Modification and Minimization of Spinel(Al<Subscript>2</Subscript>O<Subscript>3</Subscript>·<Emphasis Type="Italic">x</Emphasis>MgO) Inclusions Formed in Ti-Added Steel Melts

High-melting-point inclusions such as spinel(Al₂O₃·xMgO) are known to promote clogging of the submerged entry nozzle (SEN) in a continuous caster mold. In particular, Ti-alloyed steels can have severe nozzle clogging problems, which are detrimental to the slab surface quality. In this work, the thermodynamic role of Ti in steels and the effect of Ca and Ti addition to the molten austenitic stainless steel deoxidized with Al on the formation of Al₂O₃·xMgO spinel inclusions were investigated. The sequence of Ca and Ti additions after Al deoxidation was also investigated. The inclusion chemistry and morphology according to the order of Ca and Ti are discussed from the standpoint of spinel formation. The thermodynamic interaction parameter of Mg with respect to the Ti alloying element was determined. The element of Ti in steels could contribute to enhancing the spinel formation, because Ti accelerates Mg dissolution from the MgO containing refractory walls or slags because of its high thermodynamic affinity for Mg ( e_\textMg^\textTi = - 0. 9 3 3). ( {e_{\text{Mg}}^{\text{Ti}} = - 0. 9 3 3}). Even though Ti also induces Ca dissolution from the CaO-containing refractory walls or slags because of its thermodynamic affinity for Ca ( e_\textCa^\textTi = - 0.119 ), \left( {e_{\text{Ca}}^{\text{Ti}} = - 0.119} \right), dissolved Ca plays a role in favoring the formation of calcium aluminate inclusions, which are more stable thermodynamically in an Al-deoxidized steel. The inclusion content of steel samples was analyzed to improve the understanding of fundamentals of Al₂O₃·xMgO spinel inclusion formation. The optimum processing conditions for Ca treatment and Ti addition in austenitic stainless steel melts to achieve the minimized spinel formation and the maximized Ti-alloying yield is discussed.     

Simultaneous Modification of Alumina and MgO·Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Inclusions by Calcium Treatment During Electroslag Remelting of Stainless Tool Steel

Calcium modification of both alumina and MgO·Al₂O₃ inclusions during protective gas electroslag remelting (P-ESR) of 8Cr17MoV stainless steel and its effect on nitrides and primary carbides were studied by analyzing the transient evolution of oxide and sulfide inclusions in the P-ESR process. The oxide inclusions that were not removed during P-ESR without calcium treatment were found to retain their original state until in as-cast ingot. Calcium treatment modified all MgO·Al₂O₃ and alumina inclusions that had not been removed in the P-ESR process to liquid/partially liquid CaO-Al₂O₃-(MgO) with uniformly distributed elements, in addition to a small proportion of partially modified inclusions of a CaO-MgO-Al₂O₃ core surrounded by a liquid CaO-Al₂O₃. The modification of low-MgO-containing MgO·Al₂O₃ inclusions involves the preferential reduction of MgO from the MgO·Al₂O₃ inclusion by calcium and the reaction of calcium with Al₂O₃ in the inclusion. It is the incomplete/complete reduction of MgO from the spinel by calcium that contributes to the modification of spinels. Alumina inclusions were liquefied by direct reaction with calcium. Calcium treatment during P-ESR refining also provided an effective approach to prevent the formation of nitrides and primary carbides in stainless steel through modifying their preferred nucleation sites (alumina and MgO·Al₂O₃ inclusions) to calcium aluminates, which made no contribution to improving the steel cleanliness.     

Analysis of Mechanically Induced Reactivity of Boehmite Using Kinetics of Boehmite to <Emphasis Type="Italic">γ-</Emphasis>Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Transformation

This article focuses on the mechanically induced reactivity of boehmite prepared by thermal decomposition of gibbsite. Boehmite, which retained the morphology of gibbsite, was characterized by a specific surface area of 264 m²/g. Mechanical activation (MA) was carried out in a planetary mill up to 240 minutes. The samples were characterized in terms of morphology, characteristic particle diameters, Brunauer Emmett Teller (BET) specific surface area (SSA_BET), microcrystallite dimension (MCD), microstrain (ε) and Fourier transform infrared spectroscopy. The reactivity was construed from the kinetics of thermal transformation of boehmite into γ-Al₂O₃. The transformation observed between 600 K and 900 K (327 °C and 627 °C), manifested itself as two overlapping peaks in the differential thermogravimetric plot. These peaks correspond to two stages of dehydroxylation involving Al₂OH and AlOH groups in succession. The peaks were resolved using Gaussian deconvolution. The reactivity was assessed separately for the two stages by comparing the fraction reacted in MA samples (α) with that of nonactivated sample (α _ref). During both stages, enhanced kinetics, as revealed by α-α _ref plots, indicated an increase in reactivity with MA. The transformation mechanism conformed to n ^th order reaction (f[α] = [1 – α] ⁿ with n = 1.3–1.5 in both stages). Values of n remained similar for the activated and reference samples. Activation energies (E _a) for the first and second dehydroxylation stages were respectively 115 and 300 kJ/mol for the nonactivated sample. E _a for the second stage decreased exponentially to a value of 222 kJ/mol after 240 minutes of milling. An anomalous negative correlation between reactivity and SSA_BET was observed. Reactivity parameters were strongly correlated with MCD and ε. A plausible explanation for the observed correlations is presented.     

Thermodynamic Modeling of Metal Desulfurization with Boron-Containing Slags of the CaO–SiO<Subscript>2</Subscript>–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> System

In thermodynamic modeling of the desulfurization of steel by CaO–SiO₂–MgO–Al₂O₃–B₂O₃ slag on the basis of HSC 6.12 Chemistry software (Outokumpu), the influence of the temperature (1500–1700°C), the slag basicity (2–5), and the B₂O₃ content (1–4%)1 on the desulfurization is analyzed. It is found that the sulfur content is reduced with increase in the temperature from 1500 to 1700°C, within the given range of slag basicity. At 1600°C, the sulfur content in the metal is 0.0052% for slag of basicity 2; at 1650°C, by contrast, its content is 0.0048%. Increase in slag basicity from 2 to 5 improves the desulfurization, which increases from 80.7 to 98.7% at 1600°C. If the B₂O₃ content in the slag rises, desulfurization is impaired. At 1600°C, the sulfur content in the metal may be reduced to 0.0052 and 0.0098% when using slag of basicity 2 with 1 and 4% B₂O₃, respectively; in the same conditions but with slag of basicity 5, the corresponding values are 0.00036 and 0.00088%, respectively. Note that desulfurization is better for slag without B₂O₃. According to thermodynamic modeling, metal with 0.0039 and 0.00019% S is obtained at 1600°C when using slag of basicity 2 and 5, respectively, that contains no B₂O₃. The results obtained by thermodynamic modeling for the desulfurization of metal by CaO–SiO₂–MgO–Al₂O₃–B₂O₃ slag of basicity 2–5 in the range 1500–1700°C are consistent with experimental data and may be used in improving the desulfurization of steel by slag that contains boron.     

Effects of the Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Content on the Viscosity of CaO-SiO<Subscript>2</Subscript>-10 Pct Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Quaternary Slag

The present study experimentally investigates the effect of Cr₂O₃ on the viscosity of molten slags. The viscosities of CaO-SiO₂-10 pct Al₂O₃-Cr₂O₃ quaternary slags with two different binary basicities (R, basic slag with R = 1.2 and acidic slag with R = 0.8) were measured by the rotating cylindrical method from 1813 K to 1953 K (1540 °C to 1680 °C). The results showed that the viscosity of both types of slag decreased as the Cr₂O₃ content increased, but the viscosity of acidic slags exhibited a greater decrease. The slags showed good Newtonian behavior at such high temperatures. Cr₂O₃ could act as a network modifier to simplify the Si-O-Si tetrahedral structure, as verified by the Raman spectral analysis, which was consistent with the decreasing trend of viscosity. The activation energy of viscous flow decreased slightly with increasing Cr₂O₃, but increasing the basicity seemed to be more effective in decreasing the viscosity than adding Cr₂O₃.     

Construction of viscosity diagrams for CaO–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–8% MgO–4% B<Subscript>2</Subscript>O<Subscript>3</Subscript> slags by the simplex lattice method

The simplex lattice method of planning experiments is used to study the viscosities of CaO–SiO₂–Al₂O₃–8% MgO–4% B₂O₃ slags in a wide chemical composition range. For each viscosity, we developed an adequate mathematical model in the form of a reduced third-order polynomial. The results of mathematical simulation are presented in composition–viscosity diagrams. Composition regions with a high fluidity of slags, the viscosities of which are 0.8–1.2 Pa s in the temperature range 1500–1600°C, are indicated in the diagrams.     

Investigation into the solubility of nanopowders of the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–CeO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system in the aqueous medium at various pH

Nanopowders of ZrO₂–Y₂O₃–CeO₂ and ZrO₂–Y₂O₃–CeO₂–Al₂O₃ systems are investigated with the purpose of studying the influence of pH of the dispersed medium on the solubility of nanopowder particles of a complex composition in an aqueous medium after membrane filtration and centrifugation to further prepare the stable dispersions necessary for toxicological investigations of nanoparticles. Concentrations of elements remaining in a supernatant after the sample preparation, which includes membrane filtration and centrifugation, are measured by inductively coupled plasma optical emission spectroscopy. It is established that that the largest aggregative stability of the nanopowder dispersion without the Al₂O₃ additive corresponds to the optimal range of pH 5.5–9.5, while with the Al₂O₃ additive, it is region pH 7.0. The results evidence that, when dispersing these powders, the hydrosol of yttrium oxyhydroxide, which is dissolved at pH < 6.0, is formed. When dissolving in water of the powder with the Al₂O₃ additive in the neutral medium, aluminum hydroxide is formed; in the acidic medium (pH < 6), it is replaced by main soluble aluminum salts; and in the alkali medium (pH > 7), amphoteric aluminum hydroxide is dissolved because of the formation of aluminates.     

Effects of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and CaO/SiO<Subscript>2</Subscript> Ratio on Phase Equilbria in the ZnO-“FeO”-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO-SiO<Subscript>2</Subscript> System in Equilibrium with Metallic Iron

The phase equilibria and liquidus temperatures in the ZnO-“FeO”-Al₂O₃-CaO-SiO₂ system in equilibrium with metallic iron have been determined experimentally in the temperature range 1383 K to 1573 K (1150 °C to 1300 °C). The experimental conditions were selected to characterize lead blast furnace and imperial smelting furnace slags. The results are presented in a form of pseudoternary sections ZnO-“FeO”-(Al₂O₃ + CaO + SiO₂) with fixed CaO/SiO₂ and (CaO + SiO₂)/Al₂O₃ ratios. It was found that wustite and spinel are the major primary phases in the composition range investigated. Effects of Al₂O₃ concentration as well as the CaO/SiO₂ ratio on the primary phase field, the liquidus temperature, and the partitioning of ZnO between liquid and solid phases have been discussed for zinc-containing slags.     

Synthesis of new metal-matrix Al–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–graphene composite materials

The mechanism of formation of ceramic microparticles (alumina) and graphene in a molten aluminum matrix is studied as a function of the morphology and type of precursor particles, the temperature, and the gas atmosphere. The influence of the composition of an aluminum composite material (as a function of the concentration and size of reinforcing particles) on its mechanical and corrosion properties, melting temperature, and thermal conductivity is investigated. Hybrid metallic Al–Al₂O₃–graphene composite materials with up to 10 wt % alumina microparticles and 0.2 wt % graphene films, which are uniformly distributed over the metal volume and are fully wetted with aluminum, are synthesized during the chemical interaction of a salt solution containing yttria and boron carbide with molten aluminum in air. Simultaneous introduction of alumina and graphene into an aluminum matrix makes it possible to produce hybrid metallic composite materials having a unique combination of the following properties: their thermal conductivity is higher than that of aluminum, their hardness and strength are increased by two times, their relative elongation during tension is increased threefold, and their corrosion resistance is higher than that of initial aluminum by a factor of 2.5–4. We are the first to synthesize an in situ hybrid Al–Al₂O₃–graphene composite material having a unique combination of some characteristics. This material can be recommended as a promising material for a wide circle of electrical applications, including ultrathin wires, and as a structural material for the aerospace industry, the car industry, and the shipbuilding industry.     

The Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiB<Subscript>2</Subscript>/Fe Complex Reinforcement on Wear and Mechanical Properties of Al-Matrix Composites

In this study, the effect of Al₂O₃–TiB₂/Fe complex ceramic–metal reinforcement (CCMR) on wear and mechanical properties of Al-(Al₂O₃–TiB₂/Fe) composites were investigated. For this purpose, Al₂O₃–TiB₂/Fe CCMR was synthesized by mechanochemical process. The produced reinforcement powders were added to Al matrix, milled for 10 h and then hot extruded. The results showed that the metallic component (Fe rich phase) in this reinforcement acted as a pin, sticking the ceramic parts (Al₂O₃–TiB₂) to Al matrix. The best volume percentage of CCMR in Al matrix was recognized to be about 2.5 %. This composite showed a combination of wear resistance (0.005 mg/m), strength (500 MPa) and ductility (of about 6 %).     

Stabilization of the fluorite phase in the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The calculated and experimental vertical ZrO₂–Y₂O₃ sections of the Zr–Y–O system are compared to find the region of a stable fluorite structure of yttrium-stabilized zirconia (YSZ). X-ray diffraction (XRD) and Raman scattering are used to study the crystal and local structures of mixed oxide 0.82ZrO₂ · 0.18Y₂O₃ (18YSZ) powders prepared by isothermal annealing of a precursor precipitated from a salt solution. The formation of a fluorite-type fcc structure (space group \(Fm\overline 3 m\)) in the powders is detected by XRD. Raman scattering study of the local structure of the cubic 18YSZ powders revealed traces of the tetragonal phase in them.     

Multi-objective Optimization of Electrodeposition of Ni–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nano Composite Coating on Al6061 Substrate

Response surface methodology based Grey relation analysis has been used to optimize the coating parameters of composite coating on aluminium based alloys. This approach gives the best combination of coating parameters to get maximum coating thickness, adhesive strength, microhardness, and minimum wear rate. For each response, the effect of coating parameters at different levels have been discussed. From Grey relation grade, the optimum parameters for better composite coating performance are found to be: temperature, 34 °C; current density, 1 A/dm²; and percentage of particle loading, 1.2 g/L. At 95% significance level, the Current density shows statistical significance on overall composite coating performance.     

Interfacial Tension in the CaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>-(MgO) Liquid Slag–Solid Oxide Systems

Interfacial phenomenon is critical in metal processing and refining. While it is known to be important, there are little data available for key oxide systems in the literature. In this study, the interfacial tension (σ _LS) of liquid slag on solid oxides (alumina, spinel, and calcium aluminate), for a range of slags in the CaO-Al₂O₃-SiO₂-(MgO) system at 1773 K (1500 °C), has been evaluated. The results show that basic ladle-type slags exhibit lower σ _LS with oxide phases examined compared to that of acid tundish-type slags. Also, within the slag types (acid and base), σ _LS was observed to decrease with increasing slag basicity. A correlation between σ _LS and slag structure was observed, i.e., σ _LS was found to decrease linearly with increasing of slag optical basicity (Λ) and decrease logarithmically with decreasing of slag viscosity from acid to base slags. This indicated a higher σ _LS as the ions in the slag become larger and more complex. Through a work of adhesion (W) analysis, it was shown that basic ladle slags with lower σ _LS result in a greater W, i.e., form a stronger bond with the solid oxide phases examined. This indicates that all other factors being equal, the efficiency of inclusion removal from steel of inclusions of similar phase to these solid oxides would be greater.     

Solid Phase Equilibrium Relations in the CaO-SiO<Subscript>2</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-La<Subscript>2</Subscript>O<Subscript>3</Subscript> System at 1273 K

Silicate slag system with additions Nb and RE formed in the utilization of REE-Nb-Fe ore deposit resources in China has industrial uses as a metallurgical slag system. The lack of a phase diagram, theoretical, and thermodynamic information for the multi-component system restrict the comprehensive utilization process. In the current work, solid phase equilibrium relations in the CaO-SiO₂-Nb₂O₅-La₂O₃ quaternary system at 1273 K (1000 °C) were investigated experimentally by the high-temperature equilibrium experiment followed by X-ray diffraction, scanning electron microscope, and energy dispersive spectrometer. Six spatial independent tetrahedron fields in the CaO-SiO₂-Nb₂O₅-La₂O₃ system phase diagram were determined by the Gibbs Phase Rule. The current work combines the mass fraction of equilibrium phase and corresponding geometric relation. A determinant method was deduced to calculate the mass fraction of equilibrium phase in quaternary system according to the Mass Conservation Law, the Gibbs Phase Rule, the Lever’s Rule, and the Cramer Law.     

Deformation Behavior of Inclusion System CaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> with Different Compositions During Hot Rolling Processes

The present study was aimed at exploring the influence of compositions on the deformation behavior of inclusion system CaO–Al₂O₃–SiO₂, during hot rolling processes. The plastic deformations of four inclusions with different compositions, at different rolling temperatures (800, 850, 900, 982 and 1100 °C), were simulated using a finite element model. The equivalent plastic strain distributions and the shapes of the inclusions after rolling were obtained via the model. The influences of rolling temperature, flow stresses of inclusions and matrix, reduction, etc., on the void length and the deformation degree of inclusions were analyzed. The critical temperatures of the four inclusions during hot rolling were different. No voids occurred above the critical temperature. Voids only occurred along the length direction, but not the width and thickness directions, below the critical temperature. Low rolling temperatures led to long void length and small deformation of inclusions. The inclusion with high SiO₂ content had a high critical temperature and a high risk of void formation. Results generated by the experiment on deformation behaviors of inclusions with different SiO₂ content, were in good agreement with the simulated results.