Papers by Keyword: Electrochemistry

Abstract: This study aimed to demonstrate the susceptibility of 5% Ni steel to stress corrosion cracking, SCC, in anhydrous liquid ammonia. SCC tests using four-point bend specimens cut from welds in SPV315, HT780 and 5% Ni steel were carried out in anhydrous liquid ammonia with 5wt% NH₄CO₂NH₂ and 0.1MPa O₂ at +2.0V, which is an accelerated SCC test condition. No SCC was observed in SPV315, whose strength is within the allowable strength of IGC code 17.12, but SCC was observed in the HAZ of HT780, whose strength is higher than the upper limit of IGC code 17.12. Furthermore, SCC was recognized in the HAZ and base metal of 5% Ni steel, whose nickel content is higher than the upper limit of IGC code 17.12, and this suggests that 5% Ni steel is susceptible to SCC in anhydrous liquid ammonia.

Abstract: Sodium borohydride (NaBH₄) has several advantages as a hydrogen storage material compared to other hydrogen storage materials, such as metal hydrides, porous carbon, or other complex compounds. These advantages include a high storage capacity, the ability to release hydrogen under mild conditions, good chemical and thermal stability, and being non-toxic and environmentally friendly. These advantages make NaBH₄ the leading choice for hydrogen storage. In some of our previous investigations, we have studied the electrochemical release of hydrogen from NaBH₄, resulting in the formation of NaBO₂. The next problem is how to recover NaBO₂ to convert it back into NaBH₄. The method developed in this study is an electrochemical method with advantages in process control and scalability. This paper aims to convert NaBO₂ back into NaBH₄ electrochemically. The electrosynthesis of NaBH₄ from NaBO₂ was carried out in a two-chamber electrochemical cell separated by a bipolar membrane. The power supply controlled the current. The current used varied from 0.5 to 2 A. The concentration of NaBH₄ formed was analyzed using the iodate titration method. The formation of NaBH₄ occurs in the cathode chamber. The concentration of NaBH₄ increases with increasing electrolysis time. In general, the reaction rate of NaBH₄ formation increases at a current of 2 A. Meanwhile, the reaction rate of NaBH₄ formation at currents of 0.5 A and 1 A is almost the same. The greater the current used, the faster the NaBO₂ reduction process in the cathode chamber. The integral analysis method calculates the reaction order by integrating the reaction rate equation. The reaction orders tested are zero order, 1^st order, and 2^nd order. The best curve-matching results are shown in the second-order reaction rate equation. At a current of 2 A, the comparison curve between the data and the equation still indicates a relatively low fit. However, the second-order reaction rate equation gives the best results. The reaction rate constant is between 0.0406 and 0.0472 L mol^-1s^-1.

Abstract: In the process of oil and gas extraction, N80 steel is used as a common tubing material. CO₂ corrosion has become one of the most dangerous problems in its entire life cycle. In this paper, the conditions of different temperatures (90-220 °C) and CO₂ partial pressure (0.2-3 MPa) were selected, and the dynamic rotating high-temperature autoclave was used to simulate N80 steel corrosion in formation water environments. The results showed that the corrosion rate of N80 steel gradually decreased with the increase of temperature, and the corrosion rate was the lowest at 150 °C. In addition to this, with the increase of CO₂ partial pressure, the corrosion rate first increased and then decreased. The corrosion rate was the highest when the CO₂ partial pressure was 0.8 MPa. Through surface analysis techniques (SEM and XRD) and electrochemical tests, it was found that the corrosion resistance of N80 under high temperature and high pressure is closely related to the corrosion product film (FeCO₃). The compactness of FeCO₃ product film determines the corrosion characteristics of the matrix.

Abstract: The technology of producing stable electrochromic anode nanocomposite thin film coatings based on nickel oxide (II) has been developed, which are used as active layers for modulating light flux in the manufacture of various technical devices. The method involves introduction of carbon nanoparticles (carbon-containing particles) into outer layers of nickel oxide (II) thin films obtained by gas-phase deposition under conditions of cathodic polarization in potentiostatic mode in aqueous media containing water-soluble hydroxylated fullerene derivatives - fullerenol С₆₀(ОН)₂₄, without change of their optical density in the initial state. The technology of the method realization allows to effectively change electrochromic properties of nickel oxide (II) thin films and to obtain a nanocomposite, which is a matrix of a thin layer of nickel oxide (II), doped with carbon nanoparticles, with increased contrast and having the ability to maintain a colored state after switching off polarization under open chain conditions for a long time without energy consumption in solution and in air, i.e., characterized by an “optical memory effect”.

Abstract: Sea water resources are extensive and can be used to extinguish fires, but their corrosiveness is a major problem. Using the method of electrochemical workstation, the electrochemical corrosion behavior of aluminum sheet in artificial sea water solution and silica-coated artificial seawater was studied; by analyzing the surface morphology, polarization curve and electrochemical impedance spectroscopy, the electrochemical corrosion behavior of aluminum sheets under different immersion times and different immersion media is obtained. The conclusion is that the coating of nanosilica powder has a certain corrosion protection effect on artificial seawater.

Abstract: In this work, the effect of carbon on the electrochemical properties of multi-walled carbon nanotube (MWCNT) functionalized Lithium iron manganese phosphate was studied. In an attempt to provide insight into the structural and electronic properties of optimized electrode materials a systematic study based on a combination of structural and spectroscopic techniques. The phosphor-olivine LiFe_0.5Mn_0.5PO₄, was synthesized via a simple microwave synthesis using LiFePO₄ and LiMnPO₄ as precursors. Cyclic voltammetry was used to evaluate the electrochemical parameters (electron transfer and ionic diffusivity) of the LiFe_0.5Mn_0.5PO₄ redox couples. The redox potentials show two separate distinct redox peaks that correspond to Mn²⁺/Mn³⁺ (4.1 V vs Li/Li⁺) and Fe²⁺/Fe³⁺ (3.5 V vs Li/Li⁺) due to interaction arrangement of Fe-O-Mn in the olivine lattice. The electrochemical impedance spectroscopy (EIS) results showed LiFe_0.5Mn_0.5PO₄-MWCNTs having high conductivity with reduced charge resistance. This result demonstrates that MWCNTs stimulates faster electron transfer and stability for the LiFe_0.5Mn_0.5PO₄ framework, which demonstrates favorable as a host material for Li⁺ ions.

Abstract: We report the preparation, structural, electrochemical and photocatalytic studies of monodispersed cadmium sulphide quantum dots from didecylaminyl dithiocarbamate and 4-chloro-3-(trifluoromethyl) anilinyl dithiocarbamate cadmium(II) complexes. Powder X-ray diffraction pattern confirms hexagonal crystalline phases for the as-preapred CdS quantum dots irrespective of the precursor used with particle size of 3.39-5.51 nm. Optical absorption band edges of 515 nm were observed for the cadmium sulfide quantum dots with energy band gaps estimated from the Tauc plots of 1.97 eV for OLM-CdS1 prepared from Cd(II) didecylaminyl dithiocarbamate and 1.92 eV for OLM-CdS2 prepared from Cd(II) 4-chloro-3-(trifluoromethyl) anilinyl dithiocarbamate. These energy band gaps are blue shifted with respect to the bulk cadmium sulphide. The calculated electrochemical band gap of 2.34 V and 3.30 V are higher than band gap energy. The as-prepared CdS quantum dots were used as photocatalysts for the photocatalytic decomposition of methylene blue (MB) with efficiency of 61 % and 55 %.

Abstract: Carbon steel is widely used in the industry due to its mechanical properties and low cost, but in contrast it resists poorly to corrosion, leading to economic losses and mechanical issues. The use of surface treatment is essential to extend the life of the metallic material. In this context, niobium is being studied for its great corrosion resistance properties. The aim of this paper was to produce and evaluate the corrosion protection of a niobium-based coating produced by the Pechini Method. The resin was applied in the metallic surface by dip-coating and then calcinated at 450 oC for 1 hour. The coated material was analyzed electrochemically by open circuit potential and potentiodynamic polarization, and morphologically by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The electrochemical analyses showed that the deposition of the coating increased the corrosion resistance and the morphological analyses indicated a homogenous coating with the presence of phases of NbO and NbO₂.

Abstract: Carbon steel is one of the most commonly used alloys in industrial applications due to its physicochemical properties and low cost. However, the use of this metal material may become limited due to its vulnerability to corrosion. Thus, it is necessary to use methods that inhibit corrosion. Organic compounds with heteroatoms possess the characteristic of inhibiting corrosion by forming a protective film. The corrosion protection of SAE 1020 carbon steel, promoted by the aqueous extract of Persea pyrifolia (PP) bark, was evaluated in this work at extract concentrations of 5% and 10% v/v, in order to replace an inhibitor of synthetic origin with an ecologically benign inhibitor. Plant extracts are generally inexpensive and can be obtained through simple extraction processes. The objective of this work was to study the use of PP peel extract as a carbon steel corrosion inhibitor (SAE 1020). The electrochemical response was determined by measurements including electrochemical impedance spectroscopy (EIS) and anodic potentiodynamic polarization (PPA) in a 0.5 M sodium chloride medium. The samples were characterized by optical microscopy to evaluate the type of corrosion.

Abstract: Anodic oxide films of zinc oxide in an aqueous solution of K Cl (0.1 M; 0.5 M and 1 M) were obtained by electrochemical oxidation of zinc metal. Zinc electrode was used as anode and platinum plate as cathode. The study discusses the influence of the concentrations of K Cl solution and the voltage applied to the electrochemical cell on the morphology of the obtained anode films, as well as their thermodynamic stability. The analysis of volt-ampere curves of linear potential sweep and chronoamperometric dependences showed that oxidation in 0.1 M K Cl solution at a voltage of 7.5 V allows to obtain continuous stable defect-free Zn O films on metal zinc.