Vol 54, No 4 (2018)

Molecular-dynamics calculations confirmed the applicability of the equations of the theory of volume filling of micropores and the lattice model for describing the isotherm of adsorption onto active carbons in a wide range of temperatures below and above the critical values.

A new material resistant to acidic media to be used as a sorbent to remove anionic dyes from water has been developed by means of immobilization of chitosan-sulfate particles on a fiber substrate. Phthalocyanine dyes differing in molecular size, as well as quantity and nature of anion groups, were used as model sorbates. It has been established that the sorption rate and the limiting sorption capacity decrease along with an increase of the dyes’ molecular size. A conclusion has been drawn that the effect of solution pH on the sorption parameters is a combined result of changes in the degree of protonation of chitosan amino-groups and in the dyes’ state of association in the solution. The dyes’ experimental sorption isotherms were processed according to the Langmuir model with a correlation coefficient of 0.98–0.99. The new material has exhibited a sorption rate an order of magnitude higher than that of the initial chitosan in powder form, as well as almost twice the sorption capacity.

Composite materials resulted from impregnation of active carbons with aqueous solutions of manganese (II) chloride were studied by the methods of gas adsorption, X-ray powder diffraction, atomic absorption spectrometry, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The texture and specific characteristics of porosity, microporosity, and composition of the prepared composites were found to change depending on the acidic or basic nature of the surface of initial carbons, conditions of impregnation, subsequent treatment, and calcination temperature. It was shown that, upon the impregnation of the “acidic” carbons, the total pore volume covered 8–11 times the micropore volume, as distinct from the “basic” samples, which showed only a two- or threefold excess. The specific BET surface determined for the “acidic” carbons exceeded the value found for the samples with a “basic” surface. It was confirmed that the prepared composites contained manganese in various manganese-oxide compounds including ramsdellite, hausmannite, manganosite, bixbyite, and partridgeite at concentrations of 23–48 wt %.

The effect of a weak pulsed magnetic field (WPMF) on the hydration properties of natural aluminosilicates of different structures (clinoptilolite and glauconite) is established. Isotherms of water adsorption are analyzed using the BET equation and a more considerable decrease in the limiting capacity of a monolayer on clinoptilolite is determined as compared to that on glauconite (more than threefold), as is the corresponding decrease in the specific surface area of clinoptilolite, which is confirmed by the data of IR-spectral analysis.

Rheological properties and diffusion permeability of butadiene–styrene film in vapors of organic solvents were studied in both the equilibrium and nonequilibrium states. The investigations by quartz acoustic gravimetry showed that, under the influence of butadiene, acetone, ethanol, dimethylformamide and water vapors, the shear modulus and mechanical losses of the film decreased. This effect was inversely proportional to distance R_a between the centers of the Hansen solubility spheres of a polymer and solvent. The extent of this decrease for R_a = 13 MPa^0.5 is significantly higher than that within a range of R_a ≥ 13 MPa^0.5. The dependences describing the changes in the shear modulus coincided qualitatively with that for the swelling degrees versus distance R_a. Under the influence of vapors, the kinetics of frequency changes in a “resonator–film” system can be described by two exponents: the first short exponent characterizes the permeability of a polymer film before the exposure in vapors and during the first minutes of the process, and the second one is one to two orders slower and covers a subsequent period. The time constant of the short exponent is proportional to R_a.

The behavior of cyclic compounds in copper-plating sulfate electrolytes is directly determined by their structure (the nature of a heteroatom in a ring, the size of the cycle, and the presence of side carbonyl groups). The efficiency coefficient increases with an increase in the volume concentration of an additive in the presence of nitrogen-containing heterocycles, whereas that of oxygen-containing ones slightly depends on c_L⁰. Calculation of the kinetic parameters of the process confirmed that kinetics of a cathode reaction is mainly due to the nature of a heteroatom in the cycle. Combined analysis of chronopotentiometry and impedance data showed that the complexes formed in the surface layer block the electrode surface, increase the Ψ′ potential, and make the discharge of metal ions difficult, with their inhibitory effect increasing with an increase in ligand concentration. Effective control of deposition rate, morphology, and properties of coatings is possible as a result of changes in the nature, structure, and volume concentration of the additives.

Nanostructured titanium carbide (TiC_x) coatings are deposited on steel substrates by plasma chemical vapor deposition using three different duty cycles of 33, 40, and 50% and characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The relationship between the texture orientation/elemental concentration and duty cycle can be divided into two regimes, carbide (TiC_x) state and oxycarbide (TiC_xO_y) state. The coatings crystallize into a TiC NaCl-type crystal structure (FCC) in the carbide and oxycarbide states and a smaller “x” in the TiC_x coatings causes the transformation of the preferred orientation of (200) in the carbide state to (111) in the oxycarbide state. A poorly crystallized anatase phase is also observed from the coatings deposited using duty cycles of 40 and 50% and this anatase phase is detected from the oxycarbide state.

In this work, TiN nanostructured hard coating was deposited on the quartz and H11 hot work tool steel substrates using by plasma enhanced chemical vapor deposition (PECVD) technique. The process was performed in a hot wall chamber containing Ar, N₂, and H₂ gases along with TiCl₄ vapor for 2 h at the temperature deposition of 470°C. Field emission scanning electron microscopy (FE-SEM) and EDS were used to determine thickness and chemical composition of the coating, respectively. Crystal structure of the coating was investigated by X-ray diffraction (XRD) technique which indicated strong reflections of highly crystalline TiN. This was further confirmed by X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS). Potentiodynamic polarization test in 3.5% NaCl solution and pin-on-disc were used to evaluate the properties of the TiN coating. The results indicate that specimens coated with TiN coating has fine columnar grains and low friction coefficient (about 0.2). Also polarization curve exhibit a 10 times improvement in corrosion resistance compare to uncoated samples. This protection is attributed to formation a dense and adhesive layer of TiN nanostructured hard coating on the H11 substrate.

In this paper a new procedure for the calculation of uniform corrosion current density is presented. The procedure is based on the following criterion: corrosion current and extent of anodic and cathodic areas are such that the entropy production rate is maximum. Experimental data for the reaction Fe(s) + HCl(aq) = FeCl₂(aq) + H₂(g), taken from literature, are used to test the new model. A comparison between corrosion current density calculated from weight loss measurements and current density calculated from polarization curves by means of the proposed model is carried out. The proposed model provides a better agreement, between Tafel line extrapolation and gravimetric measurement, in comparison to the mixed potential theory usually adopted.

Green crystals of the coordination polymer (CP) [CdN₃(en)(n)], 1, was obtained by reaction of CdSO₄ · 5H₂O with ethyl nicotinate (en) in the presence of NaN₃. The structure of the CP 1 was characterized by elemental analysis, IR, ¹H-NMR, UV-Visible and X-ray single crystal analysis. The ORTEP plot of CP 1 consists of [(Cd)₄(N₃)₄(en)₄(n)₄] structure exhibiting 14-atom V-shaped cyclic configuration, which contains 8-atoms ring [(Cd)₄(N₃)₄]. The structure of CP 1 creates 1D-chain where the cyclic structures are connected by two nicotinate ligands (n). The chains are extended in three directions forming 3D-network structure via extensive H-bonds. The CP 1 was tested as corrosion inhibitor for copper in 1 M HCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results of polarization indicated that CP 1 acts as mixed type inhibitor. Adsorption of CP 1 obeyed Langmuir adsorption isotherm. Effect of temperature on the corrosion process was studied and activation parameters were calculated and discussed. The results obtained from the two different electrochemical techniques are in good agreement.

A new cationic surfactant namely, N-(2-(2-hydroxyethoxy)ethyl)-N,N-dimethylhexadecan-1-ammonium bromide (HEDHB) was prepared and its performance as a corrosion inhibitor for carbon steel in 1.0 M HCl solution was monitored by four techniques (weight loss, potentiodynamic polarization, electrochemical frequency modulation (EFM) and electrochemical impedance spectroscopy (EIS)). The temperature influence on the corrosion rate has been assessed throughout gravimetric technique. The corrosion thermodynamic and the inhibitor adsorption processes were inspected and assessed. The weight loss results confirmed that, the inhibition efficiency of the synthesized HEDHB inhibitor directly proportionally to inhibitor concentration and the temperature. Langmuir’s adsorption isotherm was the best fitted isotherm, which describes the ability of the molecule to adsorb on the steel surface. Tafel polarization reveals that the HEDHB inhibitor suppress both the anodic and cathodic reactions and thus, classified as a mixed-type inhibitor. The morphology of the treated surface with HEDHB inhibitor was monitored by two techniques (Scanning Electron Microscope (SEM) and Atomic Force Microscopy (AFM)). A quantum chemical study has been utilized to investigate the influence of molecular structure of the synthesized HEDHB inhibitor on corrosion inhibition efficiency.