Electrochemical processes and systems: application for tutors

The features of redox reactions and the principles of their balancing according to the medium composition are considered. The basic representations about electrochemical processes and systems are outlined. The reactions and principles of chemical sources of electric energy and electrolysis systems functioning are analyzed. A general idea is given about the chemical properties of metals, corrosion resistance in environments of various aggressiveness, and the protection principles are given. Multivariate tasks and exercises for students, and PhD student’s classroom and independent work are offered. For teachers, PhD students and students of universities of specialties "Chemical technologies and engineering", "Biotechnologies and bioengineering", "Oil and gas engineering and technologies".Розглянуто особливості окисно-відновних реакцій і принципи їх балансування залежно від складу середовища. Викладено фундаментальні уявлення про електрохімічні процеси і системи. Проаналізовано перебіг реакцій і принципи функціонування хімічних джерел електричної енергії та систем електролізу. Узагальнено уявлення щодо хімічних властивостей металів, корозійної стійкості у середовищах різної агресивності та наведено принципи організації захисту від руйнування. Запропоновано багатоваріантні завдання та вправи для аудиторної та самостійної роботи студентів і аспірантів. Розраховано на викладачів, аспірантів і студентів вищих навчальних закладів спеціальностей "Хімічні технології та інженерія”, "Біотехнології та біоінженерія", "Нафтогазова інженерія та технології"

Morphology and Properties of Coatings Obtained by Plasma-Electrolytic Oxidation of Titanium Alloys in Pyrophosphate Electrolytes

By means of scanning electron microscopy, atomic-force microscopy, X-ray fluorescence analysis, and X-ray spectral microanalysis it was shown that, under plasma-electrolytic oxidation (PEO) of titanium alloys in pyrophosphate electrolytes, well-adhered oxide coatings with microglobular morphology result. It was demonstrated that the chemical and phase composition of the coatings, as well as the surface topography and grain size, can be controlled by changing the concentration of a pyrophosphate electrolyte and a PEO current density. It was established that the resulting oxide layer is highly resistant to abrasive wear and enhances the titanium corrosion resistance in model media (Ringer’s solution) substantially, which suggests that the coatings are promising for use in biological applications

Study of the influence of oxidizing parameters on the composition and morphology of Al₂O₃·CoOₓ coatings on AL25 alloy

The influence of operating parameters of plasma-electrolytic oxidation in diphosphate cobalt-containing electrolyte on the process of formation of oxide coatings on alumosilicon alloy AL25 (GOST 1583) was studied. It was shown that inclusion of cobalt into the composition of surface oxide layers leads to a change of morphology and topography of the surface. Variation of current density and PEO time allows flexible control of the process of incorporation of the catalytic component into the matrix of oxide of basic metal. It was shown that at an increase in oxidation time, cobalt content in the surface oxide layer increases. The rational mode of plasma-electrolytic treatment of piston alloy in diphosphate electrolyte for obtaining oxide coatings, enriched with cobalt, was substantiated. It is advisable to perform formation of PEO-coatings on AL25 with developed globular-mosaic surface, maximum cobalt content, with minimizing impurities in the range of current densities of 3–5 A/dm² within 20–40 min. The obtained cobalt-containing oxide coatings can be used in the air and water purification systems, specifically, for intracylinder catalysis of gas emissions of internal combustion engines.Досліджено вплив робочих параметрів плазмово-електролітичного оксидування у дифосфатному кобальтвмісному електроліті на процес формування оксидних покривів на сплаві АЛ25. Встановлено, що склад та морфологія поверхні одержаних шарів Al₂O₃·CoOₓ залежать від густини струму обробки та часу оксидування. Варіювання параметрів ПЕО дозволяє гнучко керувати процесом інкорпорації каталітичного компоненту в матрицю оксиду основного металу. Обгрунтовано раціональний режим обробки поршневого силуміну для формування збагачених кобальтом оксидних покривів

Application of oxide-metallic catalysts on valve metals for ecological catalysis

Запропоновано спосіб одержання оксидно-металевих каталізаторів методом одностадійного плазмово-електролітичного оксидування вентильних металів для знешкодження токсидів природного та техногенного походження. Обґрунтовано застосування оксидів мангану та кобальту як легуючих компонентів. Встановлено, що одержані оксидні покриви характеризуються високою каталітичною активністю в модельних реакціях конверсії токсичних компонентів, зокрема відпрацьованих газів двигунів внутрішнього згоряння

Research on the improvement of mixed titania and Co(Mn) oxide nano-composite coatings

The structure and the properties of the oxide films formed on titanium in the diphosphate based electrolytes by means of plasma electrolytic oxidizing at direct current density of 2-2.5 A·dm⁻² have been studied. Oxide layers of different composition and content of alloying elements were obtained by modification of electrolytes and variation in current density. The interelectrode voltage during PEO, chemical and phase composition, topography and microstructure of the formed layers depend on the electrolyte composition and applied current density. The spark-discharge regime was shown to be reached at inter-electrode voltage 100 to 130 V depending on the composition of electrolyte. The effect of chemical composition and surface morphology formed mixed oxide films on the corrosion resistance and catalytic activity has been discussed

Electrodeposition of iron-molybdenum coatings from citrate electrolyte

Specifi c features of the electrodeposition of iron–molybdenum coatings from a citrate electrolyte based on iron(III) sulfate and sodium molybdate in dc and unipolar pulsed modes were studied. It was demonstrated that bright compact coatings with varied content of molybdenum can be produced by varying the relative concentrations of salts of the alloy-forming components and the solution pH. The current density ranges providing the high efficiency of the galvanostastic electrolysis were determined and it was shown that using the pulsed mode makes smaller the amount of nonmetallic impurities in a coating, diminishes its roughness and leads to formation of surface layers with a more uniform composition, The iron–molybdenum coatings exhibit a high corrosion resistance in corrosive media and physicomechanical properties improved as compared with the base metal, which makes it possible to recommend these coatings for protection from corrosive-mechanical disintegration and restoration of the surface of worn articles

Mixed alumina and cobalt containing plasma electrolytic oxide coatings

Principles of plasma electrolytic oxidation of the AL25 aluminum alloy in diphosphate alkali solutions containing cobalt(2+) cations are discussed. It has been established that a variation in the concentration of the electrolyte components provides the formation of mixed-oxide coatings consisting of the basic matrix materials and the cobalt oxides of different content. An increase in the cobalt oxide content in the coating is achieved by the variation in electrolysis current density as well as the treatment time due to both the electrochemical and thermo-chemical reactions at substrate surface and in spark region. Current density intervals that provide micro-globular surface formation and uniform cobalt distribution in the coating are determined. The composition and morphology of the surface causes high catalytic properties of synthesized materials, which confirmed the results of testing in model reaction CO and benzene oxidation as well as fuel combustion for various modes of engine operation