Multifunctional iron and iron oxide nanoparticles in silica

Iron and iron oxide nanoparticles in silica layers deposited by sol–gel techniques on Si wafers were formed and studied. It was shown that multifunctional nanoparticles of different iron oxides possessing various physical properties can be fabricated by means of post-growth annealing of (SiO₂:Fe)/SiO₂/Si samples in various atmospheres. The hematite, maghemite, and iron nanoparticles were found to be dominant upon annealing the samples in air, argon, and hydrogen atmosphere, respectively. The physical properties of produced hybrid structures were studied by Raman and FT-IR spectroscopy, spectroscopic ellipsometry, AFM, and magnetic measurements. The sol–gel technique with subsequent annealing procedure is demonstrated to be an effective method for the formation of multifunctional hybrid structures composed of iron or iron oxide nanoparticles in silica matrix.     

In-situ scanning electron microscopy and electron backscatter diffraction investigation on the oxidation of pure iron

Abstract

α-iron samples, with a 4 to 6 nm oxide layer on top of the surface due to preparation, were oxidised in situ within a scanning electron microscopy equipped with electron back-scatter diffraction. At 773 and 973 K, two different growth mechanisms during the initial stage of iron oxide formation could be observed, layer-by-layer growth at 773K and island growth at 973 K. The growth mechanism at 973K is correlated to the formation of a thin layer of Fe_1–XO (wüstite) prior to Fe₃O₄ (magnetite) crystallisation whereas at 773K only magnetite was found as newly grown oxide. Magnetite showed a strong epitaxial relationship to α-iron with its {111} plane growing preferentially on the {110} plane of iron.     

Surface morphological investigation of iron films during oxidation

Different stages of iron films evaporated under a vacuum of about 10⁻⁵ torr were investigated with and without the addition of aluminium impurity at different percentages. Micrographs of such films heated at 623 K for 2 h show similar network spreading of oxide growth. Addition of aluminium significantly improves the oxidation resistance of iron films by the formation of Al₂O₃ layer.     

Compound formation between polycrystalline iron and boron thin films studied by Auger electron depth profiling

Thin film couples consisting of pure iron and pure boron were evaporated onto substrates of Si(111) and glass. Auger electron depth profiling showed that in the interface region a compound was formed during annealing which was identified by X-ray diffraction techniques as Fe₂B. The growth kinetics of the Fe₂B was investigated in the temperature range 673–773 K. The compound grows according to a parabolic rate law by the diffusion of boron through the already formed Fe₂B layer. An activation energy of 2.9 eV was determined which demonstrates that in our temperature range the usual grain boundary diffusion model is not applicable for the interdiffusion of iron and boron thin films.     

Enhancement of methane production by Methanosarcina barkeri using Fe3O4 nanoparticles as iron sustained release agent

Anaerobic digestion has attracted attention because it does not require power for aeration, it reduces excess sludge and it generates methane gas. However, the growth rate of anaerobic microorganisms is slow, resulting in low treatment efficiency. In this study, the impact of Fe₃O₄ nanoparticles (NPs) on the growth of methanogens, which is the rate-determining step in anaerobic digestion, was investigated using a pure culture of Methanosarcina barkeri as the model methanogen. M. barkeri were cultivated in iron free medium, as well as in media amended with various concentrations of Fe₃O₄ NPs with a mean diameter of 8.1?±?2.4?nm. The production of methane gas was greatly increased when organisms were cultured in media containing NPs. After the methane production was saturated, methanol was newly added to the culture, which resulted in additional methane generation at a higher production rate than occurred during the initial round of cultivation in media containing 20?ppm Fe₃O₄ NPs. In addition, no evidence of negative impacts of Fe₃O₄ NPs on the growth of M. barkeri was observed. Taken together, these results strongly suggest that adding Fe₃O₄ NPs into the fermenter as an agent of sustained iron release can enable sustainable methane fermentation.     

Matrix microstructure effect on the abrasion wear resistance of high-chromium white cast iron

The two-body abrasion resistance of high-chromium white cast iron was investigated as a function of cast iron microstructure. Different microstructures were obtained by means of heat treatment. The chromium and carbon content were chosen in order to have different matrix microstructures (austenitic, martensitic and ferritic) with the same amount of eutectic carbide (M₇C₃). The results show that the cast iron with an austenitic matrix has the best wear resistance. The good wear resistance of this material is due to strong work hardening of the austenitic matrix resulting in a hardness which exceeds that of other structures. The effect of abrasive paper deterioration on abrasion has also been investigated.     

Synthesis and magnetic property of silica/iron oxides nanorods

To better understand the shape dependent property of binary nanostructure, magnetic silica/iron oxides (α-Fe₂O₃ and Fe₃O₄) nanocomposites in rodlike shape have been synthesized using β-FeOOH nanorods as the starting material. The silica layer was coated on the surface of β-FeOOH nanorods, which were prepared by hydrolyzing of FeCl₃ under hydrothermal conditions. Silica/α-Fe₂O₃ nanorods were prepared by calcining silica/β-FeOOH nanorods, and magnetic silica/Fe₃O₄ nanorods were obtained after the reduction of silica/α-Fe₂O₃ nanorods in an inert atmosphere. The role of the silica layer during the phase transformation process was discussed. The magnetic properties of silica/iron oxides (α-Fe₂O₃ and Fe₃O₄) nanorods were investigated and the results revealed that silica/iron oxides nanorods showed higher magnetic saturation value compared with the reported data.     

The fatigue strength of centrifugally cast spheroidal graphite iron pipe

The fatigue strength of centrifugally cast spheroidal graphite (SG) iron pipe was investigated. A parallel series of tests were carried out both on plain plate specimens which were extracted from an iron pipe, and on notched iron specimens. These results were compared with results for rolled steel beams, which were made from a steel with a tensile strength similar to the SG iron [1]. It was found that the strengths at a life of $\text{2 × 10}{}^6$ cycles differed only by 20% between the SG iron pipe and the rolled steel beam, whereas those of plain plate specimens of the two materials differed by 38%. The fatigue failure in the SG iron pipe initiated from the inherent gas pores existing in the inner surface of the pipe, while the fracture in the rolled steel beams originated from external notch defects. Thus, the steel beam appeared more sensitive to the external notches than the SG iron pipe, when the notch size was smaller than 1 mm. However, it was revealed from the fatigue tests on notched plates that, as the notch became severer, the fatigue strength of SG iron became more affected by the notches than did that of the steel. A fracture mechanics analysis indicated that this was because the fatigue crack growth rate for SG iron was three times as high as that for steel.     

Dispersion and reaction of TiB2 in liquid iron alloys

Abstract

The degree of reaction and dispersion achieved when TiB₂ powders are melted in contact with liquid iron based alloys has been assessed via a levitation dispersion test which had been developed earlier. Both Fe₂B and TiC were observed to form as a result of dissolution and reaction of TiB₂. The formation of TiC occurs during the reaction of commercial grade TiB₂ with liquid iron alloys containing as little as 0·08 wt-%C. The reaction of high purity TiB₂ with liquid iron alloys containing 0·24 wt-%C does not however lead to TiC formation. The formation of Fe₂B was observed for all conditions tested, owing to the effectively zero solubility of boron in solid iron. The TiB₂ remaining after dissolution and reaction was found to produce relatively good dispersions in the iron matrix and therefore additions of TiB₂ to liquid iron alloys may provide a means of producing Fe–TiB₂ composite materials. However, the brittle properties of Fe₂B will mean that, whereas such materials may be very hard, they are likely to lack toughness.

MST/1477     

Assessment of B4C reaction with liquid iron alloys

The degree of reaction achieved when B₄C powders are brought into contact with liquid iron alloys has been assessed by a levitation dispersion test. Reaction occurs rapidly, leading to boron carbide dissolution and iron boride formation. In carbon-free iron alloys borocarbide, Fe₂₃(C, B)₆, also forms and in low-carbon iron alloys free graphite was also formed. Highcarbon alloys reacted to form both Fe₃(C, B) and free graphite. Attempts to provide protection for the B₄C by forming a TiC coating on its surface byin situ reactions with liquid Fe-Ti and Fe-Ti-C alloys proved unsuccessful, with TiC forming as a dispersed phase throughout the iron matrix     

Amorphous structure of iron oxide of bacterial origin

In nature, there are various iron oxides produced by the water-habitant bacterial group called “iron-oxidizing bacteria”. These iron oxides have been studied mainly from biological and geochemical perspectives. Today, attempts are made to use such iron oxides as novel functional materials in several applications. However, their quantitative structural characteristics are still unclear. We studied the structure of iron oxide of microtubular form consisting of amorphous nanoparticles formed by an iron-oxidizing bacterium, Leptothrix ochracea, using a combination of high-energy X-ray diffraction and reverse Monte Carlo simulation. We found that its structure consists of a framework of corner- and edge-sharing distorted FeO₆ octahedral units, while SiO₄ tetrahedral units are isolated in the framework. The results reveal the atomic arrangement of iron oxide of bacterial origin, which is essential for investigating its potential as a functional material.     

Electrochemical deposition of iron nanoneedles on titanium oxide nanotubes

Iron as a catalyst has wide applications for hydrogen generation from ammonia, photodecomposition of organics, and carbon nanotube growth. Tuning the size and shape of iron is meaningful for improving the catalysis efficiency. It is the objective of this work to prepare nanostructured iron with high surface area via electrochemical deposition. Iron nanoneedles were successfully electrodeposited on Ti supported TiO₂ nanotube arrays in a chlorine-based electrolyte containing 0.15 M FeCl₂·4H₂O and 2.0 M HCl. Transmission electron microscopic analysis reveals that the average length of the nanoneedles is about 200 nm and the thickness is about 10 nm. It has been found that a high overpotential at the cathode made of Ti/TiO₂ nanotube arrays is necessary for the formation of the nanoneedles. Cyclic voltammetry test indicates that the electrodeposition of iron nanoneedles is a concentration-limited process.     

A Fourier transform interferometric study of phosphate coatings on iron

A Fourier transform interferometric study of phosphate coatings on iron plates using absorption-reflexion techniques indicated the following succession of chemical events on the surface of Armco iron dependent on time of immersion into the standard zinc phosphating solution: (a) activated formation via a redox reaction of an initial layer of hydrated iron oxide/hydroxides and nitrosyl iron complexes containing isolated PO ₄ ^3– (and possibly NO ₂ ^– ) ions in water solution; (b) chemical transformation of the initial layer into a first, adherent and chemically stable layer containing amorphous hydrated iron phosphate and acid iron phosphates; (c) growth of thicker layers progressively enriched of zinc ions, until only hydrated zinc phosphate crystals are deposited in the outer layer. This complex structure of the coating does not undergo significant chemical changes by heating to normal technological temperatures between 150 and 180° C. Only minor changes in water content are shown by the chemical evolution of the infra-red spectra up to such temperatures. Strong changes of the chemical structure of the coating (producing pyro- and metaphosphates) require temperatures higher than 200° C, and coincide with loss of adhesion of the coating to the iron support.     

Study on mechanism of iron reduction in magnesium alloy melt

This article studies the mechanism of iron reduction in magnesium alloy melt by investigating the iron concentrations in different parts in the melt with different holding time. The iron concentrations at the top, the center and the bottom of the melt are measured with the holding time of 300, 1800 and 7200 s. The elements in the sludge settling down in the crucible are also determined by ICP. With the increasing holding time, the iron content in the upper part of the melt decreases and that in the lower part of the melt increases. And the iron content in the sludge increases rapidly. The iron concentrations in the melt and the sludge change little with longer holding time than 1800 s. Among the three iron reduction agents B₂O₃, MnCl₂ and TiO₂, B₂O₃ has the highest iron reduction efficiency (IRE). IRE of B₂O₃ is as two times and five times as IRE of MnCl₂ and IRE of TiO₂ respectively. Formation of FeB and settling of it into melting sludge are believed to be the primary mechanism of iron reduction by B₂O₃ processing. The mechanism of iron reduction in magnesium melt by MnCl₂ or TiO₂ processing is studied by thermodynamic analysis. Formation of substance containing MnFeAl or TiFe with high density and high melting point and settling of them into melting sludge are suggested to be the mechanism of iron reduction by MnCl₂ or TiO₂ processing.     

Preparation of silica coated iron oxide nanoparticles using non-transferred arc plasma

Silica coated iron oxide nanoparticles were prepared using non-transferred arc plasma. The plasma was discharged with argon. Vapors of iron pentacarbonyl (Fe(CO)₅) and tetraethyl orthosilicate (TEOS, Si(OC₂H₅)₄) were injected into a plasma torch with carrier gas and reacted in the plasma chamber. In addition, two types of reaction chambers that are a hot wall reactor and a cold wall reactor were used to investigate the effect of temperature gradient on the synthesis of silica coated iron oxide nanoparticles. The synthesized nanoparticles were collected on the chamber wall and bottom. Phase compositions of the obtained nanoparticles were characterized by X-ray diffractometer (XRD) and the morphologies and the size distributions of the synthesized particles were analyzed by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Additionally, elements mapping of the coated particles was performed by energy dispersive spectroscopy (EDS). The phase composition of the prepared particles was mainly composed of amorphous silica and polycrystalline Fe₃O₄. It was confirmed that the silica was adsorbed on iron oxide particles or encapsulated iron oxide particles. Furthermore, the mechanism of the formation of silica coated iron oxide in the plasma chamber was predicted.     

Chemical constitution and microstructure of TiC x coatings chemically vapour deposited on Fe-C substrates; effects of iron and chromium

TiC _x coatings were chemically vapour deposited in an industrial reactor on Fe-C substrates with carbon contents between 0.06 and 1.20 wt % C. Electron probe microanalyses showed that significant amounts of chromium and iron were present in the coatings and that chromium was also present in the substrate region adjacent to the coatings. By comparing calculated and measured lattice parameters (corrected for the internal stresses present) it became evident that the chromium was in solid solution in TiC _x , whereas the iron was not. This was confirmed by micro Auger electron spectroscopy and X-ray diffraction phase analyses. The carbon to metal ratio,x, of the TiC _x coatings decreased with increasing distance to the coating/substrate interface. The effect of iron on the X-ray diffraction line broadening and hardness of the coatings was large (in contrast with the effect of chromium) and increased with increasing distance to the coating/substrate interface because of a decreasing iron particle size. The TiC _x crystallite size was small and constant throughout the thickness of the coatings. The chromium present in the substrate region adjacent to the TiC _x coatings influenced the microstructure of the substrate by formation of iron, chromium-carbides and reduced the growth rate of the coatings.     

Seed-mediated synthesis of iron oxide and gold/iron oxide nanoparticles

In this study, we prepared magnetic iron oxide and gold/iron oxide nanoparticles (NPs) and characterized their morphologies and properties by XRD, TEM, EDX, VSM and UV-vis measurements. The magnetite iron oxide NPs of 10 nm were synthesized by coprecipitation of Fe2+ and Fe+3 in the solution of NH4OH and then they were used as seed particles for the subsequent growth to prepare the magnetite NPs of different particle sizes and also to prepare gold/iron oxide composite NPs. All those magnetite NPs are superparamagnetic and the gold/iron oxide composite NPs combine the optical and magnetic properties, which are contributed by gold and iron oxide components, respectively.     

Fracture mechanics behaviour of austenitic compacted graphite cast iron

The fracture mechanics behaviour of high-nickel austenitic compacted graphite cast iron was studied and the effects of graphite morphology, alloying elements and specimen thickness on the mechanical properties, plane stress fracture toughness, and fatigue crack growth rate were evaluated. It was found that the graphite morphology, i.e. the percentage of compacted graphite present, was the major determinant of all properties of the materials investigated. The irons with a greater amount of compacted graphite (the balance was nodular graphite in austenitic matrix) resulted in lower tensile strength, yield strength, elongation and K _c fracture toughness but higher crack-growth index values (poorer crack-growth resistance). For 25 mm thick specimens, K _c values of the austenitic compacted graphite cast irons in this study were in the range of 58–64 MPa m^1/2. This is higher than ferritic/pearlitic ductile iron of 43–53 Mpa m^1/2, and is compatible to Ni-resist austenitic ductile iron of 64.1 Mpa m^1/2. The addition of cobalt not only contributed to slightly higher values of mechanical properties, but also higher plane stress fracture toughness and better crack growth resistance. Optical microscopy, scanning electron microscopy and X-ray diffraction techniques were applied to correlate the microstructural features to the properties attained.     

Fenton-like oxidation of Rhodamine B in the presence of two types of iron (II,III) oxide

The catalytic efficiency of iron (II, III) oxide to promote Fenton-like reaction was examined by employing Rhodamine B (RhB) as a model compound at neutral pH. Two types of iron (II, III) oxides were used as heterogeneous catalysts and characterized by XRD, Mössbauer spectroscopy, BET surface area, particle size and chemical analyses. The adsorption to the catalyst changed significantly with the pH value and the sorption isotherm was fitted using the Langmuir model for both solids. Both sorption and FTIR results indicated that surface complexation reaction may take place in the system. The variation of oxidation efficiency against H₂O₂ dosage and amount of exposed surface area per unit volume was evaluated and correlated with the adsorption behavior in the absence of oxidant. The occurrence of optimum amount of H₂O₂ or of exposed surface area for the effective degradation of RhB could be explained by the scavenging effect of hydroxyl radical by H₂O₂ or by iron oxide surface. Sorption and decolourization rate of RhB as well as H₂O₂ decomposition rate were found to be dependent on the surface characteristics of iron oxide. The kinetic oxidation experiments showed that structural Fe^II content strongly affects the reactivity towards H₂O₂ decomposition and therefore RhB decolourization. The site density and sorption ability of RhB on surface may also influence the oxidation performance in iron oxide/H₂O₂ system. The iron (II, III) oxide catalysts exhibited low iron leaching, good structural stability and no loss of performance in second reaction cycle. The sorption on the surface of iron oxide with catalytic oxidation using hydrogen peroxide would be an effective oxidation process for the contaminants.     

An electron microscope study of gadolinium iron garnet thin films prepared by the oxidation of vacuum evaporated metals

The oxidation of thin films of gadolinium, iron and Gd₃Fe₅ has been investigated by transmission electron microscopy and diffraction between 300 and 1200? C. The oxidation products for gadolinium and iron films are consistent with the oxidation mechanism proposed for bulk material. Thin films of Gd₃Fe₅ do not oxidize completely to give gadolinium iron garnet, high densities of garnet and orthoferrite inclusions are observed. An unusual form of grain growth is also observed in these films.