Zinc treatment effects on corrosion behavior of 304 stainless steel in high temperature, hydrogenated water

Trace levels of soluble zinc(II) ions (30 ppb) maintained in mildly alkaline, hydrogenated water at 260 °C were found to lower the corrosion rate of austenitic stainless steel (UNS S30400) by about a factor of five, relative to a non-zinc baseline test [S.E. Ziemniak, M. Hanson, Corros. Sci. 44 (2002) 2209] after 10,000 h. Characterizations of the corrosion oxide layer via grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy in combination with argon ion milling and target factor analysis, revealed that miscibility gaps in two spinel binaries—Fe(Fe_1−mCr_m)₂O₄ and (Fe_1−nZn_n)Fe₂O₄—play a significant role in determining the composition and structure of the corrosion layer(s). Although compositions of the inner and outer corrosion oxide layers represent solvus phases in the Fe₃O₄-FeCr₂O₄ binary, zinc(II) ion incorporation into both phases leads to further phase separation in the outer (ferrite) layer. Recrystallization of the low zinc content ferrite solvus phase is seen to produce an extremely fine grain size (∼20 nm), which is comparable in size to grains in the inner layer and which is known to impart resistance to corrosion. Zinc(II) ion incorporation into the inner layer creates additional corrosion oxide film stabilization by further reducing the unit cell dimension via the substitution reaction

0.2Zn²⁺(aq)+Fe(Fe_0.35Cr_0.65)₂O₄(s)?0.2Fe²⁺(aq)+(Zn_0.2Fe_0.8)(Fe_0.35Cr_0.65)₂O₄(s)     

Thermodynamic studies on LaFeO3(s)

The enthalpy increments and the standard molar Gibbs energies in the formation of LaFeO₃(s) have been measured using a high-temperature Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. The corresponding expression for enthalpy increments is given as:

H°(T)−H°(298.15 K)(J mol⁻¹)(±1.2%)=−36887.27+103.53 T(K)+25.997×10⁻³T²(K)+11.055×10⁵/T(K).

The heat capacity, the first differential of H°(T)−H°(298.15 K) with respect to temperature, is given as:

C_p,m°(T)(JK⁻¹mol⁻¹)=103.53+51.994×10⁻³T(K)−11.055×10⁵/T²(K).

From the measured e.m.f. of the cell, (−)Pt/(LaFeO₃(s)+La₂O₃(s)+Fe(s))//CSZ//(Ni(s)+NiO(s))/Pt(+), and the relevant Δ_fG_m°(T) values from the literature, the Δ_fG_m°(LaFeO₃, s, T) was calculated, and is given as:

Δ_fG_m°(LaFeO₃, s, T)(kJmol⁻¹)(±0.72)=−1319.2+0.2317T(K).

The calculated Δ_fH_m°(LaFeO₃, s, 298.15 K) and S°(298.15 K) values obtained using the second law method are −1334.7 kJ mol⁻¹ and 128.9 J K⁻¹ mol⁻¹, respectively.     

Zinc treatment effects on corrosion behavior of Alloy 600 in high temperature, hydrogenated water

Trace levels of soluble zinc(II) ions (30 ppb) maintained in mildly alkaline, hydrogenated water at 260 °C were found to reduce the corrosion rate of Alloy 600 (UNS N06600) by about 40% relative to a non-zinc baseline test [S.E. Ziemniak, M. Hanson, Corros. Sci., in press, doi:10.1016/j.corsci.2005.01.006]. Characterizations of the corrosion oxide layer via SEM/TEM and grazing incidence X-ray diffraction confirmed the presence of a chromite-rich oxide phase and recrystallized nickel. The oxide crystals had an approximate surface density of 3500 μm⁻² and an average size of 11 ± 5 nm. Application of X-ray photoelectron spectroscopy with argon ion milling, followed by target factor analyses, permitted speciated composition versus depth profiles to be obtained. Numerical integration of the profiles revealed that: (1) alloy oxidation occurred non-selectively and (2) zinc(II) ions were incorporated into the chromite-rich spinel: (Zn_0.55Ni_0.3Fe_0.15)(Fe_0.25Cr_0.75)₂O₄. Spinel stoichiometry places the trivalent ion composition in the single phase oxide region, consistent with the absence of the usual outer, ferrite-rich solvus layer. By comparison with compositions of the chromite-rich spinel obtained in the non-zinc baseline test, it is hypothesized that zinc(II) ion incorporation was controlled by the equilibrium for

0.55Zn²⁺(aq)+(Ni_0.7Fe_0.3)(Fe_0.3Cr_0.7)₂O₄(s)?0.40Ni²⁺(aq)+0.15Fe²⁺(aq)+(Zn_0.55Ni_0.3Fe_0.15)(Fe_0.3Cr_0.7)₂O₄(s)     

Kinetics and mechanisms of nickel metal dusting I. Kinetics and morphology

The kinetics of nickel metal dusting were investigated at different gas compositions at 680 °C. The carbon uptake rate on nickel exposed to supersaturated H₂/CO/H₂O gas mixtures (nominal a_C = 19) increased as p_CO increased from 0.31 to 0.68 atm, but decreased with further increase in p_CO. This behaviour was ascribed to the existence of parallel, independent reaction paths, and the rate was well described by

     

Thermodynamic stability of barium thorate, BaThO3, from a Knudsen effusion study

The Gibbs energy of formation of barium thorate was determined using the Knudsen effusion forward collection technique. The evaporation process could be represented by the equation

BaThO₃(s)=ThO₂(s)+BaO(g)

The vapour pressure of BaO(g) over the two-phase mixture of BaThO₃(s) and ThO₂(s) was obtained from the rate of effusion of BaO(g) and could be represented as

ln(p/Pa) (±0.39)=−50526.5/T/K+26.95 (1770≤T/K≤2136)

The Gibbs energy of formation of BaThO₃(s) could be derived from this data and represented as

Δ_fG°(BaThO₃(s))/kJ mol⁻¹±8.0=−1801.75+0.276T/K

     

Thermal properties of cerium and thorium tellurates

Enthalpy increment measurements on CeTe₂O₆ (s) and ThTe₂O₆ (s) were carried out using a Calvet micro-calorimeter. The enthalpy increment values were least squares analyzed, with the constraint that H⁰(T)−H⁰ (298.15 K) at 298.15 equals 0 and C_p⁰ (298.15 K) is equal to the value estimated by Kellog’s method.The dependence of the enthalpy increment with temperature can be given as:

H⁰(T)−H⁰ (298.15 K)(J mol⁻¹)=189.95 T (K)+15.226×10⁻³ T² (K) +15.414×10⁵/T (K)−63157 (CeTe₂O₆ (s), 391.5–848.0 K)

H⁰(T)−H⁰ (298.15 K)(J mol⁻¹)=191.34 T (K)+14.993×10⁻³ T² (K) +14.668×10⁵/T (K)−63300 (ThTe₂O₆ (s), 391.5–909.3 K)

Molar heat capacity C_p⁰(T), S(T) and Gibb’s free energy functions were evaluated.     

Generation of hydroxyl radicals by sonochemistry: Effects on the electrochemical behaviour of a 316L stainless steel

In this study, water radiolysis occurring in nuclear power plants was simulated by sonochemistry. Generated hydroxyl radicals can recombine in others species such as H₂O₂ and H₂. It is shown that solution conductivity is an important parameter on the evolution of open circuit potential due to the thickness variation of the diffusion layer which may contain sonolysed species (OH, H₂, H₂O₂) in different concentrations. Dissolved gases have also an impact on the 316L electrochemical behaviour. Increase of gas solubility leads to cavitation activity enhancement and further hydroxyl radical production. The latter leads to increased current density values under irradiation.     

Thermodynamic properties of the ternary system InSb–NiSb–Sb in the temperature range 640–860 K

The ternary InSb–NiSb–Sb system has been studied by X-ray diffraction and by potentiometry. The electromotive forces (EMF) have been measured in the temperature range 640<T/K<860 by using the following galvanic cell:

with x (0.075<x<0.498) and y (0<y<0.359). The investigated samples are located on the following lines of the Gibbs triangle: InSb–Ni_0.33Sb_0.66, InSb–Ni_0.48Sb_0.52, InSb–NiSb, Sb–(InSb)_0.75(NiSb)_0.25, Sb–(InSb)_{0. 5}(NiSb)_0.5, Sb–(InSb)_0.25(NiSb)_0.75. From these measurements, the values of the partial molar thermodynamic functions (Δμ°_m,In, ΔH°_m,In, ΔS°_m,In) (data at reference pressure p⁰=10⁵ Pa), for the liquid InSb alloy, for the three solid heterogeneous regions InSb–NiSb₂–Sb, InSb–NiSb_1±δ?–NiSb₂, InSb–NiSb_1±δ, for six ternary liquid–solid alloys, have been calculated.     

Formation, fast oxidation and thermodynamic data of Fe(II) hydroxychlorides

Iron(II) hydroxide and hydroxychloride precipitates were obtained by mixing FeCl₂ · 4H₂O and NaOH aqueous solutions with various concentration ratios R′ = [Cl⁻]/[OH⁻] = 2 [FeCl₂]/[NaOH] at [NaOH] = 0.4 mol L⁻¹. They were analysed by Infrared spectroscopy after 24 h of ageing at room temperature. Fe(OH)₂ was obtained alone only for the smallest values of R′, typically R′ ? 1.16. β-Fe₂(OH)₃Cl formed as soon as R′ ? 1.40 and was obtained alone for R′ ? 2.25. The initial precipitates were oxidised by addition of a small amount of hydrogen peroxide (5 mL of an aqueous solution containing approximately 30 vol% H₂O₂) instead of O₂. The action of H₂O₂ on Fe(OH)₂ gave rise to δ-FeOOH as already reported. Its action on Fe(II) hydroxychlorides gave rise to akaganéite β-FeO_1−2x(OH)_1+xCl_x. A transformation of the two-phase system found at R′ = 1.5 after long ageing times (6 months) was observed and β-Fe₂(OH)₃Cl remained alone. This slow transformation of Fe(OH)₂ into β-Fe₂(OH)₃Cl may explain why β-Fe₂(OH)₃Cl was only reported as a corrosion product on iron archaeological artefacts. Finally, the respective domains of stability of Fe(OH)₂ and β-Fe₂(OH)₃Cl were demarcated and an estimation of the standard Gibbs free energy of formation of β-Fe₂(OH)₃Cl could be given: .     

Formation of Fe(III)-containing mackinawite from hydroxysulphate green rust by sulphate reducing bacteria

The interactions between Fe(II–III) hydroxysulphate GR() and sulphate reducing bacteria (SRB) were studied. The considered SRB, Desulfovibrio desulfuricans subsp. aestuarii ATCC 29578, were added with GR() to culture media. Different conditions were envisioned, corresponding to various concentrations of bacteria, various sources of sulphate (dissolved  + GR() or GR() alone) and various atmospheres (N₂:H₂ or N₂:CO₂:H₂). In the first part of the study, CO₂ was deliberately omitted so as to avoid the formation of carbonated compounds, and GR() was the only source of sulphate. Cell concentration increases from 4 × 10⁷ to 7 × 10⁸ cells/mL in 2 weeks. The evolution with time of the iron compounds, monitored by Raman spectroscopy and X-ray diffraction, showed the progressive formation of a FeS compound, the Fe(III)-containing mackinawite. This result is consistent with the association GR()/SRB/FeS observed in rust layers formed on steel in seawater. In the presence of CO₂ and additional dissolved sulphate species, a rapid growth of the bacteria could be observed, leading to the total transformation of GR() into mackinawite, found in three physico-chemical states (nanocrystalline, crystalline stoichiometric FeS and Fe(III)-containing), and siderite FeCO₃.     

Experimental and theoretical calculations on corrosion inhibition of steel in 1 M H2SO4 by crown type polyethers

The corrosion inhibitive efficiencies of two crown type polyethers, namely dibenzo-bis-imino crown ether (C-1) and dibenzo-diaza crown ether (C-2), which are macrocyclic Schiff base and its reduced form (macrocyclic amine), respectively, for the steel in 1 M H₂SO₄ have been investigated by Tafel extrapolation and linear polarization methods. Corrosion and adsorption isotherm parameters were determined from current-potential curves. The studies show that C-1 and C-2 inhibit the corrosion of the steel in H₂SO₄ solution. Semiempirical AM1 method was used for theoretical calculations. The obtained results of these calculations for the compounds were found to be consistent with the experimental findings.     

Pressure–composition isotherms in the Mg2Ni–H2 system

A relatively pure Mg₂Ni intermetallic compound was prepared by partial melting and sintering. Absorption and desorption pressure–composition isotherms for the Mg₂Ni–H₂ system were obtained. The relationships between the equilibrium plateau pressure (P_eq) and the temperature were

and

The procedure to obtain the pressure–composition isotherms was explained and a method to calculate the composition for pressure–composition isotherms (“the summation method”) was also suggested.     

Electrochemical behavior of tin in sodium borate solutions and the effect of halide ions and some inorganic inhibitors

The corrosion of tin electrode in sodium borate (Na₂B₄O₇) solutions was investigated using cyclic voltammetry and potentiostatic current transient techniques. In absence of halide ions, the E/j response exhibits active/passive transition. The active region involves one anodic peak corresponding to the formation of Sn(OH)₂ and/or SnO. Addition of Cl⁻, Br⁻ or I⁻ (C ? 0.01 M) ions inhibits the active dissolution of tin, but higher concentrations enhance the active dissolution and tend to breakdown the passive film and induce pitting attack. The effect of , , and as inorganic inhibitors on the pitting corrosion of tin in (0.1 M Na₂B₄O₇ + 0.1 M NaCl) solution has also been studied. The presence of these anions (except ) inhibits pitting corrosion. Chronoamperometry measurements showed that nucleation of pit takes place after an incubation time (t_i). The rate of pit nucleation () increases with increasing halide ions concentration and applied potentials, but decreases with increasing the concentration of the inorganic inhibitors (except ). The inhibition efficiency of these inhibitors decreases in the order:

     

The influence of methylcellulose (MC) on solubility of calcium hydroxyapatite (HA) crystals in HA/MC nanocomposites

The influence of methylcellulose ([C₆H₇O₂(OH)_3–x(OCH₃)_x]_n, MC) on the morphology and solubility of calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, GA) nanocrystals (NCs) in GA/MC organomineral nanocomposites (OMCs) is studied. GA/MC OMCs with the MC content of 0.5, 1, 2, 5, 10 and 20 wt % are synthesized in the Ca(OH)₂–H₃PO₄–[C₆H₇O₂(OH)_3–x(OCH₃)_x]_n–H₂O system under biomimetic conditions (37°C). The composition and structural features of OMCs, as well as crystallographic characteristics, size, and morphology of GA NC in OMCs, are determined via chemical analysis, X-ray diffraction (XRD), infrared spectroscopy (IRS), thermal analysis (DTA and DTG), scanning (SEM) and transmission (TEM) electron microscopy, and electron diffraction (ED). It is shown that the growth in the MC concentration in OMCs leads to the change in the GA NC morphology and the increase in their solubility (for Ca²⁺ and PO₄^3- ions).     

Effect of hexamethylpararosaniline chloride (crystal violet) on mild steel corrosion in acidic media

The corrosion inhibition of mild steel in 0.5 M H₂SO₄ and 1 M HCl by hexamethylpararosaniline chloride (HMPC) was investigated using the gravimetric technique in the temperature range 303–333 K. The results indicate that HPMC inhibited the corrosion reaction in both acid media at all temperatures and inhibition efficiency increased with HMPC concentration. The inhibiting action is attributed to general adsorption of protonated and molecular HPMC species on the corroding metal surface. Adsorption followed a modified Langmuir isotherm and the Temkin isotherm, with very high negative values of the free energy of adsorption (). An increase in temperature reduced the inhibition efficiency of HPMC in 0.5 M H₂SO₄ but increased efficiency in 1 M HCl. Activation parameters such as activation energy (E_a), activation enthalpy (ΔH^∗) and activation entropy (ΔS^∗) as well as the adsorption heat (Q_ads) were evaluated from the effect of temperature on corrosion and inhibition processes.     

Influence of rare earth metals on the characteristics of anodic oxide films on aluminium and their dissolution behaviour in NaOH solution

The characteristics of oxide films on Al and Al1R alloys (R = rare earth metal = Ce, Y) galvanostatically formed (at a current density of 100 μA cm⁻²) in borate buffer solution (0.5 M H₃BO₃ + 0.05 M Na₂B₄O₇·10H₂O; pH = 7.8) were investigated by means of electrochemical impedance spectroscopy. EIS spectra were interpreted in terms of an “equivalent circuit” that completely illustrate the Al(Al1R alloy)/oxide film/electrolyte systems examined. The resistance of the oxide films was found to increase on passing from Al to Al1R alloys while the capacitance showed an opposite trend. The stability of the anodic oxide films grown in the borate buffer solution on Al and Al1R alloys was investigated by simultaneously measuring the electrode capacitance and resistance at a working frequency of 1 kHz as a function of exposure over a period of time to naturally aerated 0.01 M NaOH solution. Analyses of the electrode capacitance and resistance values indicated a decrease in chemical dissolution rate of the oxide films on passing from Al to Al1R alloys.     

On the fundamentals of electrochemical corrosion of X65 steel in CO2-containing formation water in the presence of acetic acid in petroleum production

Electrochemical corrosion behavior of X65 steel in CO₂-containing oilfield formation water in the presence of acetic acid (HAc) was investigated by various electrochemical measurements and analyses as well as thermodynamic calculations of ionic concentrations, reaction rate constants and equilibrium electrode potentials. A conceptual model was developed to illustrate corrosion processes of steel in oilfield formation water system. The anodic reactions of the steel contain a direct dissolution of Fe, Fe → Fe²⁺ + 2e, and the formation of corrosion scale, FeCO₃, by Fe + → FeCO₃ + H⁺ + 2e. The cathodic processes contain the reduction of H⁺, , H₂O and HAc, where reduction of HAc has the least negative equilibrium potential and thus dominates the cathodic process. With addition of HAc in the solution, both cathodic and anodic reaction rates increase remarkably. It is attributed to the fact that HAc inhibits or degrades the formation of protective scales due to the decrease of solution pH. Upon electrode rotation, the measured impedance decreases with the increase in HAc concentration. The FeCO₃ scale will not form on electrode surface. When HAc concentration is less than 1000 ppm, the adsorbed intermediate product is not significant, resulting in generation of a low-frequency inductive loop in EIS plots. When HAc concentration is more than 3000 ppm, the adsorption of intermediate product is significant, generating overlapped capacitive semicircles in EIS measurements.     

Inverse magnetocaloric effect in the uniaxial paramagnet with non-Kramers ions

It has been shown that, in a uniaxial paramagnet with non-Kramers ions with a spin of S = 1 and single-ion anisotropy of the easy-plane type (DS _Z ² ), there is a low-field (μ₀ H ≤ D) and low-temperature (k _B T < 0.68D) region in which the isothermal magnetization along the hard direction H||OZ increases the magnetic entropy by ΔS _M (T, ΔH = H _f - H _i > 0) > 0 and the adiabatic magnetization along the same direction reduces the sample temperature by ΔT _ad(T, ΔH > 0) < 0 (inverse magnetocaloric effect (MCE)). The main features of the inverse MCE in uniaxial paramagnets with large spins (S = 2, 3, …) of the non-Kramers ions have been discussed.