Behaviour of iron ore–fuel oil composite pellets in isothermal and non-isothermal reduction conditions

Abstract

Self-fluxing iron ore pellets as an alternative to the agglomeration process led to the use of low price fuel oil as a binder and reducing material. Composite pellets containing 5–15% fuel oil were isothermally and non-isothermally reduced at 750–1000°C in a flow of H₂ or N₂ gases. The total weight loss resulting from O₂ removal from the reduction of Fe₂ O₃ and from the thermal decomposition of fuel oil was continuously recorded as a function of time at different reduction conditions. The actual reduction extent at a given time was calculated from the chemical analysis of partially reduced samples at a given time and temperature. Microscopic examination and X-ray phase analysis were applied to characterise the reduction products. The isothermal reduction of composite pellets indicated that the reduction rate increased with the increase in fuel oil content at the early stages. At the later stages, the reduction rate increased in the order 12>10>5> 15% fuel oil containing pellets. The non-isothermal reduction of composite pellets in N₂ atmosphere showed the presence of an incubation period at initial reduction stages. The low intensity magnetic separation technique was applied with the aim of increasing the iron content at the expense of associated impurities. The magnetic and non-magnetic fractions were analysed and the overall recovery was determined.     

Increase in the efficiency of electric melting of pellets in an arc furnace with allowance for the energy effect of afterburning of carbon oxide in slag using fuel–oxygen burners

The problems of increasing the efficiency of electric steelmaking using fuel–oxygen burners to supply oxygen for the afterburning of effluent gases in an arc furnace are considered. The application of a new energy-saving regime based on a proposed technology of electric melting is shown to intensify the processes of slag formation, heating, and metal decarburization.     

Kinetics and mechanism of smelting reduction of fluxed chromite Part 1 Carbon–chromite–flux composite pellets in Fe–Cr–C–Si melts

Abstract

Experimental studies on the smelting reduction of fluxed carbon–chromite composite pellets in Fe–Cr–C–Si alloys were carried out at 1520–1600°C. The reduction reaction was found to be favoured by high temperatures, a high lime addition in the pellets, a long pellet dissolution time, and a moderate melt Cr content. For a given CaO addition, however, the reduction rate initially slowed before increasing with an increasing silica addition to the pellets. A three stage reduction mechanism is proposed. The first stage is very likely to be controlled by solid state and/or gas diffusion with an apparent activation energy of 472 kJ mol^-1 for pellets fluxed with 15%CaO and 25%SiO₂ . The third stage proceeds via smelting mechanisms, with mass transfer in the slag phase possibly rate controlling.     

Oxidation resistance and strength of a molybdenum fiber–oxide matrix composite material

The oxidation kinetics of a composite material, which consists of an Al₂O₃–Al₅Y₃O₁₂ matrix and molybdenum fibers and has a high cracking resistance, is studied. The mass loss of the composite material during oxidation is shown to be several orders of magnitude lower than that of molybdenum. Oxidation in quiet air at 1250°C for several hours weakly changes the strength of the composite material at temperatures from room temperature to 1300°C. It is also shown that the strength of the composite material as a function of the oxide matrix composition (Al: Y ratio) changes nonmonotonically. The maximum strength shifts from the Al₂O₃–Al₅Y₃O₁₂ eutectic point toward garnet.     

Estimation of rate parameters for reduction of iron ore–graphite composite pellets in packed bed reactor using genetic algorithm

Abstract

A semiempirical kinetic model has been developed to determine the course of reduction of iron ore–graphite composite pellets over time in a laboratory scale side heated packed bed reactor attached with a tailor made bottom hanging thermogravimetric set-up. The rate parameters in the model, especially the three sets of apparent activation energy values and frequency factors associated with the reduction of iron oxides in three elementary steps, namely hematite to magnetite, magnetite to wustite and wustite to iron, have been estimated based on experimental data by employing an optimisation tool, the genetic algorithm (GA). The difference between the predicted and experimental degree of reduction is minimised to obtain the rate parameters. The experimental degree of reduction is calculated based on mass loss data during reduction and the exit gas analysis. Estimated values of apparent rate parameters were found to be of the same order of magnitude to their intrinsic counterparts reported in literature. Finally, by using the predicted rate parameters the temporal evolution of various oxide phases as well as pure iron has been evaluated.     

Effect of CaO on the reduction behaviour of iron ore–coal composite pellets in multi-layer bed rotary hearth furnace

The effect of CaO on the reduction behaviour of iron ore–coal composite pellets has been studied in a laboratory scale multi-layer bed rotary hearth furnace at 1250°C for 20?min. Reduced pellets have been characterised through weight loss, porosity measurement, phase analysis by XRD, and morphology study by SEM. The addition of CaO to the composite pellets showed different effects at different carbon levels. For higher carbon-containing pellets (C/Fe₂O₃ molar ratio at the upper stoichiometric level of 3), the addition of CaO increased the extent of reduction for all three layers significantly up to a certain limit (4?wt-%); and thereafter the degree of reduction is decreased with a further increase in CaO percentage in the pellets. For low carbon-containing pellets (C/Fe₂O₃ molar ratio of 1.66), the addition of CaO to the pellets did not show any beneficial effect.     

Densification and structure formation in the sintering of composite materials based on nitrides of the IV–V group transition metals. III. Sintering of composite materials in the (VN, TaN)—Cr systems

An investigation was made of densification and structure formation in composite materials in the systems (VN, TaN)—Cr during sintering in argon. It was shown that the shrinkage of these materials during liquidphase sintering is insufficient to provide dense composites (residual porosity was 35–40%). This is attributed to the low thermodynamic stability of VN and TaN, and the rapid evolution from these of nitrogen which accumulates in closed pores. Processes of heterodiffusion and alloy formation also have a negative effect on densification. Exchange reactions between chromium and the nitride-forming metals lead to the formation of a large quantities of intermetallics which embrittle the composite materials. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 13–18, January–February, 1999.     

Preparation and characterization of Ce_(0.8)La_(0.2–x)Y_xO_(1.9) as electrolyte for solid oxide fuel cells

In this study, ultrafine Ce0.8La0.2–x Y x O1.9（for x=0, 0.05, 0.10, 0.15, 0.20） powders were successfully prepared by the sol-gel method.The samples were characterized by fourier transform infrared（FTIR）, thermogravimetric and differential scanning calorimetry（TG-DSC）, X-ray diffraction（XRD）, scanning electron microscopy（SEM）, AC impedance and thermal expansion measurements.Experimental results indicated that highly phase-pure cubic fluorite electrolyte Ce0.8La0.2–x Y x O1.9 powders were obtained after calcining at 600 °C.The as-synthesized powders exhibited high sintering activity, the Ce0.8La0.2–x Y x O1.9 series electrolytes which have higher relative densities over 96% could be obtained after sintered at 1400 °C for 4 h.Ce0.8La0.15Y0.05O1.9 electrolyte sintered at 1400 °C for 4 h exhibited higher oxide ionic conductivity（σ800 oC=0.057 S/cm）, lower electrical activation energy（E a=0.87 e V） and moderate thermal expansion coefficient（TEC=15.5×10-6 K-1, temperature range 25–800 °C）.     

Synthesis and characterization of Dy-Eu-Tm co-doped cubic phase stabilized bismuth oxide based electrolytes in terms of intermediate temperature-solid oxide fuel cells(IT-SOFCs)

In this study,a new Dy-Eu-Tm co-doped cubic phase stabilized bismuth oxide solid electrolyte system was synthesized by using solid-state reaction method in atmospheric conditions.Before conductivity measurements,X-ray diffraction(XRD) pro files of the annealed samples show that created mixtures have heterogeneous phase,but after conductivity measurements,the face-centered cubic(FCC) crystal structure is stabilized for all samples.Also,the increase in total dopant rate causes an increase in full ...     

Softening–melting–dripping characteristics and evolution mechanism of vanadium-bearing titanomagnetite carbon composite briquette used as novel blast furnace burden

Vanadium-bearing titanomagnetite carbon composite briquette (VTM-CCB) was proposed as an innovative and promising blast furnace burden to realize low-carbon and...     

Interaction of iron and aluminum in the plastic deformation and fast heating of laminar Fe–Al composite

The influence of plastic deformation and the heating rate on the solid-phase interaction of steel strip and aluminum powder is investigated. Recrystallization of the contacting materials determines the phase formation. The layer thickness of the Fe–Al intermetallides is plotted as function of the strain and heating rate. On that basis, the parameters of the transition layer may be predicted in selecting the technological conditions.     

Calculation of the titanium and zirconium activities in an aluminum–calcium oxide melt

The activities of titanium and zirconium in aluminum–calcium oxide melts are calculated using the models of collective electrons and polymer theory.     

Riction properties of composite materials of the system TiN - Ain. II. Effect of oxide films on friction and wear of a ceramic material — Steel system

Friction and wear are studied for materials of the system TiN — AlN preliminary oxidized at 800–1100°C. It was established that thin oxide films containing Al₂TiO₅ and α-Al₂O₃, that promote a decrease in frictional wear, form on the surface of composite materials of the system TiN — AlN. Our assumptions are confirmed that the improvement in tribological properties of TiN — AlN composites is caused by forming oxide screening layers that prevent direct contact between the ceramics and steel counter-body. At high rates (V=16 m/sec) and pressure (P=2.0 MPa) the oxide films form more rapidly. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(411), pp. 121–124, January–February, 2000.     

Effect of the β decay of metallic fission products on the chemical and phase compositions of the uranium–plutonium nitride nuclear fuel irradiated by fast neutrons

Thermodynamic analysis of the chemical and phase compositions of uranium–plutonium nitride (U_0.8Pu_0.2)N_0.995 irradiated by fast neutrons to a burn-up fraction of 14% shows that a structure, which consists of a solid solution based on uranium and plutonium nitrides and containing some elements (americium, neptunium, zirconium, yttrium, lanthanides), individual condensed phases (U₂N₃, CeRu₂, Ba₃N₂, CsI, Sr₃N₂, LaSe), metallic molybdenum and technetium, and U(Ru, Rh, Pd)₃ intermetallics, forms due to the accumulation of metallic fission products. The contents and compositions of these phases are calculated. The change in the chemical and phase compositions of the irradiated uranium–plutonium nitride during the β decay of metallic radioactive fission products is studied. The kinetics of the transformations of ⁹⁵Nb₄₁N, ¹⁴³Pr₅₉N, ¹⁵¹Sm₆₂N, and ¹⁴⁷NdN into ⁹⁵Mo₄₂ + Ns.s., ¹⁴³Nd₆₀N, ¹⁵¹Eu₆₃N, and ¹⁴⁷SmN, respectively, is calculated.     

Diffusion coefficients of the uranium(III) and (IV) ions in the LiCl–KCl–CsCl eutectic melt

Diffusion coefficients of the uranium(III) and (IV) ions in the eutectic melt of the lithium, potassium, and cesium chlorides in the temperature range of 573–1073 K have been determined using two independent methods: cyclic voltammetry and chronopotentiometry.     

Preparation and investigation of Ce_(0.4)Zr_(0.5–x)Y_(0.1)Mn_xO_2 oxygen-storage materials

A series of Ce0.4Zr0.5-xY0.1MnxO2(0     

Interfacial morphologies between NiO–YSZ fuel electrode/316 stainless steel as interconnect material and B‐Ni3 brazing alloy in solid oxide fuel cell system: effect of joint loading during brazing

Abstract

Joining of NiO–YSZ composite with 316 stainless steel was carried out using B‐Ni3 brazing filler alloy (Ni–4·5Si–3·2B–0·06C–0·02P, wt‐%; melting point, 982–1038°C) and two samples were fabricated. On the one hand, interfacial (chemical) reactions during brazing at the NiO–YSZ/316 stainless steel interconnect were promoted only by addition of an electroless nickel plate to NiO–YSZ composite as a coating with relevant process variables and procedures optimised during the electroless nickel plating. On the other hand, moderate loading was applied during brazing normal to the joint surface where electroless nickel plate was coated previously to improve interfacial sealing of the NiO–YSZ cermet anode/316 stainless steel interconnect structure for use in a solid oxide fuel cell. A special fixture for static loading was designed for filler metal alloy strips to be preplaced at the joint surface where static loading was applied perpendicular to it for the promotion of liquid alloy layer formation during brazing. Brazing was performed in a cold wall vacuum furnace at 1080°C and post‐brazing examination of interfacial morphologies between NiO–YSZ composite and 316 stainless steel was performed using SEM and EDS analyses. The results indicate that B‐Ni3 brazing filler alloy was fused fully during brazing and continuous interfacial layer formation and joint integrity were significantly affected by applied static loading during brazing. The loading most probably contributed to promotion of the B‐Ni3 liquid phase formation in the joint. However, the thickness of the interface area remained almost the same at 100?μm for loaded and unloaded joints.

On a assemblé le composite NiO–YSZ avec l’acier inoxydable 316 en utilisant l’alliage d’apport de brasage B‐Ni3 (4·5% en poids Si, 3·2% en poids B, 0·06% en poids C, 0·02% en poids P, et le reste, Ni, point de fusion 982–1038°C) et l’on a fabriqué deux échantillons. D’un côté, on a stimulé les réactions interfaciales (chimiques) lors du brasage à l’interconnexion NiO–YSZ/acier inoxydable 316 uniquement par addition d’un revêtement autocatalytique de nickel au composite NiO/YSZ, les variables pertinentes du procédé et les procédures étant optimisées lors du dépôt autocatalytique de nickel. D’un autre côté, lors du brasage, on a appliqué une charge modérée, normale à la surface du joint, où l’on avait auparavant déposé le nickel autocatalytique, pour améliorer le scellement interfacial de la structure de l’interconnexion de l’anode cermet NiO–YSZ/acier inoxydable 316 pour utilisation dans une SOFC (pile à combustible à oxyde solide). On a créé un montage spécifique pour charge statique pour que les rubans d’alliage de métal d’apport soient préplacés à la surface du joint où la charge statique était appliquée perpendiculaire à celui‐ci pour promouvoir la formation d’une couche d’alliage liquide lors du brasage. On a effectué le brasage dans un four à vide à paroi froide à 1080°C et, après le brasage, on a examiné les morphologies interfaciales entre le composite NiO–YSZ et l’acier inoxydable 316 en utilisant les analyses de SEM et d’EDS. Les résultats indiquent que l’alliage d’apport de brasage B‐Ni3 était complètement fusionné lors du brasage et la formation d’une couche interfaciale, continue, ainsi que l’intégrité du joint étaient affectées significativement par la charge statique appliquée lors du brasage. La charge a fort probablement contribué à la promotion de la formation de la phase liquide de B‐Ni3 dans le joint. Cependant, l’épaisseur de la région d’interface demeurait presque la même à 100?μm pour les joints avec ou sans charge.