Vol 55, No 4 (2019)

The thermodynamic vacancy model (TVM) of surface energy (SE) leads to the formula of the linear dependence of the minimum SE value of the low-index fcc (111) and bcc (110) faces on half of the vacancy formation energy or the 1/6 part of the cohesive energy of metals. Comparison of the numerical values of SE calculated by the TVM method with those calculated by the DFT method for the same faces shows negative deviations of the latter (from 2 to 17%). Using the values of these deviations, the surface energy relaxation of metals was calculated with a maximum value for Au and Pt and a minimum value for Ag and Pd.

Using the CASTEP module in Materials Studio software, the native defect model structures including O vacancy and Al vacancy in Al₂O₃(110) surface were designed and constructed. Through first-principles based on density functional theory (DFT) and pseudo potential method, the Al₂O₃(110) model structures were optimized. Formation energy, energy state structure, electric density and electron population of defect structures and primitive cell were calculation. Effect of O vacancy and Al vacancy on Al₂O₃ properties could be analyzed and probed. The results showed that formation energy of O vacancy is only 0.06 eV, which is significantly less than that of Al vacancy (2.99 eV). This indicates that the formation of O vacancy is more easily to produce. O vacancy defects reduce electronic energy in Al₂O₃(110), and make its conductivity become poorer. The impact of Al vacancy defects on conductivity are opposite. The influence of aluminum vacancy defects on electron density in Al₂O₃(110) is more than that of oxygen vacancy; oxygen vacancy increases the electronegativity around O atoms, and weakens electropositivity around Al atoms the electricity, which makes the top of energy band structure move down. The calculation results provide a theoretical guidance for the formation of functional anodic oxidation films of Al.

A method of formation of film coatings of titanium dioxide doped by bismuth ions (Bi³⁺) is developed on the basis of sol–gel synthesis and used to form film coatings of titanium dioxide with the anatase structure on the photoanode surface. Thus, samples containing 0.5 to 20 wt % of Bi are obtained. It is shown that the doping of titanium dioxide by bismuth ions results in a shift of light absorption to the visible region of electromagnetic radiation spectrum. The absorption level depends on the concentration of bismuth and reaches its maximum for samples containing 0.5 and 1.0 wt % of Bi. It is suggested on the basis of the data of X-ray phase analysis that an increase in the content of bismuth to 20 wt % leads to destruction of crystalline regions and amorphization of bismuth oxide and titanium oxide. The obtained coatings are studied as catalysts of photoelectrocatalytic oxidation of formic acid under illumination by monochromatic and visible light. It is found that the highest catalytic effect is observed on samples containing 1.0 wt % of bismuth. The forbidden gap width is estimated on the basis of absorption of monochromatic (464 nm) light, and it is shown that photoelectrocatalytic oxidation of formic acid in the visible spectral range accompanied by formiate ion adsorption on the illuminated photoanode surface is probably due to a decrease in the forbidden gap width in doped titanium dioxide to 2.7 eV.

New hybrid organosilica coatings with different amount of alkyl functional groups on a quartz fiber for solid phase microextraction (SPME) have been obtained by the of sol–gel synthesis in the presence of polyethylene glycol (PEG). The structural-sorption properties of the synthesized silica coatings of various compositions have been studied. According to the thermogravimetric analysis, the main thermolysis of the adsorption coatings’ organic layer was observed at temperatures higher than 350°C. The effect of synthesis conditions on the thermal stability of the obtained PEG-based organosilica coating has been studied. It has been established that the textural characteristics of the produced coatings for SPME and their adsorption properties can be controlled using different PEG and silica precursors and the equivalence ratio in the reaction mixture. Good prospects of application of the fabricated coatings for SPME have been demonstrated in paraben extraction and concentration in aqueous solutions at 24°C and pH 3.0–5.5 with their subsequent gas chromatography determination. The suggested technique was characterized by good accuracy and reproducibility (RSD ≤ 2.3%). Comparative studies of the obtained hybrid organosilica coatings for SPME with a commercially available fiber with a bipolar polymer coating—divinylbenzene/carboxen/polydimethylsiloxane—have been conducted.

In recent years, the discovery of efficient catalyst with low price to sulfur dioxide (SO₂) oxidation in normal temperature is a major concern in the industry. In present study, in first step the boron nitride nanotube (BNNT) with Ge were adopted and the surface of Ge-adopted BNNT via O₂ molecule were activated. In second step the SO₂ oxidation on activated Ge-BNNT surface via Langmuir Hinshelwood (LH) and Eley Rideal (ER) mechanisms was investigated. Results show that O₂ activated Ge-BNNT surface can oxide the SO₂ molecule via Ge-BNNT-O-O* + SO₂ → Ge-BNNT-O-O*-SO₂ → Ge-BNNT-O* + SO₃ and Ge-BNNT-O* + SO₂ → Ge-BNNT + SO₃ reactions. Results show that SO₂ oxidation on activated Ge-BNNT surface via the LH mechanism has lower energy barrier than ER mechanism. Finally, calculated parameters reveal that activated Ge-BNNT is acceptable catalyst with low price and high performance for SO₂ oxidation in normal temperature.

Dense alumina coatings were fabricated over aluminum alloy via dip coating method using oxime-modified aluminum(III) isopropoxide as a sol–gel precursor. The influence of important dip coating parameter; withdrawal rates on quality, thickness, uniformity and corrosion resistivity of coatings were investigated. Structural characterization of coated substrates were done by X-ray diffraction patterns (XRD), scanning electron microscopy (SEM) and atomic force microscopy studies (AFM). Corrosion tests by electrochemical studies indicated that corrosion resistive alumina coatings can be achieved by using withdrawal rate of 25 mm min^–1 and 04 cycles of coatings in 3.5% aqueous NaCl solution.

In this work, preparation of thermal barrier coatings based on zirconium oxide is shown. The phased treatment of the copper substrate is proposed in order to obtain a layered thermal barrier oxide coating on it. The sample surface is nanostructured, titanium is deposited layer-by-layer (by the vacuum-arc method) and then zirconium (by the magnetron method), and then zirconium is converted into zirconium dioxide by the microplasma method. The formed oxide-ceramic coatings contain elements from a solution, according to the results of elemental analysis, and zirconium dioxide in tetragonal and monoclinic modifications, according to the results of X-ray diffraction. A study of thermal cyclic stability was carried out. It is revealed that an increase in the time of microplasma treatment to a certain value has a positive effect on the thermal cyclic properties of the obtained layer material and it is able to sustain more than 90 cycles without serious damage to the surface layer.

The structural state and corrosion resistance of the plasma coatings based on iron (FBKh6-2 alloy) and nickel (RW 12496 alloy from Castolin Co.) in aqueous solutions of sodium hydroxide and nitric acid upon varied thermal treatment modes have been investigated. Structural and electrochemical characteristics of these coatings have been compared to those of their analogs in the as-cast state that underwent respective thermal pretreatment. The morphological heterogeneity of the coatings’ surface has been demonstrated to determine the formation of their corrosion-electrochemical characteristics. The specific character of the corrosion process evolution responsible for significant degradation of the coatings’ corrosion resistance as compared to the cast alloys has been described. It has been established that the effect of morphological defects of the coatings’ surface (cavities, microcracks, roughness, open pores, etc.) on the corrosion process evolution can be substantially reduced and, in some cases, completely excluded through impregnation by the hydrophobizing fluid Anakrol-2501 with high penetrating ability. Corrosion tests of the coatings have been performed. It has been demonstrated that impregnation results in a significant reduction of the corrosion rate that becomes compatible to that of the annealed cast samples.

TiO₂–CeO₂ ceramic oxides were prepared on magnesium alloys by laser surface alloying for corrosion protection. The microstructure and composition of laser modified surfaces were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), optical microscope (OM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The corrosion behavior was analyzed by electrochemical and salt spray tests. The effect of relative proportion between the two ceramic components on corrosion resistance of laser alloyed magnesium alloys was investigated. Results showed that there was a margin improvement in corrosion resistance after laser surface alloying with TiO₂ and CeO₂ at the ratio of 4 : 1 (wt %) due to the protection effect of oxides. When the content of CeO₂ increased, and the ratio of TiO₂ and CeO₂ was 1 : 4 (wt %), defects were introduced for the poor compatibility between CeO₂ and Mg matrix. The defects speed up the failure of the layer, and the corrosion resistance was even decreased compared with the as-received magnesium alloy.

TiO_xN_y films were grown onto 316L stainless steel substrate using radiofrequency (rf) magnetron sputtering from a pure titanium nitride target in Ar–O₂ gas mixture with various substrate bias voltages. The aim of this work is to investigate the effect of applied substrate bias Vs, varied from 0 to –100 V, on the deposition rate, structure, hardness and optical properties of the TiN_xO_y films. The characterization of the coatings by grazing incidence X-ray diffraction exhibited a crystalline structure of a mixture of TiN, rutile and anatase. The indirect and direct bad gap were found to decrease for unbiased substrate voltage to V_s = −100 V from 3.84 to 3.20 eV. In addition, the coatings exhibit high transparency (transmittance over 80%). The hardness of the coatings were found in the range of 6.2 to 12.5GPa.

The following parameters have been used to estimate the reliability of predicted first-year corrosion losses of carbon steel and zinc (\(K_{1}^{{{\text{pr}}}}\)): the standard determination coefficient \(R_{{{\text{st}}}}^{2}\) according to ASTM G 16; statistical indicators such as SMAPE and MAPE; generalized determination coefficients; confidence angle. The experimental data on corrosion losses of carbon steel and zinc (\(K_{1}^{{{\text{exp}}}}\)) and the atmosphere corrosivity parameters were taken from the UN/ECE international program and Russian program. The \(K_{1}^{{{\text{pr}}}}\) values were calculated using various dose-response functions. It is not recommended to use the standard determination coefficient \(R_{{{\text{st}}}}^{2}\) in the y = \(K_{1}^{{{\text{pr}}}},\)x = \(K_{1}^{{{\text{exp}}}}\) coordinates.

This paper presents experimental aspects of two triazolodiathiazine derivatives 1 {1-(6,7-di(furan-2-yl)-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl)ethanol} and 2 {6-phenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl)ethanol} as copper corrosion inhibitors in borate (pH 8.4 and 10.4) aggressive media. Electrochemical findings by CV, polarization and EIS experiments were found inconsistent. The η% values evaluated from all electrochemical methods were in good agreement and within the range of 93–97% at both pH. Compound 1 was found the most efficient corrosion inhibitor for Cu surface at pH 8.4 with inhibition efficiency upto 97%. Electrochemical responses and data interpretation confirmed that the process involved was charge transfer controlled and inhibitors were mixed type. Adsorption data was found best fit in Langmuir’s adsorption isotherm and indicated spontaneity and stability of the compounds on Cu surface via physiosorption. DFT computational studies further supported the experimental results.

The quaternary ammonium salt-type tetrameric surfactant with hydrocarbon chain length of 12 was synthesized, and characterized using FT-IR and ¹H NMR. The inhibition efficiencies for N80 steel in 20% hydrochloric acid were studied by weight loss, potentiodynamic polarization method, electrochemical impedance spectroscopy at 25°C. The results obtained from weigh loss measurements show that it has good inhibitive performance. Polarization data indicates that it acts as a mixed-type inhibitor. The results obtained from EIS exhibit the protective film formed by the adsorption of surfactant molecules on metal surface. The adsorption behavior of surfactants was found to follow the Langmuir adsorption isotherm.

The ratios between the film-sorbent parameters, sensitivity, and quartz sorption sensors’ sensitivity threshold have been obtained and analyzed. It has been demonstrated that, for the sorption sensors of vapors and gases based on polymer films, there exists a range of optimal values of thickness caused by its effect on the elastic properties. For acetone vapor sensors with a film made of polymethyl methacrylate (PMMA), this range is equal to 0.4–0.6% of the sensor’s plate thickness at the film deposition on both sides of the plate.