Kinetics of inhibition of aluminum corrosion in hydrogen chloride electrolytes with binary salt mixtures

The kinetics of inhibition of aluminum corrosion with SnCl₂, CdCl₂, PbCl₂, and their equimolar binary mixtures was studied under contact exchange conditions. Prerequisites for synergism in these mixtures were determined. The parameter γ of mutual influence of the components in the mixture was formally separated into the constituents associated with changes in the aluminum surface coverage with the contact deposit, γ_s, and in the free corrosion potential of aluminum, γ_ΔE . In the mixtures studied, γ_s > 1, while γ_ΔE < 1; however, the overall effect is synergism because γ_s > 1/γ_ΔE . Original Russian Text ? O.I. Barteneva, V.V. Bartenev, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 5, pp. 532–538.     

Thermodynamic vacancy model of the surface energetic state of solids

Based on the broken-bond concept of metal surface formation, a thermodynamic vacancy model of the surface metal layer (TVM), in which the Gibbs surface energy (ΔG _s ) of a metal is defined as the excess adsorption energy of vacancies (N _V(s)) in the surface layer of the metal ΔG _s = −RTlnN _V(s), is developed. The relation is derived from the Gibbs adsorption equation for a metal, which is treated as a binary system that involves atoms and vacancies. TVM enables one to estimate the concentration of vacancies and adatoms on low-index faces of cubic-lattice metals from the literature surface energies evaluated with the use of the surface physics methods. Examples of the application of TVM in the physical chemistry of surfaces and corrosion of metals are given.     

Formation, retention, and discharge of products of atmospheric corrosion of metals. 4. Model: Corrosion-discharge of products

An empirical mathematical model K = K ₀ + km _los (relating atmospheric corrosion to the weight loss of its products) for incubation + transient and steady-state stages of the process, is considered. To develop the model, we used the results of long-term (from 3 month to 1–17 years) field tests of metals according to the Russian, International ISOCORRAG, and Russia-Vietnam-Cuba programs. The K ₀ and k factors in the model were determined according to the corrosion of Ct3, copper, brass, zinc, aluminum, Δ16 alloy, and AMц alloy in the zones of cold, moderate, subtropical, and tropical climates. The model quantitatively relates the corrosion losses of a metal to those of the products discharged to the environment. It may be useful when it is necessary to estimating the amount of detrimental metals, e.g., unprotected copper and zinc dispersed to the environment, but there is no data on the weight of products that had been retained by the metal in the air. Original Russian Text ? Yu.M. Panchenko, P.V. Strekalov, T.V. Nikulina, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 2, pp. 167–191.     

Adsorption and inhibition effect of benzotriazole on brass-118 and brass-MM55 in artificial seawater

Corrosion behaviours of the new type special commercial brass alloys, called 118 and MM55, have been investigated by Tafel Extrapolation (TP) and Linear Polarization (LP) methods in artificial seawater. Inhibition effect of benzotrizole (BTA) of four different concentrations for the corrosion of brass samples was investigated. It was found that BTA was acting as mixed type inhibitor and inhibition efficiency was increasing with the increase of BTA concentration. The change of the degree of surface coverage (θ) as a function of inhibitor concentration (c) shows that BTA follows Langmuir adsorption isotherm. Values of adsorption equilibrium constants (K _ads) and values of free energies of adsorption (ΔG _ads) were calculated from adsorption isotherms. Results reveal that chemisorption is the initial step of inhibition processes.     

The inhibition effect of amides on aluminium corrosion in chloride solutions

The inhibition effect of different concentrations of benzamide (BA), sulfanilamide (SA), and thioacetamide (TA) on the corrosion of aluminium in 0.1 M NaCl solution was investigated by the methods of potentiodynamic polarization, electrochemical impedance spectroscopy, and SEM (scanning electron microscope) in this study. Impedance measurements showed that the charge transfer resistance increased whereas double layer capacitance decreased with the increase in the inhibitor concentrations. Adsorption of these inhibitors followed the Langmuir adsorption isotherm. Thermodynamic parameters of adsorption (K _ads , ΔG _ads ) of studied amides were calculated by using Langmiur adsorption isotherm. The surface films of the aluminium, both in solutions with and without the inhibitors, were then investigated by SEM. The results obtained showed that thioacetamide was much more effective in aluminium inhibition.     

The Rhodanine inhibition effect on the corrosion of a mild steel in acid along the exposure time

The corrosion performance of a mild steel (MS) exposed to a 0.5 M HCl solution with various concentrations of Rhodanine (Rh) was studied by means of anodic and cathodic voltammetric curves, electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) techniques. Rh makes the corrosion of MS in HCl solution decelerate with the exposure time so as to reach a protective value of more than 99% in 168 h. The adsorption of Rh molecules on the MS obeys Langmiur adsorption isotherm. Thermodynamic parameters, adsorption equilibrium constant (K _ads), and standard free energy of adsorption (ΔG _ads ^o ) were calculated and discussed. The high inhibition efficiency was discussed in terms of blockading the metal surface by the Rh molecules strongly adsorbing witch their active centers and thus forming a sufficiently effective protective film.      

Corrosion behavior of mild steel in the presence of scale inhibitor in sulfuric acid solution

Surfactants such as non-ionic polyethylene glycol tert-octylphenyl ether (Triton X-114) have been studied as efficient corrosion inhibitors in acid medium. In this study inhibition performance of Triton X-114 has been evaluated as corrosion inhibitor for mild steel in 0.5 mol l⁻¹ H₂SO₄. The electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and linear polarization (LPR) techniques has been applied to determine the electrochemical behaviour of Triton X-114. The maximum efficiency of Triton X-114 was found as 96% at the concentration 5.0 × 10⁻⁵ mol l⁻¹. The adsorption isotherm of inhibitor on the mild steel surface was found to be in a good agreement with the Langmuir and the standard free energy value (ΔG _ads^°) was calculated as −50.1 kJ mol⁻¹, which shows that adsorption of Triton X-114 on the mild steel surface improves the inhibition characteristics in 0.5 M H₂SO₄.     

Kinetics of forward extraction of Ti（IV） from H_2SO_4 medium by P_（507） in kerosene using the single drop technique

The kinetics of forward extraction of Ti(IV) from H2SO4 medium by P507 in kerosene has been investigated using the single drop technique.In the low concentration region of Ti(IV),the rate of forward extraction at 298 K can be represented by F(kmol·m-2·s-1)=10-5.07 [TiO 2 + ][H+]-1 [NaHA 2 ](o)·Analysis of the rate expression reveals that the rate determining step is(TiO)(i)2+ +(HA 2)(i)-[TiO(HA2)](i)+.The values of Ea,H±,S±,and G±298 are calculated to be 22 kJ·mol-1,25 kJ·mol-1,-218 J·mol-1·K-1,and 25 kJ·mol-1,respectively.The experimental negative S± values indicate that the reaction step occurs via SN2 mechanism.     

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.     

The gallium-iron system: Enthalpy of formation in liquid state

Through the use of a very high-temperature, automated calorimeter, the enthalpy of formation, Δ_f H=f(X _Fe), of the Fe-Ga liquid system was measured in the temperature and molar fraction ranges 0<X _Fe< 0.591 and 1373 <T< 1573 whereT is inK. The molar enthalpies of formation of these liquid alloys are negative with an extremum point atX _Fe = 0.55 and Δ_f H = -5.9 ± 0.6 kj/mol (all results are referred to the liquid state). From measurements performed on the Ga-rich mole fraction side, the limiting partial molar enthalpy was deduced Δh _m ⁰ (Fe_L in Ga_L) = -2 ± 0.2 kJ/mol. These results were compared with those obtained previously for the two similar systems, Ni-Ga and Co-Ga. Moreover a point of the liquidus line was obtained (X _Fe = 0.48 atT = 1466 K).     

The adiabatic correction factor for deformation heating during the uniaxial compression test

The isothermal uniaxial compression test is a common method to determine the flow stress of metals. For accurate flow stress data at strain rates >10⁻³ s⁻¹, the data must be corrected for flow softening due to deformation heating. The first step in the correction is to determine the increase in temperature. An adiabatic correction factor, η, is used to determine the temperature between strain rates of 10⁻³ to 10¹ s⁻¹. The adiabatic correction factor is the fraction of adiabatic heat retained in the workpiece after heat loss to the dies, η=(ΔT _ACTUAL)/(ΔT _ADIABATIC), where ΔT _ADIABATIC=(0.95 f σdɛ)/(ρC _p ). The term η is typically taken to be constant with strain and to vary linearly (0 to 1) with log ( ) between 10⁻³) and 10¹ s⁻¹. However, using the finite element method (FEM) and a one-dimensional, lumped parameter method, η has been found to vary with strain, die and workpiece thermal conductivities, and the interface heat-transfer coefficient (HTC). Using the lumped parameter method, an analytical expression for η was derived. In this expression, η is a function of the die and workpiece thermal conductivities, the interface heat-transfer coefficient, workpiece heat capacity, strain, and strain rate. The results show that an increase in the HTC or thermal conductivity decreases η.     

Acid corrosion of aluminum under conditions of contact plating of antimony

Specific features of the corrosion behavior of aluminum is studied in NaCl solutions with addition of antimony iodide under contact exchange conditions. It was found that the corrosion rate depends non-monotonously on the additive concentration. By varying the exposure time, the conditions for the inhibitive action of the additive are found. The analysis of the time dependences of the inhibition coefficient and partial inhibition coefficients that characterize the changes in the free corrosion potential of aluminum and the blocking of its surface with the antimony deposit demonstrates the dominating effect of the latter factor. Original Russian Text ? V.V. Bartenev, O.I. Barteneva, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 6, pp. 650–655.     

Characterization of Corrosion Product Layers from CO2 Corrosion of 13Cr Stainless Steel in Simulated Oilfield Solution

The influence of temperature and flow rate on the characterization and mechanisms of corrosion product layers from CO₂ corrosion of 13Cr stainless steel was carried out in simulated oilfield solution. Cyclic potentiodynamic polarization method as well as weight loss tests in autoclave were utilized to investigate pitting corrosion behavior at various temperatures. Weight loss tests were performed at 100 and 160 °C under dynamic and static flow conditions. At the same time, the significant pitting parameters such as E _corr, E _pit, E _pp, ∆E, and I _pass in cyclic polarization curves at various temperatures were analyzed and compared for revealing the pitting behavior of 13Cr stainless steel. The surface measurement techniques such as SEM, XRD, and XPS were used to detect the corrosion product layers. The results showed that both temperature and flow rate had significant effects on characterization of corrosion product layers or passive films formed on 13Cr stainless steel in CO₂ corrosion system. At high temperature, lots of pits were formed at the localized corrosion areas of metal surfaces. Corrosion rates under the condition of 5 m/s were higher than those under the static condition regardless of the test temperatures.     

Electrochemical characterization of the different surface states formed in the corrosion of carbon steel in alkaline sour medium

In this study the different surface states that manifest in the corrosion process of 1018 carbon steel in alkaline sour environment, solution prepared specifically to mimic the sour waters occurring in the catalytic oil refinery plants of the Mexican Oil Company (PEMEX) (0.1 M (NH₄)₂S and 10 ppm NaCN at pH 9.2) were prepared and characterized. The surface states of the carbon steel were formed by treating the surface with cyclic voltammetry at different switching potentials (E_λ+), commencing at the corrosion potential (E_corr=−0.890 V vs sulfate saturated electrode, SSE). The surface states thus obtained were characterized using electrochemical impedance spectroscopy and scanning electron microscopy techniques. It was found that for E_λ+=−0.7 and −0.6 V vs SSE a first product of corrosion formed, characterized by a high passivity. Moreover, it was very compact (with a thickness of 0.047 μm). However, at more anodic potentials (E_λ+>−0.5 V vs SSE) a second corrosion product with non-protective properties (porous with a thickness of 0.4 μm and very active) was observed. The diffusion of atomic hydrogen (H⁰) was identified as the slowest step in the carbon steel corrosion process in the alkaline sour media. The H⁰ diffusion coefficients in the first and second products that formed at the carbon steel–sour medium interface were of the order of 10⁻¹⁵ and 10⁻¹² cm²/s respectively.     

Inhibition efficiency of benzidine for mild steel in acidic media

In this study, the inhibition effect of different concentrations of benzidine possessing amine groups in its structure on the corrosion behavior of mild steel (MS) in 1.0 M HCl solution at 293 K temperature was practiced in both short and long immersion times by measuring electrochemical impedance spectroscopy (EIS), hydrogen evolution (V _H2 − t) and change of open circuit potential (E _ocp − t). For short-term tests, potentiodynamic polarization and linear polarization resistance (R _lp ) were also studied. Polarization data indicate that this compound act as mixed-type inhibitor for mild steel in 1.0 M HCl. With regard to the results cited, it was identified that the increase in the inhibitor efficiencies with concentration was emanated from the adsorption of benzidine molecules on the electrode surface. Pertinent to this adsorption, it followed Langmuir isotherm. Adsorption equilibrium constant and adsorption free energy were determined. The effect of temperature on the corrosion behaviour in the absence of any inhibitor and in the presence of 75 mM benzidine was studied in the range of 293–323 K. Activation energies (E _a ^*) were calculated from the obtained corrosion rates at different temperatures. Furthermore, in order to identify the adsorption mechanism of the inhibitor on the metal surface, the zero-charge potential (PZC) was determined by EIS measurement technique. Surface morphology of mild steel electrodes were emerged by means of the scanning electron microscope.     

Schiff-base derivatives as corrosion inhibitors for carbon steel materials in acid media: quantum chemical calculations

Quantum chemical calculations based on Hartree–Fock, AM1 and B3LYP functions were performed on the three Schiff-base compounds used as corrosion inhibitors for carbon steels in acid media. The quantum chemical calculations were conducted to determine the relationship between inhibition efficiency (IE) and the molecular structure of inhibitors. Several quantum chemical parameters, such as charge distribution, energy and distribution of the highest occupied molecular orbital (E_HOMO) and lowest unoccupied molecular orbital (E_LUMO), absolute electronegativity (χ) and the fraction of electrons (ΔN) transferred from inhibitors to the steel surface, were calculated and correlated with inhibition efficiencies. The results showed that the IE of Schiff-base compounds enhanced with increasing E_HOMO or decreasing E_LUMO; meanwhile, N atoms on Schiff-base molecules were the most probable sites for adsorption of inhibitor molecules on the metal surface. The inhibition mechanisms of three Schiff-base compounds were obtained from different calculation methods, and the results from each method are consistent.     

Experimental investigation on corrosion inhibition of thiourea on aluminum surface in 0.5 M H2SO4 acid solution

Effect of thiourea on corrosion resistance of aluminum in 0.5 M H₂SO₄ solution is experimentally investigated. Results show that the addition of thiourea inhibits the sulfuric acid corrosion of aluminum. The inhibition efficiency can be enhanced with an increase in thiourea concentration. It is found that Rp values increases and C _dl values decreases with increasing inhibitor concentration. The inhibition happens through adsorption of thiourea on the metal surface without modifying the mechanism of corrosion process. Inhibition efficiency obtained from all methods is in good agreement. The adsorption of inhibitor on aluminum surface from 0.5 M H₂SO₄ acid solution obeys Langmuir adsorption isotherm.

     

Thermodynamic calculation of the critical potentials of the selective dissolution of Ag-Au and Cu-Au alloys

A thermodynamic approach to estimating the critical potential of the selective alloy dissolution E _c at a vacancy concentration N _v(s) in the superficial layer is considered. The N _v(s) dependence on the potential and the concentration of gold N _Au in the alloy is calculated. The E _c potential corresponds to the critical concentration of vacancies N _v(s) ≈ 10⁻², and the E _c value itself is determined chiefly by the zero-point potential of the alloy, which is a pronounced function of the surface enrichment in gold. The calculated E _c-N _Au functions for Ag-Au and Cu-Au alloys satisfactorily coincide with the experimental dependences. Original Russian Text ? A.E. Kutyrev, Yu.Ya. Andreev, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 2, pp. 152–159.     

Thermodynamic causes of the high diffusion rate of atoms in the superficial layer of a metallic electrode

Concentration of vacancies N _V(S) in a superficial layer (SL) of fcc lattices of Ag, Cu, and Au metals is thermodynamically estimated and analyzed. The calculations are based on a thermodynamic vacancy model of the metal SLs, by which the N _V(S) value is related to the surface Gibbs energy ΔG _s = −RTlnN _V(S). A strong ΔG _s dependence on the electrode potential and the zero point value of the metal results in the increase in N _V(S) value, which reaches nearly 10⁻² at standard potentials of the above metals. The high surface self-diffusivity of atoms (D ≅ 10⁻¹⁵ cm²/s) calculated from the in situ STM measurements of the electrode surfaces is due to the high concentration of vacancies in the metal SLs. Original Russian Text ? Yu.Ya. Andreev, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 1, pp. 18–24.