Electrochemical Behavior Of Ti Research Articles

Breaking the Passivity Wall of Metals: Exempli Gratia Non-Aqueous Ti–Air Battery

In recent years, metal–air batteries have been gaining much attention as one crucial line of development as promising energy storage devices due to possessing high theoretical specific energies and energy densities while utilizing cost-effective, safe, and environmentally friendly electrode materials. Among various possible metal–air configurations, mostly Zn–, Fe–, and Al–air have been the research focus for many decades. Up to now, Ti has not been considered as an active anode material, although it is a light metal that can possibly transfer up to 4 electrons. The reason behind this is that the electrochemical behavior of Ti is known for its passivity in various media and, also, it is conceptually mistaken as an expensive metal.Herein, we report a novel non-aqueous primary Ti–air battery utilizing 1-ethyl-3-methylimidazolium oligofluorohydrogenate (EMIm(HF)2.3F) room temperature ionic liquid as electrolyte. Initially, the electrochemical behavior of Ti was studied by potentiodynamic polarization, which revealed the first insights into its electrochemical activity. Subsequently, the galvanostatic discharge experiments were conducted to evaluate the performance of Ti–air batteries in full-cells. The battery could successfully be operated under moderate current densities (up to 0.75 mA/cm2) with an average cell voltage of 1–1.2 V, yielding up to a discharge capacity of 66 mAh/cm2. Post-mortem characterization of the electrode surfaces was performed by SEM in combination with EDS to analyze the potentially deposited discharge products. Furthermore, ICP-OES and FTIR techniques were employed for investigating the electrolytes to gain further insights into the possible mechanisms leading to cell discharge termination over time. Additionally, the possible reaction mechanisms governing within the cell were proposed for the Ti–air battery. Such a metal–air battery holds a unique potential to be the only metal with 4 electrons transfer during its discharge once its full potential is harvested.

Electrodeposition of Ti in Molten Alkali Metal Fluoride–Chloride Mixtures: Comparative Study of Li, Na, K, and Cs Systems

1. IntroductionTitanium (Ti) is a metal with excellent properties such as high corrosion resistance and biocompatibility. However, it is still not widely used due to its high production cost and poor workability. If Ti films can be plated on a variety of substrates, the excellent surface properties of Ti can be imparted, and it is expected to be applied in a wider range of fields.We have previously studied Ti electrodeposition using KF–KCl [1-3] and LiF–LiCl [4,5] melts and reported that smooth Ti films were obtained. Here, fluoride–chloride melts containing a single cation, such as KF–KCl and LiF–LiCl, were used so that differences due to cations could be compared. As a result, we have already reported that the electrodeposition potential of Ti differs significantly between the K- and Li-based systems [4]. Therefore, in this study, we investigated the electrodeposition of Ti and the electrochemical behavior of Ti(III) ions in the CsF-CsCl and NaF-NaCl melts. This allowed us to systematically compare the effects of cations on titanium electrodeposition for the Li-, Na-, K-, and Cs-based systems.2. ExperimentalThe experiments were conducted in eutectic CsF–CsCl and NaF–NaCl melts in an Ar glove box. A2TiF6 (A = Cs, Na) and sponge Ti were added to the melts and Ti(IV) ions were converted to Ti(III) ions by comproportionation reaction. Ni plate, Mo and Au flag electrodes were used as the working electrodes. The counter and reference electrodes were Ti rods. The potential of the reference electrode was calibrated by A+/A (A = Cs, Na) potential measured at a Mo electrode. The electrochemical behavior of Ti(III) was studied by cyclic voltammetry. Samples prepared by galvanostatic electrolysis of Ni plate substrates were analyzed by X-ray diffraction (XRD) after washing with distilled water.3. Result and DiscussionFigure 1 (a) shows cyclic voltammograms measured at a Mo flag electrode in the negative potential region in molten CsF–CsCl at 823 K. After the addition of Ti(III) ions, cathodic currents around 0.3 V were larger than those before the addition, and a current shoulder was observed at 0.3 V. Furthermore, a sample prepared by galvanostatic electrolysis at a cathodic current density of 25 mA cm−2 was confirmed to be Ti metal by XRD. Considering that the potential during the electrodeposition was around 0.3 V, the cathodic currents around 0.3 V in the CV were confirmed to beTi(III) + 3e− → Ti(0).Figure 1 (b) shows cyclic voltammograms measured at a Au flag electrode in the positive potential region in molten CsF–CsCl containing Ti(III) ions at 823 K. A pair of redox currents were observed around 1.7 V. The number of electrons transferred was 0.86 which was calculated from the difference in the cathodic and anodic peak potentials. This result indicates that the redox reaction around 1.7 V isTi(IV) + e− ⇄ Ti(III).Here, the formal potential of Ti(IV)/Ti(III) was calculated to be 1.63 V from the average values of the cathodic and anodic peak potentials.We compared the obtained potentials of Ti(III)/Ti(0) and Ti(IV)/Ti(III) to those previously reported in KF–KCl and LiF–LiCl melts [2,4]. Figure 2 shows the comparison of the Ti(III)/Ti(0) and Ti(IV)/Ti(III) potentials in CsF–CsCl, KF–KCl, and LiF–LiCl melts. All potentials were calibrated using F2/F− potential for comparison because Ti(III) ions exist as fluoro-complexes in the melts. Both Ti(III)/Ti(0) and Ti(IV)/Ti(III) potentials were negative in the order of Li-, K-, Cs-based systems. Such potential differences are explained by the interactions of alkaline cations (A+) and fluoride ions (F−); smaller cations interact more strongly with F−, resulting in reduced stability of Ti fluoro-complexes. At the meeting, we will compare and discuss all the results, including those obtained with NaF-NaCl melts.AcknowledgmentA part of this work was supported by JSPS KAKENHI Grant Number 22K14507. A part of this study was conducted as a collaboration with Sumitomo Electric Industries, Ltd.

Breaking the passivity wall of metals: Exempli gratia non-aqueous Ti–air battery

A new multivalent metal–air battery employing Titanium (Ti) as active material in EMIm(HF)2.3F room temperature ionic liquid electrolyte is introduced. Ti metal is highly attractive as it is a light metal that can possibly transfer up to 4 electrons. The electrochemical behavior of Ti is known for its passivity in various media. Here, we evaluated the electrochemistry of Ti in EMIm(HF)2.3F with potentiodynamic polarization and galvanostatic discharge experiments. Ti–air battery could successfully be operated under relatively high current densities (up to 0.75 mA cm−2) with an average cell voltage of 1–1.2 V, yielding up to a discharge capacity of 66mAhcm−2. When its full potential is harvested, such a metal–battery holds a unique potential to be the only metal with 4 electrons transfer during its discharge.

Electrochemical Behaviour of Ti and Ti-6Al-4V Alloy in Phosphate Buffered Saline Solution.

The electrochemical behavior of commercially pure titanium (CP Ti) and Ti-6Al-4V (Grade 5) alloy in phosphate buffered saline solution (PBS, pH = 7.4) at 37 °C (i.e., in simulated physiological solution in the human body) was examined using open circuit potential measurements, linear and potentiodynamic polarization and electrochemical impedance spectroscopy methods. After the impedance measurements and after potentiodynamic polarization measurements, the surface of the samples was investigated by scanning electron microscopy, while the elemental composition of oxide film on the surface of each sample was determined by EDS analysis. The electrochemical and corrosion behavior of CP Ti and Ti-6Al-4V alloys is due to forming a two-layer model of surface oxide film, consisting of a thin barrier-type inner layer and a porous outer layer. The inner barrier layer mainly prevents corrosion of CP Ti and Ti-6Al-4V alloy, whose thickness and resistance increase sharply in the first few days of exposure to PBS solution. With longer exposure times to the PBS solution, the structure of the barrier layer subsequently settles, and its resistance increases further. Compared to Ti-6Al-4V alloy, CP Ti shows greater corrosion stability.

Effect of Temperature on Electrodeposition of Ti in LiF – LiCl Eutectic Melt

1. Introduction Titanium metal has superior properties such as high specific strength, high corrosion resistance, biocompatibility, etc. In addition to these properties, crustal abundance of titanium is more than 40 times larger than those of commonly used copper and nickel. However, titanium is not used widely and commonly due to two problems: the high cost of present smelting method and the poor workability of itself. Therefore, both a new smelting method and a processing method are required. Plating titanium metal on an inexpensive substrate is one of the methods to resolve these problems. Electrodeposition of titanium is a promising plating method from the viewpoints of the cost and the flexibility in shape of substrate. Thus, electrodeposition of titanium metal has been investigated for a long time using high-temperature molten salts [1–4]. We have already reported that compact, smooth, and adherent titanium films are electrodeposited in molten KF–KCl and LiF–LiCl containing Ti(III) ions at 923 K [5–8]. However, crystal grains of titanium become large with the increase of a film thickness, which results in a rough surface. Concerning the crystal grain size, Wei et al. electrodeposited titanium in molten LiCl–NaCl–KCl–K2TiF6 (+ Ti metal) at 723–973 K and reported that the grain size became small as the temperature decreased [1]. This report suggests that titanium films are expected to have a smoother surface at a lower electrodeposition temperature. Therefore, in the present study, we investigated the effect of temperature on morphology and smoothness of electrodeposited titanium films in LiF–LiCl eutectic melt at 823–973 K. The effect of temperature on the electrochemical behavior of Ti(III) ions was also studied.2. Experimental The experiments were conducted in LiF–LiCl eutectic melt (LiF:LiCl = 30:70 mol%, m.p.: 774 K [9]) in an Ar glovebox. The experimental temperature was varied from 823 K to 973 K. Li2TiF6(2.00 mol%) and Ti sponge (1.33 mol%) were added to the bath and Ti(III) ions were prepared by comproportionation reaction. Ni plate, Mo flag, and Au flag electrodes were used as the working electrodes. The counter and reference electrodes were Ti rods. The potential of the reference electrode was calibrated by Li+/Li potential measured at a Mo flag electrode. Samples prepared by galvanostatic electrolysis of Ni plate substrates were analyzed by SEM/EDX after washing with distilled water to remove adhered salts.3. Results and Discussion Galvanostatic electrolysis was conducted at 823, 873, 923, and 973 K. Fig. 1 shows the optical and surface SEM images of the samples. The cathodic current density and electrolysis time were 100 mA cm−2 and 10 min, respectively. The surface roughness (Sa) was measured by SEM, which is also shown in Fig. 1. All the samples have a metallic luster. The sample at 823 K has the highest brightness with metallic luster. The surface SEM observations indicate that the crystal grain size increases as the temperature rises. This tendency is reasonably explained by a previous work on the temperature dependent grain growth of Ti [10]. The value of Sa also increases as the temperature increases. The smoothest Ti film with Sa = 2.05 ± 0.22 μm was obtained at 823 K. These results conclude that Ti film with smoother surface can be electrodeposited at a lower temperature by suppressing the grain growth of Ti. In the presentation, more detailed analysis results and the effect of temperature on the electrochemical behavior of Ti(III) ions will be discussed.Acknowledgement A part of this work was supported by JSPS Fellows grant number 19J15015. The present address of Kouji Yasuda is Graduate School of Engineering, Kyoto Univ.

Electrochemical Behavior of Ti(III) Ions in Molten LiF–LiCl: Comparison with the Behavior in Molten KF–KCl

Ti(III) ions has been prepared by the addition of 0.50 mol% of Li2TiF6 and 0.33 mol% of Ti sponge to LiF–LiCl melt, and their electrochemical behavior has been investigated using cyclic voltammetry and square wave voltammetry at 923 K. The reduction of Ti(III) ions to metallic Ti is observed around 1.2 V vs Li+/Li, whereas the oxidation to Ti(IV) ions is observed at 2.78 V as a reversible electrochemical process. The diffusion coefficient of Ti(III) ions is determined to be 3.2 × 10−5 cm2 s−1. The electrochemical behavior of Ti(III) ions in LiF–LiCl melt is compared to that in KF–KCl melt. The potentials for Ti(IV)/Ti(III) and Ti(III)/Ti(0) couples based on the F2/F− potential in LiF–LiCl melt are more positive than those in KF–KCl melt by 0.41 V and 0.31 V, respectively. Such differences in potential are explained by the difference in interactions between Li+–F− and K+–F−.

Influence of Molar Ratio of CaO to TiO2 on Ti Electrodeposition in Molten CaCl2

In our laboratory, the direct electrowinning of liquid Ti metal in molten chloride has been studied. Based on our previous study, the electrochemical behavior of Ti in CaCl2-CaO-TiO2 bath, in which the molar ratio of CaO to TiO2 (RCaO/TiO2 ) was above 1.5, has been investigated, and the dependence of Ti metal deposition on RCaO/TiO2 was discussed. The reduction behavior changed with the type of calcium titanate, and the electrodeposition of Ti metal depended on RCaO/TiO2 . Titanium metal was obtained in the bath of RCaO/TiO2 > 1.5 more easily than that of RCaO/TiO2 < 1.5, but Ca metal was also obtained in the bath with RCaO/TiO2 = 2.0. The concentration of RCaO/TiO2 also influenced Ti deposition. It was suggested that suitable RCaO/TiO2 to obtain Ti metal was around 1.5, and that the suitable electrolysis potential was -1.8V ~ -1.9V.

Electrochemical Corrosion Behaviour of Ti–29Nb–13Ta–4.6Zr Alloy in Physiological Solution Containing Various Synovial Joint Lubricants

Ti alloys are well known for their biocompatibility and high specific strength. In the present work, the electrochemical behaviour of Ti–13Ta–29Nb–4.6Zr alloy having β structure in Hank’s solution containing various joint lubricants has been studied. The results show that Ti–13Ta–29Nb–4.6Zr alloy is a potential biomaterial for joint applications. The electrochemical behaviour of Ti–13Ta–29Nb–4.6Zr alloy is not influenced significantly by the nature of lubrication. The highest corrosion rate of investigated alloy is around 1.2 mm/year in Hyaluronic Acid containing Hank’s solution. The growth of passive layer is the slowest and the passive layer is the most porous in Hank’s solution containing hyaluronic acid.

Electrodeposition of an ultrathin TiO2 coating using a deep eutectic solvent based on choline chloride

An alternative route is proposed for direct electrodeposition of TiO2 films. The electrochemical behaviour of Ti(IV) species in the deep eutectic solvent formed between choline chloride (ChCl) and ethylene glycol (EG) was studied by chronoamperometry and cyclic voltammetry. It was discussed that during the cathodic scan soluble subvalent TiClχ species were formed using the eutectic system 1ChCl:2EG. Using ethylenediamine or LiF as additives it was possible to obtain a titanium dioxide thin film in the orthorhombic variant named brookite. Chronoamperometric investigations revealed a nucleation mechanism involving the simultaneous presence of 2D instantaneous nucleation process including lattice incorporation and a 3D diffusion-limited nucleation and growth process.

Comparison of the Electrochemical Behavior of Ti and Nanostructured Ti-Coated AISI 304 Stainless Steel in Strongly Acidic Solutions

In this study, the electrochemical behaviors of pure titanium (Ti) and nanostructured (NS) Ti-coated AISI 304 stainless steel (SS) in strongly acidic solutions of H2SO4 were investigated and compared. A type of physical vapor deposition method, cathodic arc evaporation, was applied to deposit NS Ti on 304 SS. Scanning electron microscope and X-ray diffraction were used to characterize surface coating morphology. Potentiodynamic polarization, electrochemical impedance spectroscopy, and Mott–Schottky (M–S) analysis were used to evaluate the passive behavior of the samples. Electrochemical measurements revealed that the passive behavior of NS Ti coating was better than that of pure Ti in 0.1 and 0.01 M H2SO4 solutions. M–S analysis indicated that the passive films behaved as n-type semiconductors in H2SO4 solutions and the deposition method did not affect the semiconducting type of passive films formed on the coated samples. In addition, this analysis showed that the NS Ti coating had lower donor densities. Finally, all electrochemical tests showed that the passive behavior of the Ti-coated samples was superior, mainly due to the formation of thicker, yet less defective passive films.

Electrochemical Behavior of Ti in Molten Fluoride-Oxide System

The cathodic reaction of Ti has been studied in a CaF2-MgF2 bath with CaO and TiO2 at 1373K. Cyclic voltammograms were measured in the baths of various compositions, and the dependence of the cathodic reaction of Ti on the bath composition was discussed. With reference to the results of the cyclic voltammetry, Ti metal deposition by potentio-static electrolysis was attempted. It was shown that the reduction sequence of Ti consisted of three steps, and Ti metal was deposited under the suitable condition. The cathodic behavior of Ti was influenced by the molar ratio of TiO2 to CaO in the melt. Considering the previous results of Ti electrolysis by using DC-ESR unit, it is strongly suggested that a binuclear complex ion of Ti with O, such as Ti2O7 6-, affects the reduction sequence of Ti in CaF2-CaO-TiO2 and CaF2-MgF2-CaO-TiO2 baths.

Electrochemical Behavior of Ti in Molten Fluoride-Oxide System

INTRODUCTIONAn innovative process of Ti metal production is earnestly required to supply Ti metal sufficiently at a moderate price. Some new production processes have been proposed. Our group has been studying the direct electrolytic production of liquid Ti metal by using a direct-current electro-slag remelting (DC-ESR) unit in a CaF2-CaO-TiO2 melt, and showed that Ti metal in liquid were obtained. In the previous researches, the electro-deposition of Ti by this process was strongly influenced by the electrolytic bath composition.In this study, the cathodic reaction of Ti in a similar fluoride-oxide melt containing TiO2 was studied to clarify the influence of the bath composition. Cyclic voltammetry was applied in the bath of various compositions, and potentio-static electrolysis was performed to analyze the electrodeposit at the specific potential.EXPERIMENTALThe apparatus is schematically illustrated in Fig.1. A eutectic mixture of CaF2-MgF2 (55:45 in mole) was used as an electrolytic bath. CaO and TiO2 were added to control the molar ratio of CaO to TiO2, RCaO/TiO2 , between 0~2. The mixture was fused under a pure Ar atmosphere, and kept at 1273~1373K. Some kinds of crucible material, such as graphite, Mo and BN, were used because there was a possibility that the crucible reacted with the bath.The cathodic reaction was investigated by cyclic voltammetry (CV). A Mo wire (f1mm) was used as a working electrode, and immersed in the bath at a depth of 5~10mm. A graphite rod (f5mm) was used as a counter electrode. Since no stable reference electrode was reported in this bath, another Mo wire was used as a quasi-reference electrode. The potential of the quasi-reference electrode was calibrated by the zero-current potential determined by Mg deposition and dissolution in the CV. All the potentials are represented versus this potential. Since the current density and the electrode potential should be contained inaccuracy, the CV shape is discussed qualitatively.Based on the results of the CV measurement, potentio-static electrolysis was performed using a Mo plate electrode, and the electrodeposit was analyzed by XRD.RESULTS and DISCUSSIONFig. 2 shows the change in the CV with RCaO/TiO2 . Reduction current increased below 0.4V in all the baths. The cathodic current in this potential region increased with TiO2 addition, so it was thought to correspond to the reduction of Ti ion. In the bath of RCaO/TiO2 = 1.0, a cathodic current hump was seen around 0.65V. A small hump still appeared around 0.75V in the bath of RCaO/TiO2 = 1.5, while it disappeared in the bath of RCaO/TiO2 = 2.0. Although residual current seems un-negligible in this potential region, the change in the CV shape suggests that the reduction sequence of a Ti ion strongly depends on RCaO/TiO2 .No remarkable change in the CV shape with the crucible materials was observed at 1373K. The reaction of the crucible materials with TiO2 in the bath seems negligible at this temperature.The Mo plate electrode was covered with grey deposit after potentio-static electrolysis at 0.4V in the bath of RCaO/TiO = 1.5. Fig.3 shows a typical XRD pattern of the deposit after rinse with water. Ti metal was detected in the deposit though the ingredients of the bath were contained. This result shows that the reduction to Ti metal occurs below 0.5V.The results of this study clearly indicate that Ti metal can be electrodeposited in the CaF2-MgF2-CaO-TiO2 bath, and that the reduction mechanism is influenced by the bath composition, that is the molar ratio of CaO to TiO2.

Effects of titanium-based raw materials on electrochemical behavior of Ti(C,N)-based cermets

The electrochemical behavior of Ti(C,N)-based cermets with two different kinds of titanium-based raw materials, i.e. solid solution type TiC0.7N0.3 and single interstitial phase type TiC and TiN, was investigated in H2SO4 (pH=1) and NaOH (pH=13) solutions at 25°C. Potentiodynamic polarization, electrochemical impedance spectroscopy and surface analytical techniques were used for the investigation. The results show that the cermet prepared from TiC0.7N0.3-based raw material exhibits higher corrosion resistance in the two solutions due to the differences in the chemical composition of the binder phase and hard phase and in the homogeneity of the microstructure. Both the cermets exhibit substantially higher corrosion resistance in NaOH than in H2SO4. Based on the X-ray photoelectron spectroscope analysis results, the corrosion mechanism was discussed in details.

The electrodeposition of Zn-Ti alloys from ZnCl2-urea deep eutectic solvent

The electrochemical behavior of Ti(IV) and the electrodeposition of Zn-Ti alloys were investigated in a ZnCl2-urea (1:3 molar ratio) deep eutectic solvent containing 0.27 mol L−1 TiCl4. The electrochemical reduction of Ti(IV) to Ti was complicated by the formation of intermediate oxidation states of Ti(III) and Ti(II), as well as the precipitation of TiCl3. It was possible to prepare Zn-Ti alloys containing 5.8–16.7 at.% Ti. The composition and surface morphology of Zn-Ti alloys depended on deposition potential and temperature. The deposits could be indexed to a disordered hexagonal close-packed structure similar to pure Zn and were completely chloride-free. The current efficiency for the deposition of Zn-Ti alloys varied from 38.4 to 67.9 %.

Electrochemical behavior of Ti–V–Cr alloys in alkaline solution

Electrochemical behavior of Ti–V–Cr alloys in alkaline solution

Electrochemical behaviour of Ti–Ni SMA and Co–Cr alloys in dynamic Tyrode’s simulated body fluid

The electrochemical behaviour of Ti-Ni shape memory alloy and Co-Cr alloys were investigated in dynamic Tyrode's simulated body fluid on a Model CP6 Potentiostat/Galvanostat. The results indicated that, for all alloys, the anodic dissolution and the pitting sensitivity increased with the flow rate of the Tyrode's solution increasing while the open-circuit potentials and pitting corrosion potentials decreased with the Tyrode's solution increasing. Pitting corrosion of Ti-Ni alloy was easier than Co-Cr alloys. Since the solution's flow enhanced oxygen transform and made it easy to reach the surface of electrodes, the plateau of oxygen diffusion control was diminished. All these indicated that the cathodic reduction and the corrosion reaction, which was controlled by the electrochemical mass transport process, were all accelerated in dynamic Tyrode's simulated body fluid.

Electrochemistry of TiF4 in 1-butyl-2,3-dimethylimidazolium tetrafluoroborate

Electrochemical behaviour of Ti(IV) species in the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BMMImBF4) was studied by means of chronopotentiometry (CP) and cyclic voltammetry (CV) in melts with different concentrations of TiF4 (2–35 mol%) within a temperature range of 65–180 °C. The electrochemical reduction of Ti(IV) was suggested to proceed via the sequence of one-electron steps with the formation of poorly soluble low valence intermediates (LVI). LVIs undergo further solid-state electrochemical reduction to Ti metal. Thin Ti coatings on a Pt substrate were thus obtained and characterized by ESEM method. FTIR spectroscopy was used for identification of the electrochemical active species of Ti(IV). The reaction 2BF4− + TiF4 ⇔ TiF62− + 2BF3↑ takes place in the concentrated solutions of TiF4 at elevated temperatures.

Electrochemical Investigation on the Synthesis of TiB2 out of FLINAK Electrolyte: Electrochemistry of K2TiF6 and KBF4

The electrochemical behaviour of Ti (IV) and B (III) species as sources for electrodeposition of TiB2 in FLINAK electrolyte has been studied by means of cyclic voltammetry measurements in the temperature range of 570-700ºC. At temperatures > 650ºC, the mechanism of the electrochemical reduction of TiF62- species changes in comparison to the reaction path at lower temperature. In the temperature range 570-700ºC there is no significant effect of temperature change on the electrochemical reduction process of BF4-species.

Electrochemical behavior of Ti(IV)/Ti(III) redox couple on dropping mercury electrode in sulfuric acid aqueous and aqueous-organic media

The processes of electrochemical reduction of Ti(IV) and oxidation of Ti(III) in aqueous solutions of H2SO4 not containing and containing AcOH or MeCN are studied by the methods of classical and commutation polarography. It is shown that in the absence of organic solvents the heterogenous electron transfer is irreversible in the media with the sulfuric acid concentration up to 9 M, while in aqueous-organic solution the same occurs at the concentration up to 7 M. Organic solvents are involved into the process of complex formation and like H2SO4, influence the step of heterogenous electron transfer; this effects weakens with the increase in the concentration of sulfuric acid.

The influence of chloride and sulphate ions on the corrosion behavior of Ti and Ti-6Al-4V alloy in oxalic acid

The electrochemical behavior of pure Ti and Ti-6Al-4V alloy was investigated in oxalic acid solution using various electrochemical techniques, i.e. open circuit potential (OCP), potentiodynamic polarization, electrochemical impedance measurements (EIS) and surface examination via scanning electron microscope (SEM) technique. The influence of concentration and temperature on the electrochemical behavior of TI and its alloy were also studied. The results of polarization measurements showed that corrosion current density ( i corr) increases with increasing either temperature or oxalic acid concentration for both samples. Moreover, the value of i corr for Ti was found to be lower than that for Ti–6Al–4 V alloy, where the corrosion resistance for titanium was always higher. The effect of additives as SO 4 2− and Cl − ions was studied; results indicated that the oxide film resistance ( R ox) value decreases with increasing the concentration of SO 4 2− ion. However, for Cl − ion, the value of R ox decreases with increasing Cl − ion concentration up to 1 mM before it starts to increase at higher concentrations. EIS and polarization results are in good agreement with each other. The obtained results were confirmed by surface examination.