Electrochemical synthesis of an iridium powder with a large specific surface area

The synthesis of iridium powder in a molten NaCl–KCl medium at 700°C is carried out for the first time. The influence of the ratio of the cathode to the anode current density (i _c/i _a) on the structure and the morphology of the iridium powder is investigated. Single-phase and polycrystalline iridium powders with a specific surface of 16.8 m²/g are produced. The phase composition and the surface texture of the deposits are studied. The specific surface and the particle size of iridium powders as functions of the ratio i _c/i _a are analyzed.     

Production of electrolytic manganese dioxide from purified solutions after the leaching of manganese-bearing slurry

The production of electrolytic manganese dioxide from purified solutions after the leaching of manganese-bearing slurry is investigated. The influence of the anodic current density on the electrolysis of manganese-bearing solutions is determined. The preliminary purification of manganese-bearing solutions before electrolysis is discussed. Purification of the solution at pH 6.5–7.0 ensures the maximum deposition of all the impurities that interfere with electrolysis: copper, zinc, nickel, cobalt, aluminum, phosphorus, arsenic, antimony, iron (III), and iron (II). After impurity deposition, the pulp is filtered; the hydrate deposits are washed; and the filtered liquid is sent for electrolysis to obtain electrolytic manganese dioxide. The samples of electrolytic manganese dioxide are studied by means of X-ray fluorescent analysis, X-ray phase analysis, and scanning electron microscopy. The results show that the electrolytic manganese dioxide obtained in the laboratory with anodic current density I_a = 150–200 A/m² meets all the requirements on a highly active product: the content of the basic component (MnO₂) in the experiments is 95.0–96.5 wt %.     

The current efficiency of barium during the electrolysis of chloride and oxide-chloride melts with liquid cadmium and zinc cathodes

The influence of the current density (i) and the duration of electrolysis on the current efficiency of barium (CE_Ba) in the alloy with zinc and cadmium has been investigated during the electrolysis of melts (K-Na)Cl_eq-26 mol % BaCl₂ containing up to 0.4 mol % BaO dissolved at T = 973 K. It is determined that the dependence of CE_Ba on the current density passes through a maximum: at i = 0.18 A/cm², the value of CE Ba in the alloy with Zn is 86%; with cadmium it is 74%. An increase in the electrolysis time and the presence of barium oxide in the melt decrease the current efficiency of barium in melts.     

Effect of titanium additives on carbon anode reactivity

In order to ascertain the impact of titanium additives on carbon anode reactivity, different titanium content of carbon anodes were prepared with the single factor experimental method, and test its reactivity in CO₂ and air atmosphere respectively. The micro structure of carbon anodes and pitch cokes were tested by XRD. The pyrolysis process of pitch was tested with the TG-DTG method. The results show that the residual rate and chalking rate of carbon anode can also be significantly improved by increasing titanium content. Titanium additives can refine the crystallite size of carbon anode, promote the asphalt carbonization. The titanium additives can increase the apparent activation energy and pitch coke yield of the pyrolysis process, when the titanium content is 1.5%, E _a is 56.405 KJ/ mol, reaction order is 6.4, and the rate of pitch coke yield is 50.5%.     

Manganese Capacity and Optical Basicity of Metallurgical Slag

In practice, the concept of slag capacity is used to assess the distribution of elements between condensed phases. In particular, researchers determine the sulfide, phosphate, chromate, and nitride capacity of slags. In the present work, a mathematical model of the manganese capacity is derived. To that end, two equivalent forms of the manganese capacity are derived from the equilibrium constants of the redox reaction of manganese [Mn] + (1/2)O₂ = (MnO). These indices reflect the manganese distribution between the metal and the slag and do not depend on the composition of the metal and the gas phase. One version takes the form C^Mn = K_Mn/γ_(MnO). If we take logarithms and use the known equilibrium constant K_Mn of the redox reaction, we may write logC^Mn = 21122/T–logγ_(MnO)–4.5509. To find the activity coefficient of manganese oxide, equilibrium between hot metal, cast iron, ferrosilicon, ferromanganese, and the corresponding slags is studied experimentally at various temperatures, on circulatory apparatus permitting the study of heterogeneous equilibria involving the gas phase. Using the apparatus, the change in gas volume in the reactions is monitored and automatically recorded and constant pressure is automatically maintained in the system. The attainment of equilibrium is also judged from the constancy of chemical composition of the condensed phases over time. If numerical values of γ_(MnO) are available, they may be used to calculate the manganese capacity of all the slags from the equation already given. For the sake of practical convenience, the manganese capacity is written in terms of the temperature and the optical basicity λ_ed calculated from the electron density known for elements in the periodic table: logC^Mn =–1.866λ_ed + 21049/T–3.131 (R² = 0.997). According to this equation, the manganese capacity depends only on λ_ed and the temperature and may be used for metals and slags of practically any composition.     

Solidification of the eutectic Sn–43 mol % Bi alloy

The processes of melting and solidification of the eutectic Sn–43 mol % Bi alloy are studied by cyclic thermal analysis. It is found that this alloy melts at a temperature T _L = 412 K (which corresponds to the reference melting temperature of the eutectic) upon heating and solidifies isothermally at a temperature T _S = 394 K upon cooling; that is, the temperature difference is ΔT _LS ^? = 18 K. A comparison of temperatures T _L and T _S reveals a temperature hysteresis (TH). The activities and the activity coefficients of tin and bismuth in the eutectic are calculated at temperatures T _L and T _S . The enthalpies of melting at T _L and solidification at TS are measured. The ways of changing the Gibbs energy during TH are determined.     

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.     

Microstructure and High Temperature Impression Creep Properties of Mg–3Ca–xZr (x = 0.3, 0.6, 0.9 wt%) Alloys

The current study has investigated the influence of zirconium (Zr) addition to Mg–3Ca–xZr (x = 0.3, 0.6, 0.9 wt%) alloys prepared using argon arc melting on the microstructure and impression properties at 448–498 K under constant stress of 380 MPa. Microstructural analysis of as-cast Mg–3Ca–xZr alloys showed grain refinement with Zr addition. The observed grain refinement was attributed to the growth restriction effect of Zr in hypoperitectic Mg–3Ca–0.3 wt% Zr alloys. Heterogeneous nucleation of α-Mg in properitectic Zr during solidification resulted in grain refinement of hyperperitectic Mg–3Ca–0.6 wt% Zr and Mg–3Ca–0.9 wt% Zr alloys. The hardness of Mg–3Ca–xZr alloys increased as the amount of Zr increased due to grain refinement and solid solution strengthening of α-Mg by Zr. Creep resistance of Mg–3Ca–xZr alloys increased with the addition of Zr due to solid solution strengthening of α-Mg by Zr. The calculated activation energy (Q_a) for Mg–3Ca samples (131.49 kJ/mol) was the highest among all alloy compositions. The Q_a values for 0.3, 0.6 and 0.9 wt% Zr containing Mg–3Ca alloys were 107.22, 118.18 and 115.24 kJ/mol, respectively.     

Effect of Recovery and Recrystallization on the Hall–Petch Relation Parameters in Submicrocrystalline Metals: I. Experimental Studies

Yield strength σy, macroelastic limit σ₀, and effective grain-boundary hardening coefficient K_eff in the Hall–Petch relation (\({\sigma _y} = {\sigma _0} + {K_{eff}}/\sqrt d \)) in the submicrocrystalline (SMC) materials produced by equalchannel angular pressing are experimentally studied. It is shown that, as compared to parameter σ₀ and K in the Hall–Petch relation for coarse-grained metals, the SMC metals are characterized by higher values of σ0 and lower values of K_eff. The critical grain size (d₁) at which Keff in the σ_y–d^–1/2 relations of SMC materials changes falls in the range 0.2–0.5 μm. The dependences of macroelastic limit σ₀ and coefficient K_eff on the annealing temperature are found to be determined by recrystallization. If abnormal grain growth develops in annealing of SMC metals, anomalous hardening is detected and a nonmonotonic temperature dependence of coefficient K_eff takes place. In the case of conventional recrystallization at a high annealing temperature, SMC metals exhibit a smooth decrease in σ₀ and an increase in K_eff to the values of K characteristic of coarsegrained materials.     

Procedure of calculation of lithium in intermediate products and aluminum

The procedure for calculating the amount of lithium in froth cryolite is suggested for monitoring the Li content in aluminum in those electrolysis shops where no introduction of a purpose additive of its carbonate into the electrolyte is anticipated. A content of 0.0001% Li in aluminum of shops B and C will be reached during the operation of one shop A for 2–3 months. It is calculated that an additional increase of the lithium content in aluminum in the shop with the use of Li₂CO₃ is possible due to Li ingress with flotation and regeneration cryolites, the bath removed from crucibles, and recycled cryolite. For example, an additional increase by 0.0001% in shop A for the operation of 720 baths with the use of lithium carbonate will be attained in 1 month.     

Determination of the heat-transfer coefficient between the AK7ch (A356) alloy casting and no-bake mold

The heat-transfer coefficient h between a cylindrical cast made of AK7ch (A356) aluminum alloy and a no-bake mold based on a furan binder is determined via minimizing the error function, which reflects the difference between the experimental and calculated temperatures in the mold during pouring, solidification, and cooling. The heat-transfer coefficient is h _L = 900 W/(m² K) above the liquidus temperature (617°C) and h _S = 600 W/(m² K) below the alloy solidus temperature (556°C). The variation in the heat-transfer coefficient in ranges h _L = 900–1200 W/(m² K) (above the alloy liquidus temperature) and h _S = 500–900 W/(m² K) (below the solidus temperature) barely affects the error function, which remains at ~22°C. It is shown that it is admissible to use a simplified approach when constant h = 500 W/(m² K) is specified, which leads to an error of 23.8°C. By the example of cylindrical casting, it is experimentally confirmed that the heat-transfer coefficient varies over the casting height according to the difference in the metallostatic pressure, which affects the casting solid skin during its solidification; this leads to a closer contact of metal and mold at the casting bottom.     

Kinetic features of breunnerite decarbonization

The decarbonization of breunnerite from talc waste is analyzed by thermogravimetry. The temperatures of thermal effects are determined, and kinetic models for the process are proposed to describe the mechanism of breunnerite decomposition. The unit cell parameters of breunnerite (Mg _x Fe_1–x )CO₃ and the product of its decomposition, iron–magnesium oxide (Mg,Fe)O, are calculated. The apparent activation energies E _a of the decomposition are calculated using the Ozawa–Flynn–Wall and Kissenger model-free methods and the Avrami–Erofeev one-step model. Depending on the chosen model, the values of E _a range within 180–185 kJ/mol. The conditions of breunnerite roasting for the subsequent use of the obtained material in metallurgical processes are substantiated.     

Influence of operational parameters and design of the ejection nozzle on characteristics of finely dispersed aluminum powder: Part I. Influence of operational parameters of the nozzle

The results of analyzing the influence of operational parameters of the ejection nozzle on the characteristics of highly dispersed aluminum powder in production conditions at OOO SUAL-PM are presented. Measurements of dispersed characteristics of the spray when spraying the aluminum melt by the ejection nozzle are performed when varying the consumption and temperature of spraying gas in ranges of 0.17–0.21 m³/s and 873–933 K, respectively, as well as the melt temperature in limits of 1153–1253 K. The results of determining the median diameter of the particles (d_m) and content of the highly dispersed fraction (z) (with a particle diameter no larger than 10 μm) in the spray are presented. It is shown that, when modifying the operation parameter of the nozzle, the value of d_m decreases by 3.7–12.4%, while the magnitude of z increases by 0.4–3.2%. It is established that an increase in temperature of spraying gas affects the powder properties most effectively.     

An investigation of the effect of the electrolyte composition on the consumption of fired anodes during electrolytic aluminum production

The effect of adding CaF₂, AlF₃, and KF into electrolyte on the consumption of fired anode during aluminum electrolysis is investigated. The CaF₂ content varied from 5 to 10 wt % in the electrolyte of the industrial composition. Correspondingly, the concentration of AlF₃ and KF varied from 4 to 10 and from 0 to 4.7 wt % in the modified electrolytes. Based on the procedure used, the total consumption of carbon and the amount of carbon transported into the gas phase (m _g) and foam (m _f) were determined. Electrolysis duration was 12 h, the distance between the poles was 40 mm, the temperature was 960°C, and the current density was 0.85 and 1.2 A/cm². It is established that adding CaF₂ and AlF₃ increases the consumption of anode, while adding KF decreases it. For CaF₂, ?m _f/?[CaF₂] is larger than ?m _g/?[CaF₂], 15.4 and 6.6 kg/(t_Al wt %) CaF₂, respectively. For AlF₃, ?m _f/?[AlF₃] is also larger than ?m _g/?[AlF₃] and equals 6.8 and 4.2 kg/(t_Al wt %) AlF₃. For KF, ?m _f/?[KF] is smaller than ?m _g/?[KF], being ?11.3 and ?8.1 kg/(t_Al wt %) KF.     

Influence of alloying the TiC<Subscript>0.5</Subscript>N<Subscript>0.5</Subscript> carbonitride with zirconium on an interaction mechanism with the Ni–Mo melt

The influence of alloying the TiC_0.5N_0.5 titanium carbonitride with zirconium on the mechanism and kinetic features of the contact interaction with the Ni–25%Mo melt (t = 1450°C, rarefaction 5 × 10^–2 Pa) is investigated for the first time by electron probe microanalysis and scanning electron microscopy. The main effects of the modifying influence of zirconium on the dissolution, phase formation, and structure formation processes which occur during the interaction of the Ti_1–n Zr _n C_0.5N_0.5 carbonitride (n = 0.05 and 0.20) with the Ni–Mo melt are revealed and the factors promoting their manifestation are analyzed. The practical absence of zirconium and nitrogen in the composition of the K-phase (the Ti_{1 – n} Mo _n C _x metastable solid solution, where n ≤ 0.65 and x = 0.7 ± 0.1) is confirmed experimentally. It is shown that the zirconiumenriched Ti_0.80Zr_0.20C_0.5N_0.5 carbonitride cannot be recommended as a refractory component of cermet because of the limitations of the chemical character.     

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.     

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.     

Correlation of Tensile Properties and Strain Hardening Behavior with Martensite Volume Fraction in Dual-Phase Steels

In the present study, tensile properties, strain hardening and fracture behavior of dual-phase (DP) steels were correlated with martensite volume fraction (V _M ). A series of DP steels with different amounts of V _M (28–50 %) were produced by cold rolling and subsequent intercritical annealing of a ferrite-pearlite starting structure. Hardness and tensile tests results of DP steels showed that variation of hardness, uniform elongation and total elongation with V _M was linear and obeyed the rule of mixtures, whereas yield strength and ultimate tensile strength exhibited a nonlinear variation with V _M . Analysis of strain hardening behavior of DP steels by the Hollomon analysis showed two stages of strain hardening corresponding to ferrite deformation and co-deformation of ferrite and martensite, respectively. The strain hardening exponent of first stage (n _I ) increased with increasing V _M , while the strain hardening exponent of second stage (n _II ) as well as transition strain between the deformation stages decreased.     

Calculation of the structural and thermodynamic constants of normal chromium spinels

The interstructural distances and crystal lattice parameters of complex chromium spinels of variable composition having five different cations are determined according to the earlier developed procedure taking into account their crystal lattices and calculated effective ionic radii. Using these structural characteristics, the enthalpy of the crystal lattice and the enthalpy of spinel formation are calculated. The composition-lattice parameter and composition-enthalpy of the formation diagrams are constructed for (Mg _i ²⁺ Fe _j ²⁺ )O · (Fe _x ³⁺ Al _y ³⁺ Cr _z ³⁺ )₂O₃ spinels. They make it possible to determine the lattice parameter and the enthalpy of oxide formation for any spinel composition.