THE VARIATION IN INTRINSIC COERCIVITY OF IRON–COBALT POWDERS PREPARED BY ELECTROLYSIS INTO MERCURY

Abstract

Iron, cobalt, and iron–cobalt alloy particles in mercury have been prepared by electrolysis over a mercury cathode. The intrinsic coercivity at ?70°C. of these particles has been measured, as deposited and after various heat-treatments; a marked difference in properties is found, which is dependent not only on heat-treatment, but also on whether or not the cathode was stirred during electrolysis. The effect of further metal additions to the iron–cobalt–mercury system is noted. In the discussion an attempt is made to explain the differences observed.     

Improvement of fatigue properties of PM steels by shot peening

Abstract

Shot peening was used for improving the fatigue properties of Fe–2Cu–0·5C PM steel. The steel is generally used for production of high performance sintered parts such as small connecting rods for cooling system compressors. To distinguish the effects of each alloying element, Fe, Fe–2Cu, and Fe–0·5C were also investigated. Optimum shot peening intensities are: 25A for pure iron and Fe–2Cu, 30A for Fe–0·5C, and 35A for Fe–2Cu–0·5C. For these intensities, improvements of the fatigue strengths of the materials investigated are as follows: 31% for pure iron, 48% for Fe–0·5C, 46% for Fe–2Cu, and 38% for Fe–2Cu– 0·5C. From the experimental results it could be concluded that both of the alloying additions, carbon and copper, are contributing to the fatigue strength improvements by shot peening.     

Reactive sintering in Fe-Co system

Abstract

Low porosity powder metallurgy compacts have been manufactured from treated elemental iron and cobalt powders sintered at 1150°C under an H_2(g) atmosphere. Their microstructures consist of an interconnected mixed oxide network which encapsulates both the iron and cobalt phases. The production technique employed is an innovative process termed reacto-thermitic sintering (RTS), which leads to near full density and near net shape parts utilising conventional uniaxial compaction and mesh belt furnace practices. The RTS technique relies on microscale exothermic reaction between small quantities of added elemental Al and oxides present on the surface of the bulk powder, together with the bulk powder itself. This results in the production of a transient liquid phase which freezes rapidly and consolidates the compact without slumping. In order to generate an interconnected mixed oxide network, experiments were designed such that the Al powder reacts with the cobalt and the surface of the iron powder which is artificially doped with Fe and Cr oxides.

Differential thermal analysis (DTA) and energy balance calculations revealed that the Al and the oxide coating reaction does not proceed directly. Instead the main contribution to the exothermic process is the reaction between Al and Co/Fe. The system does not exhibit true RTS behaviour and the interconnected network of mixed Al, Cr, and Fe oxides is created by subsequent reaction of Co-Al and Fe-Al intermetallics with the artificial Fe-Cr oxide coating on the Fe. The microstructure obtained exhibits negligible porosity with the metallic particles on the whole fully encapsulated by the oxide.     

Studies on Processing of an Alnico Scrap

Abstract

This paper presents the results of research and development work on processing of alnico scrap, a secondary resource of nickel and cobalt, generated during the manufacturing of alnico magnets. The scrap contains 8-10% nickel, 10-12% cobalt, 32-50% of iron, 8-10% aluminium, 2% copper and remaining silica. Various processes such as acid leaching, aqueous chlorine leaching, salt roasting and cupric chloride leaching were studied in detail. Of these cupric chloride leaching was found to be most effective with respect to recovery and purity. It has been possible to obtain pure nickel and cobalt salts by cupric chloride leaching of the scrap, solvent extraction and precipitation of the salts. The overall recovery by the above process was almost 99%.     

Investigation of kinetics of coal based reduction of oolitic iron ore

Abstract

An oolitic iron ore was isothermally reduced by coal at 1423–1573 K, and the reduction kinetics was investigated in detail. The degree of reduction and reduction rate increased with increasing temperature and C/O molar ratio to some extent at the same reduction time. In the entire reduction process, the reduction mechanism changes with changing experimental conditions. The degree of reduction under different experimental conditions should be represented by different reduction kinetic models. The reduction rate curves are similar in shape and could be analytically divided into initial, intermediate and final stages. The apparent activation energies of the three stages are 48·26, 69·80 and 127·58 kJ mol^?1 respectively. The rate controlling mechanism in the reduction process was determined by analysing the reduction process and apparent activation energy. The rate controlling steps of these stages are combined gas diffusion and interfacial chemical reaction, surface chemical reaction and combined solid state diffusion and boundary reaction.     

Experimental study on solid state recovery of metallic resources from EAF dust

Abstract

A new process to recover iron and zinc from electric arc furnace (EAF) dust in a solid state has been developed. It comprises three steps: (1) reduction of dust (<1000°C) using gas reductant with high H₂ or CO content; (2) for the solid product of step (1), wet magnetic separation to separate Fe from gangue; and (3) for the condensed fumes collected in step (1), water washing to remove soluble compounds like KCl and enrich and recover the zinc oxide. The performance of this process indicates that four kinds of resources could be obtained, iron rich materials (TFe?=?92·3%); enriched zinc-rich materials (ZnO?=?83·7%); gangue produced in the wet magnetic separation, which can be used as a building material, and KCl solution. The process is greatly energy saving since it is carried out at low temperature so that sintering would not happen. This means that the iron can be separated directly by physical methods which avoid crushing and grinding.     

Research on slag modifying agents for CaO–Mg based hot metal desulphurisation

Abstract

To improve the slag/iron separation problems in CaO–Mg based hot metal desulphurisation, experiments were carried out to generate a more fluid slag and to reduce the amount of hot iron entrapped within the desulphurising slag. The optimised slag modifying agent effectively decreased the melting temperature and viscosity of CaO–Mg based desulphurising slag. The optimised modifying agent has been successfully applied to industrial production. Industrial tests show that the average desulphurisation exceeded 82% when using the 80CaO–15Mg–5CaF₂ desulphurising agent at 3·5–4·0 kg t^–1, and with an average final S of 0·005%. The skimming time decreased from nearly 12 min to ～6·5 min. The heat loss during desulphurisation decreased to ～19°C which is favourable to the subsequent steelmaking process. Average total Fe content in post-desulphurisation slag is 34% with 0·7–0·8 kg t^–1 modifying agent, a decrease of ～30% in iron loss compared with current status.     

Behaviour of manganese oxides during magnetising reduction of Baharia iron ore by CO–CO2 gas mixture

Abstract

High manganese containing iron ore samples were isothermally reduced with a CO–CO₂ gas mixture at 600–1000°C. The course of reduction was followed by a weight loss technique. The influence of reducing gas composition and temperature on the reduction kinetics was investigated. The different phases formed during reduction were identified by X-ray phase analysis, while their structures were microscopically examined. The reduced samples were magnetically tested by means of a Davis tube tester. The effect of grain size, drum speed, and cleaning conditions on the efficiency of magnetic separation was studied using a Box-Mag wet low intensity magnetic separator. The separation efficiency was determined by analysing total iron, manganese, and acid insoluble contents in both magnetic and non-magnetic fractions. Best testing results were obtained on separation of the sample reduced with 80CO–20CO₂ (vol.-%) at 800°C. The optimum grain size for magnetic separation is below 0·15 mm while that of the drum speed is 100 rev min^-1 . The cleaning of the magnetic fraction increases the iron content and decreases the manganese and acid insoluble contents.     

The deposition of cobalt on iron powder by means of the cementation reaction

A preliminary investigation has been undertaken of the feasibility of depositing cobalt on iron powder by means of the cementation reaction. Three different solutions were considered, cobalt chloride, cobalt sulphate and cobalt nitrate. No attempt was made to control the pH although its value was monitored during the cementation reaction. The most successful salt type was found to be the chloride which gave conversions of approximately 80% from a solution that contained 150 gl⁻¹ CoCl₂·6H₂O at 70°C. The morphology of the cemented particles appeared to be independent of the type of cobalt salt used, although the rates of deposition were significantly influenced by the type of anion in solution. The cemented product appeared to nucleate heterogeneously at discrete cathodic sites on the iron-particle surface as a fine nodular deposit. These nodules eventually grew and coalesced to form a porous coating, leaving a residual iron core in the centre of the particle. Cessation of cobalt deposition occurred when the mean particle-coating composition attained approximately 80 wt% Co, 20 wt% Fe. At this stage the iron cores of the particles still had access to the solution through long, narrow, interconnecting channels within the deposit. The solution still possessed a relatively high concentration of cobalt so depletion of this cation was not responsible for cessation of the cementation reaction.     

Effect of alumina on slag–metal separation during iron nugget formation from high alumina Indian iron ore fines

Abstract

Iron nuggets can be obtained from ore–coal composite pellets by high temperature reduction. Alumina in the ore plays a vital role in slag–metal separation during nugget formation, as it increases the liquidus temperature of the slag. In this study, the effect of carbon content, reduction temperature and lime addition on slag–metal separation and nugget formation of varying alumina iron ore fines were studied by means of thermodynamic modelling. The results were validated by conducting experiments using iron ore fines with alumina levels ranging from 1·85 to 6·15%. Results showed that increase in reduction temperature enhances slag metal separation, whereas increasing alumina and carbon content beyond the optimum level adversely affects separation. Carbon below the required amount decreases the metal recovery, and carbon above the required amount reduces the silica and alters the slag chemistry. Optimum conditions were established to produce iron nuggets with complete slag–metal separation using iron ore–coal composite pellets made from high alumina iron ore fines. These were reduction temperature of 1400°C, reduction time minimum of 15 min, carbon input of 80% of theoretical requirement and CaO input of 2·3, 3·0 and 4·2 wt-% for 1·85, 4·0 and 6·15 wt-% alumina ores respectively.     

SINTERING KINETICS IN IRON-COPPER ALLOYS WITH AND WITHOUT A LIQUID PHASE

Abstract

Sintering of iron-copper alloys has been studied in the temperature range 950–1250°C. The factors involved include compacting pressure, sintering temperature, sintering time, and atmosphere. The results are interpreted as a decrease in pore volume due to the filling of voids between particles by a diffusion mechanism. An empirical equation of the Arrhenius type, based upon volume change as a function of sintering time, has been derived in order to evaluate the rate constant of the sintering process.

Volume diffusion is considered to be the primary mechanism of material transport in alloys containing 0·5–2·0% copper, when sintered in the range 950–1250°C, and in alloys containing 5·0–10·0% copper, when sintered in the range 950–1050°C. The activation energy derived for the sintering process is 53·4 kcal/mole. Surface diffusion appears to be the operative mechanism of material transport in alloys containing 5·0–10·0% copper, when sintered above the melting point of copper. The activation energy for this sintering process is 32·6 kcal/mole.     

Characteristics of steelmaking flue dust

Abstract

The physicochemical and surface properties of steelmaking flue dust have been investigated by scanning electron (SEM) and X-ray diffraction (XRD) measurements, chemical analysis, FT-IR studies, zeta potential measurement, Brunauer–Emmett–Teller (BET) surface area determination, and potentiometric titration techniques. The results show that the dust consists of very fine spherical particles, which contain mainly iron oxide, iron ferrite, calcium (magnesium) oxide, calcium (magnesium) carbonate, and other metal oxides. The dust possesses a high BET surface area (14·65 m² g^-1 ) and a reversible surface charge. The point of zero charge pH_pzc of the surface is around pH 6. Solubility tests show that the dust releases very little heavy metals in solution in the pH range 4·5–11·8 and has a high capacity to neutralise strong acid in solution.     

草酸盐湿式沉淀-煅烧分解法制备四氧化三钴及其表征

以氯化钴、草酸铵为原料,吐温80(Tween-80)为表面活性剂,通过湿式沉淀法合成氧化钴的前驱体,再通过热分解制备四氧化三钴。采用扫描电镜、X射线衍射仪、热分析仪分析了钴氧化物前驱体和钴氧化物的形貌、晶体结构和热分解等特征。结果表明:以草酸盐为沉淀剂制得的钴氧化物前驱体为CoC_2O_4·2H_2O,前驱体于600℃煅烧4 h后可得到较纯的四氧化三钴粉末,并且基本保持了前驱体原来的形貌,仍为针(棒)状,粒子边缘变得光滑。     

On suitability of novel fluidised bed technique for separation of metallic powders during commercial powder metallurgical processing

Abstract

Experiments have been performed to test the efficiency with which a novel fluidised bed technique could separate different metallic powders in terms of size and density. The overall aim was to assess the potential of this technique for the commercial separation of defective powder fractions from mechanically alloyed (MA), iron based powders. Separation in terms of size was readily achieved, with the largest powder particles sinking to the bottom of the fluidised bed. In a simulated commercial process, density separation of defective Fe₃Al powder could not be demonstrated as any differences in density were overshadowed by size and morphology differences. However, from a batch of iron based powder (ρ=8·02 g cm^?3), seeded with six other metallic powders, aluminium powder (ρ=2·70 g cm^?3) segregated strongly to the top of the bed from where samples containing 93 vol.-%Al were taken. The process is thought to be sensitive to differences in density of a factor of 1.1–3.     

THE PRODUCTION OF GRAIN-ORIENTED 50 : 50 NICKEL–IRON MAGNETIC STRIP BY COLD ROLLING FROM SINTERED COMPACTS

Abstract

50 : 50 nickel–iron strip was cold rolled from sintered compacts to thicknesses of 0·0015 and 0·004 in., with final reductions of 92–99%. After annealing at 1050°–1200° C., the cube texture developed, thus giving a material with a rectangular hysteresis loop when magnetized in either the rolling or the transverse direction.

The alloys with the best magnetic properties contained 48–50% nickel. In this range of composition the remanence ratio and coercivity varied from 0·91 to 0·94 and 0·11 to 0·19 respectively, depending upon the processing schedule used.

With the recommended processing schedule, values for the remanence ratio and coercivity of 0·92–0·94 and 0·11–0·13 respectively were obtained.

Unlike the texture of strip rolled from a conventionally cast ingot, the development of cube texture in strip rolled from a sintered compact is not critically dependent on the temperature of the final anneal.     

Solubility of oxygen in Fe–Co melts containing titanium

Solutions of oxygen in Fe–Co melts containing titanium are subjected to thermodynamic analysis. The first step is to determine the equilibrium reaction constants of titanium and oxygen, the activity coefficients at infinite dilution, and the interaction parameters in melts of different composition at 1873 K. With increase in cobalt content, the equilibrium reaction constants of titanium and oxygen decline from iron (logK(FeO · TiO₂) =–7.194; logK(TiO₂) =–6.125; logK(Ti₃O₅) =–16.793; logK(Ti₂O₃) =–10.224) to cobalt (logK(CoO · TiO₂) =–8.580; logK(TiO₅) =–7.625; logK(Ti₃O₅) =–20.073; logK(Ti₂O₃) =–12.005). The titanium concentrations at the equilibrium points between the oxide phases (Fe, Co)O · TiO₂, TiO₂, Ti₃O₅, and Ti₂O₃ are determined. The titanium content at the equilibrium point (Fe, Co)O · TiO₂ ? TiO₂ decreases from 1.0 × 10^–4% Ti in iron to 1.9 × 10^–6% Ti in cobalt. The titanium content at the equilibrium point TiO₂?Ti₃O₅ increases from 0.0011% Ti in iron to 0.0095% Ti in cobalt. The titanium content at the equilibrium point Ti₃O₅ ? Ti₂O₃ decreases from 0.181%Ti in iron to 1.570% Ti in cobalt. The solubility of oxygen in the given melts is calculated as a function of the cobalt and titanium content. The deoxidizing ability of titanium decline with increase in Co content to 20% and then rise at higher Co content. In iron and its alloys with 20% and 40% Co, the deoxidizing ability of titanium are practically the same. The solubility curves of oxygen in iron-cobalt melts containing titanium pass through a minimum, whose position shifts to lower Ti content with increase in the Co content. Further addition of titanium increases the oxygen content in the melt. With higher Co content in the melt, the oxygen content in the melt increases more sharply beyond the minimum, as further titanium is added.     

Studies on Processing of an Alnico Scrap

This paper presents the results of research and development work on processing of alnico scrap, a secondary resource of nickel and cobalt, generated during the manufacturing of alnico magnets. The scrap contains 8–10% nickel, 10–12% cobalt, 32–50% of iron, 8–10% aluminium, 2% copper and remaining silica. Various processes such as acid leaching, aqueous chlorine leaching, salt roasting and cupric chloride leaching were studied in detail. Of these cupric chloride leaching was found to be most effective with respect to recovery and purity. It has been possible to obtain pure nickel and cobalt salts by cupric chloride leaching of the scrap, solvent extraction and precipitation of the salts. The overall recovery by the above process was almost 99%.     

Separation behaviour of zinc dross from hot dip galvanising melts of different aluminium concentrations by alternating magnetic field

Abstract

Dross in zinc pots is the most important factor that impairs the surface quality of hot dip galvanising automobile steel sheet. Separation behaviour of zinc dross from galvanising melts of different Al concentrations (0·12, 4·5 and 55·0 wt-% by an alternating magnetic field has been investigated in order to reduce the dross defects on steel sheets. The properties of different zinc drosses were investigated by means of EDAX and the quantitative metallographic method and the conductivities were measured by physics property measurements system. The experimental results show that the zinc dross in different hot dip galvanising melts has different morphologies, compositions and structures, and the average particle size of the dross increases with the Al concentration. In the case of extra iron (above the solubility limit) in the zinc melt, zinc dross quantity also increases with the Al concentration. All of the three types of zinc dross particles >5 μm can be successfully separated when the magnetic frequency is 17·5 kHz, effective magnetic flux intensity is 0·05 T, imposed time is 15 s and the cross-section of the ceramic square pipe is 5 × 5 mm.     

Reaction mechanism of cobalt cementation from high cobalt zinc sulphate solution by zinc dust

Abstract

The experiments in this paper were performed to research the mechanism of cobalt cementation from high cobalt zinc sulphate solution by zinc dust. The reduction potential of zinc during cementation was determined to investigate the morphology of products. Residues after the cementation process from zinc sulphate solution were analyzed by SEM and EPMA to investigate the morphology of products. Different temperature will cause different structure of particles. The reaction mechanism of cobalt removal by zinc dust is thought to be as follows: first, the Co2+ forms Co–Zn alloy with zinc particles, and the reaction reaches equilibrium quickly; second, the Co–Zn alloy continues reacting to Co with Co2+, which is the control process of the whole reaction.     

Zinc accumulation during recycling of iron oxide wastes in the blast furnace

Abstract

Byproducts/wastes of iron- and steelmaking processes and steel scrap are the main sources of iron units recycled in the steel plants. Direct recycling of the iron oxide wastes (dusts and sludge) in the blast furnace (BF) is however hampered by its chemistry (>0·1%Zn in the charge). Vaporisation, condensation, oxidation and circulation of zinc may collectively lead to the accumulation in the furnace. Very fine particles are deposited on other particles that have high surface areas which diminish BF refractory life and impair the quality of high quality pig iron produced. For effective continuous recycling of iron units, it is necessary to identify their sources, determine their composition and evolve device and appropriate technology for the treatment of zinc bearing units. The present paper analyses the process of zinc accumulation in the BF and derives an algebraic model to determine the extent of the accumulation. On the basis of analysis of zinc base formation, its recirculation in the furnace and other related productive units, a homograph (alignment chart) of zinc accumulation is designed. The paper also outlines the feasible processes of zinc removal from the close-looped system (sinter plant–BF–sinter plant).