Chemical Structures of Benzoimidazoles and Their Protective Effects on Zinc and Copper in Phosphate Electrolytes

The effects of the concentration and chemical structure of 2-substituted benzoimidazoles (BIs) on copper and zinc dissolution in phosphate electrolytes were studied. X-ray photoelectron study of copper or zinc electrodes revealed that their surface coverages with an inhibitor depend on its concentration in solution; metal complexes with the inhibitor form a protective surface film. The protective effects of substituted BIs on copper and zinc in phosphate electrolytes vary with the chemical structure of an inhibitor and the metal nature. Electron-withdrawing groups enhance the inhibitive effects of BIs on copper dissolution, while electron-donating groups are favorable for zinc protection; this is associated with the different - and -bonding abilities of these metals. The formation of protective copper complexes is facilitated by -bonding between the metal and an inhibitor, while zinc is protected best in the presence of strong -bonds.     

Evolution of the structure upon heating of submicrocrystalline and nanocrystalline copper produced by high-rate deformation

Methods of electron microscopy, dilatometry, and microhardness and resistivity measurements have been used to study the effect of annealing on the process of recrystallization of a mixed submicrocrys-talline+nanocrystalline (SMC+NC) structure of 99.8% copper produced by high-rate (∼10⁵ s⁻¹) deformation using dynamic channel angular pressing (DCAP). It has been shown that the SMC+NC structure of copper is thermally stable upon heating to a temperature of 150°C. It has been found that the ρ/ρ⁰ ratio of copper with an SMC+NC structure at a temperature of 4.2 K is considerably (by 5 times) higher than ρ/ρ⁰ of copper in the annealed coarse-grained state. This effect is due to a high concentration of defects and a high degree of dispersity of the copper structure after DCAP. Changes in the microhardness and in the resistivity (at a temperature of 4.2 K) of the SMC+NC copper after annealing characterize the level of relaxation processes.     

Production and mechanical properties of aluminum alloys with dispersed nanoscale quasicrystalline and amorphous particles

By the dispersion of nanoscale quasicrystalline and amorphous particles in Al phase, new Al-based alloys with good mechanical properties were developed in a high Al concentration range of 93–95 at.% for Al−Cr−Ce−Co, Al−V−Fe, Al−Ti−M and Al−Fe−Cr−Ti alloy systems. The Vickers hardness of a melt-quenched (MQ) Al_84.6Cr_15.4 alloy with almost a single icosahedral quasicrystalline phase (QC) was 710. The addition of Ce and Co in the Al−Cr binary alloys was effective for the extension of the concentration range of the QC to a lower solute concentration range. The fracture strength (σ_f) increased to 1340 MPa for the MQ Al_94.5Cr₃Ce₁Co_1.5 alloy in which the particle size and volume fraction were approximately 40 nm and 70%, respectively. The σ_f of the MQ Al₉₄V₄Fe₂ alloy was 1390 MPa and the particle size and volume fraction were about 10 nm and 50%, respectively. Similarly, σ_f of the MQ Al₉₃Ti₄Fe₃ alloy was 1320 MPa and the particle size and volume fraction were about 11 nm and 30%, respectively. Power metallurgy (P/M) Al₉₃Fe₃Cr₂Fe₂ alloy with dispersed nanoscale QC exhibited ultimate tensile strength (σ_UTS) of 660 MPa, 0.2 % proof stress (σ_0.2) of 550 MPa, plastic elongation (ε_P) of 4.5%, Young's modulus (E) of 85 GPa, Vickers hardness (Hv) of 192 and specific strength (σ_UTS/ρ) of 2.20×10⁵ Nm/kg at room temperature and σ_UTS of 350 MPa, σ_0.2 of 330 MPa and ε_P of 1.5% at 573 K. The QC structure in the P/M Al₉₃Fe₃Cr₂Ti₂ alloy remained almost unchanged even after annealing for 720 ks at 573 K and good wear resistance against S50C steel was also maintained for the extruded alloy tested at sliding velocity of 0.5 to 2 m/sec. These mechanical properties are promising for the future extension of the new Al-based alloys to practical materials. This article is based on a presentation made in the symposium “The 3rd KIM-JIM Joint Symposium on Advanced Powder Materials”, held at Korea University, Seoul, Korea, October 26–27, 2001 under auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

The effect of alloying with molybdenum on the corrosion—cracking resistance of a Γ20Φ2 type manganese steel against

Molybdenum, which is introduced in amount of 2 to 6% into manganese steel of the basic composition (0.15–0.25) Γ20Φ2, enhances its strength upon the maximum age-hardening at 650°C (to σ_y). However, its stress-corrosion cracking resistance in a 3.5% NaCl solution increases insufficiently (1500 h at a stress of 40 to 50% breaking stress in air σ_air). After the overaging (prolonged exposures at 750°C), steel (with any aforementioned molybdenum content) does not fail in the test medium in 4000 h at σ = 0.8σ_air.     

Influence of Al-Ti-B addition on the microstructure and mechanical properties of A356 alloys

The mechanical properties (σb,σ0.2,and δ) and fracture behavior of tensile specimens of the refined A356 alloys were investigated as a function of the addition level of Al-Ti-B master alloy under both as-cast and T6 heat-treated conditions. The results show that as the addition level of Al-5Ti-1B master alloy increases from 0.1 wt.% to 5.0 wt.%,the mechanical properties of refined A356 alloys improve steadily and then decrease slightly under both as-cast and T6 heat-treated conditions. Also,they display exc...     

The effect of complexing on the zinc dissolution in dichromic acid with HF additions

Two concentration ranges of activating hydrofluoric acid additions were distinguished when dissolving zinc in a 2.5 M CrO₃ solution. Zinc dissolves slowly in a range of 0.05 to 0.3 and quickly from 0.4 to 1 mol/l HF. The effect is explained by the involvement of F^- ions in the formation of Cr(III) fluoride complexes during the reduction of dichromic acid anions and ZnF⁺ cations during zinc ionization. Ionic equilibrium was calculated after long-term holding zinc in the CrO₃ solutions with various HF contents. It was shown that complexing hinders the growth of passive oxide and salt films based on ZnF₂ or basic Cr(III) chromate on zinc. Original Russian Text ? A.M. Shcherbakov, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 3, pp. 300–305.     

Low-alloy steel with elevated strength for apparatuses for complex preparation and processing of natural gas containing hydrogen sulfide

Apparatuses for complex preparation and processing of hydrogen sulfide-containing natural gas are commonly produced from carbon steels of the 20Yuch type. However, the strength level of these steels is low (σ_0.2≥240 N/mm²). Low-alloy weldable steel 09G2S has a higher strength, namely, σ_0.2≥300 N/mm² for rolled stock up to 32 mm thick and σ_0.2≥275 N/mm² for rolled stock up to 80 mm thick. At the same time, steel 09G2S has a low cold strength (the semibrittleness temperatureT ₅₀≥−30°C) and a low resistance to hydrogen sulfide cracking (the threshold stress σ_th=0.6σ_0.2). The present paper is devoted to the effect of the composition and structure on the set of properties of new low-alloy plate steel 09GSNBTs, which possesses elevated strength and is resistant to hydrogen sulfide cracking. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 2–5, February, 1997.     

Kinetics of Cr/Mo-rich precipitates formation for 25Cr-6.9Ni-3.8Mo-0.3N super duplex stainless steel

The amount and composition of Cr-rich (σ) and Mo-rich (χ) precipitates in super duplex stainless steels was analyzed. An isothermal heat treatment was conducted at temperatures ranging from 700 °C to 1000 °C for up to 10 days. A time-temperature transformation (TTT) diagram was constructed for the mixture of σ and χ phases. The mixture of the σ and χ phases exhibited the fastest rate of formation at approximately 900 °C. Minor phases, such as Cr₂N, M₂₃C₆, and M₇C3, were also detected using a transmission electron microscopy (TEM). Also, a continuous cooling transformation (CCT) diagram was constructed for the mixture of σ and χ phases using the Johnson-Mehl-Avrami equation. Compared with the known CCT diagram of the σ phase, this study revealed faster kinetics with an order of magnitude difference and a new CCT diagram was also developed for a mixture of σ and χ phases. The calculated fraction of σ and χ phases obtained at a cooling speed of 0.5 °C/s was in good agreement with the experimental data.     

Formation, retention, and waste of products of the atmospheric corrosion of metals. 3. Corrosion losses and the weight of retained products

The dependence m/K = f(K) (m is the weight of retained products per the unit weight of corrosion losses) on the integral weight of corrosion losses K, which is observed for zinc, carbon steel, copper, brass, aluminum, as well as Д16 and AM_д alloys, in cold, temperate, and tropical cimates, is analyzed. Two groups of empirical equations are proposed to express the functional dependence m/K = f(K). The weight of retained products of outdoor corrosion on zinc, steel, aluminum, and copper, which was calculated from these equations, adequately agree with the experimental weights of products after 1-year outdoor tests of these metals carried out since the late 50s of the past century in Russia and China. Original Russian Text ? Yu.M. Panchenko, P.V. Strekalov, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 1, pp. 90–102.     

Optimization of aging regimes of alloys in the Al−Mg system for stabilizing the structure and mechanical properties

The previous study of the authors has resulted in the development of an Al−10% Mg composition alloyed additionally by zinc, manganese, antimony, and zirconium. The alloy was to be cast into sand molds and had σ_r=380-400 N/mm², σ_0.2=240-260 N/mm², and δ=10–12%. The main difficulty in the development and use of the given alloy consisted in attaining stable properties in the operating process. The present paper is devoted to this problem. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 32–34, August, 1997.     

Magnetoresistance of the La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> single crystal

The dependence of the resistance ρ of the La_0.7Ca_0.3MnO₃ single crystal on the temperature (in a range of 77 < T < 410 K) and magnetic field H is studied. The dependence of the magnetoresistance Δρ/ρ of the ferromagnetic phase on the field is shown to be determined by the competition of two mechanisms. In low magnetic fields, the magnetoresistance is positive Δρ/ρ > 0 and is determined by changes in the resistance with changing magnetization orientation with respect to the crystallographic axes; in high magnetic fields, the magnetoresistance is negative Δρ/ρ < 0, since it is the suppression of spin fluctuations in the magnetic field that plays the principal role. The phase transition from the ferromagnetic to paramagnetic state is a first-order transition close to the second-order one. In the transition range, the magnetoresistance is determined by the resistivity in the zero field ρ(T) and by the shift of the transition temperature T _C(H) in the magnetic field. In the paramagnetic state, the resistivity ρ(T) has an activation character; similarly to the magnetoresistance of other lanthanum manganites, the magnetoresistance of this single crystal is controlled by a change in the activation energy in the magnetic field.     

Preparation of sintered Nd-Fe-B magnets by pressless process

Pressless process used for the preparation of sintered Nd-Fe-B magnets has been studied. The effect of the average particle size D _av, filling density ρ_f, and powder-texturing conditions for obtaining density ρ and desired magnetic hysteretic properties of sintered magnets has been investigated for both traditional technology (TT) and low-oxygen technology (LOT). The ρ_f magnitude ensuring the optimum relation between the density ρ of sintered magnets and their degree of texture was shown to be 2.5–3.0 and 2.2 g/cm³ for the TT and LOT, respectively. At lower ρ_f magnitudes, no required density of sintered magnets is reached, whereas at higher filling densities, a low level of texture and low remanence are realized. Optimum parameters of pulsed field inducing the high degree of texture in powders have been determined. The following properties were achieved for magnets prepared by pressless LOT: B _r ≥ 14.2 kG, H _c ≥ 8 kOe, and (BH)_max ≥ 47.9 MG Oe.     

On the passivation of iron in aqueous solutions of zinc 1-hydroxyethane-1,1-diphosphonate

This work is devoted to studying the passivating ability of the zinc complex of the 1-hydroxyethane-1,1-diphosphonic acid (HEDP) in a borate buffer solution. For the first time, we used the in situ ellipsometric method to study the mechanism of formation of a protective film on iron in the presence of HEDP, HEDPZn, and ZnSO₄ in the course of the cathodic polarization of the electrode. The investigations of adsorption of HEDPZn on iron (at E = −0.65 V) in combination with X-ray photoelectron spectroscopy (XPS) have shown that on the metal surface there is formed a multilayer protective film consisting of an internal layer of Zn(OH)₂ and an outer layer consisting of HEDP complexes with Fe²⁺ and/or Zn²⁺. It has been found that the thickness of the passivating film does not exceed 60 ?, of which 7–10 ? correspond to the low-soluble zinc hydroxide. Original Russian Text ? Yu.I. Kuznetsov, G.V. Zinchenko, L.P. Kazanskii, N.P. Andreeva, Yu.B. Makarychev, 2007, published in Korroziya: Materialy, Zashchita, 2006, No. 9, pp. 19–26.     

Magnetoelastic effect in plastically deformed ferromagnetic steels in weak magnetic fields

A sharp decrease in the magnitude of magnetoelastic effect M _σ as a result of unloading after preliminary plastic extension has been revealed in ferromagnetic steels in weak magnetic fields. The physical origin of this effect and the dependence of M _σ on σ (in the elastic region) and on deformations ɛ (in the plastic region) are considered.     

Peculiarities of electrochemical behavior of copper in alkaline solutions in the presence of alanine

Anodic oxidation of copper in alkaline solution in the presence of alanine is studied by electrochemical and ellipsometric methods. Thickness of films formed on the metal in the working solutions, are determined. Small additives of β-alanine (10⁻⁴–10⁻³ mol/l) cause additional stabilization of copper passivity due to an increase in the film thickness. The adsorption kinetics of α-and β-alanine is studied. It is shown experimentally that β-alanine adsorbs on copper according to the Frumkin isotherm. By contrast, no definite type isotherm can be obtained for α-alanine due to its higher activity and ability to form soluble complexes with copper ions. Original Russian Text ? E.V. Nikitchenko, S.A. Kaluzhina, N.P. Andreeva, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 3, pp. 279–284.     

Corrosion product formation on Zn55Al coated steel upon exposure in a marine atmosphere

The formation of corrosion products on Zn55Al coated steel has been investigated upon field exposures in a marine environment. The corrosion products consisted mainly of zinc aluminium hydroxy carbonate, Zn_0.71Al_0.29(OH)₂(CO₃)_0.145·xH₂O, zinc chloro sulfate (NaZn₄(SO₄)Cl(OH)₆·6H₂O), zinc hydroxy chloride, Zn₅(OH)₈Cl₂·H₂O and zinc hydroxy carbonate, Zn₅(OH)₆(CO₃)₂ were the first three phases were formed initially while zinc hydroxy carbonate Zn₅(OH)₆(CO₃)₂ was formed after prolonged exposure in more corrosive conditions. The initial corrosion product formation was due to selective corrosion of the zinc rich interdendritic areas of the coating resulting in a mixture of zinc and zinc aluminium corrosion products.     

Acid corrosion of iron in the presence of mixtures of anionic additives and compounds of the reaction series of o-hydroxyazomethine derivatives with nucleophilic substituents

The effects of halide-and sulfur-containing additives on iron corrosion in 1 M H₂SO₄ in the presence of nucleophilic o-hydroxyazomethine derivatives are studied. Dependences of the inhibition factor (as well as its sensitivity to a change in the polarity of the substituents) and the effective activation energy on the nature and concentration of both the groups of additives are interpreted in terms of the Linear Gibbs Energy Relation (LGER) and the principle of Hard and Soft Acids and Bases (HSAB). Original Russian Text ? V.P. Grigor’ev, V.V. Boginskaya, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 6, pp. 627–631.     

Nature of the potential of nonpolarized zinc electrode in zincate solutions

The effect of components of alkaline zincate solution and surface compounds, which form on metal zinc in the alkaline solutions, on the nature of nonpolarized electrode potential (E) is studied. It is proposed to determine the nature of E by taking into account more rigorously the activities of all solution components. It is found that in the zincate solutions, the potential of nonpolarized metal zinc is the potential of Zn/Zn(OH)₂, OH⁻ electrode of the second kind. Original Russian Text ? V. Rezaite, L. Deresh, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 4, pp. 368–372.     

Technical note Inhibition of dezincification of 70–30 brass by aminoalkyl mercaptotriazoles

Abstract

Corrosion inhibition efficiencies of triazole derivatives for 70–30 brass in water containing 3%NaCl have been evaluated by means of weight loss, electrochemical polarisation, and impedance techniques. The triazole derivatives, namely aminomethyl mercaptotriazole (AMMT), aminoethyl mercaptotriazole (AEMT), and aminopropyl mercaptotriazole (APMT), gave inhibition efficiencies in the order APMT (94·5%) > AEMT (93·6%) > AMMT (91·5%). Nyquist plots showed Warburg impedance, i.e. the reaction was under diffusion control. The inhibition efficiencies of the triazoles did not drop under dynamic flow conditions. Solution analysis showed selective dissolution of zinc compared with copper. The lowest concentration of zinc, achieved in the tests with the optimum inhibitor addition, was 0·35 mg L ^-1.     

Phase Diagram of the Quaternary Al(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>-Cu(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-Zn(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-H<Subscript>2</Subscript>O System

The phase diagram of the H₂O-Zn(NO₃)₂-Al(NO₃)₃-Cu(NO₃)₂ quaternary system at 30 °C has been established by using the conductivity measurements. The solid-liquid equilibria of the H₂O-Zn(NO₃)₂-Al(NO₃)₃, H₂O-Zn(NO₃)₂-Cu(NO₃)₂, H₂O-Al(NO₃)₃-Cu(NO₃)₂ ternary systems and two isoplethic sections were determined experimentally. The solid phases in equilibrium with the saturated solution are the tri- and hemipentahydrate of copper nitrate, the hexahydrate α and β of the zinc nitrate and the nonahydrate of aluminum nitrate. The copper and zinc nitrates are relatively soluble in opposition to the aluminum nitrate which presents some important precipitation domains.