The Effect of Calcium Carbonate on the Reducibility of Iron-Oxide Agglomerates

Abstract

The work described is a continuation of that previously carried out at the University of Toronto (1, 2). The object was to gain a better understanding of the effect of lime and calcium carbonate on the reducibility of iron oxides and to remove discrepancies arising out of earlier experiments.

Briquettes, consisting of pure ferric oxide and ferric oxide with 1, 2, 5, and 10 per cent calcium carbonate, were sintered at 1200°C. Then they were reduced by hydrogen in a loss-in-weight furnace at temperatures ranging from 600 to 1000°C. It was found that calcium carbonate increased the, reducibility in all instances. At low reduction temperatures, the effect was more pronounced as the calcium carbonate content increased. This, in turn, corresponded to a greater, initial porosity which was developed during sintering. At higher reduction temperatures, however, this effect was more pronounced for briquettes with small calcium carbonate additions. In this instance, the porosity which was developed during reduction became more important than that which was developed during sintering.     

Effect of impurity additions on the remanence and coercivity of reduced hematite ores

Abstract

Synthetic ores of pure ferric oxide, and ferric oxide with additions of CaO, SiO₂, MnO₂ and TiO₂ were made up by sintering the mixtures at 1100°C. Subsequent crushing, grinding and screening yielded ores with particle between 149 and 208 microns. The ores were reduced to mainetite between 500°C and 1000°C in a CO-CO₂ atmosphere.

The coercive force and remanence of the reduced ores were determined using a 60 cps hysteresis loop tracer. The addition of CaO decreased the coercive force and remanence of the reduced ore as compared to pure magnetite, whereas the effects of the other additions were not significant. Explanations for the findings are offered.

Résumé

Des minerais synthétiques d'oxide ferrique pur et d'oxyde ferrique additionné de CaO, SiO₂, MnO₂ et TiO₂ ont été élaboré par frittage à 1100°C. Après broyage et tamisage, la tail1e des particules de minerai s' échelonnait de 149 à 208 microns. Ces minerais étaient ensuit réduits en magnétite à des températures variant de 500 à 1000°C en atmosphére de CO-CO₂.

La force coercitive et la rémanence des minerais ainsi réduits, on été mesurees it 60 htz sur une boucle d'hystérésis. On a trouvé qu'une addition de CaO fait diminuer la force coercitive et la rémanence des minerais réduits par rapport à la magnétite pure, tan dis que les effets des autres additions sont sans signification. Une interprétation des résultats est donnee.     

The Effect of Lead Oxide Additions on the Viscosity of Sodium Borosilicate Slags

Abstract

The viscosities of sodium borosilicate slags containing lead oxide were measured with a Brookfield Rotational Viscometer at temperatures in the range of 950–1000°C. Increasing additions oflead oxide produced a marked decrease in viscosity. Also, the viscosity decreased as the borax to silica ratio in the melt increased, at constant lead oxide contents. The role of lead oxide and sodium oxide in rupturing the rigid silica network and effectively depolymerizing the melt is discussed and a mechanism is proposed which explains the observed changes.     

Production and properties of burnt lime coated with dicalcium ferrite

Abstract

Ferruginous lime is the term applied to burnt lime (CaO) coated with dicalcium ferrite (2CaO.Fe₂O₃). Its high degradation strength, its resistance to hydration, and its capacity for fast and complete solution of fluxes in the basic oxygen and electric arc furnaces make it extremely attractive as a steelmaking flux. The objectives of the present work were to assess the feasibility of producing ferruginous lime in a rotary kiln type reactor, and to determine the operating conditions favourable for both the formation of a hydration resistant product and the minimisation of problems such as accretions and agglomerations within the reactor. With respect to processing conditions, the trials suggested that ferruginous lime be generated using a peak reaction temperature of 1260°C and allowing 45 min at greater than 1200°C. The optimal oxide addition is 10% by weight of the limestone charge to the rotary lime kiln. When subjected to short duration hydrating conditions, i.e. 30 min in contact with steam at 100°C (according to ASTM specification X6), the ferruginous lime product exhibited good resistance to hydration (relative to pure CaO) and moderate physical degradation. Laboratory tests demonstrated the significantly enhanced rate and degree of dissolution of ferruginous lime (compared with uncoated lime) in a steelmaking slag.     

The Recrystallization Behaviour of Zinc Alloys Containing Magnesium,Cadmium, Copper,Silver, Lead and Iron

Abstract

Small amounts of magnesium, cadmium, copper, silver, lead and iron were studied for their effect on the recrystallization rate of 99.999 per cent zinc. Additions of cadmium and magnesium as small as 0.02 atomic per cent markedly retarded recrystallization rate. The other additions had less influence than the h.c.p. solutes. Lead and iron, which are almost insoluble in zinc, had no effect on recrystallization rate.

Résumé

On a étudié l'influence de petites quantités de magnésium, cadmium, cuivre, argent, plomb et fer sur le taux de recristallisationdu zinc à 99.999 pour cent.

La vitesse de recristallisation fut nettement retardée en ajoutant aussi peu que 0.02 pour cent atomique de cadmium et magnésium.Les autres additifs eurent moins d'influence que les solutés à réseau hexagonal compact. Le plomb et le fer, qui sont presque insolubies dans la zinc, n'eurent aucun effet sur la vitesse de recristallisation.     

Galvanic cell measurements on the sodium-oxygen system

Abstract

The sodium - disodium oxide equilibrium was studied by means of galvanic cells using thoria-based solid electrolytes of various compositions and the accurately known nickel- nickel oxide system as the reference electrode. The free energy of formation of disodium oxide, per gram-mole of oxygen, was found to be given by

?G° =? 193,890 +61.66 T ±800 cal (714°–934°K)

Unsaturated solutions of oxygen in sodium, with oxygen concentrations ranging from 0.56 to 6.85 ppm, were studied in similar cells where the tin - tin oxide system was used as the reference electrode. The measurements yielded the following expression for the solubility of oxygen in sodium equilibrated with disodium oxide:

log (ppm) = (7.076 ± 0.004) ? 2865 ± 180/T

Evidence is incontrovertible that free disodium oxide corrodes heavily the thoria-based electrolytes and pure thoria and pure yttria to a much smaller extent As these tests were carried out on specimens of very high purity, this corrosion cannot be attributed to impurities.

Résumé

L'équilibre sodium-oxyde de sodium a été étudié par des mesures de piles utilisant des électrolytes solides à base de thorine et Ie système de référence Ni/NiO. L'enthalpie libre de formation de Na₂0, par mole d'oxygène s'écrit:

?G° =?193,890 + 61.66T ± 800 cal (714° ? 934°K)

Des solutions non saturées d'oxygéne dans Na, avec des concentrations en O₂ variant de 0.56 à 6.85 ppm, ont été étudiées dans des cellules semblables mais avec le système étain/oxyde d' étain comme référence. Ces mesures ont conduit à l'expression suivante pour la solubilité de l'oxygéne dans le sodium en équilibre avec Na₂O.

log (ppm) = (7.076 ± 0.004) ? 2865 ± 180/T

Il est incontestable que le Na₂O corrode fortement l'électrolyte à base de thorine et beaucoup moins la ThO₂ pure et Y₂O₃ pure. Comme ces tests ont été effectués sur des spécimens de très haute pureté, cette corrosion ne peu t être attribuée aux impuretés.     

Thermodynamic and experimental study of role of sintering atmospheres and graphite additions on oxide reduction in Astaloy CrM powder compacts

Abstract

Several atmospheres based on N₂–H₂ gaseous mixtures, with occasional additions of CH₄ were used to study the sintering behaviour of Astaloy CrM at temperatures of 1100 and 1240°C. Theoretical thermodynamic calculations and sintering experiments, with and without admixed graphite additions, were carried out devoting particular attention to the oxide reduction reactions. The role of carbon in the reduction of oxides is discussed with reference to Boudouard's reaction, proposing the indirect carbothermal reduction as the controlling mechanism. The microstructural characterisation of the material included inspection of the powder particles as well as sintered specimens. It was established that the Astaloy CrM particles contain two distinct types of oxides. One associated with the particle surface and another, mainly constituted by Cr, forming a dispersion of internal oxides. These internal oxides were microstructurally characterised, both directly and by carbon extraction replicas. A selection of powder mixtures containing 0 and 0.4%C additions were used for obtaining tensile specimens in order to assess neck development, by the strength and elongation obtained under various atmospheres and temperature combinations.     

The Oxidation of Sulphur Dioxide and the Formation of Sulphuric Acid in Situ at Atmospheric Pressure in the Leaching of a Uranium Ore

Abstract

The oxidation of SO₂ to form H₂SO₄ in situ, at atmospheric pressure and temperatures from 25 to 80°C, was examined by passing a mixture of SO₂ dioxide and air for 7 hrs through a reaction vessel containing quartz- or uranium-bearing solids moistened with H₂O to 85% solids. At the end of the contact period the solution was analyzed for free acid and other constituents of SO₂ and extraction of Uranium.

In tests with quartz at 80°C, the addition of Fe₂(SO₄)₃ or Fe₂O₃ increased the amount of SO₂ converted to H₂SO₄. E.g. without Fe₂(SO₄)₃ added the conversion obtained was 2% with 0.7 and 2.3 1b/ton quartz of Fe₂(SO₄)₃ the conversions were 18 and 24% respectively.

Tests were conducted on a mixture of flotation tailings, and a residue, which contained 24.3 per cent Fe⁺⁺⁺ as oxide, derived from the roasting of a sulphide concentrate at 500°C. The tailings and sulphide concentrate were obtained from the flotation of a uranium ore containing brannerite and about 9 per cent pyrite Roasting of the sulphide concentrate yielded "160 to 180 lb per ton of ore of sulphur dioxide of which 80,to, 100 lb was introduced into the conversion system over a 7-hour period. At 80°C, 40 per cent of the sulphuric dioxide introduced was converted to sulphuric acid which dissolved 93 per cent of the uranium in the mixturet of solids.     

The Effect of Prior Beta Grain Size on the Ductility of Zirconium-2.5 Weight Per Cent Niobium Alloy

Abstract

Data was collected establishing a time-temperature-beta grain size relationship for the alloy zirconium-2.5 weight per cent niobium. The effect of multiple heat treatments on the beta grain size was also investigated to some extent. Tests were done to determine the effect of the prior beta grain size on the room temperature tensile properties of the alloy. It was found that the ultimate tensile strength and the offset yield strength were not significantly changed with increasing prior beta grain size. There was, however, a change in ductility; over the mean grain diameter range of 0.002 inch to 0.10 inch, the elongation decreased from 20 per cent to 8 per cent and the reduction in area from 63 per cent to 12 per cent.     

The Preparation of a Haifnium-Free Magnesium-Zirconium Alloy by Process Separation of Hafnium

Abstract

Magnesium zirconium alloy for sheathing uranium elements in gas-cooled reactors was successfully prepared from high-purity magnesiumt and zirconium produced by the magnesium reduction of a crude oxide. Hafnium separation, suggested by a higher ratio Hf to Zr in the sludge than in the melt was considered possible owing to its higher density and melting point and its isomorphous behaviour to the strongly electropositive zirconium which readily forms compounds and exhibits a two-phase melt when added in excess of 0.5 per cent. Precipitation of excess zirconium by settling was aided by the development of a flux of high density and low inclusion-flux interfacial energy. Removal of hafnium and other high neutron capture cross-section impurities was achieved.     

Influences of non-stoichiometry on thermodynamics and kinetics of iron oxides reduction processes

Abstract

Non-stoichiometry influences both the thermodynamic and kinetic analyses of the iron oxide redox processes. The thermochemical data of iron oxide redox reactions in various textbooks are not consistent, and the kinetic characteristics are not well understood because of the non-stoichiometry. To clarify such confusions, some famous thermodynamic data are compared, and highly precise experimental work conducted for verification. It is shown that the thermodynamic data for the pure iron oxide reduction reactions from JANAF agree well with the experimental results; the eutectoid temperature of iron oxides was proven to be 576°C; Dieckmann’s defect model of magnetite was proven in good agreement with the experimental results only at high oxygen activities but not low oxygen activities; and the dependences of iron deficiency on Δwt-% (weight loss ratio) and Fe²⁺% (ferrous ratio) were calculated and experimentally verified in pure iron oxides reduction processes.     

THE SINTERING OF URANIUM-CARBON-IRON ALLOYS IN THE PRESENCE OF A LIQUID PHASE

Abstract

The preparation of uranium mono carbide bodies containing ～1% open porosity and with a density of ～12·4 g/c.c. by cold compacting and sintering uranium/graphite mixtures is described. The effect of iron additions in producing a liquid phase during sintering has been studied, and it is shown that the addition of 10 wt.-% UFe₂ to the stoichiometric mixture of uranium and graphite raises the sintered density to ～13·1 g/c.c. and reduces the open porosity to ～0·5%. The mechanism of carbide formation and densification in the presence of a liquid phase is discussed.     

In situ observations of crystalline oxide formation during aluminum and aluminum alloy oxidation

Anin situ morphological study of the oxidation of electron transparent specimens of aluminum and aluminum alloys containing zinc and magnesium has been carried out in the temperature range 400 to 520°C using the hot stage of a 1 MeV transmission electron microscope. The structure and morphology of the crystalline oxide produced in each alloy has been carefully examined by selected area electron diffraction and stereomicroscopy. In pure aluminum, oxidation takes place after a temperature dependent induction period, by the nucleation of crystalline γ-Al₂O₃ at the amorphous oxide/metal interface. This process is delayed by additions of zinc which modify the structure of the oxide. In alloys containing magnesium, oxidation takes place by the rapid nucleation and growth of MgAl₂O₄ or MgO, with a secondary form of magnesia developing from the reduction of the amorphous γ-Al₂O₃ surface layer.

     

Metallic iron whisker formation and growth during iron oxide reduction: basicity effect

Abstract

The effect of basicity on the metallic iron whisker growth during wüstite reduction was studied in the present investigation. Compacts of pure and CaO/SiO₂ doped wüstite were synthesised. The annealed compacts were isothermally reduced in thermogravimetric apparatus with CO gas at 800–1100°C. The course of reduction was followed by measuring the weight loss as a function of time. X-ray diffraction (XRD), scanning electron microscope (SEM), optical microscope and porosity measurements were used to characterise the annealed and reduced samples. The influence of temperature and basicity (CaO/SiO₂) on the reduction behaviour and the morphology of the annealed samples were investigated. The reduction rate increased with temperature but decreased by increasing basicity value. Metallic iron whisker shape structure was detected in the pure wüstite samples after reduction at high temperatures while in basic wüstite samples, whiskers were formed at the surface of the compacts. From the activation energy values, the reduction of pure wüstite is most likely controlled by a combined effect of gaseous diffusion and interfacial chemical reaction mechanisms. The reduction of basic wüstite compacts with 0·2 and 0·5 basicity ratios are most likely controlled by chemical reaction mechanism while for 0·8 basicity ratio, the reduction rate is most likely controlled by solid state reaction mechanism.     

The gaseous reduction of solid calciowustites in Co/Co2 and H2/H2O gas mixtures

The reduction of calciowustites has been carried out in CO/CO₂ and H₂/H₂O gas mixtures at temperatures between 1073 and 1373 K. The effect of lime additions to the wustite is to extend considerably the range of gas conditions over which porous iron morphologies are observed compared to those found on reduction of pure wustite. The products obtained at low oxygen potentials consisted of porous iron containing a dispersion of CaO particles, at intermediate oxygen potentials a two phase structure consisting of porous iron and dicalcium ferrite was formed, and at high oxygen potentials a dense iron layer over the oxide surface is observed throughout reduction. F. NAKIBOGLU, formerly Graduate Student, Department of Mining and Metallurgical Engineering, University of Queensland, Brisbane, Australia D.H. St. JOHN, formerly Postdoctoral Fellow, University of Queensland     

Separation of copper from steel

Abstract

Copper has been separated from iron and steel by chlorine–air mixtures at 800°C. It was found that, contrary to predictions based upon thermodynamics, cupric chloride was the favoured copper product rather than cuprous chloride. This was due to the high vapour pressure of cupric chloride. It was found that in order to prevent the reaction between iron and cupric chloride it was necessary to preoxidise the iron to form an impervious oxide film. Copper contents lower than 0·05 wt-% were readily obtained after 10 min exposure to the gas, even when starting with several per cent of copper mixed with the iron or steel.     

The properties and production of iron‐coated burnt lime

Ferruginous lime is the name given to burnt lime (CaO) coated with di‐calcium ferrite (2CaO·Fe₂O₃). Its high degradation strength, its resistance to hydration and its capacity for fast and complete solution of fluxes in the BOF and EAF make it extremely attractive as a steelmaking flux. The objectives of the present work were to assess the feasibility of producing ferruginous lime in a rotary‐kiln‐type reactor and to determine the operating conditions favourable both for the formation of a hydration resistant product and the minimisation of problems such as accretions and agglomerations within the reactor. With respect to processing conditions, the trials suggest that ferruginous lime should be generated using a peak reaction temperature of 1260 °C and allowing 45 min at greater than 1200 °C. The optimal oxide addition is 10 % (referring to mass contents) of the limestone charge to the rotary lime kiln. When subjected to short duration hydrating conditions i.e. 30 min in contact with steam at 100 °C (as per ASTM specification X6) the ferruginous lime product exhibited good resistance to hydration (relative to pure CaO) and moderate physical degradation. Laboratory tests demonstrated the significantly enhanced rate and degree of dissolution of ferruginous lime (cf. uncoated lime) in a steelmaking slag.     

Recrystallization Kinetics of Martensitic Extra-Low Carbon Steels

Abstract

An experimental study has been made of the mechanism of tempering of extra-low carbon martensitic steels. This mechanism presents several interesting features but perhaps the most important is the recrystallization that starts at about 550°C and constitutes the final stage of softening. This paper presents isothermal recrystallization curves for 0.03 and 0.021 per cent C steels at various tempering temperatures following the martensitic transformation. The effects of purity and temperature on the rates of growth and recrystallization have been studied and the energies of activation for these processes are given.     

The Density of Nickel in the Superheated and Supercooled Liquid States

Abstract

A.levitation melting. technique has been used to obtain the density of liquid nickel between 1149 and 1866°C. Goodagreement is found with recent measurements by an Archimedean method for superheated liquid metal, although the levitation results are higher than those obtained by apparently reliable maximum-bubble-pressure measurements.

Extensive supercooling occurs under levitation melting conditions and densities have been measured over a 300°C range below the melting temperature. The density varies linearly with temperature over the whole temperature range studied, showing no discontinuity at the melting temperature. The density is expressed by the relation:

ρ(g/cm²) = 9.966 – 12.000 × 10^?4T(°K)± 0.055 at the 68 per cent confidence level.     

The bioactivity of titanium-cuttlefish bone-derived hydroxyapatite composites sintered at low temperature

ABSTRACT

The most limiting features of titanium as a bone substituent are lack of bioactivity and high Young’s modulus. We have prepared titanium-hydroxyapatite (Ti-HAp) composites using titanium hydride as sintering agent to provide titanium sintering at lower temperature and preserve the stability of apatite phase. After low temperature sintering, no hydroxyapatite decomposition was detected. Pure titanium samples sintered in the presence of hydride showed smooth surface indicating good densification at 800°C. Higher HAp content resulted in decreased density and higher porosity due to the formation of micro- and macro-pores caused by the integration of HAp particles into titanium matrix and titanium hydride decomposition. However, Vickers microhardness test showed increased hardness for Ti-HAp composite with 10% of HAp regarding pure Ti. The bioactivity of Ti-HAp composites evaluated in simulated body fluid significantly improved with HAp content. The presence of HAp has lowered the cytotoxic effect of Ti-based composites on Hek293 cells.