Study of Reaction Between Slag and Carbonaceous Materials

The chemical interaction of a typical slag of EAF with three different carbon sources, coke, rubber-derived carbon (RDC), coke-RDC blend, was studied in atmospheric pressure at 1823 K (1550 °C). Using an IR-gas analyzer, off-gases evolved from the sample were monitored. While the coke-RDC blend exhibited the best reducing performance in reaction with molten slag, the RDC sample showed poor interaction with the molten slag. The gasification of the coke, RDC, and coke-RDC blend was also carried out under oxidizing conditions using a gas mixture of CO₂ (4 wt pct) and Ar (96 wt pct) and it was shown that the RDC sample had the highest rate of gasification step \( C_{0} \mathop{\longrightarrow}\limits{{k_{3} }}{\text{CO}} + nC_{\text{f}} \) (11.6 site/g s (×6.023 × 10²³/2.24 × 10⁴)). This may be attributed to its disordered structure confirmed by Raman spectra and its nano-particle morphology observed by FE-SEM. The high reactivity of RDC with CO₂ provided evidence that the Boudouard reaction was fast during the interaction with molten slag. However, low reduction rate of iron oxide from slag with RDC can be attributed to the initial weak contact between RDC and molten slag implying that the contact between carbonaceous matter and slag plays significant roles in the reduction of iron oxide from slag.     

Microstructural Analysis of Multi-phase Ultra-Thin Oxide Overgrowth on Al–Mg Alloy by High Resolution Transmission Electron Microscopy

High-resolution transmission electron microscopy analyses are carried out to understand the microstructure of the ultra-thin oxide-film grown on a (native) amorphous Al₂O₃-coated Al-0.8 at.% Mg alloy substrate at T = 600 K for t = 2 h and at pO₂ of 1 × 10^?2 Pa. This oxide-film is found to be non-uniformly thick with thicknesses varying from 1.50 to 4.60 nm. Occasionally, this oxide is found to diffuse into the Al–Mg alloy substrate, forming oxide thicknesses up to 10.5 nm. Overall, this oxide-film is found to consist of a mixed amorphous, (poly) crystalline and an intermediate amorphous-to-crystalline transition regions, with crystalline regions consisting mostly of MgO and the diffused oxide regions into the Al–Mg alloy substrate coated with γ-Al₂O₃. These observations are then compared with the experimental results obtained using angle-resolved X-ray Photoelectron Spectroscopy analysis and thermodynamic predictions for the growth of an ultra-thin oxide-film due to dry, thermal oxidation of Al–Mg alloy substrates.     

Construction of a mathematical model of sulfide sublimation of germanium from middlings

Based on empirical dependences of the value of a variable Y—the degree of sublimation of germanium (%) in the mode of sulfide melting (T = 1350°C, τ = 1 h)—on the values of the parameters that are characteristic of the content in charge, %, X ₁ × 10^?2, of the basicity {[CaO] + [MgO])/[SiO₂]}; X ₂ × 10^?3, of germanium; X ₃, of the slag-forming components (Σ[CaO], [MgO], [SiO₂]); X ₄, of carbon; and X ₅, of sulfur, by the method of computer mathematics with the use of the standard program packets Excel, Mathcad, and Maple, an adequate mathematical model of the influence of the charge composition on the degree of pyrometallurgical sublimation of germanium has been constructed.     

Synthesis and Non-isothermal Carbothermic Reduction of FeTiO<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Solid Solution Systems

To investigate the carbothermic reduction behaviors of xFeTiO₃·(1 ? x)Fe₂O₃ solid solutions, the solid solutions with different x values were synthesized and used in the corresponding reactions. With an increase in x, the temperature pertaining to the onset of carbothermic reduction increased, while the rate of reduction of the solid solutions, α, decreased. The lattice parameters calculated from XRD patterns indicated that the solid solution with a higher x led to a larger lattice distortion. The non-isothermal kinetics were calculated, and an average activation energy E value of 3.0 × 10² kJ/mol was obtained.     

Effect of Deoxidation Process on Inclusion and Fatigue Performance of Spring Steel for Automobile Suspension

55SiCrA spring steel was smelted in a vacuum induction levitation furnace. The liquid steel was treated by Si deoxidation, Al modification with Ca treatment and Al modification, and the steel samples were obtained with deformable Al₂O₃-SiO₂-CaO-MgO inclusions closely contacted with steel matrix, Al₂O₃-CaO-CaS-SiO₂-MgO inclusions surrounded by small voids or Al₂O₃(> 80 pct)-SiO₂-CaO-MgO inclusions surrounded by big voids, respectively. Effect of three types of inclusions on steel fatigue cracks was studied. The perpendicular and transverse fatigue cracks around the three types of inclusions leading to fracture were found to vary in behavior. Under the applied stress amplitude of 775 MPa, the fatigue lives of the three spring steels decreased from 4.0 × 10⁷ to 3.8 × 10⁷, and to 3.1 × 10⁷ cycles. For the applied stress amplitude of 750 MPa, the fatigue lives of the three spring steels decreased from 5.2 × 10⁷ to 4.1 × 10⁷, and to 3.4 × 10⁷ cycles. Based on the voids around inclusions, the equivalent size of initial fatigue crack has been newly defined as \( \sqrt {\frac{{{\text{area}}_{\text{inclusion}} }}{{(1 - {\text{CC}})}}} \), where the contraction coefficient CC of inclusion was introduced. A reliable forecast model of the critical size of inclusion leading to fracture was established by the incorporation of actual width b_inclusion or diameter d_inclusion of internal inclusion; the model prediction was found to be in agreement with experimental results.     

Environmentally Assisted Cracking of Alloy 7050-T7451 Exposed to Aqueous Chloride Solutions

The stress corrosion cracking (SCC) behavior of 7050-T7451 plate material was investigated in short-transverse direction performing constant load and constant extension rate tests. Smooth and notched tensile specimens were permanently immersed in substitute ocean water and in an aqueous solution of 0.6 M NaCl + 0.06 M (NH₄)₂SO₄. Alloy 7050-T7451 exhibited high SCC resistance in both synthetic environments. However, conducting cyclic loading tests, environment-induced cracking was observed. Applying a sawtooth waveform, notched tensile specimens were strained under constant load amplitude conditions at constant displacement rates ranging from 2 × 10^?6 to 2 × 10^?4 mms^?1. The stress ratio R = σ _min/σ _max was 0.1 with maximum stresses of 300 and 400 MPa. When cyclically loaded in substitute ocean water, notched specimens failed predominantly by transgranular environment-induced cracking. Striations were observed on the cleavage-like facets. The number of cycles-to-failure decreased with decreasing displacement rate. A slope of 0.5 was obtained by fitting the logarithmic plot of number of cycles-to-failure vs nominal loading frequency, indicating a hydrogen embrittlement mechanism controlled by diffusion.     

Regularities of Metallurgical Reactions of Ti1 –n$${\text{Me}}_{n}^{{\text{V}}}$$C0.5N0.5 Carbonitrides with the Ni–Mo Melt

The influence of alloying TiC_0.5N_0.5 carbonitride by transition metals of Group V (V, Nb, and Ta) on the contact interaction mechanism with the Ni–25%Mo melt (T = 1450°C, τ = 1 h, rarefaction is 5 × 10^–2 Pa) is systematically studied by X-ray spectral microanalysis and scanning electron microscopy for the first time. It is established that the dissolution of single-type Ti_1 –n\({\text{Me}}_{n}^{{\text{V}}}\)C_0.5N_0.5 carbonitrides (n = 0.05) is an incongruent process (alloying metal and carbon preferentially transfer into the melt), and the relative rate and degree of incongruence of the dissolution process of carbonitrides in a series of alloying metals V–Nb–Ta vary nonmonotonically. An explanation for the discovered effects is proposed. The causal-effect relation between the initial composition of Ti_0.95\({\text{Me}}_{{0.05}}^{{\text{V}}}\)C_0.5N_0.5 carbonitride (the grade of the alloying metal) and composition of the Ti_{1 – n – m}Mo_n\({\text{Me}}_{m}^{{\text{V}}}\)C_x K-phase that is precipitated from the melt upon system cooling is analyzed. It is shown that the factor determining the composition of the forming K-phase is the ΔT factor (the degree of exceeding crystallization temperatures of carbide eutectics Ni/Me^VC over the crystallization temperature of the Ni/Mo₂C eutectic that is the lowest melting in these systems). The conclusion is argued that the interrelation between the initial carbonitride composition and the composition of the K-phase is a consequence of a microinhomogeneous structure of metallic alloys. It is shown that this interrelation is rather common and manifests itself in all studied systems irrespective of the type of alloying Group V metal and presence or absence of molybdenum in the melt.     

Composition and Mobility of Ionic Ensembles in Slags for Steel Refining in the Ladle–Furnace Unit

High-lime synthetic slags for refining steels in the ladle–furnace unit are investigated. The content of the slag mixtures is as follows: 60 wt % CaO, 7 and 8 wt % MgO, 7–23 wt % Al₂O₃, and 9–18 wt % SiO₂, with additions of 8 wt % CaF₃ and 5–15 wt % Na₂O. Polymer theory is used to calculate the composition of the anionic subsystem in the slag melts. The log-mean polymerization constants K _p ^* for multicomponent melts are calculated from the known polymerization constants in binary systems. It is found that K _p ^* ≈ 10^–3–10^–2 in the range 1500–1600°C. In that range, the melt’s degree of polymerization is 3 × 10^–4–8 × 10^–3. In the most polymerized melt, the ionic content of the dimers Si₂O ₇ ^6- and Al₂O ₇ ^8- is no more than 0.1 and 1.5% of the values for the corresponding monomers. Therefore, we assume, with an error of about 2%, that the structural units of the anionic subsystem are monomers AlO ₄ ^5- and SiO ₄ ^4- simple O^2– and F^– ions (slag 7). The cationic subsystem consists of Ca²⁺, Mg²⁺, Na⁺, and Al³⁺ ions in octahedral coordination with oxygen (less than 3% of all the Al atoms). In all the melts, the concentrations of free oxygen ions O^2– and Ca²⁺ ions are similar. In half the cases, the content of O^2– ions is greater than the content of Ca²⁺ ions. The mean mobility U and self-diffusion coefficient D for all the cations are calculated from data for the electrical conductivity and the density. With increase in temperature from 1500 to 1600°C, U and D increase by 50 and 60%, respectively, in all the slags. With increase in the mutual substitution of the components in the slag mixtures M = n(Na₂O, CaF₂)/n(Al₂O₃ + SiO₂), mol/mol, at 1600°C, U increases from 1.14 × 10^–8 to 1.46 × 10^–8 m²/(V s) for slags 1–6 (0 ≤ M ≤ 1.1) and from 1.01 × 10^–8 to 1.66 × 10^–8 m²/(V s) for slags 7–10 (0.25 ≤ M ≤ 0.65). Correspondingly, D increases from 9.2 × 10^–10 to 12.8 × 10^–10 m²/s for slags 1–6 and from 8.2 × 10^–10 to 14.3 × 10^–10 m²/s for slags 7–10. The temperature dependence of U and D may be approximated by an Arrhenius equation with activation energies E _U and E _D . With increase in M in the given ranges, E _U declines from 146 to 100 kJ/mol (slags 1–6) and from 124.5 to 109 kJ/mol (slags 7–10). Likewise, E _D declines from 159 to 116.5 kJ/mol (slags 1–6) and from 139.5 to 124 kJ/mol (slags 7–10). The mean values of E _U and E _D correlate with the mean distance between the cations in the melts. On the basis of the proposed alternative model of the conductivity, the O^2– ions may also transfer electric charge. Preliminary estimates show that the oxygen transport number at 1600°C may exceed 0.1 in some slags.     

Thermodynamics of carbon and oxygen solutions in manganese melts

The thermodynamics of carbon and oxygen solutions in manganese melts is studied. An equation for the temperature dependence of the activity coefficient of carbon in liquid manganese is obtained (γ _C(Mn) ⁰ = ?1.5966 + (1.0735 × 10^?3)T). The temperature dependence of the Gibbs energy of the reaction of carbon dissolved in liquid manganese with the oxygen of manganese oxide is shown to be described by the equation ΔG _T ⁰ = 375264 ? 184.66T(J/mol). This reaction can noticeably be developed depending on the carbon content at temperatures of 1700–1800°C. The deoxidation ability of carbon in manganese melts is shown to be much lower than that in iron and nickel melts due to the higher affinity of manganese to both oxygen and carbon. Although the deoxidation ability of carbon in manganese melts increases with temperature, the process develops at rather high carbon contents in all cases.     

LaCoO<Subscript>3 – δ</Subscript> as the Material of an Oxygen Electrode for a Molten Carbonate Fuel Cell: I. Electrophysical Properties of Lithiated LaCoO<Subscript>3 – δ</Subscript>

Oxides LaCoO_{3 – δ} + (z/2) Li₂O (0 ≤ z ≤ 0.15) are synthesized to determine the boundaries of changing the electrophysical properties of LaCoO_{3 – δ} due to its in situ lithiation in the (Li_0.62K_0.38)₂CO₃ eutectic melt. A perovskite-like solid solution (La_{1 – x}Li _x )(Li _x Co_{1 – x})O_{3 – δ}, where x = z/(z + 2), is found to form as a result of Li doping. The region of existence of the solution does not exceed 2x = 0.072. At a higher concentration of Li, LiCoO₂ forms along with the perovskite-like phase. At the operating temperature of the carbonate fuel cell (T = 920 K), the single-phase samples have metallic conduction and positive thermopower. The electrical conductivity of the Li-doped samples decreases as compared to that of LaCoO_{3 – δ} by no more than 1.5 times and varies from 3.2 × 10⁴ to 3.8 × 10⁴ S/m.     

Influence of Grain Coarsening on the Creep Parameters During the Superplastic Deformation of a Severely Friction Stir Processed Al-Zn-Mg-Cu Alloy

During grain boundary sliding in ultrafine-grain materials at intermediate temperatures and high strain rates (~10^?2 s^?1), apparent creep parameters usually deviate from the theoretical values, due to microstructural coarsening. An analysis has been carried out in a severely friction stir processed (FSP) 7075 alloy with three different ultra-fine grain sizes (L), obtaining explicit grain size dependence of the creep parameters n _ap = n _ap(L) and Q _ap = Q _ap(L), confirming the validity of the theoretical values of these parameters in the constitutive equation.     

Dissolution and Interface Reactions between Palladium and Tin (Sn)-Based Solders: Part I. 95.5Sn-3.9Ag-0.6Cu Alloy

The interface microstructures and dissolution behavior were studied, which occur between 99.9 pct Pd substrates and molten 95.5Sn-3.9Ag-0.6Cu (wt pct, Sn-Ag-Cu) solder. The solder bath temperatures were 513 K to 623 K (240 °C to 350 °C). The immersion times were 5 to 240 seconds. The IMC layer composition exhibited the (Pd, Cu)Sn₄ (Cu, 0 to 2 at. pct) and (Pd, Sn) solid-solution phases for all test conditions. The phases PdSn and PdSn₂ were observed only for the 623 K (350 °C), 60 seconds test conditions. The metastable phase, Pd₁₁Sn₉, occurred consistently for the 623 K (350 °C), 240 seconds conditions. Palladium-tin needles appeared in the Sn-Ag-Cu solder, but only at temperatures of 563 K (290 °C ) or higher, and had a (Pd, Cu)Sn₄ stoichiometry. Palladium dissolution increased monotonically with both solder bath temperature and exposure time. The rate kinetics of dissolution were represented by the expression At ⁿ exp(?H/RT), where the time exponent (n) was 0.52 ± 0.10 and the apparent activation energy (?H) was 44 ± 9 kJ/mol. The IMC layer thickness increased between 513 K and 563 K (240 °C and 290 °C) to approximately 3 to 5 µm, but then was less than 3 µm at 593 K and 623 K (320 °C and 350 °C). The thickness values exhibited no significant time dependence. As a protective finish in electronics assembly applications, Pd would be relatively slow to dissolve into molten Sn-Ag-Cu solder. The Pd-Sn IMC layer would remain sufficiently thin and adherent to a residual Pd layer so as to pose a minimal reliability concern for Sn-Ag-Cu solder interconnections.     

Evaluation of Thermal Stability of Multilayered Nanostructured Coatings Based on Analysis of Diffusion Mobility of Components of the Layers

The thermal stability of multilayered nanostructured coatings is evaluated by analyzing the diffusion mobility of layer components. The possibility of increasing the thermal stability of multilayered coatings based on mutually soluble Ti–Al–N and Cr–N layers due to the introduction of an additional barrier layer based on Zr–N into a multilayered nanostructure is investigated in detail. Calculated diffusivities of basic metallic elements of the coating into corresponding nitride layers upon heating in a temperature range of 800–1000°C evidence the absence of noticeable diffusion spread of layer boundaries in the presence of the Zr–N-based barrier layer. For example, their values lower upon its introduction (it is found at t = 1000°C, cm²/s: D_Cr/TiN = 5 × 10^–17, D_cr/ZrN = 2 × 10¹⁸, \({D_{Ti/C{r_2}N}}\) = 9 × 10^–18, and D_Ti/ZrN = 3 × 10^–18). The physicomechanical properties of coatings do not vary upon their vacuum annealing at t < 900°C; however, they noticeably lower with a further increase in temperature due to the degradation of a multilayered coating structure during annealing.     

Diffusion of copper along the grain boundaries in aluminum

The grain boundary diffusion (GBD) of copper in aluminum is investigated in the range t = 300?400°C. Investigations were performed on a scanning electron microscope equipped with an attachment for electron probe X-ray microanalysis. The triple product sδD _gb (where s is the segregation coefficient, δ is the width of the grain boundary, and D _gb is the GBD coefficient) was calculated by the Fisher criterion using two methods (namely, the copper concentration in the grain boundary, depending on the penetration depth, was determined and the angles in the vertex of the concentration profile was measured using an optical microscope). In the first case, sδD _gb was 5.1 × 10^?11 exp(?102/(RT)) m³/s; in the second case it was 1.4 × 10^?11 exp(?94/(RT)) m³/s. The obtained results are compared with innumerous literature data.     

Technology and properties of porous permeable aluminum-based materials

Results of the investigation of preparation conditions (pressure of powder pressing and time of sintering of compacts) and of the effect of aluminum additions (5–20 wt %) on the properties of a sintered porous material of an aluminum powder and its mixture with an Al₂O₃ powder are given. The possibility is shown of the production of porous (P = 30–35%), highly permeable (k = 2.0 to 2.5 × 10^?13 m²) aluminum-based sintered material with an addition of 20% Al₂O₃ and maximum size of pores equal to 1.3–1.5 μm in the following regime: p = 60 MPa, T = 723–823 K with an isothermal holding for 30–60 min.     

Preparation and Characterization of Plasma Electrolytic Oxidation Coating on 5005 Aluminum Alloy with Red Mud as an Electrolyte Additive

A coating with red mud as an electrolyte additive was applied to 5005 aluminum alloy using plasma electrolytic oxidation (PEO). The phase composition of the coating was investigated using X-ray diffraction. Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDS) was used to determine the microstructure and composition profiles of the coating. The coating/substrate adhesion was determined by scratch testing. The corrosion behaviors of the substrate and coating were evaluated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). The results indicated that the PEO coating with red mud consisted mainly of α-Al₂O₃ and γ-Al₂O₃, with small amounts of Fe₂O₃, CaCO₃, and CaTiO₃. The surface of the coating was the color of the red mud. The coating had a uniform thickness of about 80 μm and consisted of two main layers: a 6-μm porous outer layer and a 74-μm dense inner layer, which showed typical metallurgical adhesion (coating/substrate adhesion strength of 59 N). The coating hardness was about 1142 HV, much higher than that of the substrate (60 HV). The corrosion potential E _corr and corrosion current density i _corr of the coating were estimated to be ?0.743 V and 3.85 × 10^?6 A cm^?2 from the PDP curve in 3.5 wt pct NaCl solution, and the maximum impedance and phase angle of the coating were 11 000 Ω and ?67 deg, respectively, based on EIS. PEO coating with red mud improved the surface properties and corrosion resistance of 5005 aluminum alloy. This study also shows a potential method for reusing red mud.     

A Thermodynamic Model to Estimate the Formation of Complex Nitrides of Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mg<Subscript>(1–<Emphasis Type="Italic">x</Emphasis>)</Subscript>N in Silicon Steel

A complex nitride of Al _x Mg_(1?x)N was observed in silicon steels. A thermodynamic model was developed to predict the ferrite/nitride equilibrium in the Fe-Al-Mg-N alloy system, using published binary solubility products for stoichiometric phases. The model was used to estimate the solubility product of nitride compound, equilibrium ferrite, and nitride compositions, and the amounts of each phase, as a function of steel composition and temperature. In the current model, the molar ratio Al/(Al?+?Mg) in the complex nitride was great due to the low dissolved magnesium in steel. For a steel containing 0.52 wt pct Al_s, 10 ppm T.Mg., and 20 ppm T.N. at 1100 K (827 °C), the complex nitride was expressed by Al_0.99496Mg_0.00504N and the solubility product of this complex nitride was 2.95?×?10^?7. In addition, the solution temperature of the complex nitride increased with increasing the nitrogen and aluminum in steel. The good agreement between the prediction and the detected precipitate compositions validated the current model.     

Liquid Inclusions in Heat-Resistant Steel Containing Rare Earth Elements

Abundant thermodynamic data of pure substances were incorporated in the coupled thermodynamic model of inclusion precipitation and solute micro-segregation during the solidification of heat-resistant steel containing rare earth elements. The liquid inclusions Ce_2x Al_2y Si_1?x?y O _z (0 < x < 1, 0 < y < x and z = 1 ? x ? y) were first introduced to ensure the model more accurately. And the computational method for generation Gibbs free energy of liquid inclusions in molten steel was given. The accuracy of accomplished model was validated through plant trials, lab-scale experiments, and the data published in the literature. The comparisons of results calculated by FactSage with the model were also discussed. Finally, the stable area of liquid inclusions was predicted and the liquid inclusions with larger size were found in the preliminary experiments.     

Investigation of the End-Point Temperature Control Based on the Critical Temperature of Vanadium Oxidation During the Vanadium Extraction Process in BOF

To solve the problem related to the end-point temperature control during the vanadium extraction, industrial experiments and thermodynamic analyses were implemented to find out and verify the foundation for the new standard. The transition temperatures of carbon-vanadium oxidation (T _tr ) and the molten bath temperature measured on the industrial experiments showed a negative temperature difference after smelting for 3.5 min. However, for about 30 wt% vanadium was removed when the molten bath temperature exceeded T _tr . T _tr was only suitable for achieving the goal of “keeping carbon while extracting vanadium” in the early and medium period. The critical temperature of vanadium oxidation (T _cr ) stood for the thermodynamic equilibrium between the oxidation and reduction of vanadium in the later period. It served as the basis to control the end-point temperature to satisfy the demand of “deep vanadium extraction”. As the molten bath temperature increased above T _cr , the residual vanadium neither decreased further nor increased, but showed an equilibrium state.     

Kinetic Analysis of Isothermal Decomposition Process of Zinc Leach Residue in an Inert Atmosphere. The Estimation of the Apparent Activation Energy Distribution

Thermal decomposition of zinc leach residue has been studied in a tubular furnace under a constant nitrogen gas flowing, at four different operating temperatures (600°C, 750°C, 950°C, and 1150°C). Using a detailed kinetic analysis, it was shown that the investigated process can be described by a two-parameter autocatalytic ?esták–Berggren reaction model. It was noted that the apparent activation energy values E_a increase progressively with a degree of conversion, accompanied by the appearance of a convex Arrhenius dependence. This behavior is a characteristic of a system of parallel competing reactions. It was concluded that the investigated isothermal decomposition process is characterized by unusually very low preexponential factor and low values of the apparent activation energy. Based on the derived density distribution function of E_a values, it was concluded that the isothermal decomposition process probably occurs through four reaction steps, where each step is characterized by one parallel reaction.