Volume 55, Nº 5 (2019)

The effect of adsorption on the characteristics of equilibrium rough surfaces of vapor–liquid and vapor–solid interfaces at a temperature close to the melting point is investigated. A discrete model of a dense phase—the lattice gas model, which includes direct correlations of all neighboring components of the system in a quasi-chemical approximation—is applied in the calculations. For simplicity, the model implies commensurability of the component size and the considered vibrations of particles through the effective contributions of the lateral interaction parameters for both adsorbent atoms and adsorbate molecules. The equilibrium profiles of adsorbent A and adsorbate B inside the transition area are calculated (provided that the adsorbent’s bulk phase remains unchanged) for physical adsorption and chemisorption. The effect of adsorption on the surface tension of the dense phase is examined. The probability of fluctuation processes of a new phase formation determined by the surface roughness of the pure adsorbent A, taking into account the adsorption of B particles on it, is estimated.

The form of elution curves in the linear frontal dynamics of adsorption is studied based on the exact solution of a direct problem. It is determined that there is an intersection of the elution curves calculated in dimensionless coordinates under different values of the effectiveness of the adsorbent layer at a relative concentration corresponding to about 0.68. The determined principle allows us to develop an algorithm to determine the adsorption and kinetic constants for the initial values of effectiveness. The solution of an inverse problem of the linear dynamics of adsorption on the example of the model elution curve is demonstrated.

The effect of temperature and the cesium concentration in the external solution on the sorption capacity of titanium phosphate obtained upon the heterogeneous interaction of the (NH₄)₂TiO(SO₄)₂ · H₂O crystalline salt with phosphoric acid is studied. Sorption on titanium phosphate is shown to be best described by the Langmuir isotherm. When describing the sorption kinetics of solutions, it is necessary to consider both the possibility of diffusion and adsorption limiting the process rate. The use of the chemical kinetic models shows that the stage of chemical interaction of metal ions with functional groups of the sorbent also contributes to the overall rate of the process.

The results of studying the equilibrium and kinetics of Cu²⁺ ions’ sorption from aqueous solutions by the initial and modified wool keratin are presented. The modified sorbent’s strong sorption properties are the result of the formation of hydroxamic acid groups on its surface on retention of the initial keratin’s excess carboxyl groups. The sharp change of sorption by wool keratin in the range of an isoelectric point is related to the change in the degree of the dissociation of the excess carboxyl groups. The IR-spectra and SEM-images of the initial and modified sorbent samples that indicate the structural changes caused by the immobilization of new functional groups on the wool keratin surface are presented.

Geopolymer samples prepared through alkali activation of metakaolin under varying conditions of synthesis (100°C (14 h); 130°C (3 h); clinoptilolite filler) are employed as formaldehyde sorbents from aqueous solutions. The structure and physicochemical properties of geopolymer sorbents are studied using XRD, XRF, SEM, N₂ adsorption–desorption, and chemical methods. Zeolite A is the main component among the structural components in the synthesized specimens (zeolite А, hydroxysodalite, and quartz). Addition of the clinoptilolite filler in the synthesis of geopolymers has resulted in a slight increase in their specific surface and pore volume. Geopolymer sorbent specimens display strong adsorption ability in relation to sorbate molecules in aqueous solutions of formaldehyde (0.064–0.366 M). The cation-exchange capacity of the geopolymers, which is 2–3 times as large as that of the natural clinoptilolite specimen, is the probable reason of their strong adsorption capacity to formaldehyde. The nature of the exchanged cation (Na⁺, \({\text{NH}}_{4}^{ + },\) Cu²⁺) determines the magnitude and the predominant mechanism of sorption uptake of formaldehyde (physical adsorption, chemisorption, and complexation). Higher adsorption values of formaldehyde are obtained in the case of \({\text{NH}}_{4}^{ + }\)- and Cu²⁺-forms of geopolymer sorbents compared to the Na⁺-form.

As a model for a nanoparticle we use a nanocube. We assume that the potential of the cube is separable. Therefore, we can split Schrödinger’s equation into three one-dimensional ones. The potential in each of the one-dimensional sub-systems has a Meander-like run. For the calculation of the surface free energy of the nanoparticles we split a nanocube into smaller ones. We calculate the difference of the electron energies in the original nanocube and in the disintegrated cubes. If we divide the energy increment by the newly generated surface we have a very easy and correct procedure for the calculation of the surface free energy resulting from the cleavage of a nanocube into nanocubes. For an exact calculation of the surface free energy emerging in the disintegration of a macroscopic body into nanocubes we have to calculate the energy levels in an infinitely extended body with the same type of potential. Also a formula for the calculation of the surface stress for a nanocube has been derived. Approximating methods are given for the calculation of the surface free energy and the surface stress of nanocubes. In the case that the mean electron energy for a material with completely occupied energy bands is known it is possible to calculate, at least approximately, with this easy method the surface free energy and the surface stress. In this way, the surface free energy as a function of the chemical potential and temperature has been calculated. For a nanocube with 10 × 10 × 10 atoms with a completely occupied energy band the surface free energy amounts to 0.4 J/m² and the surface stress is – 0.19 N/m.

A study of the optical properties of iron nanoparticles prepared using the molecular-by-molecular method in the reactions of ion chemical and radiation-chemical reduction in inverse micelles, which were considered as microreactors, made it possible to reveal the features of the formation of metal nanoparticles (NPs) at various stages of physicochemical processes including a spontaneous formation of ordered spatial nanostructures in the postradiation period. The analysis of the spectral data obtained from the measurements in inverse micellar solutions (IMS), which were free of metal ions, provided important information on the evolution of colloid systems. After adding iron ions into an IMS, the Fe NP formation induced by self-assembly processes was detected via characteristic optical absorbance spectra. Based on the results obtained, some peculiarities of the self-assembly processes in IMSs occurring upon various ignition reactions of iron ion reduction and the Fe NP formation were discussed in the work.

In this study electrochemical deposition of nanostructure poly (aniline-co-4-hydroxy phenyl acetic acid) (PAHPA), polyaniline (PANI) and poly (4-hydroxy phenyl acetic acid) (PHPA) were carried out using cyclic voltammetry (CV) in aqueous solution of oxalic acid 0.3 M as reaction medium to achieve a protective coating for ferritic and economic 430SS in high corrosive solutions as 3.5% NaCl. In the electropolymerization of PAHPA, the monomer ratio was 1 : 1 (mol/mol). FT-IR and CV techniques were applied to characterize electrodeposited coatings. The morphological and structure analyses of the deposited films were done using scanning electron microscopy (SEM). Anticorrosive behaviors of coated steels were investigated by two techniques, potentiodynamic polarization and EIS (Electrochemical Impedance Spectroscopy) and were compared with protection efficiencies of PANI and PHPA. Our results showed that PAHPA coatings provided a noticeable better corrosion protection than homopolymers. The protection efficiency value for the PAHPA coated 430SS electrode was 97%, that it was higher than protection efficiencies of the hompolymers. Also effect of long immersion times on the protective films and their corrosion behaviors was studied. The PAHPA protection efficiency decreased about %3 when immersion time increased to 10 days. These results demonstrated the copolymer film can be highly corrosion resistant coating for 430SS in corrosive solutions that have chloride ions.

The results of structural studies and mechanical, abrasion, and erosion tests of single-layer and multi-layer TiN, Ti–Cr–Al–N, and Cr–Al–Ti–N coatings deposited on a closed-field unbalanced magnetron sputtering (CFUBMS) system using the ion-plasma technique are reported. It is demonstrated that, despite their low level of hardness (17–18 GPa versus 40 GPa for TiN), Ti–Cr–Al–N and Cr–Al–Ti–N coatings are superior to single-layer titanium nitride coatings in terms of their abrasive wear resistance and erosion resistance due to their structural features.

A WC-17 wt % Co coating was deposited onto a ST37 mild steel substrate by HVOF-spray technique and then vacuum heat treated at 1100°C. The cross sectional microstructure of the produced coating was characterized before and after heat treatment by optical microscopy. X-ray diffraction (XRD) was also utilized to evaluate the effects of heat treatment on the phase composition of the WC-17Co coating. To study the electrochemical corrosion behavior of both as-produced and heat treated samples, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods were performed in 3.5 wt % NaCl solution. Our results reveal that the WC-17Co coating had a dense structure with an average thickness of about ~500 μm. However, heat treating the coating resulted in an adhesion failure and therefore partial separation of the coating from the substrate. The as-produced coating was also composed of both crystalline WC and amorphous phases whilst the heat treated layer was fully crystalline. According to the corrosion tests, the WC-17Co coating improved the corrosion resistance of the substrate. However, heat treating the coating at 1100°C decreased anticorrosion performance which was due to the precipitation of η-phases with different electrochemical potential than the WC phase together with the formation of microgalvanic cells between the crystalline phases with different compositions.

In the current study, the inhibitive performances of tertiary amine methacrylate based water soluble diblock copolymers on the corrosion behavior of AISI 304 stainless steel were investigated in double distilled water (DDW, at pH 7.6) using potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM) and inductively coupled plasma optical emmision spectrometry (ICP OES) methods. Related diblock copolymers were poly[2-(dimethylamino)ethylmethacrylate] (PDMA), poly[2-(diethylamino)ethylmethacrylate] (PDEA), poly[2-(diisopropylamino)ethylmethacrylate] (PDPA) homopolymers and poly[2-(dimethylamino)ethylmethacrylate]-b-poly[methylmethacrylate] (PDMA-b-PMMA), poly[2-(diethylamino)ethylmethacrylate]-b-poly[methylmethacrylate] (PDEA-b-PDMA) and poly[2-(diisopropylamino)ethylmethacrylate]-b-poly[2-(dimethylamino)ethylmethacrylate] (PDPA-b-PDMA). Diblock copolymers having different molecular weight and different comonomer ratios. Polarisation curves indicated that all the studied polymers were acting as a mixed type inhibitors. All electrochemical measurements showed that inhibition efficiencies increased with an increase in the inhibitor concentration. It was determined that the increase of inhibitor efficiency by concentration resulted from the adsorption of polymers to metal surface, and the adsorption fitted to Langmuir adsorption equation. Adsorption equilibrium constant (K_ads) and free energy of adsorption(ΔG_ads), which were thermodynamic parameters of adsorption were calculated by benefiting from the drawn adsorption isotherms. The variation in inhibitive efficiency mainly depended on the type and the nature of the substituents present in the inhibitor molecule and also depended on the molecular weight of the inhibitors. The best inhibition in DDW showed VB207 diblock copolymer. Surface images obtained with SEM, EDX and AFM methods, determined by verifying these results that inhibitors decreased the dissolution of metal, and prevented the corrosion.

The effect of an heterocycle triazole, namely (1-(4-methoxyphenyl)-1H-1,2,3-triazol-4-yl)methanol (MTM) on the corrosion of mild steel in hydrochloric acid solution has been investigated using electrochemical methods for a wide temperature range, FT-IR spectroscopy and SEM techniques. MTM was found to inhibit the corrosion of steel by adsorbing to a great extent, even at high temperatures. Computational results point to the phenyl ring as the main structural part which is responsible of the adsorption by electron-accepting to the mild steel surface, while the triazol ring is responsible for the electron-donating. Molecular dynamics simulations (MD), reduced density gradient (RDG), radial distribution function (RDF) provides further insights into the interpretation of inhibition mechanism in a more realistic condition, confirming that the MTM can effectively protect mild steel against corrosion by constraining the diffusion of the particles present on the steel surface.

The inhibition effect of N,N ′-bis(1-(3,5-dihydroxyphenyl)ethylidene)propane-1,3-diamine was studied on steel corrosion in 1 M hydrochloric acid solutions. The density functional theory was applied to calculate quantum chemical parameters such as the highest occupied molecular orbital energy, the lowest unoccupied molecular orbital energy, electron affinity, global electrophilicity index, the fraction of electron transferred, global nucleophilicity index, and Mulliken charges. According to quantum calculation, the diamine compound showed high interaction and effective adsorption on steel surface and high inhibition efficiencies and therefore nitrogen atoms of inhibitor indicated more tendencies for the electrophilic effect in the adsorption. Electrochemical impedance and potentiodynamic polarization indicated that this material has excellent inhibiting features in very low concentrations. The influence of DC trend on the explanation of electrochemical noise data was evaluated by polynomial fitting and the optimum polynomial order m = 4 was obtained. Noise resistance and the inhibition efficiency was calculated and compared in different methods. The theory of shot noise in frequency domain was used to obtain the electrochemical event charge. The corroded surface of steel in the absence and existence of thiazole compound was studied by Atomic force microscopy.

The effect of pulse neutron gamma-radiation on material made from sintered ceramics of hexagonal boron nitride α-BN is studied using positron annihilation spectroscopy (PAS). The radiation vacancy defects of the α-BN crystal lattice are effective traps of the positrons diffusing into the bulk particles of the material. The positrons’ lifetime (LT) spectra and angular correlation curves of annihilation gamma-ray quanta (ACAR) in ceramic specimens irradiated by neutrons with a cumulative dose of the neutron flow of 10¹³ to 10¹⁴ neutron/cm² (the average energy of the neutrons is 1.7 MeV) and gamma radiation of 10³ to 10⁵ Р (E_γ = 1 MeV) with the subsequent annealing of the irradiated specimens at 600°C are measured. The observed changes of the annihilation characteristics of the LT and ACAR in the irradiated and sintered specimens allow us to conclude that there is an effective capture of the alpha particles formed upon neutron irradiation via the nuclear reaction B¹⁰(n, α)Li⁷ with vacancy defects. Helium atoms are released from vacancies to the surface of the α-BN plates upon annealing of the irradiated specimens at 600°C. This mechanism explains the high level of radiation stability of α-BN ceramic dielectrics in ionizing radiation fields.