Dynamic electrochemical impedance spectroscopy was used to examine the corrosion behavior of AZ31 magnesium alloy in 0.05 mol/dm(3) sodium chloride solution containing Na2MoO4 inhibitor, which was gradually added to the solution up to the concentration of 50 mmol/dm(3). The parameters of multisinusoidal impedance monitoring obtained under these conditions corresponded to the instantaneous concentration of the inhibitor at a specific point in time. This made it possible to establish the dependence of the calculated values of the protective effect on the concentration of molybdate ions in the solution. Based on the assumption that complete coverage of the surface by the inhibitor provides 100 % reduction of the corrosion rate and the surface degree coverage corresponds to the protective effect of the inhibitor, the adsorption curves of molybdate ions on the surface of AZ31 magnesium alloy were constructed utilizing Langmuir, Temkin, Flory-Huggins, and Frumkin adsorption models.

Lithium-containing magnesium alloys are promising materials for high-demanding industrial applications. In the present contribution, three different AZ31 magnesium alloys AZ31-xLi (x = 4, 8, and 12 wt.%) were cast and their corrosion processes were examined in 0.05 M NaCl solution utilizing potassium permanganate as a potential corrosion inhibitor. The microstructure of the alloys was analyzed by scanning electron microscopy. Scanning Kelvin probe force microscopy demonstrated high susceptibility of the alloys to localized corrosion attack. Electrochemical techniques showed high effectiveness of the permanganate inhibitor (up to 97 %) at concentrations starting from 10 to 50 mM. Post-corrosion surface analyses allowed establishment of the corrosion inhibition mechanism based on the reduction of permanganate ions on the surface of AZ31-xLi alloys to form an insoluble protective layer of Mn(IV) oxide.

In this work, corrosion inhibition of lithium-containing AZ31 magnesium alloys AZ31-xLi (x = 4, 8, and 12 wt.%) has been examined in 0.05 M NaCl solution with and without 10–150 mM of sodium molybdate as the corrosion inhibitor. X-ray diffraction, scanning electron microscopy (SEM), and energy dispersive spectroscopy analyses have been used to investigate the phase composition and microstructure of the alloys. The effectiveness of the molybdate inhibitor has been evaluated by a set of electrochemical methods, including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and dynamic electrochemical impedance spectroscopy (DEIS). Instantaneous DEIS measurements allowed to evaluate the effectiveness profile of sodium molybdate, giving high inhibition efficiency (>85%) at concentrations higher than ca. 35 mM. Post-corrosion SEM, Raman, and X-ray photoelectron spectroscopy analyses confirmed the morphology, ionic and valence composition of the formed passive layers on the surface of AZ31-xLi alloys. Based on experimental observations, a two-stage corrosion mechanism of AZ31-xLi alloys in molybdate-containing NaCl solutions has been proposed.

Методами сканирующей электронной микроскопии, энергодисперсионной рентгеновской спектроскопии, рентгенофазового анализа, а также электрохимическими методами исследовано влияние параметров процесса плазменно-электролитического оксидирования магниевого сплава WE43 в пирофосфатном электролите на структуру, состав и защитные свойства формируемых покрытий. Показано, что при увеличении продолжительности плазменно-электролитического оксидирования происходит уменьшение пористости формируемых покрытий и увеличение содержания в их составе ортофосфата магния. Установлено, что по сравнению с исходным образцом сплава WE43 ПЭО способствует уменьшению скорости коррозии в растворе Хэнкса в 4.1–31.6 раза.

This paper investigates the impact of heat treatment (T5) on the structure of magnesium alloy WE43. The study employs physicochemical research methods, including scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray phase analysis. The results indicate that the surface of WE43 alloy exhibits a reticulated microstructure consisting of α-Mg and β-Mg phases that contain rare-earth elements (Y - up to 3.7 wt.%; Nd - up to 1.1 wt.%). The microstructure of heat-treated alloy WE43-T5 comprises of α-Mg phase and evenly distributed phases of globular and plate-like forms. The studied samples exhibit contrasting regions related to metallic phases of alloying elements (Mg41Nd5, Mg12Nd, Mg5Gd, MgY, Mg24Y5). The corrosion behavior of WE43 and WE43-T5 alloys was studied in model solutions that simulate the bone tissue environment using a set of electrochemical methods. The solutions used were Hank's solution with a pH of 7.4 and acidified Hank's solution with a pH of 5.0, which corresponds to the injured state of bone tissue. The study focused on the effects of heat treatment on the corrosion of magnesium alloys. The study found that the heat treatment process of magnesium alloy WE43 reduced the corrosion rate by 4.4 times and 2.7 times in Hank's solutions with pH 7.4 and pH 5.0, respectively. The exponential values n1 and n2 are shown to be in the range 0.81 to 0.97. Values close to 1 indicate that the constant phase element models the impedance of the distributed capacitive element. Heat treatment results in a 2.5-fold increase in the polarization resistance of the WE43 alloy in Hank's solution (pH=7.4). However, in Hank's solution (pH=5.0), the polarization resistance of the heat-treated alloy decreases by 68%. The Rp values of WE43 and WE43-T5 samples in Hank's solution (pH=5.0) are similar. For citation: Paspelau A.V., Kasach A.A., Kurilo I.I., Tsyganov А.Р. Influence of heat treatment on the corrosion properties of we43 magnesium alloy doped with rare earth elements. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 5. P. 128-135. DOI: 10.6060/ivkkt.20246705.7076.

Galvanic deposition of copper, tin and their alloys is widely used in microelectronics, printed circuit boards, anticorrosive and decorative finishing of products for various purposes. One of the main factors determining the structural and morphological characteristics of the deposited coatings is the value of cathodic polarization during the deposition, which depends on the presence of complexing ions and surfactants. Complexation is one of the most effective and widespread ways to increase the cathodic polarization, as well as the convergence of deposition potentials of copper and tin. In this work we studied the combined effect of thiourea and N-octylpyridinium bromide additives on the kinetics of Cu, Sn, and Cu-Sn electrocrystallization from sulfuric acid electrolytes. The combined presence of these additives allows obtaining homogeneous and fine-grained Cu-Sn coatings. The results of theoretical studies agree well with experimental data and show that the introduction of thiourea and N-octylpyridinium bromide leads to the inhibition of cathodic reduction of hydrated copper(II) and tin(II) ions.

The degradation profile of Mg alloys in biomedical environments can be controlled by applying various types of surface coatings. Phosphate chemical conversion coatings (CaP) and polylactic acid (PLA) biopolymer coatings are biocompatible and promising for the corrosion protection of Mg alloys. The aim of this work was to investigate the physicochemical properties and corrosion performance of inorganic, organic, and mixed inorganicorganic coatings. Three types of surface modification, CaP, PLA, and a combined CaP-PLA coating were obtained on the surface of the magnesium alloy WE43. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and infrared spectroscopy were employed to characterize the surface and interfacial morphology, along with the composition of the coatings before and after corrosion experiments. The protective performance of obtained coatings was examined by electrochemical impedance spectroscopy and immersion testing in Hank's solution. Coated samples showed significantly improved corrosion resistance. The values of polarization resistance based on impedance measurements were 164; 8688; 69,410; and 228,369 omega cm2 for WE43 alloy, CaP, PLA, and CaP-PLA coatings, respectively. The results allowed to propose the mechanism of the coatings growth and their further corrosion degradation. A two -component CaP-PLA coating provided reliable corrosion resistance in Hank's solution for 14 days.

Mild steel is essential in modern industry due to its favorable mechanical properties and economic availability. However, its high susceptibility to corrosion, especially in acidic environments, poses a significant challenge, reducing service life, increasing operating costs, and raising the risk of failures. This study investigates the corrosion inhibition mechanism of mild steel St1 in a 2 M H2SO4 solution at various temperatures using the broad-spectrum antibiotic azithromycin (AZM). Experimental results indicate that AZM presence increases the polarization resistance of mild steel in the acidic solution. AZM acts as a mixed-type inhibitor, influencing the kinetics of both cathodic and anodic processes. The introduction of 200 mM AZM leads to an increase in the polarization resistance of the steel electrode in 2 M H2SO4 by up to 2.4 times. The inhibition mechanism involves forming a protective layer of protonated AZM forms on the negatively charged Fe surface. These protonated forms can also adsorb on cathodic areas, competing with hydronium ions (H3O+) and thereby inhibiting hydrogen evolution processes. The protective effect of AZM diminishes with increasing temperature of the corrosive environment, as confirmed by Monte Carlo simulations showing decreased adsorption energies for AZM and its protonated forms at higher temperatures. An assessment of the protective effect of 200 mM AZM showed that an increase in the temperature of the corrosive environment from 293 to 333 K leads to a decrease in the protective effect by almost 5.6 times. Quantum chemical calculations determined the reactivity of AZM and its protonated forms, identifying the molecular groups involved in the adsorption mechanism.

The influence of the parameters of the plasma-electrolytic oxidation process of WE43 magnesium alloy in a pyrophosphate electrolyte on the structure, composition, and protective properties of the formed coatings was studied using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray phase analysis, and electrochemical methods. It has been shown that, with an increase in the duration of plasma electrolytic oxidation, the porosity of the formed coatings decreases and the content of magnesium orthophosphate in their composition increases. It was found that, compared to the original sample of WE43 alloy, PEO helps to reduce the corrosion rate in Hanks solution by 4.1–31.6 times.

The purpose of our study was to synthesize and analyze the structure, qualitative and quantitative composition, and protective properties of phosphate-containing conversion coatings on WE43, ZRE1, and QE22 magnesium alloys doped with rare earth elements in the Hank’s Balanced Salt Solution. Scanning electron microscopy, energy dispersive X-ray analysis, and X-ray phase analysis methods were used to study the morphology, microstructure, the elemental and phase compositions of QE22, ZRE1, and WE43 magnesium alloys doped with rare earth elements, as well as conversion coatings formed on their surface during phosphating. Linear voltammetry and electrochemical impedance spectroscopy were used to study the kinetic properties of corrosion of the analyzed samples in the Hank’s Balanced Salt Solution (рН = 7.4) imitating the human body environment before and after phosphating. The study showed that the phosphating of magnesium alloys doped with rare earth elements results in the formation of low-soluble fine-grained coatings with a pronounced crystal structure and a thickness from 16 to 21 μm. The obtained conversion coatings are characterized by the following elemental composition: Са ≈ 40 wt.%; Р ≈ 15 wt.%; and О ≈ 35 wt.%. The crystal structure of phosphate-containing coatings is presented by the brushite phase (CaHPO4·2H2O). The electrochemical studies of the corrosion behavior of magnesium alloys in the model Hank’s Balanced Salt Solution (рН = 7.4) demonstrated that the corrosion current density decreases in the sequence QE22, ZRE1, WE43 and is icorr, A/cm2: 5.2·10–5; 2.5·10–5; 2.0·10–5. The obtained conversion coatings based on brushite reduce the corrosion rate of QE22, ZRE1,and WE43 magnesium alloys by 15.2, 7.8, and 6.3 times, respectivel

In the present study, chitosan coatings modified with g-C3N4 were prepared for AZ91 magnesium alloy. The microstructure of the chitosan–g-C3N4 coatings, depending on the concentration of the particles of the modifying phase in the chitosan solution, was investigated by scanning electron microscopy and X-ray phase analysis. It was found that coatings prepared in suspension of chitosan containing more than 30 g/dm3 g-C3N4 exhibited a complete wettability with a sodium-phosphate buffer solution. Confocal microscopy established the degree of inhibition of E. coli biofilm formation on the surface of the prepared coatings. It was found by using linear voltammetry and electrochemical impedance spectroscopy that the modification of chitosan by the g-C3N4 particles led to an improvement in the protective properties of coatings.

In this work, corrosion of the AZ31 magnesium alloy was examined in 0.05 M NaCl solutions containing 0.01–0.150 mol/dm 3 of potassium permanganate as a corrosion inhibitor. A set of electrochemical impedance spectroscopy, linear sweep voltammetry, and hydrogen evolution measurements revealed high inhibitor effectiveness at relatively high (0.150 mol/dm 3 ) KMnO 4 concentrations. Based on data of energy-dispersive X-ray analysis, scanning electron microscopy, and Raman spectroscopy, a mechanism of the corrosion inhibition of AZ31 alloy by potassium permanganate in chloride-containing media was proposed.

This research aims to develop and utilize an impedance-based tool for monitoring non-stationary electrochemical processes, coupling the multisinusoidal perturbation signal approach and distribution of relaxation times (DRT) analysis for the first time. The approach was used to distinguish independent processes occurring at the surface of AZ31 and WE43 Mg alloys undergoing corrosion in Hank's Balanced Salt Solution at 37 degrees C. We highlighted two common processes related to corrosion product layer formation. Detailed DEIS-DRT analysis was capable of realtime identification of a unique third process for the WE43 alloy, resulting from a spatially localized filiform corrosion attack in the vicinity of intermetallic particles. The proposed tool proved to be highly efficient in terms of studying non-stationary processes, while the DRT analysis allowed for an in-depth and precise localization of the number and the kinetics of the ongoing processes. The corrosion mechanism description was supported by numerous microscopic and spectroscopic tools.

На основе системы Na2O–CaO–MgO–SiO2–P2O5 при различном соотношении компонентов синтезированы образцы опытных стекол. Изучены их структурные особенности и физико-химические свойства. Показано, что биологическая активность стекол, проявляющаяся при их изотермической выдержке в SBF-растворе (simulated body fluid) при температуре 37 °С в течение 2–7 суток, обусловлена образованием поверхностного слоя гидроксиапатита. Указана область составов стекол, характеризующихся максимальной склонностью к кристаллизации, что приводит к снижению биоактивности материала. Установлено, что основным фактором, определяющим биологическую активность стекол, является соотношение в их составе CaO/P2O5.

The interaction of amino acids with clay minerals plays an essential role in many natural processes. Understanding the mechanisms of their adsorption on natural clays opens the way to a wide range of nanobiotechnological applications and helps to clarify the origin of life on Earth. In this work, the adsorption mechanisms and behavior of aliphatic amino acids (glycine, alanine, valine, leucine, and isoleucine) on kaolinite surfaces have been studied by the Density Functional Theory (DFT) method. The role of functional groups of aliphatic amino acids (AA) and their orientational behavior during the formation of hydrogen bonds with siloxane and hydroxyl surfaces of kaolinite have been systematically scrutinized. It has been found that the carboxyl group plays a crucial role in the mechanism of interaction between AA and kaolinite surfaces. The strongest hydrogen bonds are formed between the H-atom of the carboxyl group of AA and the O-atom of the hydroxyl surface of kaolinite. An additional hydrogen bond can be formed between the N-atom of the amino group and the surface –OH groups of kaolinite. The adsorption energy of AA on a hydroxyl surface is ~3 times higher than that on the siloxane surface. The obtained theoretical results comply with and help to explain the experimental data available in the scientific literature.

АннотацияЦель статьи -установление особенностей электрохимического получения композиционных покрытий Cu-Sn-TiO 2 в сернокислом электролите при периодическом перемешивании в условиях стационарного и импульсного режимов электролиза.Методами линейной вольтамперометрии, а также стационарной и импульсной хронопотенциометрии изучены кинетические особенности электрокристаллизации композиционных покрытий Cu-Sn-TiO 2 в сернокислом электролите при использовании периодического перемешивания.При перемешивании электролита происходит смещение катодного потенциала в область положительных значений.Показано, что после выключения перемешивания электролита значение катодного потенциала, при котором происходит сплавообразование меди и олова при катодной плотности тока -0.013 А/см 2 , устанавливается за 70 с, а при использовании импульсного электролиза -за 80 с.Методом сканирующей электронной микроскопии установлено, что наиболее однородные и равномерные покрытия Cu-Sn-TiO 2 формируются при использовании импульсного электролиза.Использование периодического перемешивания сернокислого электролита приводит к формированию упорядоченных мультислойных структур, состоящих из микрослоев сплава Cu-Sn и меди, за счет периодического устранения диффузионных ограничений разряда

In this work, corrosion inhibition of the AZ31 magnesium alloy was investigated in NaCl solutions containing different amounts of sodium molybdate inhibitor. Electrochemical, hydrogen evolution, microscopic, and spectroscopic experiments were utilized to examine the mechanism of corrosion inhibition by molybdates. The results showed that Na2MoO4 inhibitor provides reliable inhibition at high concentrations (150 mM). Surface examination by Raman and XPS spectroscopy confirmed the formation of a protective surface layer of mixed Mo(VI, V, IV) species. Based on these results, the mechanism of corrosion inhibition of the AZ31 alloy by aqueous molybdates was proposed.

Development of the effective technology for recovery of critical rare-earth elements (REEs) from end-of-life permanent magnets is one of the important technological challenges. In this study, chemical and electrochemical leaching of NdCeFeB magnets was investigated in 0.5 mol/L sulfuric acid containing varying concentration of oxalic acid. The influence of H2C2O4 concentration on leaching efficiency and morphological properties of the NdCeFeB surface, as well as on the chemical composition and zeta-potential of the oxalate precipitate particles was discussed. Efficient separation of REEs can be achieved at H2C2O4 concentrations of 0.05-0.20 mol/L and the maximum REE purity was 97.2%. In electrochemical leaching, the leaching rate was substantially higher than in chemical leaching, where blocking of the magnet surface by precipitate layer was observed.