• Corrosion Science and Technology
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• 제18권3호
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• pp.110-116
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• 2019

Resistances to pitting corrosion of additive manufactured (AM) Ti-6Al-4V alloys in 0.6 M NaBr and 0.6 M NaCl aqueous solutions were compared using micro-droplet cell techniques. With respect to the pitting corrosion resistance, this study focused on two different types of halide anions in aqueous solutions, i.e. $Br^-$ and $Cl^-$. The differences between $Br^-$ and $Cl^-$ halide anions for breakdown on passive films of AM Ti-6Al-4V alloy were explained using Langmuir adsorption model with their equilibrium adsorption coefficients. The results of the analysis showed that the lower resistance to pitting potential of AM Ti-6Al-4V alloy in $Br^-$ aqueous solution was attributed to the higher equilibrium adsorption coefficient of Br-. In addition, micro-electrochemical test results showed that the pitting corrosion resistance of dark grains in additive manufactured Ti-6Al-4V alloy was lower as compared to that of bright grains due to the larger volume of ${\alpha}^{\prime}$ phase that caused the susceptibility to pit initiation.

• Computers and Concrete
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• 제8권2호
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• pp.177-192
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• 2011

This research paper aims at computer based modeling of carbonation induced corrosion under extreme conditions and its experimental verification by incorporating enhanced electrochemical and mass balance equations based on thermo-hygro physics with strong coupling of mass transport and equilibrium in micro-pore structure of carbonated concrete for which the previous research data is limited. In this paper the carbonation induced electrochemical corrosion model is developed and coupled with carbon dioxide transport computational model by the use of a concrete durability computer based model DuCOM developed by our research group at concrete laboratory in the University of Tokyo and its reliability is checked in the light of experiment results of carbonation induced corrosion mass loss obtained in this research. The comparison of model analysis and experiment results shows a fair agreement. The carbonation induced corrosion model computation reasonably predicts the quantitative behavior of corrosion rate for normal air dry relative humidity conditions. The computational model developed also shows fair qualitative corrosion rate simulation and analysis for various pH levels and coupled environmental actions of chloride and carbonation. Detailed verification of the model for the quantitative carbonation induced corrosion rate computation under varying relative conditions, different pH levels and combined effects of carbonation and chloride attack remain as scope for future research.

• Journal of Electrochemical Science and Technology
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• 제2권1호
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• pp.14-19
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• 2011

Quasi-equilibrium profiles are analyzed through galvanostatic intermittent titration technique (GITT) and potentiostatic intermittent titration technique (PITT) to study the charge/discharge mechanism in multicomponent olivine structure ($LiMn_{1/3}Fe_{1/3}Co_{1/3}PO_4$). From GITT data, the degree of polarization is evaluated for the three regions corresponding to the redox couples of $Mn^{2+}/Mn^{3+}$, $Fe^{2+}/Fe^{3+}$ and $Co^{2+}/Co^{3+}$. From PITT data, the current vs. time responses are examined in each titration step to find out the mode of lithium de-intercalation/intercalation process. Furthermore, lithium diffusivities at specific compositions (x in $Li_xMn_{1/3}Fe_{1/3}Co_{1/3}PO_4$) are also calculated. Finally, total capacity ($Q^{total}$) and diffusional capacity ($Q^{diff}$) are obtained for some selected voltage steps. The entire study consistently confirms that the charge/discharge mechanism of multicomponent olivine cathode is associated with a one-phase reaction rather than a biphasic reaction.

• 대한화학회지
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• 제33권5호
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• pp.496-503
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• 1989

란탄나이드 3가 (Pr(III)와 Yb(III))와 2,2,6,6-tetramethyl-3,5-heptanedione(dipivaloylmethane) 착물들의 전기화학적 거동을 DC와 DP 그리고 CV 방법으로 조사하였다. 란탄나이드 3가 착물들 중 Pr(III)의 환원은 Ag-AgCl 전극으로 Epc = -0.13 V와 -0.80 V 그리고 Yb(III)는 -0.02 Ⅴ로 1전자이동에 의한 것임을 알았고, 1차 화학평형반응이 가역과 비가역으로 진행되는 ErCr전극과정임을 DP와 CV로부터 알았다. 평형상수 lnK는 여러 용매들로부터 얻었고, 이들 상수는 용매의 유전상수가 감소함에 따라 증가됨을 알았다. 이들 반응에서 lnK는 여러 용매에 대한 ln(1/D)을 도시하면 좋은 직선관계에 있었고, 이 때 란탄나이드의 거동은 원자번호가 증가함에 따라서 lnK가 감소하였다.

• Corrosion Science and Technology
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• 제3권5호
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• pp.198-208
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• 2004

Although there has been no general agreement on the mechanism of primary water stress corrosion cracking (PWSCC) as one of major degradation modes of Ni-base alloys in pressurized water reactors (PWR's), common postulation derived from previous studies is that the damage to the alloy substrate can be related to mass transport characteristics and/or repair properties of overlaid oxide film. Recently, it was shown that the oxide film structure and PWSCC initiation time as well as crack growth rate were systematically varied as a function of dissolved hydrogen concentration in high temperature water, supporting the postulation. In order to understand how the oxide film composition can vary with water chemistry, this study was conducted to characterize oxide films on Alloy 600 by an in-situ Raman spectroscopy. Based on both experimental and thermodynamic prediction results, Ni/NiO thermodynamic equilibrium condition was defined as a function of electrochemical potential and temperature. The results agree well with Attanasio et al.'s data by contact electrical resistance measurements. The anomalously high PWSCC growth rate consistently observed in the vicinity of Ni/NiO equilibrium is then attributed to weak thermodynamic stability of NiO. Redox-induced phase transition between Ni metal and NiO may undermine the integrity of NiO and enhance presumably the percolation of oxidizing environment through the oxide film, especially along grain boundaries. The redox-induced grain boundary oxide degradation mechanism has been postulated and will be tested by using the in-situ Raman facility.

• 한국수소및신에너지학회논문집
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• 제5권2호
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• pp.99-109
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• 1994

To develop high capacity hydrogen storage alloys for secondary Ni/MH batteries, electrochemical charge/discharge characteristics of $Zr_{1-x}Ti_xMn_{1-y}V_yNi_{1-z}M_z$ (M=Al,Co,Fe) alloys were investigated, in which $0.2{\leq}x{\leq}0.6$, $0.2{\leq}y{\leq}0.8$, $0.2{\leq}z{\leq}0.4$. With increasing Ti content(x) and/or decreasing V content(y), lattice constants and maximum theoretical capacities of the alloys were decreased and equilibrium pressure of hydrogen absorption were increased. Electrochemical discharge capacities were increased with increasing Ti content(x). Especially, the alloys of x= 0.4~0.6 showed better charge/discharge efficiencies than those of x<0.4. Discharge capacities of $Zr_{0.4}Ti_{0.6}Mn_{0.4}V_{0.6}Ni_{0.8}Fe_{0.2}$, $Zr_{0.4}Ti_{0.6}Mn_{0.4}V_{0.6}Ni_{0.8}Al_{0.2}$ and $Zr_{0.5}Ti_{0.5}Mn_{0.4}V_{0.6}Ni_{0.6}Co_{0.4}$ were 385, 328 and 333mAh/g, respectively. These alloys were fully activated within five charge/discharge cycles and had a good charge and discharge rate capabilities and temperature characteristics.

• 전기화학회지
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• 제6권2호
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• pp.119-129
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• 2003

The Langmuir adsorption isotherms of the over-potentially deposited hydrogen (OPD H) fur the cathodic $H_2$ evolution reaction (HER) at the poly-Au and $Rh|0.5M\;H_2SO_4$ aqueous electrolyte interfaces have been studied using cyclic voltammetric and ac impedance techniques. The behavior of the phase shift $(0^{\circ}{\leq}{-\phi}{\leq}90^{\circ})$ for the optimum intermediate frequency corresponds well to that of the fractional surface coverage $(1{\geq}{\theta}{\geq}0)$ at the interfaces. The phase-shift profile $({-\phi}\;vs.\;E)$ for the optimum intermediate frequency, i.e., the phase-shift method, can be used as a new electrochemical method to determine the Langmuir adsorption isotherm $({\theta}\;vs.\;E)$ of the OPD H for the cathodic HER at the interfaces. At the poly-Au|0.5M $H_2SO_4$ aqueous electrolyte interface, the equilibrium constant (K) and the standard free energy $({\Delta}G_{ads})$ of the OPD H are $2.3\times10^{-6}$ and 32.2kJ/mol, respectively. At the poly-Rh|0.5M $H_2SO_4$ aqueous electrolyte interface, K and ${\Delta}G_{ads}$ of the OPD H are $4.1\times10^4\;or\;1.2\times10^{-2}$ and 19.3 or 11.0kJ/mol depending on E, respectively. In contrast to the poly-Au electrode interface, the two different Langmuir adsorption isotherms of the OPD H are observed at the poly-Rh electrode interface. The two different Langmuir adsorption isotherms of the OPD H correspond to the two different adsorption sites of the OPD H on the poly-Rh electrode surface.

• 한국수소및신에너지학회논문집
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• 제20권3호
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• pp.194-201
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• 2009

The e1ectrocatalytic properties of heteropolyacids(HPAs) entrapped in covalently cross-linked sulfonated polyetheretherketone(CL-SPEEK/HPA) membranes have been studied for water electrolysis. The HPAs, including tungstophosphoric acid(TPA), molybdophosphoric acid(MoPA), and tungstosilicic acid(TSiA) were used as additives in the composite membranes. The MEA was prepared by a non-equilibrium impregnation-reduction(I-R) method, using reducing agent, sodium borohydride(NaBH4) and tetraamineplatinum(II) chloride(pt(NH$_3$)$_4$Cl$_2$). The electrocatalytic properties of composite membranes such as the cell voltage were in the order of magnitude CL-SPEEKlMoPA40 (wt%) > /TPA30 > /TSiA40. In the optimum cell applications for water electrolysis, the cell voltage of PtlPEM/Pt-Ru MEA with CL-SPEEKlTPA30 membrane was 1.75 V at 80$^{\circ}$C and I A/cm$^2$ and this voltage carried lower than that of 1.81 V of Nafion 117. Consequently, in regards of electrochemical and mechanical characteristics and oxidation durability, the newly developed CL-SPEEKITPA30 composite membrane exhibited a better performance than the others, but CLSPEEKlMoPA40 showed the best electrocatalytic activity (1.71 Vat 80$^{\circ}$C and 1 A/cm$^2$) among the composite membranes.

• 전기화학회지
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• 제7권4호
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• pp.194-200
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• 2004

The constant correlation factors between the Temkin and the Langmuir or the Frumkin adsorption isotherms of over-potentially deposited hydrogen (OPD H) for the cathodic H2 evolution reaction (HER) at poly-Pt and Re/0.5M $H_2SO_4$ and poly-Ni/0.05 M KOH aqueous electrolyte interfaces have been experimentally and consistently found using the phase-shift method. At intermediate values of the fractional surface coverage $(\theta),\;i.e.,\;02<{\theta}<0.8$, the Langmuir and Temkin adsorption isotherms of OPD H for the cathodic HER are correlated to each other even though the adsorption conditions or processes are different from each other. At the same range of $\theta$, correspondingly, the Frumkin and Temkin adsorption isotherms of OPD H for the cathodic HER are correlated to each other. The equilibrium constants $(K_o)$ for the Temkin adsorption isotherms $({\theta}\;vs.\; E)$ are consistently ca. 10 times greater than those (K, Ko) for the corresponding Langmuir or Frumkin adsorption isotherms ($({\theta}\;vs.\; E)$. The interaction parameters (g) for the Temkin adsorption isotherms $({\theta}\;vs.\; E)$ are consistently ra. 4.6 greater than those (g) for the corresponding Langmuir or Frumkin adsorption isotherms $({\theta}\;vs.\; E)$. These numbers (10 times and 4.6) can be taken as constant correlation factors between the corresponding adsolftion isotherms (Temkin, Langmuir, Frumkin) at the interfaces. The Temkin adsorption isotherm corresponding to the Langmuir or the Frumkin adsorption isotherm, and vice versa, can be effectively verified or confirmed using the constant correlation factors. Both the phase-shift methodand constant correlation factors are useful and effective for determining or confirming the suitable adsorption isotherms (Temkin, Langmuir, Frumkin) of intermediates for sequential reactions in electrochemical systems.

• Journal of Electrochemical Science and Technology
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• 제13권2호
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• pp.279-291
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• 2022

In this report the thermochemical conversion of Sm₂O₃ to SmCl₃ using AlCl₃ in LiCl-KCl melt at 773 K is discussed. The final product was a mixture of SmCl₃, Al₂O₃, unreacted Sm₂O₃ and AlCl₃ in the chloride melt. The electrochemical attributes of the mixture was analyzed with cyclic voltammetry (CV) and square wave voltammetry (SWV). The crystallographic phases of the mixture were studied with X-ray diffraction (XRD) technique. The major chemical conversion was optimized by varying the effective parameters, such as concentrations of AlCl₃, duration of reaction and the amount of LiCl-KCl salt. The extent of conversion and qualitative assessment of efficiency of the present protocol were evaluated with fluorescence spectroscopy, UV-Vis spectrophotometry and inductively coupled plasma atomic emission spectroscopy (ICP-AES) studies of the mixture. Thus, a critical assessment of the thermochemical conversion efficiency was accomplished by analysing the amount of SmCl₃ in LiCl-KCl melt. In the process, a conversion efficiency of 95% was achieved by doubling the stoichiometric requirement of AlCl₃ in 50 g of LiCl-KCl salt. The conversion reaction was found to be very fast as the reaction reached equilibrium in 15 min.