Formation of Metallic Phase on Reducing-Gas Injection in Multicomponent Oxide Melt. Part 3. Separation of Ferronickel and Oxide Melt

Using the equations of physicochemical hydrodynamics and experimental results regarding the surface and interphase properties of metallic and oxide melts, the conditions in which metallic phase is formed in the bubbling of carbon monoxide through molten oxidized nickel ore are described. The critical dimensions of the gas bubble (R_b.cr) and the metal droplet (r_d.cr) moving in oxide melt without change in size are determined in the range 1550–1750°C. It is found that R_b.cr increases slightly from 6.35 × 10^–2 m at 1550°C to 6.58 × 10^–2 m at 1750°C. With change in the droplet composition and the temperature, r_d.cr varies from 2.1 × 10^–3 to 2.9 × 10^–3 m. The dimensions of the metal droplet formed at a single bubble during the reduction of nickel and iron from oxide melt are determined. As the content of nickel and iron oxides in the melt decreases with increase in the overall CO consumption, the nickel content in the ferronickel droplets falls from 89 to 18%, while the droplet diameter decreases from 1.4 × 10^–3 to 8.0 × 10^–4 m. The droplet mass falls correspondingly from 9.4 × 10^–5 to 1.6 × 10^–5 kg. The conditions in which the bubble–droplet system rises through the melt are determined. Over the whole range of temperature and Ni content, the bubble–droplet system begins to rise through the oxide melt when r_d/R_b is less than 0.68–0.78. To assess the stability of the bubble–droplet system, with the given bubble and droplet dimensions, the parameters determining their joint motion are calculated. It is found that breakaway of the metal droplet from the bubble is not possible in pyrometallurgical systems. The formation of metal phase as a result of the bubbling of carbon monoxide through the oxide melt is described. In this process, the interaction of the oxide melt with the gas is accompanied by the formation of metal droplets, which become attached to the surface of gas bubbles and move to the surface of the oxide melt. Metal with 80–90% Ni is formed at first. With decrease in the nickel content in the oxide melt, its content in the metal declines to 20%. At the surface of the oxide melt, the metal droplets coalesce. When their diameter is greater than 5 × 10^–3 m, they break away from the surface and fall to the bottom. If the falling drop collides with ascending bubble–droplet systems, they may coalesce with it or flow around it. On coalescence, the small droplets will be assimilated and rise to the surface. The breakaway force of the droplet from the bubble significantly exceeds the gravitational force on the droplet. Therefore, the bubble–droplet system is stable for all the size ratios considered.     

Effect of exogenous refractory nanophases on the structural properties of nickel melts

The surface tension and density of nickel and Ni-S melts containing Al₂O₃ and TiN refractory-phase nanoparticles (RPNPs) are studied by the sessile drop method using a digital camera and computer processing of images. The dependences of the structural properties of Ni, Ni-(Al₂O₃,TiN), Ni-S, and Ni-S-(Al₂O₃,TiN) melts on temperature and the type and size of RPNPs are determined. It is found that the surface tension decreases with increasing temperature, the temperature dependence of the surface tension is inverted, the degree of loosening in the Ni-S-(Al₂O₃,TiN) melts decreases, and Ni-S-RPNP ensembles affect the melt structure.     

Interaction of refractory compound nanoparticles with a surfactant in a nickel melt: II. Surface tension and density

The surface tension and density of Ni-S melts with Al₂O₃ or TiN nanoparticles are studied by the sessile drop method using a digital photographic camera and computer processing of images with special-purpose computer programs. The dependences of the surface tension and density of (Ni-S) + (Al₂O₃, TiN) melts on the temperature and the type of introduced refractory compound nanoparticles are determined, and the inversion of the temperature dependence of the surface tension of the Ni-S-Al₂O₃ system is detected. Metallographic analysis of polished sections demonstrates the presence of aluminum, nickel, and sulfur in nonmetallic inclusions at grain boundaries in the first series of experiments and the presence of titanium, nickel, and sulfur in globular nonmetallic inclusions in the second series of experiments.     

Oxygen activities in Cr-containing Fe and Ni-based melts

Plug-type, ZrO₂-based oxygen sensors have been used for long-term measurements of oxygen activity in Fe–O–Cr and Ni–O–Cr melts. In these melts, equilibrated with chromium oxide, oxygen activities a_O were determined as a function of Cr content. From the experimental results, data were derived for activity coefficients f_O and of 1st and 2nd order interaction parameters e_O^Cr and r_O^Cr. Cr₂O₃ has been identified as the oxide phase in equilibrium with the metal melt at ≥ 5 wt.% Cr in the case of iron and at ≥ 0.2 wt.% Cr in the case of nickel. Oxygen activities and oxygen contents in Cr-containing iron melts are lowered with increasing additions of nickel. Further investigations were directed to a_O determination in Fe–O–Cr–C and Fe–O–Cr–Al melts.     

Interaction of exogenous refractory nanophases with antimony dissolved in liquid iron

The heterophase interaction of Al₂O₃ refractory nanoparticles with a surfactant impurity (antimony) in the Fe–Sb (0.095 wt %)–O (0.008 wt %) system is studied. It is shown that the introduction of 0.06–0.18 wt % Al₂O₃ nanoparticles (25–83 nm) into a melt during isothermal holding for up to 1200 s leads to a decrease in the antimony content: the maximum degree of antimony removal is 26 rel %. The sessile drop method is used to investigate the surface tension and the density of Fe, Fe–Sb, and Fe–Sb–Al₂O₃ melts. The polytherms of the surface tension of these melts have a linear character, the removal of antimony from the Fe–Sb–Al₂O₃ melts depends on the time of melting in a vacuum induction furnace, and the experimental results obtained reveal the kinetic laws of the structure formation in the surface layers of the melts. The determined melt densities demonstrate that the introduction of antimony into the Fe–O melt causes an increase in its compression by 47 rel %. The structure of the Fe–Sb–O melt after the introduction of Al₂O₃ nanoparticles depends on the time of melting in a vacuum induction furnace.     

Absorption of gaseous oxygen by liquid cobalt,copper, iron and nickel

An experimental investigation of the rates of oxygen solution in molten cobalt, copper, iron and nickel was carried out using pure oxygen and a constant-volume Sieverts’ method. It was found that the volume of gaseous oxygen which initially reacted with the inductively stirred metals was strongly dependent on the physical nature of the oxide film which formed during the first stage of reaction. The initial temperature of the molten iron, cobalt, and nickel was 1600°C, and for copper was 1250°C. For initial oxygen pressures above the melt of about one atmosphere both molten iron and copper, which formed liquid surface oxides, initially absorbed nearly 20 cm³ (STP) O₂/cm² of melt surface area, while molten cobalt and nickel, which formed solid oxides, absorbed about 6 cm³ (STP) O₂/cm² under the same experimental conditions. For approximately 30 s after the initial reaction between these liquid metals and gaseous oxygen, the oxygen absorption rate was proportional to the square root of the oxygen pressure above the melt, and proportional to the melt surface area, but independent of melt volume. The rate-limiting step for oxygen absorption by liquid iron, cobalt and copper can be described by dissociative adsorption of oxygen molecules at the gas/oxide interface. After 30 s of reaction, the rate of oxygen absorption became less dependent on the oxygen pressure above the melt. This indicated that the rate-controlling step was changing from a surface reaction to growth of the oxide layer by cationic diffusion in the bulk oxide. The oxidation rate of liquid nickel appears to be too complex to be described by models for dissociative adsorption of oxygen molecules at the gas/oxide interface and parabolic growth of the oxide layer. The formation of a thin layer of nickel oxide which allows oxygen to migrate through cracks or grain boundaries may be responsible for the relatively high oxygen absorption rate compared to that of liquid cobalt. R. H. RADZILOWSKI, formerly a Graduate Studient at The University of Michigan     

On the interaction between alumina batch and cryolite-alumina melt

The influence produced by the bulk density of alumina powder on the rate of its dissolution in a cryolite-alumina melt of the composition, wt %, 5.5 CaF₂, 1.5 MgF₂, 0.3 Al₂O₃, 2.28 CR is studied. The melt temperature is 950°C; the dissolution rate is determined visually and by changes in the concentration of aluminum oxide in the melt. It is discovered that the dissolution rate of alumina increases in proportion to its bulk density.     

Effect of the size factors on the heterophase interaction of exogenous refractory compound nanoparticles with sulfur in a model nickel melt

The dependence of the degree of sulfur removal on the size factors is studied during the heterophase interaction of refractory compound nanoparticles in a nickel melt. These factors are the time of holding of Al₂O₃ and TiN nanoparticles in a liquid metal (2?C10 min), the size and number of Al₂O₃ and TiN nanoparticles, the time of processing of a nickel powder with nanoparticles in a planetary mill (0?300 min), and the sulfur concentration in a Ni-(0.0775?0.1750 wt %) S melt. It is shown that the degree of sulfur removal increases as the average size of Al₂O₃ nanoparticles decreases from 150 to 35 nm and that of TiN nanoparticles decreases from 2 × 10⁴ to 30 nm. The effect of the number of Al₂O₃ nanoparticles in a metal on the degree of sulfur removal is considered. A change in the time of processing of a powder mixture in a planetary mill is found to weakly affect the degree of sulfur removal.     

Absorption of gaseous oxygen by liquid cobalt, copper, iron and nickel

An experimental investigation of the rates of oxygen solution in molten cobalt, copper, iron and nickel was carried out using pure oxygen and a constant-volume Sieverts' method. It was found that the volume of gaseous oxygen which initially reacted with the inductively stirred metals was strongly dependent on the physical nature of the oxide film which formed during the first stage of reaction. The initial temperature of the molten iron, cobalt, and nickel was 1600‡C, and for copper was 1250‡C. For initial oxygen pres-sures above the melt of about one atmosphere both molten iron and copper, which formed liquid surface oxides, initially absorbed nearly 20 cm³ (STP) O₂/cm² of melt surface area, while molten cobalt and nickel, which formed solid oxides, absorbed about 6 cm³ (STP) 0₂/cm² under the same experimental conditions. For approximately 30 s after the initial reaction between these liquid metals and gaseous oxygen, the oxygen absorption rate was proportional to the square root of the oxygen pressure above the melt, and pro-portional to the melt surface area, but independent of melt volume. The rate-limiting step for oxygen absorption by liquid iron, cobalt and copper can be described by dissocia-tive adsorption of oxygen molecules at the gasJoxide interface. After 30 s of reaction, the rate of oxygen absorption became less dependent on the oxygen pressure above the melt. This indicated that the rate-controlling step was changing from a surface reaction to growth of the oxide layer by cationic diffusion in the bulk oxide. The oxidation rate of liquid nickel appears to be too complex to be described by models for dissociative ad-sorption of oxygen molecules at the gasJoxide interface and parabolic growth of the oxide layer. The formation of a thin layer of nickel oxide which allows oxygen to migrate through cracks or grain boundaries may be responsible for the relatively high oxygen ab-sorption rate compared to that of liquid cobalt. Formerly a Graduate Student at The University of Michigan     

Volume and Surface Properties of Antimony-Containing Nickel Melts

A decrease in the detrimental effect of an antimony impurity in nickel is considered using structure-sensitive parameters, namely, density and surface tension. Samples of experimental heats containing 0.01–0.05 wt % Sb are prepared from a preliminarily cast master alloy. Antimony additions are found to increase the density of the nickel melt substantially. A negative density hysteresis appears in the temperature dependences recorded upon cooling. Antimony in the nickel melt is found to have a high surface activity and to decrease its surface tension strongly. When the melt is heated, its surface tension increases, which is accompanied by the passage of antimony into the volume and by changes in the volume and surface solution compositions.     

Surface tension of a titanium-containing oxide–fluoride melt calculated by the polymer theory

The surface tension of an aluminum–calcium oxide–fluoride melt is calculated using the polymer theory. It is shown that, at 15 mol % titanium oxide in the melt, aluminum–fluorine–oxygen complexes mainly form. When the titanium oxide content increases further, these complexes disappear and are partly replaced by titanium–oxygen TiO ₄ ^4- and Ti₂O ₇ ^6- anions and titanium–fluorine–oxygen groups.     

Calculation of the reduction rate of copper,nickel, and cobalt from oxide melts by carbon(II) oxide

The kinetic equation for the calculation of the reduction rate, which takes into account the physicochemical properties of contacting phases, is derived under the assumption of the electrochemical nature of interaction between the reducing gas (CO) and the oxide melt. Satisfactory agreement of calculated and experimental data is shown by the example of the interaction of the oxide melt of the CaO-SiO₂-Al₂O₃ system containing up to 6.0 wt % Me _n O _m (NiO, CoO, Cu₂O) blown by the gas phase with partial pressure P _CO = (0.4–5.0) × 10² MPa at T = 1623 K.     

Anodic behavior of the NiO-Fe2O3-Cr2O3-Cu composite during the low-temperature electrolysis of aluminum

In order to fabricate oxide-metallic composites with the composition 25.3NiO-41.2Fe₂O₃-13.5Cr₂O₃-20.0Cu (wt %), the temperature and duration of sintering (1350°C, 30 min) that ensure the formation of the solid solution of chromium oxide in nickel ferrite have been determined. This material is tested as an anode for the electrolysis of the low-temperature solution with the composition 12.0NaF-36.8KF-51.2AlF₃ (wt %), which was saturated with Al₂O₃ (t = 800°C). The amount of gaseous oxygen evolved on the anode was measured. It is shown that the main reaction on an anode at current density i = 0.015–1.0 A cm^?2 is the oxidation of oxygen-containing anions from a melt with the formation of gaseous O₂ and a substantial increase in the oxidation rate of the composite anode is observed at i > 1.0 A cm^?2. The voltage across the electrolyzer (4.5 ± 0.5 V) and the anodic potential (2.43 ± 0.2 relative to the Al reference electrode) during a prolonged experiment (for 89 h, i = 0.4 A cm^?2) indicate a stable and acceptable electrical conductivity of the material, while the dissolution rate, which was calculated by the weight loss (0.6 kg/yr) and volume loss (0.7 cm/yr), satisfy the requirements to inert anodes.     

Modeling of porosity during spray forming: Part II. Effects of atomization gas chemistry and alloy compositions

In this article, the effects of gas chemistry and alloy composition on the level of porosity in deposited materials are investigated by using a porosity model established in Part I of this article. The calculated results reveal that atomization gas chemistry has a significant influence on the level of porosity during spray forming, which can be rationalized on the basis of the influence of gas properties such as gas density, viscosity, and gas constant on the melt flow rate. The alloy properties that predominantly affect the variation of porosity with melt flow rate include melt viscosity, density, surface tension, solvent melting point, liquidus temperature, and equilibrium partition coefficient. A material property factor, μ _mγ_m/ρ ² _m , plays an important role in determining the processing conditions required to attain a minimum amount of porosity in deposited materials.     

Effect of Exogenous Zirconia Nanophases on the Structural Properties of the Sulfur- and Tin-Containing Nickel Melts

The surface tension and the density of the nickel melts with introduced ZrO₂ nanoparticles are studied by the sessile drop method using a digital camera and computer processing of images. The revealed differently directed effects of nanoparticles on the surface tension in the Ni–Sn and Ni–S systems points to a change in the structure of the melt–gas surface layer. The nanoparticles are shown to affect the adsorption of surfactants, and the surface layer is likely to consist of adsorbed Ni + (ZrO₂–surfactant) ensembles. The ZrO₂ content in a metal is determined using the technique of separate determination of the zirconium content dissolved in a metal and zirconium in the form of ZrO₂. It was found that, at 0.10 wt % ZrO₂ initially present in a metal, 0.021–0.031 wt % ZrO₂ are retained in samples; that is, about 70 rel % ZrO₂ are removed to the interface in the form of ensembles. Auger spectroscopy analysis of the Ni–Sn–ZrO₂ surface film detected 5–10 rel % Zr in the surface layer.     

Corrosion-electrochemical behavior of nickel in an alkali metal carbonate melt under a chlorine-containing atmosphere

The corrosion-electrochemical behavior of a nickel electrode is studied in the melt of lithium, sodium, and potassium (40: 30: 30 mol %) carbonates in the temperature range 500–600°C under an oxidizing atmosphere CO₂ + 0.5O₂ (2: 1), which is partly replaced by gaseous chlorine (30, 50, 70%) in some experiments. In other experiments, up to 5 wt % chloride of sodium peroxide is introduced in a salt melt. A change in the gas-phase composition is shown to affect the mechanism of nickel corrosion.     

Deoxidation of the tantalum powder produced by self-propagating high-temperature synthesis

The possibility of removal of oxygen and magnesium from the products of the magnesium reduction of tantalum pentoxide under self-propagating high-temperature synthesis conditions that contain 30 wt % Mg₄Ta₂O₉ is studied. Additional reduction of this material can decrease the magnesium content to <0.01%. The oxygen content in the fabricated tantalum powder does not exceed its amount in the surface oxide (3 × 10^?3 g/m²). The specific surface area of the powder is an order of magnitude higher than that of the initial material, which can result from the formation of a tantalum powder with a specific surface area >30 m²/g during the reduction of Mg₄Ta₂O₉.     

Effect of titanium dioxide on the surface tension and density of an aluminocalcium oxide-fluoride melt

The effect of titanium oxides on the surface tension and density of an Al₂O₃-CaO-CaF₂ melt is studied. At 1773–1923 K, an addition of 4–25 mol % TiO₂ to an oxide-fluoride melt decreases the surface tension and increases the density. The complexation properties of titanium in the oxide-fluoride slags are revealed, and the size and character of the structural units are determined.     

Modification of cast aluminum-matrix composite materials by refractory nanoparticles

The effect of SiO₂ and Al₂O₃ oxide ceramic nanoparticles on the solidification of model samples based on a commercial D16 alloy is studied. The composite samples are fabricated by reaction casting when titanium, nickel, and ceramic powders are mixed with an aluminum melt. The grain size in a matrix, the size and shape of Al₃Ti intermetallic inclusions, and the interphase distances in eutectics are determined with optical and scanning electron microscopes. A certain modifying effect of oxide ceramic nanoparticles on the structure of model CMs during their in situ formation is detected, and the inoculation effect of SiO₂ added to a melt on the reaction products is most pronounced.     

Structure and properties of the slags of continuous converting of copper nickel-containing mattes and concentrates: III. Influence of the slag composition on the surface tension and density of slag melts

The surface tension and density of the slags that form during the continuous converting of copper mattes and concentrates into blister copper are determined. The slag melt compositions are varied over a wide range of (Fe + Ni) concentrations and SiO₂/CaO and (Fe)/(Cu + Ni) ratios. The surface tension and density are measured by the bubble pressure technique. The concentration of iron and nickel in a slag and the (Fe)/(Cu + Ni) and SiO₂/CaO ratios affect the density and surface tension.