Compacted Iron Research Articles

Analysis of a compact iron ore sintering process based on agglomerated biochar and gaseous fuels using a 3D multiphase multicomponent mathematical model

One of the most challenging issues of the actual steelmaking industry is the mitigation of CO2 emissions. To cope with this target, the massive use of granulated biomass and fuel gas in the iron ore sintering process are a promising technological solution and can contribute to mitigating the environmental impacts of the steel plant. We focused on the development of a comprehensive computational tool to analyze and suggest new practices for the sintering process, which mitigates CO2 emissions. The modeling approach uses an integrated multiphase and multicomponent theory. New phases, chemical species and rate equations are included. The model predictions were confronted with industrial data showing good adherence. New scenarios for utilizing the combined technologies of granulated biomass and gas fuel injections are investigated. The model predictions indicated that the high performance of the process with suitable sinter quality could be achieved. The conditions for operating the sintering process with fully renewable energy resources are demonstrated and new sustainable practices are proposed. Calculated results indicated that productivity could increase 50% for the best conditions analyzed.

Solidification, Macrostructure and Shrinkage Formation of Ductile and Compacted Irons

This manuscript summarizes recent investigation of the authors into the solidification and shrinkage defect formation of ductile and compacted graphite cast irons. The study makes use of the DAAS (direct austempering after solidification) technique, developed earlier by some of the authors, to reveal the solidification grains. In addition, color metallography is used to reveal the microsegregation pattern. The formation of shrinkage defects is related to both the solidification macrostructure and the microsegregation pattern. The examination of the macrostructure shows that large solidification grains, composed by dendritic austenite and graphite, characterize the solidification of compacted graphite irons of carbon equivalent values ranging from hypoeutectic to hypereutectic. Similar results are observed for ductile iron, but in this case, the hypereutectic irons display a finer macrostructure. The characteristics of the primary austenite dendrites are revealed by the microsegregation pattern, which is exposed by the color etching reagent. This pattern also clarifies the nature of the interaction between the growing austenite and the compact and spheroidal graphite particles. The microshrinkage cavities in both ductile and compacted graphite irons form at the interior of the austenite grains, where fluid feeding cannot compensate the contraction of the last-to-freeze portions of the melt. Schematics of the solidification of ductile and compacted irons are proposed, accounting for the experimental observations.

Kinetics of dielectric coating formation on iron powders to obtain soft magnetic composite materials

The paper justifies the significance and effectiveness of silicate-containing inorganic coating usage as an electric insulator in the production of soft magnetic composite materials (SMCM) from iron powders. The study demonstrates the effect of sodium silicate (Na 2 O–SiO 2 ) concentration in the water solution on the kinetics of dielectric coating formation on different iron powder grades, as well as on their weight gain, average coating thickness, as well as physical and process characteristics. It is experimentally established that the influence of iron powder particle morphology and surface tension coefficient at solid-liquid interface on the coating thickness can be assessed indirectly by the wettability indicators, in particular, by the contact angle. The features of SMCM interlayer boundary structure formation are described. Elemental mapping using the energy dispersive X-ray spectrometer shows that after sample pressing at 600 MPa and their subsequent heating within 400–600°C, the coating thickness changes and silicon is partially redistributed in the dielectric layer. This is determined by the fact that silicon featuring higher oxophilicity than iron actively reacts with oxygen adsorbed on the iron particle surface and/or reduces iron oxides forming SiO 2 in the form of a dense film, which on the one hand protects iron particles from oxidation, and on the other hand forms a dielectric layer in the zone of iron particle contact that affects specific magnetic losses. It is determined that the distinctive feature of coated iron powder compaction is the structural deformation predominance during pressing since the coating reduces the internal friction coefficient. It is shown that according to its magnetic characteristics, the developed SMCM meets essential contemporary requirements for soft magnetic composite materials.

Regeneration of zero-valent iron powder by the cocatalytic effect of WS2 in the environmental applications

One of the biggest problems of microsized iron powder (mZVI) is that with the occurrence of redox reactions, a compact iron oxide shell can be formed on the surface of mZVI, which eventually leads to the catalyst poisoning and inactivation. Here, commercial WS2 is employed for accelerating Fe3+/Fe2+ cycle and foreclosing passivation of mZVI to achieve the regeneration of mZVI for the first time. After 10 cycles oxidation, WS2 cocatalytic effect can make the mZVI/H2O2 maintain the degradation rate of 99% for the remediation of organic pollutants. Moreover, it is found that WS2 can realize the regeneration of mZVI after the reduction of heavy metal ions (Cr6+, Cu2+ and Ni2+), especially, the removal rate of Ni2+ can be recovered from 9.2% back to 30.8%. The enhanced activity and stability can be ascribed to the double active sites on WS2 and mZVI surfaces. The exposed active W4+ sites on WS2 surface can accelerate the Fe3+/Fe2+ cycling reaction, and the active Fe0 active sites can increase the circulation of iron and tungsten ions simultaneously. This research provides a new approach for the regeneration of mZVI during the redox reaction in environmental application, which makes it possible to use mZVI to treat sewage on a large scale.

Three-dimensional transfer of Cr(VI) co-precipitated with ferrihydrite containing silicate and its redistribution and retention during aging

Understanding the redistribution and retention of chromium(VI) (Cr(VI)) co-precipitated with silicate-containing ferrihydrite during aging is essential to the stabilization and immobilization of Cr(VI) in nature. In this work, Cr(VI) was removed by co-precipitated with silicate-containing ferrihydrite with various Si/Fe ratios at different precipitating pH. The co-precipitates were characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy before and after aging for 9 days at 80 °C. Results showed that silicate not only competed with Cr(VI) adsorbed on ferrihydrite surface by forming inner-sphere complexes, but also inhibited ferrihydrite transforming into more stable and compact iron phases. Ferrihydrite only transformed to hematite at pH0 5.0, and converted to hematite and goethite at pH0 7.5 and 10.0. Cr(VI) was initially removed by silicate-containing ferrihydrite with the removal efficiencies > 99.64% at initial pH of 5.0, and it was obviously incorporated into hematite and goethite during the transformation of ferrihydrite. The transformation products influenced the redistribution of Cr(VI), which was beneficial to the retention of Cr(VI) inside the co-precipitates, but not conducive to the adsorption for Cr(VI). The findings that Cr(VI) was removed by a common and metastable precursor of silicate-containing ferrihydrite can promote understanding of three-dimensional transfer and behavior of Cr(VI) during the transformation of silicate-containing ferrihydrite.

Enhanced magnetic properties of Fe-based nanocrystalline composites by addition of carbonyl iron powders

Fe-based nanocrystalline/carbonyl iron hybrid soft magnetic composites (N/C HSMCs) with excellent comprehensive magnetic properties were fabricated by cold compaction of gas-atomized FeSiBPNbCu amorphous powder and carbonyl iron powder (CIP). Upon annealing at the optimum temperature, the N/C HSMCs demonstrated excellent magnetic properties including a high permeability range from 104 to 124, high-frequency stability up to 1 MHz, superior DC-bias permeability increase from 58 to 86% at a bias field of 50 Oe, and low core loss that regulated less than 1200 mW/cm3 and reduced to as low as 732 mW/cm3 at 100 kHz for Bm = 0.1 T. The ameliorative magnetic properties of the present N/C HSMCs can be attributed to the addition of CIP, which typically enhances the monolithic saturation magnetic flux density and rebuilds the chain structures in a more integrated formation. Further, the precipitation of an ultrafine α-Fe(Si) phase in the amorphous matrix and a uniform insulation layer covered with the powder were the foundation for numerous other superior performance results.

Dielectric barrier discharge plasma assisted CO2 conversion: understanding the effects of reactor design and operating parameters

The experimental study of CO2 conversion is carried out in a coaxial cylinder dielectric barrier discharge reactor at atmospheric pressure, investigating the effects of internal electrode and different plasma processing parameters (discharge frequency, input power and feed flow rate) on CO2 conversion and energy efficiency. The major products of CO2 splitting are CO and O2. The results show that the use of compact conductive powder as internal electrode gives rise to a stronger discharge, higher energy efficiency, maximum CO2 conversion and CO yield. Using copper powder as inner electrode obtains the enhanced CO yield, increasing by 138.46% than that of an electrode made of compact carbon powder and 50.33% than that of an electrode made of compact iron powder. Discharge frequency has a weak effect on CO2 conversion and energy efficiency when other parameters are kept constant. The higher input power or the lower CO2 flow rate leads to the increase of CO2 conversion, while energy efficiency descends. In addition, the produced activated species in CO2 plasma are detected via spectrum analysis, including CO, and OH.

Compaction of porous powder body consisting of the elastic­plastic medium

In the development of technological processes of producing cold-pressed sintered parts of low porosity, special attention is paid to the mechanism of density variation. In powder metallurgy, a multicomponent charge consisting of plastic metals, as well as poorly compressible inclusions and compounds, is often used. Such charge can equally be attributed to the charge consisting of iron powder, cast iron and glass. In this charge, the first component (base) is ductile iron, and the other two, cast iron and glass, are elastic components. It is of some interest what kind of compaction can be obtained in this case and what resulting equations can be used to estimate the mechanics of compaction of such a powder charge. The resulting equations of compaction of porous powder bodies of iron-cast iron-glass are proposed. The analysis of the isotropic, rigid-plastic hardening material such as iron-cast iron-glass is given. When compacting such a material, the rate of energy dissipation (pressing pressure) is determined by the rate of volume and form change of the body. It is shown that the difference between compressed (cast iron and glass) and plastic compacted (iron) materials forms special mechanical properties of the matrix. Consequently, hydrostatic pressure can affect the form change of the body, and shear stresses – volume change. The results of the mathematical approach to obtaining the resulting equations of compaction of the elastic-plastic medium showed the way to build a theory of plasticity of the compacted body, which eliminates the need to take into account the type of loading surface. When accounting the loading surface, it is impossible to obtain universal equations of compaction of the porous elastic-plastic medium. It is shown that to apply the classical formulation of the model of the elastic-plastic compacted body, it is necessary to assume that the loading surface is convex-closed

Polydopamine-Derivated Hierarchical Nanoplatforms for Efficient Dual-Modal Imaging-Guided Combination in Vivo Cancer Therapy.

Exploring multifunctional nanomaterials from biocompatible constituents, with integrated imaging and targeted combination therapeutic modalities of tumors in vivo, provides great prospects for clinical cancer theranostic applications. Here, we report a combination strategy for functionalization of polydopamine (PDA) nanohosts with magnetic response and stimuli-controlled drug release capabilities for in vivo cancer theranostic. The high processability of PDA as nanotemplates and surface coating layers as well as its natural affinity to metals facilitated the sandwich of a compact iron oxide nanoparticle layer into the PDA matrix, realizing enhanced near-infrared (NIR) photothermal conversion and strong superparamagnetic responsiveness. Additionally, the high reactivity of the PDA surface allowed facile linkage with reduction-responsive prodrugs and polyethylene glycol chains for in vivo chemotherapy of cancer. Under the magnetic resonance imaging/photoacoustic imaging dual-modal tumor imaging and active magnetic tumor targeting of the nanoagents in vivo, the effective tumor eradication was achieved via synergetic NIR photothermal ablation and anticancer drug delivery.

Prevention of seizure in ejection of compact by control of internal diameter of container

To decrease the ejection force and to prevent the seizure during ejection in compaction of iron powder without lubricant, a compaction process using control of an internal diameter of a die using a shrinkage ring is developed. The internal diameter before the compaction is decreased by inserting the container into the shrinkage ring, and the internal diameter after the compaction is increased by releasing the shrinkage ring from the die. The friction during the ejection of the compact is decreased by the difference in elastic recovery between the die and compact.

A modified diametrical compression test technique (MDCTT) for mode II fracture toughness of iron powder compact

A sound knowledge of the fracture properties of a powder metallurgy (PM) component is essential for a design engineer to predict or prevent sudden fracture failure. Though iron powder is the most used base material in the PM industries, only its tensile mode fracture toughness (KIC) has been documented. This lack of adequate data can be traced to the non-availability of suitable test technique. In this paper, we present a new test approach for determining the mode II (shear mode) fracture toughness (KIIC) of iron powder compact. This method is known as the modified diametrical compression test technique (MDCTT). The MDCTT combined the qualities of diametrical compression test specimen with the pure shear mode failure of a riveted lap joint. The fracture toughness of copper powder compacts was also studied to corroborate the results of this technique. A comparison of the ratios KIICKIC for both powder compacts with theoretical predictions made using the maximum tangential stress criterion show strong agreement. Hence, the MDCTT is a suitable technique for determination of the KIIC values for iron and other metallic powder compacts.

Dry sliding of a low steel friction material against cast iron at different loads: Characterization of the friction layer and wear debris

Pin-on-disc testing was used to investigate the sliding behavior and the wear products of a low-steel friction material against a cast iron disc at different applied loads, to investigate the effect of the temperature rise induced by frictional heating. The testing rig was operated in a clean chamber with a purified incoming air flux. The outgoing flux carries the wear particles to an impactor that counted and sorted them by average diameter and weight. At increasing applied loads, corresponding to a proportional increase of the pin-disc contact temperature, the coverage of both the pin and disc surface by a friction layer was found to increase too. The relevant X-Ray diffraction patterns revealed the presence of a large amount of graphite and different compounds originating from the friction material and from the counterface disc, mainly iron oxides, as concerns this latter. After the test at the lowest investigated load, i.e., 1kg, the disc worn surface exhibited abrasive grooves and a discontinuous friction layer mainly made of compacted iron oxide particles. After the test at higher loads, i.e., 5 and 7kg, the disc surface was covered by a compact friction layer. As concerns the friction layer on the pins, most of the ingredients from the friction material were detected, in association with the iron oxides from the disc. These results can be interpreted in terms of the temperature stability range of the phenolic resin used as a binder of the friction material. The characterization of the collected airborne wear debris showed that the particles produced by the low temperature (i.e., low load) test were mostly equiaxed; whereas those produced by the high temperature (i.e., high loads) tests, predominantly displayed a plate-like morphology. The mechanisms of their formation in relation to the characteristics of the friction layers are illustrated and discussed.

Discrete particle simulation of solid flow in a melter-gasifier in smelting reduction process

Smelting reduction process is one of the promising technologies that produce liquid iron with advantages in the reduction of costs and adverse effect on environment. In this process, the main reactor of Melter-Gasifier (MG) involves complicated multiphase flow, heat and mass transfer phenomena, in which solid flow plays a dominant role. In this work, the solid flow behavior in an MG is investigated by discrete particle simulation under different conditions. The results show a good agreement with the observations in experiments. It reveals that three stagnant zones are formed: one is at the MG central bottom, and the other two are located on the side walls. The analysis indicates that charging method, MG geometry, and particle-wall frictional force are factors affecting the size of the stagnant zones on the side walls. Rolling friction does not affect solid flow much. Particle scale analysis of solid flow and force structures is also conducted, showing that strong forces exist in the regions with low porosity. The analysis of particle mass fraction shows that at the MG upper part, HCI (hot compacted iron) particles dominate the MG center, and coal particles tend to distribute to the side walls.

Pin-on-disc tribotests with the addition of Cu particles as an interfacial media: Characterization of disc tribosurfaces using SEM-FIB techniques

The present paper focuses on the effect of Cu addition (400μm, 20μm and 50nm) on the microstructure and topography of discs after pin-on-discs tribotests (steel/steel). These results were compared with the condition without any particulate addition. SEM, FIB, EDS and XEDS techniques were used to characterize the discs’ tribosurfaces. X-ray mapping characterization showed O associated with Fe adhered to the tribosurfaces for all conditions. Additionally, expressive adhesion of Cu particles on the disc tribosurface was detected via FIB combined with XEDS mapping for the 20μm and 50nm conditions. The formation of a compact iron oxide layer on the discs´ tribosurface was only observed for the 400μm Cu condition and without any Cu addition.

Effect of cooling rate and of titanium additions on the microstructure of thin-walled compacted iron castings

This article addresses the effect of cooling rate and of titanium additions on the exhibited microstructure of thin-walled compacted graphite iron (TWCI) castings as determined by changing moulding media, section size and ferrotitanium. Various moulding materials were employed (silica sand and insulating sand ‘‘LDASC’’) to achieve different cooling rates. This study shows that the cooling rates exhibited in the TWCI castings varies widely (70–14 °C/s) when the wall thickness is changed from 2 to 5 mm. In turn, this is accompanied by a significant variation in the compacted graphite fraction. The resultant cooling rates were effectively reduced by applying an insulating sand in order to obtain the desired graphite compactness. Ti additions in combination with LDASC sand moulds were highly effective in promoting the development of over 80% compacted graphite in castings with wall thicknesses of 2–3 mm as evidenced by quantitative metallographic analyses.

Microstructure and Mechanical Properties of Austenitic Compacted Cast Iron with Additive Manganese

High composition of austenitic matrix in microstructure is contributed to its special characteristic in reducing cracking and distortion. This special alloy will be in austenitic matrix when high temperature and also at room temperature which make it successful avoid matrix volume changes. In this study, austenitic compacted iron with minimum nickel contain of 12wt% is produced by using in-mould magnesium treatment. Magnesium Ferro Silicon (MgFeSi) used in determining the graphite form. Some of nickel replace by manganese in range of 9wt% to 12wt% Mn while Nickel remain at 12wt% Ni at all parameter. This research focuses on to investigate the effect of alloying elements on microstructure and mechanical properties. The outcome compared to standard of unmodified austenitic cast iron as in ASTM standard. The matrix obtained was all in austenitic matrix with the presence of compacted graphite distribution throughout the matrix. It is appeared that result shows increment of manganese at the centre region between graphite in the microstructure. It is occurred when percentage of manganese addition was increased. There are increases in hardness compared to unmodified austenitic iron. Tensile strength decreases when the manganese content increases in alloy.

Simulation of Cylinder Deformations during Honing of Thermally Coated Running Surfaces in Crankcases

The internal combustion engine of the future has to cope with increasing high requirements. A large potential is seen in reducing friction in the piston group. For this purpose a coating technology for cylinder running surfaces, including mechanical machining processes was developed. By substituting the compact cast iron liners (4 mm wall thickness) for the thin coating layer (0.1 mm) the normal forces become more important in the honing process. Due to the different stiffness of the crankcase roundness deviations occur caused by the machining forces as a result of elastic deformation. Content of this paper is the calculation of the elastic deformations using the finite element method. Based on a honing tool model, the effective normal forces are calculated, which afterwards are used as input variables for the crankcase model.

Magnetic properties of iron-based soft magnetic composites with SiO2 coating obtained by reverse microemulsion method

Abstract In this work, iron-based soft magnetic composites coated with the amorphous SiO2 layer have been fabricated by utilizing tetraethoxysilane in the reverse microemulsion method, and then the effects of addition amount of SiO2 and annealing temperature on the magnetic properties were investigated. The results show that the surface of iron powders contains a thin amorphous SiO2 insulation layer, which effectively decreases the magnetic loss of synthesized magnets. The magnetic loss of coated samples decreased by 87.8% as compared with that of uncoated samples at 150 kHz. Magnetic measurements show that the sample with 1.25 wt% SiO2 has an acceptable real part and minimum imaginary part of permeability in comparison with other samples. Also, the annealing treatment increased the initial permeability, the maximum permeability and the magnetic induction and decreased the coercivity with increasing temperature in the range 300–600 °C. The results of the loss separation imply that the annealed SMCs have a higher hysteresis loss coefficient (k2) and lower eddy current loss coefficient (k3) as compared with the pure iron compacts after the same heat treatment due to the preservation of the SiO2 layer.

Examination of Electrical Conduction of Carbonyl Iron Powder Compacts

In this study, we report the electrical conduction of carbonyl iron powder compacts when a constant voltage/current source is supplied, especially under a typical voltage 9.7V of electric current activated sintering (ECAS). The potential driving forces for resistance drop during stressing, including bulk temperature-dependent and -independent, were discussed. By using a proposed competition mechanism and percolation theory, it can successfully describe electrical behavior in metal powder compacts. The results indicate bulk temperature rise resulting from Joule heating is the main cause for the formation and growth of metallic contact at particle interfaces during ECAS. [doi:10.2320/matertrans.M2014311]

Iron oxide nanoparticle layer templated by polydopamine spheres: a novel scaffold toward hollow–mesoporous magnetic nanoreactors

Superparamagnetic iron oxide nanoparticle layers with high packing density and controlled thickness were in situ deposited on metal-affinity organic templates (polydopamine spheres), via one-pot thermal decomposition. The as synthesized hybrid structure served as a facile nano-scaffold toward hollow-mesoporous magnetic carriers, through surfactant-assisted silica encapsulation and its subsequent calcination. Confined but accessible gold nanoparticles were successfully incorporated into these carriers to form a recyclable catalyst, showing quick magnetic response and a large surface area (642.5 m(2) g(-1)). Current nano-reactors exhibit excellent catalytic performance and high stability in reduction of 4-nitrophenol, together with convenient magnetic separability and good reusability. The integration of compact iron oxide nanoparticle layers with programmable polydopamine templates paves the way to fabricate magnetic-response hollow structures, with high permeability and multi-functionality.