Fe Particle Size Research Articles

Avrami Kinetics of Phase Transformations in Nanoparticle Agglomerates of Battery Electrodes

LiFePO4 (LFP) has been extensively studied as an exemplar of electrode-active materials that undergo a phase transition during (de)lithiation. The proposed phase transition mechanisms can be categorized as three main types: 1) first-order phase transformation with growth being interface-source-limited; 2) first-order phase transformation with growth being bulk-diffusion-limited; 3) phase-transformation being bypassed by a continuous solid-solution reaction. A recent study has also reported particle-level spatial variations in the (de)lithiation rate, the extent of which depends on the overall charge/discharge rate. [1] Time- and current-rate dependences of the phase transition mechanism may explain why phase boundaries are found in ex situ TEM studies while metastable solid solutions have been reported in operando studies at high rates or high overpotentials. [2-5] What is still missing, however, is how nucleation and growth proceeds across the mesoscale multiparticle ensembles that represent actual battery electrodes. This study aims to understand the mesoscale transformation process. We studied a series of LiMnyFe1-yPO4 (y=0, 0.4, 0.8) powders with equivalent spherical diameter ranging from 50 nm to 150 nm, primarily using the potentiostatic intermittent titration technique (PITT). Thousands of current responses were collected and then analyzed within the framework of Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory. While JMAK analysis has previously been applied to electrode materials,[6-7] some of its principal assumptions (homogeneous nucleation in an infinite-sized system) are so clearly not satisfied by nanoscale particles that the justification for such an exercise should be questioned. Here, we show for the first time, that the JMAK approach is valid for a mesoscopic system in which secondary particles are composed of well-connected nanoscale primary particles. We show that the Avrami exponent n can be generally expressed as n = a + b*c, where the value of the parameter a describes nucleation kinetics (a=0, instantaneous nucleation; a = 1, constant nucleation rate), b represents the growth dimensionality and c is determined by phase boundary migration mechanism (diffusion- vs interface reaction-limited). In LiMnyFe1-yPO4 (y=0, 0.4, 0.8) samples of varying Mn:Fe ratio and particle size, under different overpotentials and temperatures, we find that the Avrami exponent n systematically varies between 0.5 and 1.5 (Figure 1). These results lead to the following new insights: (1) Nucleation occurs through heterogeneous two-dimensional surface nucleation followed by one-dimensional phase growth (i.e. b =1) into individual primary particles. (2) Phase boundary movement is controlled by bulk Li diffusion, i.e. c = 1/2. (3) Variations in the Avrami exponent indicates a variation in nucleation rate since n = a + 1/2 based on (1) and (2). The nucleation rate decays with time; the decay rate is directly correlated to a nucleation barrier modulated by particle size, composition, overpotential and temperature. (4) The decay in nucleation rate is much faster during discharge, which implies that nucleation occurs more instantaneously during discharge. The same analysis was conducted for results obtained on a commercial Li4Ti5O12 (LTO) sample (NEI NANOMYTE® BE-10C) with primary particle size ranging from 40 to 80 nm and micron-sized secondary particles. The Avrami exponent was found to systematically vary from 0.5 to 1.5 as well, indicating b = 1. Since LFP has 1-D bulk diffusion whereas LTO has 3-D, this result suggests that the dimensionality of growth within mesoscale secondary particles is independent of dimensionality of lithium diffusion inside the primary particles. The similarity in results for LMFP and LTO imply that this type of transformation kinetics may be general for nanoscale battery electrodes with electrochemically-induced phase transitions. Acknowledgement: This work was supported by DOE project number DE-SC0002626. MT acknowledges support from the DOE BES Physical Behavior of Materials Program under grant number DE-SC0014435.

Effects of microstructure and heat treatment on mechanical properties and corrosion behavior of powder metallurgy derived Fe–30Mn alloy

Microstructures, mechanical properties and corrosion rates (CR) of powder metallurgy derived Fe–Mn alloys have been investigated with respect to the particle size of the iron (Fe) powder and the extent of manganese (Mn) diffusion and alloying during sintering. By applying different heat treatments on Fe–30wt%Mn alloy, a phase transformation (γ → ε) for this composition and its influence on mechanical and corrosion properties have been studied. X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) have been conducted to characterize the transformation and identify the austenite (γ) and epsilon martensite (ε) phases in the system. Microstructures and tensile fracture surfaces were examined by Scanning Electron Microscope (SEM). The results show that the Fe particle size affects the overall Mn alloying significantly, i.e., coarse Fe particles (30–200µm) result in Fe–Mn alloys with σy = 48.2MPa, σu = 73.6MPa, fracture strain of 2.42% and CR = 1.36mmpy, while ultrafine particle size (< 44µm) leads to σy = 134.2MPa, σu = 215.8MPa, fracture strain of 10.91% and CR = 0.29mmpy. Heat treatments and formation of ε martensite have shown minor effect on tensile properties, but increased hardness and corrosion rate noticeably.

Effects of the Functionalization of the Ordered Mesoporous Carbon Support Surface on Iron Catalysts for the Fischer-Tropsch Synthesis of Lower Olefins.

Ordered mesoporous carbon (CMK‐3) with different surface modifications is applied as a support for Fe‐based catalysts in the Fischer–Tropsch to olefins synthesis (FTO) with and without sodium and sulfur promoters. Different concentrations of functional groups do not affect the size (3–5 nm) of Fe particles in the fresh catalysts but iron (carbide) supported on N‐enriched CMK‐3 and a support with a lower concentration of functional groups show higher catalytic activity under industrially relevant FTO conditions (340 °C, 10 bar, H2/CO=2) compared to a support with an O‐enriched surface. The addition of promoters leads to more noticeable enhancements of the catalytic activity (3–5 times higher) and the selectivity to C2–C4 olefins (≈2 times higher) than surface functionalization of the support. Nitrogen surface functionalization and removal of surface groups before impregnation and calcination, however, further increase the activity of the catalysts in the presence of promoters. The confinement of the Fe nanoparticles in the mesopores of CMK‐3 restricts but does not fully prevent particle growth and, consequently, the decrease of activity under FTO conditions.

Structural and elemental influence from various MOFs on the performance of Fe@C catalysts for Fischer-Tropsch synthesis.

The structure and elementary composition of various commercial Fe-based MOFs used as precursors for Fischer-Tropsch synthesis (FTS) catalysts have a large influence on the high-temperature FTS activity and selectivity of the resulting Fe on carbon composites. The selected Fe-MOF topologies (MIL-68, MIL-88A, MIL-100, MIL-101, MIL-127, and Fe-BTC) differ from each other in terms of porosity, surface area, Fe and heteroatom content, crystal density and thermal stability. They are re-engineered towards FTS catalysts by means of simple pyrolysis at 500 °C under a N2 atmosphere and afterwards characterized in terms of porosity, crystallite phase, bulk and surface Fe content, Fe nanoparticle size and oxidation state. We discovered that the Fe loading (36-46 wt%) and nanoparticle size (3.6-6.8 nm) of the obtained catalysts are directly related to the elementary composition and porosity of the initial MOFs. Furthermore, the carbonization leads to similar surface areas for the C matrix (SBET between 570 and 670 m2 g-1), whereas the pore width distribution is completely different for the various MOFs. The high catalytic performance (FTY in the range of 1.9-4.6 × 10-4 molCO gFe-1 s-1) of the resulting materials could be correlated to the Fe particle size and corresponding surface area, and only minor deactivation was found for the N-containing catalysts. Elemental analysis of the catalysts containing deliberately added promoters and inherent impurities from the commercial MOFs revealed the subtle interplay between Fe particle size and complex catalyst composition in order to obtain high activity and stability next to a low CH4 selectivity.

Novel ferrihydrite sand coating process as a first step for designed technosols

The production of technosols to remediate polluted or sealed urban soils to sustain new green areas is mainly empirical. For this, our research aims to contribute with the scientific knowledge base for purpose designing of technosols. Since iron minerals play an important role for many different functions of soils, we simplified a technique to incorporate and stabilize iron minerals in a substrate: a sand coated with an amorphous iron (hydr)oxide, a 2-line ferrihydrite (2L-FH). The 2L-FH was precipitated by neutralization of a concentrated FeCl3 solution. The suspension was homogeneously mixed with the sand and the mixture was dried at 35 °C. The mechanical stability of the 21 2L-FH-coated sand was determined by shaking the aggregates in water for 0, 1, 10, 100, and 1 000 min. The degree of coating detachment and the properties of the coating after shaking were characterized through (a) Fe content, (b) zeta-potential and particle size of the detached particles, (c) the specific surface area (SSA) of the coated sand, and (d) its surface structure using scanning electron microscopy (SEM). A phosphate adsorption isotherm was performed to measure the P-sorption capacity of the shaken samples and to test the 2L-FH-quartz attachment stability against the surface charge reduction of the 2L-FH associated with P adsorption. A reduced Fe loss (30 %) and smaller sizes of the coating detached particles in the sample shaken for 1 000 min indicate that a fractioning and reattachment of these aggregates occurred during the agitation process, resulting in a smoother surface (SEM), and a larger SSA and P-sorption capacity. The coated shaken samples showed P-adsorption capacities (5.3–6.34 μmol P g−1) comparable to high loadings of phosphate in soils, and low detachment of Fe (7–14 %) in spite of negativity surface charge increase. The practical novel coating process along with the 1 000-min shaking produced a mechanical resistant and P-adsorptive effective coated sand that could sustain the needs of plants in further experiments.

Size and Promoter Effects on Stability of Carbon-Nanofiber-Supported Iron-Based Fischer-Tropsch Catalysts.

The Fischer–Tropsch Synthesis converts synthesis gas from alternative carbon resources, including natural gas, coal, and biomass, to hydrocarbons used as fuels or chemicals. In particular, iron-based catalysts at elevated temperatures favor the selective production of C2–C4 olefins, which are important building blocks for the chemical industry. Bulk iron catalysts (with promoters) were conventionally used, but these deactivate due to either phase transformation or carbon deposition resulting in disintegration of the catalyst particles. For supported iron catalysts, iron particle growth may result in loss of catalytic activity over time. In this work, the effects of promoters and particle size on the stability of supported iron nanoparticles (initial sizes of 3–9 nm) were investigated at industrially relevant conditions (340 °C, 20 bar, H2/CO = 1). Upon addition of sodium and sulfur promoters to iron nanoparticles supported on carbon nanofibers, initial catalytic activities were high, but substantial deactivation was observed over a period of 100 h. In situ Mössbauer spectroscopy revealed that after 20 h time-on-stream, promoted catalysts attained 100% carbidization, whereas for unpromoted catalysts, this was around 25%. In situ carbon deposition studies were carried out using a tapered element oscillating microbalance (TEOM). No carbon laydown was detected for the unpromoted catalysts, whereas for promoted catalysts, carbon deposition occurred mainly over the first 4 h and thus did not play a pivotal role in deactivation over 100 h. Instead, the loss of catalytic activity coincided with the increase in Fe particle size to 20–50 nm, thereby supporting the proposal that the loss of active Fe surface area was the main cause of deactivation.

Bimetallic Fe15Pt85 nanoparticles as an effective anodic electrocatalyst for non-enzymatic glucose/oxygen biofuel cell

The present work describes an abiotic energy harvesting strategy from electrocatalytic glucose oxidation based on bimetallic FePt nanoparticles (NPs) with a unique onset oxidation potential of −0.63V vs. Ag/AgCl and a maximum current density of 3.7mAcm−2 at the physiological-like condition (pH 7.4). At first, the effect of Fe proportion and particle size on the electrocatalytic activity is investigated and it is found that the small size of Fe15Pt85 have the highest activity toward glucose oxidation. For the proposed abiotic system the cathode material is constructed from nitrogen doped graphene decorated with Pt NPs. The anode material is prepared via a simple one-step co-precipitation method and the cathode material was synthesized through a one-pot electrochemical synthesis route. The morphology, crystal structure and chemical composition of prepared nanostructure materials are characterized by various techniques. Based on the polarization profile and power density plot the designed glucose biofuel cell has an open-circuit potential of 0.64V and provides a maximum power density of 95μWcm−2 at a cell voltage of 0.44V. Such abiotic glucose fuel cells have a great promise to be optimized, miniaturized to power bioimplantable devices without utilizing any complex system.

Size-Dependent Activity and Selectivity of Fe/MCF-17 in the Catalytic Hydrogenation of Carbon Monoxide Using Fe(0) Nanoparticles as Precursors

Monodisperse Fe(0) nanoparticles with diameters between 1.8 and 9.0 nm were prepared from organometallic {Fe[N(SiMe3)2]2}2 and intercalated into mesoporous MCF-17 silica. We observed high turnover frequencies of the catalytic CO hydrogenation; they increased with Fe particle size. Methane and short-chain olefin selectivities were highest for small particles, while the opposite trend applied to long-chain terminal olefins and oxygenates. The Anderson–Schulz–Flory chain lengthening probabilities were found to increase with Fe particle size for both paraffins and terminal olefins. Reaction-induced sintering of the metal particles was limited and could be explained by the transformation of Fe(0) precursors into (mainly) Fe-carbides. The results cast new light on the structure sensitivity of the catalytic CO hydrogenation.

Size-dependent structure and magnetic properties of co-evaporated Fe-SiO2 nanoparticle composite film under high magnetic field

Composite film of Fe nanoparticles embedded in a SiO2 matrix has been prepared by the co-evaporation of Fe and SiO2. Both source temperature and in-situ high magnetic field (HMF) have been used to adjust the Fe particle size and the growth of Fe-SiO2 film. The size of Fe particle decreased with increasing the source temperature without HMF. When HMF was presented during the growth of the film, the size of Fe particle was enlarged and reduced for source temperatures of 1300 °C and 1400 °C, respectively. Meanwhile, the preferred orientation of the film grown at 1400 °C became uniform with the application of HMF. In addition, it is also found that the film was formed in two layers. One layer is formed by the Fe particle, while the other is free of Fe particles due to the existence of more SiO2. The structural variation has a significant effect on the magnetic properties. The coercivity (90 Oe) of the 1300 °C film is much higher than that (6 Oe) of the 1400 °C film with a small particle size and uniform orientation. The saturation magnetization can be increased by increasing the Fe particle volume fraction. This study develops a new method to tune the soft magnetic properties by the co-evaporation of Fe and SiO2.

Microstructure and Impression Creep Behavior of Al Based Surface Composite Produced by Friction Stir Processing

Al–Fe surface composites were prepared through friction stir processing route by using commercial pure aluminium sheet and iron powder. Friction stir processing was done with a tool made up of high speed steel having a 3 mm pin at the tip. Microstructural features of the friction stir nuggets were characterized by using X-ray diffractometry, scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy. Creep behaviour of the friction stir zone was studied using impression creep techniques. Impression creep experiments were done on substrate aluminium and friction stir region. The results show that the surface of Al substrate is converted into a composite, consisting of Al, Fe powders and iron aluminides. The aluminium grain size is drastically reduced, with a large fraction of crystallites having size in the range of 70 nm. Fe particle size was reduced drastically resulting in interparticle spacing in the range of 500 nm. Dislocation density was drastically increased. Impression creep experiments indicated that friction stirred region shows marginally lower activation energy compared to the base metal. This is attributed to the metastability in the structure in the form of extremely fine grain size and high dislocation density. Because of the combined effect, creep in stir zone takes place with a smaller activation energy compared to creep in base aluminium.

Comparison of Magnetism and Transport Properties in Fe/X (X = C, Si, Ge) Films

The Fe/X (X = C, Si, Ge) films were deposited on glass substrates by magnetron sputtering, and then they were annealed in vacuum. Their magnetic and transport properties are compared. For Fe/C films, the annealing process gives rise to the enhancement of saturation magnetization, the increase of the Fe particle size, and the reduction of the magnetoresistance (MR). For Fe/Si films, the annealing process causes the appearance of the Fe particles and the enhancement of MR. For Fe/Ge films, no Fe particles can be formed in the films. The unsaturated MR was observed in the as-deposited Fe/Ge film. Thus, the microstructures, magnetism, and transport properties can be tuned by the group-IV elements and the postannealing process. This paper may be beneficial to the group-IV-based spintronics.

Heating behavior of ferromagnetic Fe particle-embedded thermoplastic polyurethane adhesive film by induction heating

The heating behavior of micrometer-sized Fe ferromagnetic particle-embedded thermoplastic polyurethane adhesive (TPU) under induction heating is examined in this study. The effects of particle size and content, TPU film thickness, and output power of the induction heater were considered. According to this study, heat generation, including the heating rate and maximum temperature, is proportional to the size and content of Fe particles. Greater film thickness and output power also led to higher heat generation. The permeability of the micrometer-sized Fe particles is the most important parameter for higher heat generation of TPU films with larger Fe particles.

Influence of Fe Content and Particle Size of Carbonyl Iron Powder on Shear Yield Stress of Magnetorheological Fluids

The influence of Fe content and particle size of carbonyl iron powder on shear yield stress of magnetorheological fluids were investigated. The results show that the max shear yield stress of magnetorheological fluids with different carrier oil increases with the increasing Fe content, as well as the increasing particle size respectively. A formula is deduced to assess the weight factor related with the effect of Fe content and particle size on the performance of MRF, which was then optimal through experimental approach. It follows that the Fe content of carbonyl iron powder weighs higher than the particle size in terms of their contribution to the enhancement of shear yield stress. In the end, the possible errors have been analyzed, so that to prove the validity of experiments carried out above.

Semiconducting properties of a ferromagnetic nanocomposite: Fe@ZnO

The ferromagnetic and semiconducting nanocomposites, Fe@ZnO are prepared by ball milling technique. X-ray diffraction studies reveal that the average size of ZnO particles decreases with milling time, although the average size of Fe particles (16 nm) remains unaltered for the milling time 3–7 h. The optical band gap of ZnO estimated from UV–Vis spectra is found to be 3.2 eV which is almost independent of the particle size. Interestingly, this value is less than the value for the bulk counterpart. We note that this tailoring of band gap is observed in pure dilute magnetic semiconductor where Fe atom directly substitutes Zn atom. The nonlinear I–V curves have been found in the temperature range of 250–320 K. Analysis of the I–V curves infers that the inelastic tunneling is dominant in the conduction mechanism. The activation energy obtained from the voltage independent conductance is 0.30 eV, displaying the semiconducting properties. The detailed magnetization studies display the typical characteristic features of a soft ferromagnet at room temperature.

The influence of iron powder size on pore formation, densification and homogenization during blended elemental sintering of Ti–2.5Fe

In this study it was determined that the addition of Fe to a Ti powder mixture results in pore formation either through the slow, solid state diffusion of Fe below the eutectic point (1085°C), or as a result of Fe rich liquid formation above 1085°C. The size of the pores scales proportionally with the size of the Fe particles used. Subsequent densification at 1200°C increased with a decrease in Fe particle size. The rate of Fe in-situ alloying and microstructural homogenization during sintering was determined using a newly developed differential scanning calorimeter (DSC) method. The rate of homogenization increased with a decrease in Fe particle size. The use of sub 10μm Fe powder resulted in improved densification compared to pure Ti and leads to complete homogenization during heating to 1200°C.

Fischer–Tropsch synthesis: Iron catalysts supported on N-doped carbon spheres prepared by chemical vapor deposition and hydrothermal approaches

Conventional carbon supports are generally treated in acid or base solutions to produce functionalized groups on the carbon surface in order to anchor active metal or metal oxide species. The use of nitrogen-doped carbon materials as supports can avoid this environmentally unfriendly step because the N atoms in the carbon materials can act as the anchoring sites. In this study, we have synthesized three different nitrogen-doped carbon sphere (NCS) supports by two different strategies: chemical vapor deposition (CVD), in either a horizontal or a vertical furnace, or using a hydrothermal approach. The three different NCSs were found to have different physical and chemical properties as revealed by TGA, XPS, Raman spectroscopy, and electron spectroscopy studies. NCSs prepared by CVD in a vertical furnace (NCSver) gave the smallest diameter and highest surface area materials. The NCSver material presented the most defected sites and the highest N content. The NCSs prepared by the hydrothermal method (NCShyd) gave the largest diameter, the lowest surface area and the least amount of defect sites and the materials with the lowest N content. The NCShor prepared by CVD in the horizontal furnace exhibited defect sites and an N content between the amounts measured for the NCSver and NCShyd materials. The surface N types, determined by XPS, varied with the synthesis strategy used. Iron species were successfully deposited on the three NCSs without a functionalization step. The Fischer–Tropsch synthesis (FTS) performances of the three Fe/NCS catalysts were found to correlate with the Fe particle size which was influenced by the different N contents, the N type, and the defect sites. It is suggested that pyrollic and pyridinic N atoms play a key role in binding the Fe atoms and that quaternary N atoms play a minor role. The Fe/NCSver contained well-dispersed Fe oxide particles on CSs that had the highest N content (made of pyrollic/pyridinic N atoms) and this led to the highest FT activity. The Fe/NCShor catalyst showed the lowest FT activity due to the presence of the largest Fe oxide particle sizes (50% quaternary N atoms).

FePt magnetic particles prepared by surfactant-assisted ball milling

High-energy ball milling of Fe and Pt elemental powders has been carried out under dry and wet (in presence of solvent and surfactants) conditions. Dry milling leads to the formation of the disordered FCC-FePt alloy whereas by the wet milling procedure the main process is the decrease of Fe and Pt particle size, although some dissolution of Pt into Fe grains cannot be ruled out, and no hint of the formation of the FCC-FePt phase is observed even to milling times up to 20h, as X-ray diffraction, electron microscopy and Mössbauer spectroscopy indicates.The as-milled particles were annealed at 600°C for 2h under Ar atmosphere. It is noticed that the disordered fcc-FePt phase observed in particles milled under dry conditions transform to ordered fct phase characterized by a hard magnetic behavior with a coercive field up to 10,000Oe. However, those particles milled in the surfactant/solvent medium exhibit a soft magnetic behavior with a coercive field of 600Oe. These results indicate that wet high-energy ball milling is not an adequate technique for obtaining single-phase FePt particles.

A novel sequential process of bioleaching and chemical leaching for dissolving Ni, V, and Mo from spent petroleum refinery catalyst

Two step leaching experiments were carried out to extract nickel, vanadium, and molybdenum present in spent refinery catalyst. A bioleaching process was applied in the first step. Pulp density, initial Fe(II) concentration, initial pH, particle size, and temperature were varied to optimize the bioleaching process. Ni, V, and Mo were leached out with maximum recoveries of 97%, 92% and 53%, respectively, at an optimized bioleaching condition of initial ferrous ion of 2g/L, initial pH of 2, pulp density of 10% (w/v), particle size of (−106+45) μm, and a temperature of 35°C. As the Mo leaching rate was very low, a second leaching step for the bioleached residue was applied with different concentrations of (NH4)2CO3, Na2CO3, or H2SO4. The second step leaching was optimum at a concentration of 30g/L (NH4)2CO3 with respect to Mo extraction. The rate of Mo dissolution with respect to concentration of lixiviant in the second leaching step was evaluated. The percentages of Ni, V, and Mo leached were 97%, 97% and 99%, respectively, by combining the first step under optimized conditions and the second step with 30g/L (NH4)2CO3.

Effect of Applied Current Density on Morphological and Structural Properties of Electrodeposited Fe–Cu Films

A detailed study has been carried out to investigate the effect of applied current density on the composition, crystallographic structure, grain size, and surface morphology of Fe–Cu films. X-ray diffraction (XRD) results show that the films consist of a mixture of face-centered cubic (fcc) Cu and body centered cubic (bcc) α-Fe phases. The average crystalline size of both Fe and Cu particles decreases as the applied current density becomes more negative. Compositional analysis of Fe–Cu films indicates that the Fe content within the films increases with decreasing current density towards more negative values. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used to investigate the surface morphology of Fe–Cu films. It is observed that the surface morphology of the films changes from dendritic structure to a cauliflower structure as the applied current density becomes more negative. The surface roughness and grain size of the Fe–Cu films decrease with decreasing applied current density towards more negative values.

Electrochemical Aspects of the Synthesis of Iron Particles

The preparation of Fe-particles by reduction of FeSO4 with either sodium borohydride or lithium triethylborohydride in water, and reverse micelles in rapeseed and mineral oil phases is described in electrochemical terms. The influence of surfactants on the electrochemical parameters and resulting size of iron particles was studied as well. The resulting size of Fe-particles synthesized in water (with and without surfactants) correlates with the determined values of open circuit potential (OCP): the more negative OCP, the obtained Fe-particles are bigger, because values of OCP correspond to different range of polarization determined for the reduction of Fe2+. The sizes of Fe-particles synthesized in water or oil phases without surfactants using LiBEt3H are less than using NaBH4 because of electrochemical factors. By varying oils and surfactants it is possible to obtain opposite results as in water phase: smaller Fe-particles obtained using NaBH4 than using LiBEt3H. It is explained by the simultaneous influence of electrochemical and steric stabilization factors, and the last one becomes dominating in some cases.DOI: http://dx.doi.org/10.5755/j01.ms.18.3.2429