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.     

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.     

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.     

Formation of metallic phase on reducing-gas injection in multicomponent oxide melt. Part 2. Density and surface properties

The density and surface tension of melts of ferronickel (0–100% Ni) and oxidized nickel ore are measured by the sessile-drop method, as well as the interface tension at their boundary in the temperature range 1550–1750°C. The composition of the nickel ore is as follows: 14.8 wt % Fetot, 7.1 wt % FeO, 13.2 wt % Fe₂O₃, 1.4 wt % CaO, 16.2 wt % MgO, 54.5 wt % SiO₂, 4.8 wt % Al₂O₃, 1.5 wt % NiO, and 1.2 wt % Cr₂O₃. In the given temperature range, the density of the alloys varies from 7700 to 6900 kg/m³; the surface tension from 1770 to 1570 mJ/m²; the interface tension from 1650 to 1450 mJ/m², the density of the oxide melt from 2250 to 1750 kg/m³; and its surface tension from 310 to 290 mJ/m². The results are in good agreement with literature data. Functional relationships of the density, surface tension, and interphase tension with the melt temperature and composition are derived. The dependence of the alloy density on the temperature and nickel content corresponds to a first-order equation. The temperature dependence of the surface tension and interphase tension is similar, whereas the dependence on the nickel content corresponds to a second-order equation. The density and surface tension of the oxide melt depend linearly on the temperature. The results may be used to describe the formation of metallic phase when carbon monoxide is bubbled into oxide melt.     

Dissolution Behavior of Mg from Magnesia-Chromite Refractory into Al-killed Molten Steel

Magnesia-chromite refractory materials are widely employed in steel production, and are considered a potential MgO source for the generation of MgO·Al₂O₃ spinel inclusions in steel melts. In this study, a square magnesia-chromite refractory rod was immersed into molten steel of various compositions held in an Al₂O₃ crucibles. As the immersion time was extended, Mg and Cr gradually dissolved from the magnesia-chromite refractory, and the Mg and Cr contents of the steel melts increased. However, it was found that the inclusions in the steel melts remained as almost pure Al₂O₃ because the Mg content of the steel melts was low, approximately 1 ppm. On the surface of the magnesia-chromite refractory, an MgO·Al₂O₃ spinel layer with a variable composition was formed, and the thickness of the MgO·Al₂O₃ spinel layer increased with the immersion time and the Al content of the steel melts. At the rod interface, the formed layer consisted of MgO-saturated MgO·Al₂O₃ spinel. The MgO content decreased along the thickness direction of the layer, and at the steel melts interface, the formed layer consisted of Al₂O₃-saturated MgO·Al₂O₃ spinel. Therefore, the low content of Mg in steel melts and the unchanged inclusions were because of the equilibrium between Al₂O₃-saturated MgO·Al₂O₃ layer and Al₂O₃. In addition, the effects of the Al and Cr contents of the steel melts on the dissolution of Mg from the magnesia-chromite refractory are insignificant.     

Effect of Al2O3 and MgO on Interfacial Tension Between Calcium Silicate‐Based Melts and a Solid Steel Substrate

The effect of Al₂O₃ and MgO on the interfacial tension between the molten CaO–SiO₂‐based slag and solid steel at 1773 K was studied. The interfacial tension of molten slags slightly increased with increasing Al₂O₃, but no significant change of interfacial tension was observed with higher MgO. Fourier transform infrared (FTIR) of as‐quenched slag samples indicated the slag structure to polymerize with Al₂O₃ additions, but depolymerize with MgO additions. Further detailed studies of the slag surface using X‐ray photoelectron spectroscopy (XPS) showed the fraction of free oxygen ions to decrease with higher Al₂O₃ but remained constant at higher MgO. The results suggested that interfacial tension decreases not only with the depolymerization of the melt, but also with an increase in the free oxygen ions at the molten slag/solid steel interface.     

Effect of the mechanical activation of Ln2O3 Oxides (with Ln = Gd, Dy, Ho, and Lu) on the surface tension and density of borate melts

Effect of the mechanical activation of Gd₂O₃, Dy₂O₃, Ho₂O₃, and Lu₂O₃ oxides on surface tension ?? and density ?? of borate melts is studied. Linear temperature dependences of ?? and ?? are found, and the temperature coefficients are calculated. The dependence of ?? on the lanthanide number in the periodic table is found and exhibits nonmonotonic behavior of the melts. The effect of mechanical activation on ?? and ?? is explained by the formation of complex lanthanide ions, which have uniform geometry in the borate melts.     

Effect of Al2O3 and TiO2 on Viscosity,Surface Tension,and Density of Blast Furnace Slag with CaO/SiO2 = 1.13

The influence of Al₂O₃ in the range of 10–20 mass% and TiO₂ in the range of 0.55–5 mass% on the flow behavior, viscosity, density, and surface tension of molten industrial blast furnace slag with CaO/SiO₂ = 1.13 is investigated using a high-temperature microscope, a rotating viscometer, and the maximum bubble pressure method. The measurement results show that Al₂O₃ acts as a network former in the studied CaO–SiO₂–MgO–Al₂O₃–TiO₂ slags. With an increase in the Al₂O₃ content from 10 to 20 mass%, the viscosity and surface tension of the slags increase and the density decreases. In contrast to Al₂O₃, the TiO₂ acts as a surfactant and network breaker in the range of up to 15 mass%. The addition of TiO₂ up to 15 mass% results in a decrease in the viscosity in the liquid-dominated region and a decrease in the surface tension of the studied slags. Therefore, the density increases with the addition of TiO₂ due to increasing molar volume. The behavior of the breakpoint temperature on all the viscosity curves is in complete agreement with the behavior of the flow point temperature and crystallization temperatures of melilite and perovskite.     

Inclusions for Ultra-pure Ferritic Stainless Steels Containing 21% Chromium

As stabilizing elements added into ultra-pure ferritic stainless steels, niobium and titanium react with carbon and nitrogen to form carbonitrides and have great effects on the ratio of equiaxed zone and the grain size of solidification structure of ingots, which remarkably affect the quality of cold-rolled sheets. Combined with thermodynamic calculation, style and precipitation progress of inclusions in ultra-pure ferritic stainless steels were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy. The results indicate that the inclusions are mainly Ti-Al-N-O system inclusions in ultra-pure ferritic stainless steels. Al₂O₃ starts to precipitate firstly and then TiO_x and TiN precipitates sequently. The inclusions are mainly single TiN particles and complex inclusions with Al₂O₃-Ti₂O₃ as cores and covered with TiN under the condition of 0.31% titanium addition and mainly Al₂O₃ under the condition of 0.01% titanium addition. A few (Nb, Ti) N particles precipitate because of no enough titanium to react with nitrogen when titanium addition is 0.01%. In addition, fine Nb(C, N) particles with size of less than 500 nm precipitate at relatively low temperature.     

Flux Entrapment and Titanium Nitride Defects in Electroslag Remelting of INCOLOY Alloys 800 and 825

Electroslag remelted (ESR) ingots of INCOLOY alloys 800 and 825 are particularly prone to macroscale slag inclusions and microscale cleanliness issues. Formation of these structures near the ingot surface can cause significant production yield losses (~10 pct) due to the necessity of extensive surface grinding. Slag inclusions from near the outer radius of the toe end of alloy 800 and 825 ingots were found to be approximately 1 to 3 mm in size and have a multiphase microstructure consisting of CaF₂, CaTiO₃, MgAl₂O₄, MgO, and some combination of Ca₁₂Al₁₄O₃₂F₂ and/or Ca₁₂Al₁₄O₃₃. These inclusions were often surrounded by fields of 1- to 10-μm cuboidal TiN particles. A large number of TiN cuboids were observed in the ESR electrode with similar size and morphology to those observed surrounding slag inclusions in the ESR ingots, suggesting that the TiN particles are relics from the ESR electrode production process. Samples taken sequentially throughout the AOD processes showed that the TiN cuboidals that are found in ESR ingots form between tapping the AOD vessel into the AOD ladle and the casting of ESR electrodes.     

Refining of Aluminum and Steel Melts by the Use of Multi-Cellular Extruded Ceramic Filters

Abstract

Laboratory prepared melts of steel containing Al₂O₃ inclusions and aluminum containing TiB₂ inclusions have been successfully filtered using multicellular extruded ceramic filters. Relatively high inclusion removal efficiencies have been achieved in both low temperature and high temperature melt systems —68 % inclusion removal efficiency in the Al-TiB₂ system (1020 K) using cordierite multicellular filters and 96 % inclusion removal efficiency in the steel–Al₂O₃ system (1873 K). The results have been analysed using Apelian and Mutharasan's kinetic model for filtration of the metallic melts [1]. The inclusion capture kinetics and filtration characteristics of the porous media used in this investigation are discussed.     

Kinetics studies on the dissolution of nitrogen in the CaO-Al2O3-SiO2 and CaO-Al2O3-TiO x melts

The rate of nitrogen dissolution in CaO-Al₂O₃-SiO₂ and CaO-Al₂O₃-TiO _x melts was measured by ¹⁴N–¹⁵N isotope exchange reaction. The rate constant for the CaO-Al₂O₃-SiO₂ melts at the ratio of mass pct CaO/mass pct Al₂O₃ = 1 increases as SiO₂ content increases, whereas the rate constant for the same melts at the ratio of mass pct CaO/mass pct SiO₂ = 1 increases as Al₂O₃ content increases. The rate constant for the CaO-Al₂O₃-TiO _x melts at the ratio of mass pct CaO/mass pct Al₂O₃ = 1 decreases as the TiO _x content increases. The activation energies of nitrogen dissolution in CaO-Al₂O₃-SiO₂ melts are about 1.5 to 3 times larger than that of molten pure iron. Moreover, the rate constant of nitrogen dissolution is independent of the ratio of Ti³⁺/Ti⁴⁺.     

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.     

Control of Non‐metallic Inclusions by Slag‐metal Reactions for High Strength Alloying Steels

A laboratory study was carried out to investigate non‐metallic inclusions in high strength alloying steel refined by high basicity slag. The results indicated that the inclusions were mainly of the CaO? MgO? Al₂O₃ system, Al₂O₃? MgO and MgO‐based inclusions. The steel/slag reaction time and Al₂O₃ content in slag had a great effect on inclusions characteristics. With the reaction time increasing from 30 to 180 minutes, inclusions experienced a transformation process: from mainly Al₂O₃? MgO system and MgO‐based inclusions to spherical CaO? MgO? Al₂O₃ system inclusions surrounded by a lower melting temperature surface layer of CaO? Al₂O₃. Formation and transformation mechanisms of the inclusions were given based on the results. It was also found that with Al₂O₃ content in slag reduced from 40% to 30%, [Mg] contents in steel melts were increased and MgO in slag reached saturation, which contributed to the formation of more MgO‐based inclusions and a more scattered inclusion composition distribution after 90 min reaction.     

The dissolution of aluminum oxide in cryolite melts

Several modifications of Al₂O₃ were prepared. Al₂O₃ samples pressed to tablets were dissolved in cryolite melts at temperatures between 975 and 1090°C. The dissolution rates obtained are consistent with the consecutive occurrence of two rate laws. The dissolution rate changes at an Al₂O₃ content of 5 to 6 pct in the cryolite melts. The results are discussed with consideration of other experimental and theoretical work. It is concluded that the alteration of the rate law may be explained by structural changes in the melts.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Concentration on Density and Structure of (CaO-SiO<Subscript>2</Subscript>)-xAl<Subscript>2</Subscript>O<Subscript>3</Subscript> Slag

The effect of Al₂O₃ concentration on the density and structure of CaO-SiO₂-Al₂O₃ slag was investigated at multiple Al₂O₃ mole percentages and at a fixed CaO/SiO₂ ratio of 1. The experiments were conducted in the temperature range of 2154 K to 2423 K (1881 °C to 2150 °C) using the aerodynamic levitation technique. In order to understand the relationship between density and structure, structural analysis of the silicate melts was carried out using Raman spectroscopy. The density of each slag sample investigated in this study decreased linearly with increasing temperature. When the Al₂O₃ content was less than 15 mole pct, density decreased with increasing Al₂O₃ content due to the coupling of Si (Al), whereas above 20 mole pct density of the slag increased due to the role of Al³⁺ ion as a network modifier.     

Effect of CaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO slags on the formation of MgO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> inclusions in ferritic stainless steel

A thermodynamic equilibrium between the Fe-16Cr melts and the CaO-Al₂O₃-MgO slags at 1823 K as well as the morphology of inclusions was investigated to understand the formation behavior of the MgO-Al₂O₃ spinel-type inclusions in ferritic stainless steel. The calculated and observed activities of magnesium in Fe-16Cr melts are qualitatively in good agreement with each other, while those of aluminum in steel melts exhibit some discrepancies with scatters. In the composition of molten steel investigated in this study, the log (X _MgO/X _{Al 2}O₃) of the inclusions linearly increases by increasing the log [a _Mg/a _Al ² ·a _O ² ] with the slope close to unity. In addition, the relationship between the log (X _MgO/X _{Al 2}O₃) of the inclusions and the log (a _MgO/a _{Al 2}O₃) of the slags exhibits the linear correlation with the slope close to unity. The compositions of the inclusions are relatively close to those of the slags, viz. the MgO-rich magnesia-spinel solid solutions were formed in the steel melts equilibrated with the highly basic slags saturated by CaO or MgO. The spinel inclusions nearly saturated by MgO were observed in the steel melts equilibrated with the slags doubly saturated by MgO and MgAl₂O₄. The spinel and the Al₂O₃-rich alumina-spinel solid solutions were formed in the steel melts equilibrated with the slags saturated by MgAl₂O₄ and MgAl₂O₄-CaAl₂O₄ phases, respectively. The apparent modification reaction of MgO to the magnesium aluminate inclusions in steel melts equilibrated with the highly basic slags would be constituted by the following reaction steps: (1) diffusion of aluminum from bulk to the metal/MgO interface, (2) oxidation of the aluminum to the Al³⁺ ions at the metal/intermediate layer interface, (3) diffusion of Al³⁺ ions and electrons through the intermediate layer, and (4) magnesium aluminate (MgAl₂O₄ spinel, for example) formation by the ionic reaction.     

Temperature dependence of the refractive index of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Na<Subscript>2</Subscript>O-SiO<Subscript>2</Subscript> melts: Role of electronic polarizability of oxygon controlled by network structure

Refractive indexes for the Al₂O₃-Na₂O-SiO₂ system have been measured using an ellipsometer for a wavelength of 632.8 nm over a wide temperature range (1100 to 1800 K). Two kinds of sample were used: xAl₂O₃-(40-x)Na₂O-60SiO₂ and yAl₂O₃-yNa₂O-(100-2y)SiO₂, where x ranged between 6 and 20 mol pct and y between 12.5 and 25 mol pct. In the former samples, the temperature coefficient of refractive indexes changed from negative to positive on increasing the concentration of Al₂O₃. In the latter samples, the refractive indexes increased monotonically with decreasing concentration of SiO₂, and the temperature coefficient was always positive. It has been found that the temperature dependence of refractive indexes in these melts is determined by the coefficient of thermal expansion, which would be relevant to the degree of polymerization of the melts. In addition, the electronic polarizability of oxygen derived from the refractive indexes increased with increasing temperature in each melt. This suggests that the basicity of the alumino-silicate melts increases as temperature increases. The positive temperature coefficient of the electronic polarizability of oxygen can be attributed to an increase in the distance between cation and oxygen ion due to thermal expansion. The dependence of the electronic polarizability of oxygen on the concentration of Al₂O₃ has also been discussed in terms of the electronic polarizabilities of three types of oxygen contained in the melts. This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties & Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002.     

Genetic Evolution of Inclusions in Interstitial-Free Steel During the Cold Rolling Processes

In present work, the genetic evolution behavior of inclusions in interstitial-Free steel sheets during the cold rolling processes have been investigated based on nano-indentation. The genetic evolution of inclusions in shape and position has been calculated by 2-D finite element model. The inclusions spread along the rolling direction and compress along the IF steel sheets thickness direction. The inclusion’s profiles calculated by simulation are consistent with that obtained by experiments. After multi-pass cold rolling, the inclusions can be moved a short distance toward the sheet surface. When the Al₂O₃ and TiN sizes are less than 30 and 20 μm, the displacements are approximately 6 and 10 μm respectively. While the diameter of Al₂O₃ is 100 μm, the maximum displacement is approximately 30 μm. Both the Al₂O₃ and TiN in the position of 1/2 of the sheet have little displacements after multi-pass rolling. On the contrary, the inclusion located at 1/8th position of the sheet, the actual displacements are more than 30 μm. The shorter the distance between the inclusion and the IF steel sheet surface, the larger the inclusion displaces. Furthermore, the relationship between inclusions and surface defects have also been discussed.     

Computer study of structure, thermodynamic, and electrical transport properties of Na3AlF6-Al2O3 and CaF2-Al2O3 melts

Structure, thermodynamic, and electrical transport properties of Na₃AlF₆-Al₂O₃ and CaF₂-Al₂O₃ melts were examined by molecular dynamics. Ionic models were constructed for Na₃AlF₆-Al₂O₃ and CaF₂-Al₂O₃ melts at 1283 and 2000 K, respectively. It was found that in the Na₃AlF₆-Al₂O₃ melts, stable aluminum-fluorine-oxygen groups are formed. Although bonds between F⁻ and Al³⁺ ions in the first coordination shell are weaker than between O²⁻ and Al³⁺ ions, very stable negatively charged AlF ₆ ³⁻ groups are formed at low oxygen concentrations in the Na₃AlF₆-Al₂O₃. This results in migration of aluminum to the anode in an external electric field. In the CaF₂-Al₂O₃ melts, positively charged aluminum-oxygen groups dominate. This results in migration of aluminum to the cathode at almost all Al₂O₃ concentrations. Therefore, in Na₃AlF₆-Al₂O₃ melts, the Al³⁺ ion as a component of the complex anion has a negative partial conductivity and the O²⁻ ion has positive partial conductivity; in CaF₂-Al₂O₃ melts, Al³⁺ has a positive transport number while O²⁻ has a negative transport number.