Surface Engineering and Applied Electrochemistry最新文献

Eu²⁺ doped strontium aluminate (SrAl₂O₄:Eu²⁺) nanosized phosphorescent powders were prepared by the urea-nitrate solution combustion method at 500°C for 5 min. The average particle size of the powders was about 80 nm. The photoluminescent properties were studied using ultraviolet excitation as well as high energy synchrotron radiation, and electron beam excitation. Broad photoluminescence bands were observed in SrAl₂O₄:Eu²⁺ peaking at λ_max = 450 and 520 nm which arise due to transitions from the 4f ⁶5d¹ to 4f ⁷ configuration of the Eu²⁺ ions situated in two sites with a different symmetry. One additional emission band was also observed at 360 nm. The nature of that band is under discussion.

The article deals with the study of factors participating in the extraction of humic acids from plant substrates under the action of electric discharges. Using the example of the electric discharge treatment of the peat-water suspension, it was demonstrated that the main factor affecting the intensity of extraction is the degree of the biosubstrate-water suspension solid phase grinding, which depends on the pressure amplitude at a distance equal to the inner radius of the chamber and the number of discharge pulses. The experimental research has shown that the amount of chemical reagents (alkalis) commonly used in the extraction of humic acids from peat can be significantly reduced due to the appearance of radicals and peroxide compounds in the peat-water suspension during the action of an electric discharge. The perspectives of the nonthermal electric discharge method to intensify the extraction of humic acids from biosubstrates are determined.

The possibility of obtaining thin continuous plasma-electrolyte protective oxide coatings on VT1-0 titanium in a nickel sulfate alkaline electrolyte without the addition of silicates in the sparking mode was studied. The elemental composition and the microstructure of coatings manufactured via plasma electrolytic oxidation (PEO) both on the substrate and after the destruction of the coating in 25% sulfuric acid were studied. As a result of the research, a possibility of forming thin (1–7 μm) continuous PEO coatings, with a treatment duration of 3–10 min, respectively, was established. The introduction of additives (for example, nickel sulfate) into the electrolyte is effective when the duration of PEO is more than 10 min. It was supposed that nickel was incorporated into the coating mainly due to the action of plasma microarcs. The limited corrosion resistance of the resulting coatings in aggressive media was noted. An analysis of the elemental composition of the dry residues of the coating after destruction in a 25% sulfuric acid solution gives grounds to assume the electrochemical nature of the corrosion destruction of such coatings.

The characteristics of a pulse periodic source of a long-range UV radiation with overvoltage pumping by a bipolar discharge of nanosecond duration between copper electrodes in argon at atmospheric pressure are investigated. Copper vapors were introduced into the discharge due to the ectonic mechanism when a sufficient amount of the electrode material vapors is introduced into the discharge gap due to microexplosions of inhomogeneities of the surface of metal electrodes in a strong electric field of an overvoltage high-current nanosecond discharge. The characteristics of an overvoltage nanosecond discharge at a distance between the electrodes of 2 mm are studied. The emission spectra of the discharge were analyzed, and the intensity of the UV radiation of a point emitter was optimized depending on the supply voltage of the high-voltage modulator and the repetition rate of discharge pulses. The identification of the emission spectra of plasma made it possible to establish the main excited plasma products that form the spectrum of the UV radiation of the plasma. The study of the spectral characteristics of plasma based on gas-vapor mixtures “copper–argon” showed that the most intense were the spectral resonance lines of the copper atom and ion. It was found that a space-uniform overvoltage nanosecond discharge was ignited between copper electrodes at an interelectrode distance of 2 mm. It was found that the maximum value of the average UV power at p(Ar) = 101 kPa was observed for the UV-A range.

The phase and elemental compositions of electrospark coatings of nickel and titanium deposited on steel, nickel, and titanium, that is, coatings from TiNiMo-20 and WC92-Co8, on steel during high-frequency electrospark alloying are investigated. It is established that the material of the electrode, of the substrate, and the modes of deposition have the main impact on the physical and chemical properties of the formed coatings. A positive influence of high-frequency alloying on the quality indicators of the processed surfaces is shown. Both the phase and chemical analyses showed availability of the compounds considerably improving the corrosion resistance of the processed surfaces. Alloying with WC92-Co8 electrodes at a high frequency makes it possible to obtain an increased content of tungsten carbide in the deposited layer.

Organic molecules are often considered to be the best way to protect a material from corrosion, but the synthesis process is very expensive. In the present work, the ethanol solvent was investigated as efficient inhibitor of the mild steel corrosion in a molar hydrochloric acid solution via several methods including polarization and, electrochemical impedance spectroscopy to evaluate the concentration effect of the studied compound. The result shows that ethanol as inhibitor protects mild steel against corrosion in an acidic solution with the inhibition efficiency of 84% at 10^–3 M concentration obtained by EIS method. The polarization curves data show the studied inhibitor to be of the mixt type. Also, a good correlation between the impedance and the Tafel curves data were observed. Various adsorption isotherm models were tested to elucidate the adsorption mechanism of ethanol. In addition, the scanning electron microscopy with energy dispersive X‑ray analysis was applied to confirm the adsorption of ethanol onto the surface of mild steel and its anti-corrosion effect by a formed protective layer. Also, this result was supported by theoretical studies such as the Monte Carlo simulations and the density functional theory.

In this work, the surface oxidation of commercially pure titanium (CP-Ti grade 4) was performed by means of a Nd:YAG in a continuous wave mode in an air environment. The morphology, structure and chemical composition of the formed layers were analyzed by different characterization techniques, such as X‑ray diffraction, scanning electron microscope coupled to an electron microprobe, optical microscopy, and optical profilometry. The diffusion of light atmospheric elements (oxygen and nitrogen) was also investigated. The corrosion resistance of the treated samples was examined in 3.0 wt % NaCl solution using potentiodynamic polarization measurements. The results were compared with those obtained from untreated CP-Ti tested under the same conditions. The analysis indicates that ultra-short pulses (in a nanosecond scale) from a Nd:YAG laser effectively enhanced the corrosion resistance of the studied alloy in 3.0 wt % NaCl (simulated marine environment). An improved corrosion resistance was obtained due to the microstructural changes caused by rapid solidification after laser treatment. A notable enhancement in hardness was reached as well.

Three nonionic gemini surface active agents on the base of sebacic acid with different propoxylated units were prepared for this research work, and their forms were studied using infra-red and hydrogen nuclear magnetic resonance spectroscopy. The surfactants physical characteristics were determined. They were found to be inhibitors of the corrosion for carbon steel in a HCl solution. In this investigation, the weight loss and the electrochemical techniques were applied. All of the studied agents were shown to be persuasive inhibitors of corrosion, with inhibition efficiency values exceeding 99%. The efficiency of the inhibition was shown to improve as the surfactant concentration and the exposure time increased, as well as the number of propylene units per a surfactant molecule. The studied surfactants acted as mixed-type inhibitors, according to polarization studies. Surfactants were found to protect steel from acidic corrosion by physically adsorbing their molecules onto the steel surface and forming a protective barrier between the metal and the corrosive liquid, decreasing the corrosion rate. Surfactants adsorption followed the Langmuir adsorption isotherm. Atomic force spectroscopy was used to investigate the surface of the carbon steel as blank specimen and in an acidic solution. The acquired images, as well as the surface properties measured, agree with the results obtained via other techniques used.