Growth Of Iron Particles Research Articles

Growth of metal nanoparticles in hydrocarbon atmosphere of arc discharge

A direct current (DC) arc discharge is a widely used method for large-scale production of metal nanoparticles, core–shell particles, and carbon nanotubes. Here, the growth of iron nanoparticles is explored in a modified DC arc discharge. Iron particles are produced by the evaporation of an anode, made from low-carbon steel. Methane admixture into argon gas serves as a carbon source. Electron microscopy and elemental analysis suggest that methane and/or products of its decomposition adhere to iron clusters forming a carbon shell, which inhibits iron particle growth until its full encapsulation, at which point the iron core growth is ceased. Experimental observations are explained using an aerosol growth model. The results demonstrate the path to manipulate metal particle size in a hydrocarbon arc environment.

A novel method of enhancing valuable element recovery for ultra-high-titanium magnetite

The metallization reduction-magnetic separation process was adopted to carry out the experiments to promote the recovery ratio of valuable elements by adding diboron trioxide additive in this work. It is demonstrated that diboron trioxide has the function of destroying Si–O–Si bond for the reduction of ultra-high-titanium magnetite. The optimum experimental condition is found to be the reduction temperature of 1125 °C, the reduction time of 30min, and the diboron trioxide percent of 8 wt% for which the metallization ratio is 92%, and the recovery ratio of ferrum, vanadium, titanium is 90.9%, 78.5%, 76.1%, respectively. V and Ti are synchronously concentrated in non-magnetic materials. The phase composition transformation rule of the valuable components was Fe3O4 (FeTiO3) → FeO → Fe; FeTiO3 (→ FeTi2O5) → (Fe,Mg)Ti2O5; FeTiO3 → TiO2 → Ti3O5 → Ti2O3; (Fe3O4 + TiO2) → Fe3Ti3O10 → Fe. Increasing the temperature can promote the aggregation and growth of iron particles, but too high temperature is not conducive to the separation of Fe, V and Ti. It is evidently observed that when the temperature exceeds 1150 °C, the iron particles are closely connected with the gray titanium oxide, while at 1125 °C, the iron particles are relatively independent. Meanwhile, part of Ti is observed in silicate phase as solid-dissolved form because of high temperature and cause loss. Overall speaking, the metallization reduction-magnetic separation process with diboron trioxide as an additive has achieved the better separation of valuable components, with a higher degree of metallization, and large-scale lowered reaction temperature and time.

Individual enrichment of titanium and iron from low-titanium beach titanomagnetite via preconcentration-reduction roasting and magnetic separation with calcium fluoride

Reduction roasting-magnetic separation realizes the separation of titanium and iron in high-titanium beach titanomagnetite. However, the TiO 2 grade in titanium concentrate is low, and few studies have investigated low-titanium beach titanomagnetite. The preconcentration-reduction roasting and magnetic separation process was developed to utilize the low-titanium beach titanomagnetite. The effects of graphite dosage, reduction temperature, calcium fluoride dosage, and time on the product indices were optimized. The direct reduction iron containing 94.95% iron and 0.75% TiO 2 , titanium concentrate assaying 31.10% TiO 2 were produced under optimal conditions, and metal recovery for both products exceeded 80%. Calcium fluoride increased the liquid phase and reduced the viscosity of the slag system, thereby improving the growth of iron particles. However, an excess liquid phase produced by adding more calcium fluoride inhibited the reduction of iron minerals and promoted the formation of low-titanium minerals, which affected the iron recovery and the quality of the titanium concentrate. • The process was proposed for efficient recovery of iron and titanium. • Direct reduction iron and titanium concentrate were produced. • Calcium fluoride reduced the liquidus temperature and viscosity.

Study on the factors affecting the deep reduction of coal gangue containing high contents of iron and sulfur

Although coal gangue (CG) contains various valuable metal elements, it has not been utilized efficiently. It is of great significance for the sustainable development of the coal industry to improve the added value of comprehensive CG utilization by adopting a deep reduction method. In this study, the effects of a reducing agent and desulfurizer on the properties of the CG reduction products were studied via deep reduction experiments. The results show that CG exhibits a self-reduction effect, which can reduce the amount of external reductant. In addition to the lignite coal (LC) reducing agent, the iron grade reaches its maximum when the other reducing agents are added at a ratio of 10%. Due to the high content of iron minerals in CG, the H2 produced by the individual pyrolysis of CG undergoes a reduction reaction with iron minerals. The addition of CaCO3 improves the reduction condition of iron minerals and promoted their direct reduction. However, an excessive amount of CaCO3 leads to the failure of iron particles to aggregate into large particles or iron-linked crystals, which reduces the recovery of iron. Prolonging the reduction time promotes the migration and diffusion of the iron phase, which is conducive to the aggregation and growth of iron particles. The finer the particle size of the raw material, the worse the permeability of the material layer which results in the incomplete reaction of the sulfur-containing minerals contained in the particles and lead to a higher the S content in the direct-reduction iron obtained after magnetic separation.

Influence Mechanisms of Additives on Coal-based Reduction of Complex Refractory Iron Ore

ABSTRACT Additives play an important role in the recycling of complex refractory iron ore by coal-based reduction to improve the self-sufficiency rate of the ore. In this work, the influence mechanisms of CaF2, Na2CO3, and MgCO3 additives on the coal-based reduction of complex refractory iron ore were studied by x-ray diffraction, thermogravimetry and differential scanning calorimetry, scanning electron microscopy, and energy dispersive spectrometry. The results indicate the three additives could greatly improve the quality of reduction and magnetic separation products. A reduction product metallization degree 93.42%, iron grade 91.23%, and iron recovery 95.48% were obtained under conditions of CaF2 dosage 6%, reduction temperature 1225 °C, and reduction time 50 min. These results were 3.38%, 8.09%, and 0.39% higher, respectively, than could be obtained without additives. The CaF2, and the Na2O and MgO produced by the decomposition of Na2CO3 and MgCO3, could not only replace the FeO from (Mg,Fe)SiO4 and FeAl2O4, but also react with SiO2 and Al2O3 in ore to form their corresponding complex compounds. Moreover, all compounds were benefitted by the increase of the FeO content. The F− ion could replace the O2- ion in the silicon oxygen tetrahedron to reduce the viscosity and surface tension of reduced ore, thus reducing the resistance of iron particle aggregation and growth. In addition, the formation of a local micro melting phase under the action of additives could promote the diffusion of crystalline particles, which is more conducive to the reduction of iron minerals and the formation and growth of iron particles.

Growth Characteristics of Metallic Iron Particles in the Direct Reduction of Nickel Slag

Coal-based direct reduction of nickel slag and magnetic separation of iron are effective methods of secondary resource utilization. The growth characteristics of metallic iron particles in this process are of great significance for subsequent grinding and magnetic separation process. The nickel slag is mixed with coal powder and other additives in a certain proportion, and then subjected to a direct reduction experiment in a high-temperature furnace. Chemical analysis is made to obtain the components of the direct reduction product. The microstructure of the metallic iron particles in the reduction product was studied and the curves of average diameter change and the cumulative diameter percentage of the iron particles are obtained in the reduction process. The results show that the coal-based direct reduction technology can effectively reduce the iron oxides in the nickel slag, and the degree of metallization of the product can reach 91.89 pct. When the reduction time is increased from 10 to 60 minutes, the maximum size of metallic iron particles increases from 13 to 135 μm. The control mechanism of iron particle growth is complicated, and the process is divided into two stages. The growth kinetic parameters (kinetics index, activation energy, and pre-exponential factor) in the two stages are 0.4697, 249.04 kJ mol−1, 3.81 × 108 and 1.0774, 92.93 kJ mol−1, 217.30, respectively. The growth model of metallic iron particles in the direct reduction of nickel slag is also constructed in the paper.

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.

Growth of metallic iron particles during coal-based reduction of a rare earths-bearing iron ore

Coal-based reduction followed by magnetic separation is an innovative technology used in processing refractory iron ores. Given that size is essential to the separation of the metallic iron from the gangue, the morphology of metallic iron particles and their evolution during coal-based reduction are investigated in the present work. The size of the metallic iron particle increased from 128.76 μm to 565.70 μm when the reduction time increased from 20 min to 60 min at 1,225° C and C/O (i.e., the amount of coal addition in terms of the gram-atomic ratio of the fixed carbon in the coal added to the combined oxygen in iron oxides) of 2.5. Based on our microstructural and metallographic analysis, the iron ore reduction process can be divided into three stages: (1) metallic iron particle formation, (2) iron oxide reduction and metallic iron assembly and (3) metallic iron particle growth. Almost all iron oxides are reduced to metallic iron in the second stage. These newborn metallic iron particles are energetically active and able to assemble and grow, and are eventually separated from the gangue. The large metallic iron particles benefit the subsequent magnetic separation process.

Carbon nanotube reactor: Ferrocene decomposition, iron particle growth, nanotube aggregation and scale-up

Abstract We describe a mathematical model for iron particle formation and growth within a chemical reactor, which we use to study carbon nanotube (CNT) formation. This model was used to understand the effect of reactor conditions (e.g. temperature and flow rate) on the CNT diameters, which are known to be coupled to the iron particle dynamics, since the CNT size has a major effect on material properties of the final product. The CNTs were made at 1144 – 1265 ∘ C in a vertical tubular reactor, 7.0 cm diameter × 1 m high , fed with ethanol, ferrocene and thiophene carried into the top by hydrogen gas. The ferrocene decomposed to form iron particles, which acted as a catalyst to form CNTs from the decomposed ethanol. The CNTs then agglomerated, giving a ‘sock’ concentric with the reactor, but of smaller diameter; the sock converged near the bottom of the reactor, emerging as a vertical thread wound onto a spindle. This paper gives analyses to predict: (i) velocity and temperature profiles for the gas; (ii) iron particle number, balancing chemical rate of ferrocene decomposition against diffusion and convection; (iii) iron particle volume fraction, governed by ferrocene decomposition, coagulation, and diffusion. The results show that at the top of the reactor, flow from the 1 cm diameter injection tube generates an annular vortex of hydrogen; however below about 10 cm from the top, the hydrogen flow is well described by a parabolic velocity profile (Poiseuille). The gas temperature is uniform ( 1265 ∘ C ) below about 40 cm from the top. The iron particle size in the reactor is controlled by the non-dimensional groups k ^ c and β ^ , which relate ferrocene dissociation and coagulation to axial gas convection through the reactor. For increasing values of these groups the iron particle size is smaller at a given distance below the injector. We then compare this model to experimental results for CNT diameter within the fibre, which show good qualitative agreement with the results for catalyst size. Two hypotheses may account for sock formation: (1) The model predicts that the iron particles grow bigger near the wall, because of their longer residence times. These big particles are unsuitable for CNT growth and moreover likely to be poisoned by coking. Near the reactor centre-line, there is insufficient shear to promote CNT agglomeration. These two effects imply an optimum radius for agglomeration, and hence sock formation. (2) Several investigators have observed that, in Poiseuille flow, spherical particles accumulate at about 0.185× tube radius measured from the wall. If this applies to CNTs, it might explain sock formation. Furthermore, use of the groups β ^ and k ^ c implies that for scale-up, the ratio of the radius to the average vertical velocity in the reactor remains constant, so the reactor output is proportional to the cube of the reactor radius. Thus, an industrial-scale reactor should be practicable.

Analysis of iron particle growth in aerosol reactor by a discrete-sectional model

The growth of iron particles by thermal decomposition of Fe(CO)5 in a tubular reactor was analyzed by using a one dimensional discrete-sectional model with the coalescence by sintering of neighboring particles incorporated in. A thermal decomposition of Fe(CO)5 vapor to produce iron particles was carried out at reactor temperatures varying from 300 to 1,000°C, and the effect of reactor temperature on particle size was compared with model prediction. The prediction exhibited good agreement with experimental observation that the primary particle size of iron was the largest at an intermediate temperature of 800°C. Model prediction was also compared with Giesen et al.’s [1] experimental data on iron particle production from Fe(CO)5. Good agreement was shown in primary particle size, but a considerable deviation was observed in primary particle size distribution. The deviation may be due to an inadequate understanding of the sintering mechanism for the particles within an agglomerate and to the assumption of an ideal plug flow in model reactor in contrast to the non-ideal dispersive flow in actual reactor.

Incorporation of iron particles into carbon films derived from polyimide

Incorporation of iron particles into carbon films was carried out by mixing an iron complex with polyimide in solution and by following carbonization. Iron in the polyimide film promoted the carbonization of matrix polyimide and increased the electrical conductivity of films. The growth of iron particles in carbon films and the change from paramagnetic to ferromagnetic behavior were observed with the increase of carbonization temperature.

Thermal plasma synthesis of ultrafine iron particles

Ultrafine iron powder was synthesized in an atmospheric-pressure radio-frequency plasma reactor by injecting relatively course iron powder into the plasma, where it evaporated. The renucleated iron particles were characterized by means of a sampling capillary and dilution system interfaced to an electrical aerosol analyzer, a condensation nucleus counter and an electrostatic aerosol sampler. Volume-mean particle diameters for samples obtained near the downstream end of the reactor ranged from about 20 to 70 nm, with particle size increasing as the feed rate of injected iron powder was increased. A two-dimensional numerical model was developed, which solved the plasma conservation equations to predict temperature and velocity distributions, heating and evaporation of the injected iron powder, nucleation and growth of iron particles, and particle transport by convection, diffusion and thermophoresis. Mean particle diameters predicted by the model were in good agreement with the experimental data, although the data indicated broader size distributions and flatter radial profiles of particle concentration than predicted by the model.

Particulate iron formation dynamics in surface waters of the eastern Caribbean

Both the ability of membrane filters to retain iron added (as both Fe(II) and Fe(III)) to surface waters from various sources, and the ability of near ultraviolet light to induce dissolution of colloidal iron oxides suspended in waters from different locations are examined here. In brief, the presence of naturally occurring organic matter exerts a dominating effect on the tendency of iron oxide particles to interact with each other (both in suspension and on or within the membrane matrix). In coastal waters in the vicinity of the Orinoco River, growth of iron oxide particles initiated on addition of either Fe(II) or Fe(III) to the sample of interest, is significantly retarded in comparison to iron particle growth in open ocean waters. Near‐UV light appears to retard particle growth following both Fe(II) and Fe(III) addition to a coastal sample but does little to induce the dissolution of colloidal oxides.

Physical characterization of [formula omitted] model supported catalysts : I. Electron microscopic studies of reduction behavior

The morphology of Fe TiO 2 model supported catalysts has been monitored using transmission electron microscopy following hydrogen reduction at progressively higher temperatures. Nucleation and growth of iron particles from an initially contiguous iron overlayer was observed in the temperature range 608 to 707 K. Following reduction at 773 K, the smaller iron crystallites (less than 10 nm in size) were observed to spread over or wet the support surface, and reduction at temperatures of 875 K or higher extended this spreading behavior to larger crystallites. In addition, reduction at these latter temperatures caused decreases in the average iron particle size and the amount of iron present on the support as distinct iron crystallites. This can be attributed to a diffuse spreading of iron over the support or a diffusion of iron into the support.