Influence of the solvent on ultrasonically produced SbSI nanowires

The influence of the substitution of methanol in place of ethanol during the ultrasonic production of antimony sulfoiodide (SbSI) nanowires is presented. The new technology is faster and more efficient at temperatures greater than 314 K. The products were characterized by using techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), optical diffuse reflection spectroscopy (DRS) and IR spectroscopy. The coexistence of Pna2₁ (ferroelectric) and Pnam (paraelectric) phases at 298 K was observed in the SbSI nanowires produced in methanol. The methanol decomposes during the sonication or due to the adsorption process on SbSI nanowires.     

Infrared analysis of nano organic particles produced in laminar flames

In this work we present the first infrared investigation of nano-sized organic carbon (NOC) particles produced in premixed laminar ethylene flames. We analyzed the chemical transformation of NOC when the combustible/oxidant ratio (C/O) passed from lean to slightly sooting conditions. We also demonstrate the increase of the aromatic character for samples under thermal treatment. The analysis of the infrared spectra clearly shows the persistence of this material after soot inception. PACS 33.20.Ea; 82.33.Vx     

Comparison of simulated X-ray conversion efficiency of laser produced iron plasma with experimental results

X-ray resonance lines between 11 Å and 17 Å emitted from iron plasmas created by a modest KrF laser have been simulated by modifying the atomic and hydrodynamic code EHYBRID. Free–free and free–bound emission from the Si-, Al-, Mg-, Na-, Ne- and F-like ions is calculated in the simulation. In the original experiments, a KrF laser (249 nm wavelength) with focused irradiances between 1×10¹² W/cm² and 1×10¹⁵ W/cm² was focused on iron targets. The laser pulse duration was varied between 10 ps and 20 ns. We have calculated X-ray conversion efficiencies to be, for example, 0.5% over 2 sr for 2×10¹³ W/cm² and 20 ns pulse duration, in good agreement with experimental measurements. The simulation of X-ray emission is also presented for an experiment where a train of eight 7 ps KrF laser pulses is incident onto an iron target. PACS 52.50.Jm; 52.38.Ph; 52.65.Kj; 52.30.Ex; 32.30.Rj     

Aspects of ultrasonically assisted transesterification of various vegetable oils with methanol

The batch transesterification of vegetable oil with methanol, in the presence of potassium hydroxide as catalyst, by means of low frequency ultrasound (40 kHz) was studied with the aim of gaining more knowledge on intimate reaction mechanism. The concentration of fatty acid methyl esters, of mono-, di- and triglycerides of the actual reaction mixture were determined at short reaction time by HPLC. The effect of ultrasounds on the lipids transesterification correlated with triglyceride structures is discussed. It was found that under ultrasonic activation the rate-determining reaction switches from DG-->MG (classical mechanic agitation) to MG+ROH-->Gly+ME (ultrasonically driven transesterification).     

Iron oxide and iron carbide particles produced by the polyol method

Iron oxide (γ-Fe₂O₃) and iron carbide (Fe₃C) particles were produced by the polyol method. Ferrocene, which was employed as an iron source, was decomposed in a mixture of 1,2-hexadecandiol, oleylamine, and 1-octadecene. Particles were characterized using Mössbauer spectroscopy, X-ray diffraction, and transmission electron microscopy. It was found that oleylamine acted as a capping reagent, leading to uniform-sized (12-16 nm) particles consisting of γ-Fe ₂O₃. On the other hand, 1-octadecene acted as a non-coordinating solvent and a carbon source, which led to particles consisting of Fe₃C and α-Fe with various sizes.     

Synthesis of nano onion-like fullerenes by chemical vapor deposition using an iron catalyst supported on sodium chloride

Nano-carbon materials were synthesized by the catalytic decomposition of acetylene at 420 °C using iron supported on sodium chloride as catalyst. The catalysts contain about 0.3, 1.6, 3.3, and 5.2 wt% iron. The samples were examined by scanning and transmission electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The results show that nano onion-like fullerenes (NOLFs) surrounding an Fe₃C core were obtained using the catalyst containing 0.3 wt% iron. These had a structure of stacked graphitic fragments, with diameters in the range 15–50 nm. When the product was further heat treated under vacuum at 1,100 °C, NOLFs with a clear concentric graphitic layer structure were obtained. The growth mechanism of NOLFs encapsulating metallic cores is suggested to be in accordance with a vapor–solid growth model.     

Mössbauer and EXAFS studies of amorphous iron produced by thermal decomposition of carbonyl iron in liquid phase

Decomposition of iron carbonyl Fe(CO)₅ and Fe₂(CO)₉ in liquid phase gave amorphous and crystalline iron powders in the absence and presence of catalyst, respectively. The hyperfine fields were large in amorphous phases prepared from Fe(CO)₅ than from Fe₂(CO)₉. Crystalline iron, iron carbide and a trace amount of Fe₃O₄ were detected in the decomposition products of the amorphous phase prepared from Fe(CO)₅, and iron carbide was mainly included in the decomposition products of the amorphous phase prepared from Fe₂(CO)₉.     

Spin-polarizing properties of heterostructures with magnetic nano elements

The problem of electron resonant and non-resonant scatterings on two magnetized barriers is studied in the one-dimension. The transfer-matrix is built up to exactly calculate the coefficient of the electron transmittance through the system of two magnetic barriers with non-collinear magnetizations. The polarization of the transmitted electron wave for resonance and non-resonance transmittances is calculated. The transmittance coefficient and spin polarization can be drastically enhanced and controlled by the angle between the barrier magnetizations.     

Magnetic iron oxide nanopowders produced by CO2 laser evaporation

Magnetic iron oxide nanopowders were produced with the laser evaporation technique under normal process gas pressure. In addition, the generated particles were coated in situ with stearic acid and separated on magnets. The methods and the used laboratory setup are briefly described. Influences of essential process conditions, particularly the use of continuous and pulsed laser radiation as well as the properties of the process gas, were experimentally investigated. The produced nanopowders were analysed with TEM, XRD, and magnetic measurements and confirmed the in-principle suitability of the presented method.     

Surface science studies of environmentally relevant iron (oxy)hydroxides ranging from the nano to the macro-regime

In this prospective, new developments in the study of the structure and reactivity of iron oxyhydroxides are reviewed. These materials are of particular interest, since their surfaces control an extraordinary amount of environmental chemistry. Understanding the environmental interfaces at a molecular level often appears to be a daunting scientific endeavor at first glance. Surfaces of interest range from the nano to micron regime and appear in the environment in varying shapes and sizes. Often the powerful suite of vacuum-based surface science tools are not applicable, since the surfaces of environmental particles can vary from amorphous to semi-crystalline and their surface reactivity is often affected by varying levels of surface hydration. However, the introduction of new and powerful surface probes and advancements in computational chemistry are allowing surface scientists to shed light on these hidden interfaces and how they control environmental chemistry.     

Evanescent-wave photoacoustic spectroscopy with optical micro/nano fibers

We demonstrate gas detection based on evanescent-wave photoacoustic (PA) spectroscopy with tapered optical fibers. Evanescent-field instead of open-path absorption is exploited for PA generation, and a quartz tuning fork is used for PA detection. A tapered optical fiber with a diameter down to the wavelength scale demonstrates detection sensitivity similar to an open-path system but with the advantages of easier optical alignment, smaller insertion loss, and multiplexing capability.     

Development of recrystallization in various ultrafine structures produced in iron by severe plastic deformation

It has been shown that the behavior of iron upon heating depends on the type of the ultrafine structure produced in iron upon deformation by shear under pressure. The type of the structure is related to the multistage development of deformation.     

Protection against corrosion of iron alloys by aluminized coatings produced using two different processes

Aluminized coatings were produced on iron by means of two different processes: electron beam deposition under UHV of Al on iron samples previously covered with ⁵⁷Fe films, and hot-dipping of iron samples in molten aluminium. Aluminized samples were submitted to thermal treatments in order to promote interdiffusion at the Fe–Al interface and favour the formation of Fe–Al intermetallic compounds of composition suitable to protect the underlying iron from oxidation. Phase composition, structure and morphology of both as deposited and thermally treated coatings were characterized by means of X-ray diffraction, Mössbauer spectroscopy and metallographic techniques. Significant differences among the effects of the Fe–Al interdiffusion occurring for Al layers produced with the two processes are pointed out and discussed.     

MEAM study of carbon atom interaction with Ni nano particle

Carbon, Ni, and C-Ni alloy modified embedded atom method (MEAM) potentials were developed to study the initial process of carbon nanotube growth on Ni catalyst particles. The MEAM potentials were used to study the atomistic interaction between a carbon atom and a fcc Ni nano particle, both on the particle surfaces and inside the Ni nano particles. The result shows that surface carbon atom is more stable than those in the bulk and sub-surface interstitial positions. Carbon atoms are expected to diffuse from the bulk to the surface, and the single walled and double-walled carbon nanotubes would be more favorable to form on Ni nano particle catalyst. The carbon and Ni nano particle interaction calculation shows that the corner and the edge of the particle are the energetically more favorable sites for the carbon adatom. The carbon nanotube may grow from the corner and edge of the particle.     

Compositional and structural characterization of nanoporous films produced by iron anodizing in ethylene glycol solution

We report on the composition and morphology of as-grown anodic oxide films onto the iron surface in an ethylene glycol solution containing some NH₄F and H₂O by anodizing under direct current bias. Decrease in the content of NH₄F and the temperature of electrolyte allow us to form either nanochannel or nanotubular films over a larger potential window, ca. from 30 to 100 V. By this way, the films in thickness of up to10 μm have been formed. Mössbauer spectra recorded at room to cryogenic temperatures under conversion electron and transmission modes revealed the formation of lepidocrocite (γ-FeOOH) film containing some Fe(OH)₂ and/or FeF₂·4H₂O. An increase in anodizing voltage results in fabrication of more porous and less Fe(II) compounds containing films.     

Thermo-mechanical behavior of nano aluminum particles with oxide layers during melting

Molecular dynamics simulations were performed to study the thermo-mechanical behavior of nano aluminum particles coated with crystalline and amorphous oxide layers during melting. The analysis employs the Streitz–Mintmire potential, along with micro-canonical (NVE) and isobaric–isoenthalpic (NPH) ensembles. The effect of particle size in the range of 5–10 nm with oxide thickness in the range of 1–2.5 nm was investigated. The melting phenomenon was characterized using a combination of structural and thermodynamic parameters. Various fundamental processes, including structural changes, stress development, and phase transformations in both the aluminum core and the oxide shell, were examined and quantified systematically. The diffusion of aluminum cations through the oxide layer was also explored. In addition, a structural analysis was applied to determine the stress field in the oxide shell due to the volume dilatation in the aluminum core. In the particle-size range considered here, the oxide layer melts at ~1,100 K, substantially lower than the value for bulk alumina (2,327 K). The oxide thickness exerts a weak influence on the melting temperature of the shell. The aluminum core melts at a temperature considerably lower than its bulk value of 940 K, a situation comparable to that of a pure nano aluminum particle. This study is an important milestone in the development of a multi-scale theory for the ignition and combustion of nano-particulate aluminum.     

Properties of backscattered particles produced by protons of energy above 1 TeV in an iron absorber

Backscattered-particle production is studied by means of a detailed simulation of cascade processes in a dense medium. The energy dependence of the albedo and the spatial and angular distributions of various components of this flux are analyzed.     

Magnetic properties of iron oxides produced by bacterial oxidation of Fe2+ under acid conditions

Iron oxides synthesized under acid conditions in a bioreactor using the bacteriumThiobacillus ferrooxidans or formed in nature under similar conditions resemble relatively “well”-crystallized ferrihydrites. Mössbauer spectra, however, show up significant differences between these and ferrihydrites, indicating sulfate to play a major role in determining the properties of the bacterial samples.     

Polar antiferromagnets produced with orbital order

Polar states are realized in pseudocubic manganite films fabricated on high-index substrates, in which a Jahn-Teller (JT) distortion remains an active variable. Several types of orbital orders (OOs) were found to develop large optical second harmonics, signaling broken-inversion symmetry distinct from their bulk forms and films on (100) substrates. The observed symmetry lifting and first-principles calculation both indicate that the modified JT q2 mode drives Mn-site off centering, which can be controlled by a magnetic-field-induced phase transition via a coupling of OO and spin orders.