Vol 52, No 1 (2016)

The influence of methylcellulose ([C₆H₇O₂(OH)_3–x(OCH₃)_x]_n, MC) on the morphology and solubility of calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, GA) nanocrystals (NCs) in GA/MC organomineral nanocomposites (OMCs) is studied. GA/MC OMCs with the MC content of 0.5, 1, 2, 5, 10 and 20 wt % are synthesized in the Ca(OH)₂–H₃PO₄–[C₆H₇O₂(OH)_3–x(OCH₃)_x]_n–H₂O system under biomimetic conditions (37°C). The composition and structural features of OMCs, as well as crystallographic characteristics, size, and morphology of GA NC in OMCs, are determined via chemical analysis, X-ray diffraction (XRD), infrared spectroscopy (IRS), thermal analysis (DTA and DTG), scanning (SEM) and transmission (TEM) electron microscopy, and electron diffraction (ED). It is shown that the growth in the MC concentration in OMCs leads to the change in the GA NC morphology and the increase in their solubility (for Ca²⁺ and PO₄^3- ions).

The methods of sonochemistry and “green” nanotechnology were used to develop a single-stage process to transfer iron nanoparticles from their micellar solution in isooctane to aqueous solution of carboxymethyl chitin excluding an intermediate stage of producing iron nanoparticulate dispersion in water. The structure and dimensions of iron nanoparticles in a macromolecular system based on 6-O-carboxymethyl chitin were examined using X-ray microanalysis and selected-area electron diffraction analysis, transmission electron microscopy (TEM), and atomic force microscopy (AFM). According to TEM and AFM data, the sizes of ultradispersed particles were within the range of 2–4 nm. The X-ray investigations indicated that iron nanonoparticles in the carboxymethyl chitin–iron nanoparticles system consisted mainly of zero-valent alpha-iron particles (α-Fe⁰) and a number of magnetite Fe₃O₄ nanoparticles. Because both types of particles exhibit magnetic properties, these metal–polymer nanocomposites may have a wide range of applications in medicine, electronics, biotechnology, ecology, and catalysis.

In this work, thermal stability and oxidation resistance at temperatures up to 800°C are studied for (Ti,Al)N–(8–10 at %)Ni coatings with a thickness on the order of 4 µm and a crystallite size below 20 nm, which have been prepared via ion–plasma vacuum arc deposition. The composition and structural characteristics of coatings remain stable during 1-h heating in vacuum of 10_–4 Pa at temperatures of 600 and 700°C. Heating at a temperature of 800°C leads to an increase in the crystallite size and a decrease in microstrains of a ceramic phase, which is accompanied by a reduction in the hardness of the coating from 51–53 to 31–33 GPa. The coatings are heat resistant up to 800°C and characterized by cohesive failure in scribing. The adhesive strength of coatings with a substrate exceeds 85 N. Studying electrochemical behavior reveals the high efficiency of (Ti,Al)N_0.87–Ni coatings in corrosion protection of cutting tools in acid and alkaline environments.

This study examines the effect of film thickness ranging from 230 to 404 nm on the corrosion resistance of Nb₂O₅ thin films grown by chemical solution deposition. The films were characterized to obtain the relationships between the deposition parameters and the most relevant physical properties (structural, surface morphology and corrosion resistance). From X-ray diffraction and XPS analyses we can conclude that the films were stoichiometric Nb₂O₅ and crystalline. The internal strain and morphology of the film changes as the number of layers increases indicating a thickness dependent grain size. The surface roughness, corrosion resistance were also affected by the film thickness. Electrochemical impedance spectroscopy (EIS) shows that the thicker film have higher passive and charge transfer resistance than the control samples. These results coating layer of Nb₂O₅ improves the corrosion resistance on an API 5L X80 steel alloy due to the formation of a film on the surface.

Fundamentals of numerical analysis of linear tension of two-dimensional drops of molecules adsorbed on uniform crystal faces have been developed. A lattice-gas model has been applied for description of adsorption. Molecular distributions have been computed in a quasi-chemical approximation, allowing for the effects of direct correlations of interacting particles. Differences in the algorithms of calculation of linear tension on a two-dimensional vapor–liquid interface connected with the effect of the transition region structure, taking into account metastability of coexisting small phases, and a variation in methods of determining line tension at a curved interface according to the material balance condition (equimolecular line) or mechanical equilibrium condition. This has allowed us to compute the equilibrium molecular distribution in small two-dimensional drops and the linear tension value at the interface as a function of the drop size and temperature.

Equilibrium geometries of Al₁₂Zr cluster were systematically studied on the basis of density functional theory with generalized gradient approximation. To gain insights into high catalytic activity we use the CO oxidation as a benchmark probe. In Al–Zr bimetallic clusters, Zr site is the catalytically active centre, the adsorption of CO and O₂ on the same site respectively (single-site mechanism), a Langmuir-Hinshelwood (LH) mechanism is proposed, which proceed via two steps, CO + O₂ → CO₂ + O and CO + O → CO₂. Two CO oxidation mechanisms of two CO₂ molecules as product have been simulated. For the later mechanism, the key step is the O–O bond scission in the OCOO* intermediate, which is significantly accelerated due to the attack of the neighboring CO molecule. The calculated barriers for the later reactions are lower compared with the former reaction. Detailed reaction paths corresponding to this case are calculated. Our study suggests that the CO oxidation catalyzed by Al₁₂Zr cluster is likely to occur at the room temperature.

Methods describing isotherms and thermodynamic properties of methane adsorption on various cationic forms of X-type zeolite at temperatures above critical ones are considered.

Multiwalled carbon nanotubes (CNTs) were synthesized by catalytic pyrolysis of methane on iron-cobalt or cobalt-molybdenum catalyst and investigated by electrochemical and physico-chemical methods before and after chemical or electrochemical corrosion treatment. It is shown that CNTs have a higher corrosion resistance than does turbostratic carbon (carbon black) in corrosion testing under the same conditions. This is expressed in a smaller change in the amount of oxygen on the surface of the carbon material, the values of the electrochemically active surface area (EAS), and in significant differences of these quantities for the CNTs compared to carbon black. Quantitative comparison of the results of chemical and electrochemical treatment of CNT and carbon black, which was performed in this paper for the first time, leads to the conclusion regarding the advantages of corrosion testing by chemical method. Chemical testing simulates to a greater extent the long-term testing conditions of the supported catalysts composed of membrane-electrode assemblies of fuel cells in terms of evaluating the stability of the carbon material as a support of the catalytically active centers.

In this work a special regard is given to the morphology of the nickel deposited layers, onto AA1370 aluminum section and central longitudinal surfaces, with and without a weak magnetic field oriented in parallel and perpendicular to the coated surface in modified Watt bath. The obtained results show the formation of honeycomb structure nickel deposits for samples treated with weak parallel oriented field under approximately 0.3 A/cm₂, and partial dendritic structure nickel deposit for samples treated with weak perpendicular oriented magnetic field, the perimeter deposits with and without magnetic field is different to the deposits in the remain surface. We attributed the defect of nickel deposits on the surfaces with and without magnetic field to the distribution of the intermetallics particles and we attributed the honeycomb structure to the escapement of hydrogen and oxygen.

The results of a study of the structure of hardened surface layers formed by the micro-arc oxidation method (MAO) on Al-Si alloys are presented. The influence of the concentration of electrolyte components on the formation mechanism of MAO layers and the properties of the formed surfaces, such as the microhardness, thickness, porosity, and elemental composition of the surface, is shown.

The corrosion behavior of aluminum and aluminum silicon alloys in 0.1 M NaOH solution in the absence and presence of gelatin was studied using potentiostat polarization, electrochemical impedance spectroscopy (EIS), cyclic voltammetry and potentiodynamic anodic polarization techniques. The percentage inhibition efficiency increases with increasing the concentration of gelatin and with decreasing temperature as well as Si content. This was attributed to a lower affinity of the inhibitor to adsorb on Si than on Al. The inhibitory action of gelatin was explained in terms of adsorption of gelatin on the surface of Al or Al–Si alloys forming a barrier of mass and charge transfer leading to protect the metal surface from the aggressive ones. The adsorption of gelatin on the metal surface follows Freundlich isotherm. Some activated thermodynamic parameters were calculated and discussed.

Atomistic simulations are becoming increasingly important in the field of corrosion inhibition. New research and development efforts using computational chemistry in studying the behavior of corrosion inhibitors on the metal surfaces are introduced. Accordingly, the density functional theory (DFT) at the B3LYP/6-31G++(d,p) basis set level, ab initio calculations using the HF/6-31G++(d,p) and MP2/321G+(d) methods are performed on some triazoles and sulphur containing compounds, namely, 1,2,4-triazole (TA), 3-amino-1,2,4-triazole (ATA), benzotriazole (BTA) and 2-mercaptobenzothiazole (MTA), used as corrosion inhibitors. The correlation between its quantum chemical parameters and the corresponding inhibition efficiency (IE%) is investigated. Quantum chemical parameters, such as the energy of the highest occupied molecular orbital energy (E_HOMO), the energy of the lowest unoccupied molecular orbital energy (E_LUMO), energy gap (ΔE), dipole moment (µ), sum of total negative charges (TNC), molar volume (MV), polarizability (α), chemical potential (Pi), electronegativity (χ), hardness (η), softness (σ), electrophilicity (ω) and the total energy change (ΔE_T), are calculated. Furthermore, Monte Carlo simulation technique incorporating molecular mechanics and molecular dynamic is used to simulate the adsorption of the investigated inhibitors on Al (1 1 1) surface. A good correlation is found between the theoretical data and the experimental results.

The content of the article is about the principle of maximum entropy production rate applied to the description of uniform corrosion. The corroding metal surface is described as an ensemble of microcells randomly moving on the surface. The theory allows to calculate the ratio of the anodic to cathodic areas, as well as the corrosion current, under the hypothesis that the concentration overvoltages and the ohmic drops are both negligible.