a hard template with phenanthroline complexes of Fe3+ and Co2+ allowed the simultaneous dispersion of nitrogen, iron and cobalt species on the surface of the obtained carbonaceous CMK-3 silica replica, with potential as bifunctional heterogeneous catalysts for the cathodic oxygen reduction and evolution reactions (ORR and OER). The textural properties and mesopore structure depended on the composition of the material. The carbonaceous FeCoNCMK-3 (1/1), obtained with an Fe/Co molar ratio of 1/1, exhibited an ordered cylindrical mesoporous structure with a high mesopore volume, a rather homogeneous composition in terms of total and surface concentrations of iron and cobalt, and a balanced presence of pyridinic-, pyrrolic- and graphitic-N species. FeCoNCMK-3 (1/1) could improve the ORR kinetics by adsorption and reduction of O2 through the 4-electron mechanism with a current density of -17.37 mA cm-2, Eonset of 1.13 V vs. RHE and E1/2 of 0.75 V when compared to metal-free, monometallic or bimetallic electrocatalysts with a higher amount of cobalt than that of iron. In addition, FeCoNCMK-3 (1/1) exhibited activity for the OER, presenting lower values of Eonset (1.52 V), Ej10 (1.78 V) and the Tafel slope (76.3 mV dec-1) with respect to other catalysts. When evaluated as a cathode in a prototype of a Zn-air battery, FeCoNCMK-3 (1/1) exhibited a high open circuit voltage of 1.41 V, a peak power density of 66.84 mW cm-2, a large specific capacity of 818.88 mA h gZn-1, and cycling for 20 h but with deactivation upon cycling.

Iron and manganese co-limit growth of the Southern Ocean diatom Chaetoceros debilis.

In some parts of the Southern Ocean (SO), even though low surface concentrations of iron (Fe) and manganese (Mn) indicate FeMn co-limitation, we still lack an understanding on how Mn and Fe availability influences SO phytoplankton ecophysiology. Therefore, this study investigated the effects of Fe and Mn limitation alone as well as their combination on growth, photophysiology and particulate organic carbon production of the bloom-forming Antarctic diatom Chaetoceros debilis. Our results clearly show that growth, photochemical efficiency and carbon production of C. debilis were co-limited by Fe and Mn as highest values were only reached when both nutrients were provided. Even though Mn-deficient cells had higher photochemical efficiencies than Fe-limited ones, they, however, displayed similar low growth and POC production rates, indicating that Mn limitation alone drastically impeded the cell’s performance. These results demonstrate that similar to low Fe concentrations, low Mn availability inhibits growth and carbon production of C. debilis. As a result from different species-specific trace metal requirements, SO phytoplankton species distribution and productivity may therefore not solely depend on the input of Fe alone, but also critically on Mn acting together as important drivers of SO phytoplankton ecology and biogeochemistry.

Determination of Adsorbates on the Surface of Polymer with Low Absorption Capacity by Thermal Lens Spectrometry

Thermal lens spectrometry in a coaxial configuration is used for the direct determination of adsorbates on a planar surface of polyethylene terephthalate (PET). A possibility of the direct measurement of the rate of adsorption from solutions and the determination of the parameters of the adsorbed layer is demonstrated by the example of an investigation of the adsorption of iron(II) tris(1,10-phenantrolinate) on a PET surface. The adsorption isotherm of iron(II) tris(1,10-phenantrolinate) on the PET surface is described by the Langmuir equation and is linear in the concentration range in solution from 0.02 to 0.7 mM. The method for calculating the thermal perturbation in surface-absorbing solids was used to interpret the results of the adsorption study, and a possibility of determining iron(II) tris(1,10-phenantrolinate) on the surface at a level smaller than a monolayer was shown. Thermal lens spectrometry enables the determination of the absorption of the surface layer at a level up to 5 × 10–5 absorbance units, which corresponds to the surface concentration of iron(II) tris(1,10-phenanthrolinate) 2 × 10–13 mol/cm2. Using the example of the adsorption of 4-(2-pyridylazo) resorcinol on the PET surface, it is demonstrated that, in the case of strong absorption of the surface layer, the thermal destruction of substance and the deformation of the substrate may occur. A local increase in temperature in the layer is also confirmed by theoretical calculations.

Asbestos Fiber Preparation Methods Affect Fiber Toxicity.

To measure the toxic potential of asbestos fibers-a known cause of asbestosis, lung cancer, and malignant mesothelioma-asbestos minerals are generally first ground down to small fibers, but it is unknown whether the grinding condition itself changes the fiber toxicity. To evaluate this, we ground chrysotile ore with or without water for 5-30 min and quantified asbestos-induced reactive oxygen species generation in elicited murine peritoneal macrophages as an indicator of fiber toxicity. The toxicity of dry-ground fibers was higher than the toxicity of wet-ground fibers. Grinding with or without water did not materially alter the mineralogical properties. However, dry-ground fibers contained at least 7 times more iron than wet-ground fibers. These results indicate that grinding methods significantly affect the surface concentration of iron, resulting in changes in fiber-induced reactive oxygen species generation or toxicity. Therefore, fiber preparation conditions should be accounted for when comparing the toxicity of asbestos fibers between reported studies.

The effect of particulate matter on paper degradation

In this work we explore the chemical effects of particulate matter on paper. We exposed paper made of pure cellulose to the environment in different locations in central London, outdoors (in sheltered conditions) and indoors, for a period of up to 6 months. We monitored particulate matter (PM) deposition by counting the particles deposited every month with a scanning electron microscope. We analysed elemental composition of the deposited particles using inductively coupled plasma mass spectrometry. After accelerated degradation of the exposed samples, we determined the degree of polymerisation using viscometry. We observed higher deposition rates and higher metal concentration outdoors than indoors. Elemental analysis of the deposited particles revealed the presence of some transition metals (Fe, Cu, Cr) that can contribute to the degradation of cellulose fibres through the Fenton reaction. By comparing the degree of polymerisation of protected, unprotected and unexposed samples we could determine the relative contribution of PM deposition on the increase of the degradation rate. We found that the surface concentration of iron correlates with the reduction in the degree of polymerisation of the exposed paper. The results suggest that the presence of Fenton metals in PM has a significant effect on the acceleration of the degradation of cellulose. However, we estimate that this will unlikely occur at the levels of area coverage by PM that are typically avoided in indoor heritage through preventive maintenance and cleaning.

Chemical effects on UV irradiation absorption of fouled quartz sleeves in ultraviolet disinfection

The effects of foulant chemical composition on ultraviolet (UV) absorbance of fouled quartz sleeves in UV disinfection systems were studied. Statistical analysis was conducted to examine the effects of nine fouling chemicals on the UV transmittance changes of fouled quartz lamp sleeves. The results demonstrated that the main effects were attributable to surface concentrations of iron and manganese. The surface concentrations of calcium and copper had no significant effects on the UV absorbance of fouled sleeves. The interaction effects of copper with iron and magnesium with manganese were also revealed from the statistical analysis. The model is able to give reasonable predictions of the UV absorbance characteristics of foulants from other UV systems. However, several limitations of this model were identified. First, the model does not accurately predict the absorbance at relatively high chemical surface concentrations. Second, the model does not account for the possible effects of anions and organics on UV absorption of fouled quartz sleeves.

Surface termination dependence of the reactivity of single crystal hematite with CCl4

We describe ultrahigh vacuum Auger electron spectrometric measurements of the uptake of chlorine following the room temperature exposure of single crystal hematite, α-Fe2O3, to CCl4. We compare the surface chemistry of two specific surface phases formed on the basal plane of α-Fe2O3: the Fe3O4(111)-(2×2) “selvedge” and the α-Fe2O3/Fe1−xO “biphase.” For Fe3O4(111)-(2×2) an estimated saturation level of Cl of ∼75% of a monolayer is readily attained. Carbon uptake is well below that expected for simple stoichiometric dissociative chemisorption, consistent with desorption of organic products during the surface reaction. Low energy electron diffraction measurements suggest that, dependent upon preparation procedures, at least two types of α-Fe2O3/Fe1−xO biphase structures can be formed. Surprisingly, upon exposure to CCl4, Cl uptake does not occur on either of these biphase surfaces, despite the fact that these surfaces are thought to have the same surface concentrations of iron and oxygen as Fe3O4(111). The dramatic difference between the reactivity of the Fe3O4 and biphase surfaces suggests that the active site for the dissociative adsorption of CCl4 on Fe3O4(111)-(2×2) comprises both an iron cation and an oxygen anion with a surface-normal-oriented dangling bond that is uncapped by iron cations. Electron stimulated and thermal desorption of Cl from the saturated Fe3O4(111)-(2×2) selvedge is also reported.

Generation of hydroxyl radical by crocidolite asbestos is proportional to surface [Fe 3+

Differences among fibrous silicates to effect injury in biological systems have been postulated to reflect oxidant generation by structural iron within the crystal lattice of amphiboles. Iron is also coordinated to the surface of all silicates in concentrations which depend on the density of acidic functional groups. We tested the hypothesis that oxidant generation by crocidolite is proportional to surface-complexed iron rather than variance in the lattice concentrations of this transition metal. Surface iron was quantified after its reduction to Fe 2+ and chelation by citrate. Thiobarbituric acid (TBA) reactive products and dihydroxybenzoic acid products of salicylate were employed as indices of nonspecific oxidant and hydroxyl radical generation, respectively. Surface iron, TBA reactive products, and dihydroxybenzoic acid products all diminished after pretreatment of crocidolite with the metal chelator deferoxamine in concentrations varying from 0 to 250 m m. Inclusion of deferoxamine in the reaction mixture provided similar results of diminishing both TBA reactive products and dihydroxybenzoic acid generation. We conclude that oxidant generation by crocidolite is proportional to surface concentrations of iron which can be chelated using deferoxamine. The design of synthetic fibers without health effects after exposure will likely necessitate decreasing the number of surface acidic functional groups to diminish the capacity to complex iron (i.e., minimize the percentage SiO 2).

Changes in iron oxidation state and surface composition of iron-chromium catalyst reduced by hydrogen

X-ray photoelectron spectroscopic studies of the reduction of iron-chromium catalysts have been carried out to determine changes in the relative surface concentrations of iron(II) and (III) oxides and metallic iron and in its surface composition at 100–500°C.

Impurity deposition on ALT-I limiter heads

Detailed spatial profiles of impurities deposited on the surface of the ALT-I pumped limiter heads used in TEXTOR have been measured using proton induced X-ray emission in the external ion beam analysis system. The TiC coated, ATJ graphite ALT-I limiter head was analyzed after each of two plasma exposure periods. Measurements were also made on the uncoated ATJ limiter head. For limiter operation at plasma radii ranging from 40 to 46 cm we find large accumulations of metal impurities on the ion and electron sides of the limiter. The composition implies that the source of these impurities is predominantly the stainless steel main limiters in TEXTOR. Surface concentrations of iron as high as 10 18/cm 2 have been measured. On each of the limiter front faces a relative maximum in metal concentration occurs near the tangency point and relative minima are found near the toroidal extremities. An analysis of impurity transport in the edge region of TEXTOR using Redep is also presented. The calculations predict impurity atom migration patterns that strongly resemble the measured metal atom deposition profiles. The analysis provides considerable insight into impurity transport in the tokamak edge. Benchmark calculations of this type are valuable for the design of future limiter or divertor systems.

Coke formation during steam cracking of hydrocarbons. Part 2. Effect of preoxidation and prereduction of the reactor surface

AbstractCoke formation by steam cracking of propane over preoxidised and prereduced alloy foils has been studied in a tubular reactor at 810–850°C. Coke formation on preoxidised steel involves coke formation on the oxide scale which is low and coke formation on metal exposed by spalling of the scale which is high. Surface analysis by Auger spectroscopy (AES) reveals that the surface concentration of iron and nickel is low on the oxide scale and high on the exposed metal. Coke formation on the surface of the prereduced steel is low and the surface contains chromium and manganese as the predominant metal components. Differences in the product spectra obtained over preoxidised and prereduced steels is suggested to be due to the presence of surface iron and nickel which increases the production of coke and hydrogen and decreases the production of olefins in steam cracking.

Surface composition of promoted iron catalysts

Auger electron spectroscopy (AES) has been used to estimate the surface composition of promoted iron catalysts for ammonia synthesis. An equation was developed from which the surface concentrations of iron and promoter are calculated from the Auger current. The equation validity as an estimation tool is verified by the agreement between the calculated iron surface mole fraction and the iron area fraction determined by the reliable technique of CO chemisorption. On doubly (K 2O-Al 2O 3) promoted catalysts, the K 2O mole fraction determined by AES agrees with the area fraction determined by CO 2 chemisorption. On multiply (CaO-K 2O-Al 2O 3 ) promoted catalysts CO 2 chemisorption is not applicable. AES results show that most of the surface is covered with CaO and K 2O. A surface model is proposed for the doubly promoted catalyst. The promoter is believed to be present in surface islands, approximately 2 nm in diameter and less than 1 nm in thickness, an area of pure iron between them. Within the island, the Al 3+ is proposed to lie below the K 2O, thus being screened from the surface.

Surface Spectroscopic Studies of High-Strength Low-Alloy Steels before and after Annealing

Surface analyses of two high-strength low-alloy steels are reported before and after annealing. The surface analysis techniques used include ESCA, AES, and SIMS. The steel samples were hand polished and cleaned before annealing; the effects of cleaning have been investigated. Samples were annealed in flowing N2 or in vacuum at 650°C. Changes in the steel surface as the annealing time and atmosphere were changed are reported. Additionally, differences between surfaces of two steels having similar bulk compositions were investigated both before and after annealing. Cleaning high-strength low-alloy steels generally decreased carbon contamination on the surface without affecting the nature or surface concentrations of iron, oxygen, or manganese. Vacuum annealing the steel produces a steady state much faster than when the steel is nitrogen annealed; however, the composition of the steel surface after vacuum annealing is similar to the surface after annealing in flowing N2. Although the two steels investigated have similar bulk concentrations, type B steel has much higher Mn concentration on the surface than type A steel. The amount of Mn on the surface appears to affect the surface concentrations of Fe and O as the sample is annealed.

Quantitative Auger spectroscopic analysis of segregation of phosphorus in iron

The segregation of phosphorus to a clean iron surface has been studied by Auger spectroscopy in an Fe-0.063 wt % P alloy, as a function of temperature. It is shown that with certain plausible assumptions and the help of the Crank diffusion equation for strongly adsorbed elements, a calibration of the relative surface concentrations of iron and phosphorus can be achieved. The empirical proportionality factor so derived agrees closely with the factor derived theoretically on the basis of relative ionization cross-sections, with the inclusion of Coster-Kronig contributions to ionization.