Iron Metal Particles Research Articles

(Invited) Iron Catalyst Facilitated Synthesis of Ammonia from N2 and Water at High Efficiency By Electrolysis

An electrosynthetic process to produce ammonia that avoids the greenhouse gas carbon dioxide is presented here. The electrocatalytic process combines water and nitrogen directly to generate ammonia at high coulombic efficiency. Catalyst enhancements were studied and improved on from our early advances,1-5by varying particle size, catalyst calcination preparation conditions, variation of catalyst carbon conductive matrix support, type and amounts of additives for better carbon coating of the catalyst, etc. Two sets of iron oxide catalysts were probed, nano-sized iron oxides and micron sized nano-oxides formed by calcination of micron sized iron metal particles. A 2µm nano-graphite carbon as the catalyst coating yields higher rates of ammonia than larger sized carbons or iron oxides without the coating. The catalysts from iron metal were made by first mixing iron powder (sized either 1-3 µm, 6-10µm, ~74µm,~149µm, ~841µm). Subsequently, the catalyst was converted to iron oxide coated partially with nano-graphiteby calcination (heating in air at a series of increasing stepped temperatures). Ammonia syntheses were investigated in two configurations (1) with free catalyst suspended in the electrolyte, and (2) with the catalyst confined to the cathode. The ammonia electrosynthesis was conducted between nickel and Monel electrodes in concentrated Na0.5K0.5OH electrolyte. The coulombic efficiency of the electrosynthesis, ηNH3, is measured by comparing the applied charge (the integrated constant current) to the 3 Faraday efficiency per mole of measured synthesized NH3.The highest performance (efficiency and ammonia rate of production) at 100°C was achieved by the catalyst synthesized with 1-3µm iron and prepared with nano-graphite coating. At 100 °C for catalysts prepared respectively with either 1-3µm, 6-10µm, ~74µm,~149µm, ~841µm iron powder, the synthesis coulombic efficiencies ηNH3 are 47%, 39%, 34%, 31%, 25%respectively and maximum ammonia formation rates are 4.7×10−9, 3.8×10−9, 3.4×10−9, 3.0×10−9, 2.4×10−9mol·(s·cm2)−1respectively. Lower temperature and/or confining the catalyst to the cathode will permit future cell variations such as polymer membrane separations in the synthesis cell. The synthesis is also effective at a lower temperature of 60°C, the formation rate using the 1-3µmiron with nano-graphite prepared catalyst is 2.2 mol·(s·cm2) −1with 21% ηNH3. Smaller sized catalysts can be effective, but are a challenge to confine in a stable configuration at the cathode. Rather than dispersing the catalyst in the electrolyte, we also introduce here a configuration that confines the catalyst to the cathode region. This consists ofsealed tea-bag shape Monel mesh cathode separated into 8 individual layers confining equal amounts of catalyst within each layer. At 60°C, the formation rate is 2.3×10−9mol·(s·cm2)−1with 23.7% ηNH3. The catalyst is stablized for ammonia synthesis ata current density of 3 mA/cm2. (1) Licht, S. Cui, B. Wang, Li, F.-F. Lau, J. Lui., S. Ammonia synthesis by N2 and steam electrolysis in molten hydroxide suspensions of nanoscale Fe2O3.Science2014, 345, 637-640. (2) Li, F.-F. Licht, S. Advances in understanding the mechanism and improved stability of the synthesis of ammonia from air and water in hydroxide suspensions of nanoscale Fe2O3. Inorg. Chem., 2014, 53, 10042-10044. (3) Cui, B. Zhang, J. Liu, S.,Liu, X., Xiang, W. Liu, L., Xin, H., Lefler, M. J. Licht, S. Electrochemical synthesis of ammonia directly from N2and water over iron-based catalysts supported on activated carbon. Green Chem., 2017, 19, 298-304. (4) Peng, P., Li, F.-F., Liu, X., Ren, J. Stuart, J., Lefler, M., Johnson, M., Vicini, J., Licht, S.. Chemical transformation of Fe, air & water to ammonia: variation of reaction rate with temperature, pressure, alkalinity, and iron. ChemRxiv.org,posted 31.07.2018. (5) Li, F.-F., Singhal, R., Ren, J., Johnson, Lefler, M., Licht, Solar electrochemical thermal process (STEP ammonia: Optimization of the electrolysis conditions. ChemRxiv.org,posted 25.06.2018. Illustration: The ammonia synthesis from water and nitrogen, avoiding the emission of carbon dioxide, and illustrated using a multi-layer cathode configuration via the mechanism: Cathode: Fe2O3+ 3H2O + 6e−→ 2Fe + 6OH− Anode: 6OH−→ 3／2 O2(g) + 3H2O + 6e− Chemical: 2Fe + N2+ 3H2O → 2NH3+ Fe2O3 Net: N2+ 3H2O → 2NH3+ 3／2 O2 Figure 1

Fe-containing nanoparticles used as effective catalysts of lignin reforming to syngas and hydrogen assisted by microwave irradiation

Active iron-containing nanosized components have been formed on the lignin surface. The metal was deposited on the lignin from an ethanol solution of Fe(acac)3 and from a colloid solution of iron metal particles obtained beforehand by metal vapor synthesis. These active components are able to absorb microwave radiation and are suitable for microwave-assisted high-rate dehydrogenation and dry reforming of lignin without addition of a carbon adsorbent, as a supplementary radiation absorbing material, to the feedstock. The dependence of the solid lignin heating dynamics on the concentration of supported iron particles was investigated. The threshold Fe concentration equal to 0.5 wt.%, providing the highest rate of sample heating up to the reforming and plasma generation temperature was identified. The microstructure and magnetic properties of iron-containing nanoparticles supported on lignin were studied before and after the reforming. The Fe3O4 nanoparticles and also core-shell Fe3O4@γ-Fe-С nanostructures are formed during the reforming of lignin samples. The catalytic performance of iron-based nanoparticles toward the lignin conversion is manifested as increasing selectivity to hydrogen and syngas, which reaches 94% at the Fe concentration of 2 wt.%. It was found that with microwave irradiation under argon, hydrogen predominates in the gas. In the СО2 atmosphere, dry reforming takes place to give syngas with the СО/Н2 ratio of ~ 0.9. In both cases, the degree of hydrogen recovery from lignin reaches 90–94%.

Adsorption of Poly(vinyl formamide-co-vinyl amine) (PVFA-co-PVAm) Polymers on Zinc, Zinc Oxide, Iron, and Iron Oxide Surfaces

The adsorption of poly(vinyl formamide) (PVFA) and the statistic copolymers poly(vinyl formamide-co-vinyl amine) (PVFA-co-PVAm) onto zinc and iron metal particles as well as their oxides was investigated. The adsorbates were characterized by means of XPS, DRIFT spectroscopy, wet chemical analysis, and solvatochromic probes. Dicyano-bis-(1,10-phenanthroline)-iron(II) (1), 3-(4-amino-3-methylphenyl)-7-phenyl-benzo-[1,2-b:4,5-b']difuran-2,6-dione (2), and 4-tert-butyl-2-(dicyano-methylene)-5-[4-(diethylamino)-benzylidene]-Δ(3)-thiazoline (3) as solvatochromic probes were coadsorbed onto zinc oxide to measure various effects of surface polarity. The experimental findings showed that the adsorption mechanism of PVFA and PVFA-co-PVAm strongly depends on the degree of hydrolysis of PVFA and pH values and also on the kind of metal or metal oxide surfaces that were employed as adsorbents. The adsorption mechanism of PVFA/PVFA-co-PVAm onto zinc oxide and iron oxide surfaces is mainly affected by electrostatic interactions. Particularly in the region of pH 5, the adsorption of PVFA/PVFA-co-PVAm onto zinc and iron metal particles is additionally influenced by redox processes, dissolution, and complexation reactions.

Fixation of heavy contaminants of a dirty bomb attack: Studies with uranium and metal simulants

AbstractAsphalt emulsions were evaluated as a means to immobilize radiological contaminants deposited on urban surfaces after a dirty bomb attack. Contaminated surfaces would be sprayed with thin coatings of asphalt emulsion to encapsulate the radioactive particles until the site can be safely remediated. This research investigated applications of an asphalt emulsion (Topein C, Encapco Technologies, LLC, Napa, CA) to treat (zero‐valent) iron, lead, and uranium powders on various building material surfaces. Initial studies found that some of the building materials (limestone, concrete, and metal) reacted with the emulsion producing gas bubbles, which formed 0.001 to 1 cm vesicles in the cured asphalt emulsion. These vesicles, however, did not expose the building material surface, and the reaction appeared to aid in the setting of the emulsion. Powdered lead did not react with the asphalt emulsion, but iron powder and uranium did. Iron powder and the emulsion formed vesicles up to 0.5 mm (but not exposing the building material surface), while the uranium (U3O8) had a moderate reaction when compared with to the lead and iron powders. Scanning electron micrographs showed that the lead powder formed nonreactive layers adjacent to the concrete surface while iron particles were evenly distributed in the asphalt matrix due to the reaction with the asphalt, indicating that the physical and chemical reactions between the iron metal particles, asphalt, and concrete affected particle distribution in the asphalt matrix. A vertical operation sediment tube was used to determine the flowing shear stress durability of the asphalt/metal/substrate complex. The asphalt treatment with iron had no loss at the shear range tested (0.1–2.5 Pa), while the asphalt stabilized powdered lead lost 8% asphalt and lead at 2.5 Pa mean shear stress applied for 5 h. The chemical reaction between asphalt emulsion and iron increased the resistance of the asphalt/metal/substrate complex to shear when compared with lead. Some hydrogen was formed in reactions with iron, but the amount formed was well below the lower flammability limit. Treatment of uranium indicated that the emulsion was effective at reducing leaching of the uranium 10 fold. These experiments indicate that asphalt emulsions may be a viable means for containing metallic or dense radiological contaminants on common building materials. © 2007 American Institute of Chemical Engineers Environ Prog 26:94–103, 2007

Storage and Supply of Pure Hydrogen from Methane Mediated by Modified Iron Oxides

Storage and supply of pure hydrogen through the reduction of Fe3O4 with methane and the subsequent oxidation of the formed iron metal with water vapor were demonstrated. The modification of iron oxides with Cr cations prevented the sintering of Fe3O4/Fe particles during the redox, whereas the mediator without Cr cations was deactivated quickly, because of the sintering. The addition of Cu species into the iron oxides modified with Cr cations enhanced both the reduction with methane and the oxidation with water vapor at lower temperatures. The iron oxides modified with Cu and Cr (denoted as Cu−Cr−FeOx) can store and supply pure hydrogen repeatedly through the reduction with methane and the subsequent oxidation with water vapor. During the redox of Cu−Cr−FeOx, the Cu species were always present as copper metal and Cr cations were always stabilized on the B-sites in ferrite CrxFe3-xO4. Copper metal in the Cu−Cr−FeOx must activate methane in the reduction and water in the oxidation. The CrxFe3-xO4 ferrite in the Cu−Cr−FeOx might prevent the sintering of iron metal particles by blocking their contacts with each other.

Functional Effects of Carbon-Coated Iron Metal Particles for Magnetic Recording Media

Magnetic particles with finer size, higher coercive force, and lower electrical resistance are required to produce better magnetic recording media. Metal has become one of the most suitable materials for high-density magnetic recording media; however metal particles are chemically unstable and their magnetic properties such as coercive force and saturation magnetization are easily ruined. We have tried carbon coating using a chemical agent to aid the carbon to adhere to the surface of metal particles. The carbon-coated particles become chemically stable and their oxidation is gradual enough to extinguish the ignition point. Magnetic tapes prepared using the carbon-coated metal particles in the recording layer exhibit improvements in both electrical resistance and orientation properties. A decrease in the electrical resistance of about two orders of magnitude relative to conventionally prepared tapes is achieved when about 10% of the particle weight is carbon black. The squareness and orientation ratio are also raised and viscosity is lowered because the dispersibility of these particles in magnetic lacquer is better than that of the uncoated metal particles. Transmission electron microscopy photographs indicate that all of the carbon black is bound to the surface of the metal particles. © 2002 The Electrochemical Society. All rights reserved.

Tribological comparisons of particulate magnetic tape coatings in destructive wear testing

Particulate magnetic tape coatings are composed of many ingredients, all of which either add or subtract from the overall durability of the tape coating. The ingredients that make up the surface of the coating such as the binders and lubricants are the ones of greatest interest in this work since they determine its wear performance. A test was developed that subjects the coating to accelerated wear conditions, until coating failure, to determine how each ingredient contributes to the overall wear properties of the tape. The test measures tape tensions at two points before and after the wear surface using a continuous spliced loop of tape sliding at any constant speed from 1 to 6 m/s under controlled humidity. Coating failure occurred when the friction coefficient increased above 0.3 and coating debris is deposited at the point of wear on the non-rotating tape guides. The debris is removed from the guides and visually rated on a scale of 0 to 4. Tape coatings that were studied contained Co– γFe 2O 3, iron metal particles (MP), and various backside coatings on these tapes. All formulation variables were studied but the main focus of this study is on the effect of variable internal and surface applied lubricants along with analysis of the cycled tape surface and the debris formed in an attempt to determine the failure mechanism.

Thermal Decomposition of the Iron(III) Hydroxide and Magnetite Composites of Poly(vinyl alcohol). Preparation of Magnetite and Metallic Iron Particles

Abstract Upon the precipitation of iron(III) hydroxide (Fe(OH)3) and magnetite in the presence of poly(vinyl alcohol) (PVA) at R < 3, PVA is bound to the precipitates in very high yields, where R = [PVA polymer residue]/[Fe ion]. The thermal decomposition of the Fe(OH)3–PVA composite at R = 1.0 by heating at ca. 700 °C in nitrogen for 10 min or more affords almost pure iron metal particles of ca. 200 Å in diameter; almost no residues originating from the PVA remain. Before formation of the metallic iron, magnetite particles are produced as its precursor in the 250—650 °C temperature range, where the particle size increases with increasing temperature from ca. 80 up to ca. 350 Å in diameter, although these iron and magnetite products are not uniform, but are agglomerate or sintered particles. In these processes, the initially bound PVA effectively functions as a reducing agent during its own decomposition.

Kinetic studies of iron metal particle degradation at various temperature and humidity conditions

Passivated iron metal particles suitable for use in magnetic recording media were exposed to various water concentrations at different temperatures to determine their magnetic and chemical stabilities. It was observed that degradation of the magnetic moment was affected more by increases in water concentration than by increases in temperature. Coercivity, however, was less affected under these conditions. The degradation of the magnetic moment of the iron particles was observed in two stages; a rapid initial stage followed by a much slower second stage was evident by measurements of the magnetic moment as a function of the exposure time to high temperature and humidity. The degradation products of these particles were identified by electron diffraction techniques as amorphous Fe304. The rate of degradation in both stages was modeled to be pseudo-zero order. Life expectancies of these particles from Arrhenius relationships are predicted.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Preparation and Properties of Iron(II) Hydroxide–(Sodium Fluoride Tetrasilicic Mica) Intercalation Complexes

Abstract Iron(II) hydroxide–(sodium fluoride tetrasilicic mica) intercalation complexes, which have a chloritelike structure, were prepared by titrating iron(II) sulfate solutions in the presence of mica with sodium hydroxide under oxygen-free conditions. The formation of iron(II) hydroxide sheets between the silicate layers was evaluated by chemical analysis, XRD, DTA-TGA, and surface-area measurement. The presence of water is essential for the oxidizing of these complexes to occur at room temperature by air, because the O2 attack on the surface of these iron(II) hydroxide sheets is hindered by the silicate layers. Fine highly dispersed iron metal particles (α-Fe) were formed on the external surface of the silicate by the H2 reduction of the complexes.

Limitations of Atomic Absorption Spectrophotometry Applied to Spectrometric Oil Analysis

The response of atomic absorption spectrophotometry (AAS) to iron-based wear debris in gas-turbine lubricating oils was measured. It was discovered that the absolute content of wear metal in oil samples was not attainable because of two factors. First, the engine filter system removed substantial amount of debris and secondly, under normal working conditions, the AAS was completely insensitive to iron metal particles and only partially sensitive to iron oxide. Engine health monitoring based on selecting maximum wear debris cutoff values can be misleading if an AAS is used. AAS results however, can be of practical value to show wear metal accumulation trends.