Vol 52, No 3 (2016)

A single-component adsorption isotherm has been derived for liquid on the solid surface, considering its finite deformation with a new surface layer equation that includes its independent influence on the rate of the rising adsorbate surface concentration. New thermodynamic conditions for the Rebinder effect are obtained as well.

The possibility of using cellulose-containing biosorbents obtained on the basis of agro-industrial wastes and byproducts to recover heavy metal ions from aqueous solutions was considered. The influence of the nature of sorbents (composition of biopolymers, content of carboxyl groups, specific surface, pore diameter and pore volume, swelling) on the kinetics and thermodynamics of distribution of heavy metal ions in a heterophase system consisting of water and biopolymer sorbent was determined. It was established that cellulose-based sorbents act as cationites at pH of 1–7, being inferior in their kinetic characteristics and sorption properties to commercial sorbents. Relying on literature data and the experimental results, it was found that the Langmuir, Freundlich, and TVFM models and other theories describe reasonably well the process (the correlation coefficients were 0.99); however, the Langmuir model provided the most exact determination of maximum sorption capacity of sorbents. It was concluded that, despite the comparatively low equilibriumkinetic characteristics, the cellulosic sorbents have received greater attention from researchers around the world due to their clear advantages with respect to ecological cleanliness, availability, and renewability of raw materials.

A method of modification of carbon sorbents by copolymers of glycolic and lactic acids is developed. Control over the polycondensation process and adjustment of the synthesis conditions and parameters are done using the methods of NMR spectroscopy and thermogravimetric analysis. Optimal conditions for the modification of a carbon material are selected, allowing one to obtain predominantly the oligomers of glycolic and lactic acids. The surface shape and morphology, porous structure, elemental composition and composition of the functional groups, and mechanical strength of the carbon sorbent samples are investigated using a set of physicochemical methods. It is established that the adjusted conditions of polycondensation allow one to affix the modifying agent on the carbon sorbent.

The kinetics and equilibrium of the process of sorption of heavy metals from aqueous electrolyte solutions by polystyrene, fullerene, and polystyrene/fullerene composites have been studied. The kinetics of sorption of copper, nickel, zinc, and cadmium ions by the studied sorbents is described by the pseudo-firstand pseudo-second-order kinetic models. The rate constants of the process of sorption are determined. It is established that the equilibrium isotherm of sorption of copper ions by fullerene is related to the Langmuirtype isotherms. The sorption capacity of a monomolecular layer with reference to the Cu(II) ions is determined as equal to 14.6 mmol/g. Based on the calculated Henry constants, it is shown that the sorption efficiency increases in the series polystyrene < composition < fullerene.

It is shown that an oxide layer saturated by chromium oxides is formed on the surface of chromium steel at a higher rate under electrocontact (10⁴–10⁵ A/cm²) vacuum dc annealing (10^–2 Torr, 300°C) than under furnace heating. Such activation of oxidation is due to the formation of an electrodiffusion zone in the surface steel layer. At further stages, grain boundaries emerge to the metal surface that act as oxidant transportation channels from the surrounding medium into the conductor bulk, which results in accelerated oxide formation in the bulk of the surface metal layer. Apart from the uniform oxide layer, individual hematite nanoflakes and nanoleaves with the thickness of 50–40 nm and average diameter of 450 nm are formed on the positive electrode and grow vertically on the steel surface. The average surface density of nanoparticles is 10⁸ 1/cm². Such activation of metal oxidation over the zone of electrodiffusion can provide pronounced properties for accelerated formation of protective surface layers, in addition to its intrinsic functional (sensor, catalytic, semiconductor, adsorption) properties.

Steel manufacturing technology has changed drastically in last few decades to meet the demand of high purity and quality of steel from the steel users. The advancements in steel making process have also demanded high quality refractories to withstand severe operating conditions and to produce desired steel quality. Magnesia carbon refractories, being essential for making and processing of steel, have gone through many modifications since its inception and still are one of the major challenging areas for refractories development. Only a few years ago higher use of carbon was assumed to be beneficial for the refractories performances and life but the concept has been proven wrong and low carbon containing MgO-C refractories are becoming the point of attention. Reduction in carbon content in MgO-C refractories without much affecting their properties have been tried by many ways by many researchers, amongst them use of nano carbon is widely popular. This review discusses the prospects for using nano carbons in MgO-C refractory and various research works that are going on and also on the development of low carbon containing magnesia carbon refractories.

Dual band (3–5 μm and 8–12 μm) multilayer nano-structured antireflection thin films comprising alternate layers of ZrO₂ and SiO₂ were deposited on Silicon (100) substrate by RF magnetron sputtering. Peaks of both spectral windows were optimized during the design process to match the peak response of the sensor in the two spectra. The multilayer structure and morphology of the deposited films were analyzed by RBS, XRD, AFM and SEM. The transmission measurements showed an average transmission of T_avg ~ 93% in 3–5 μm and T_avg ~ 83% in 9–12 μm, making the structure effective in both spectral windows and useful in dual channel imaging applications.

In this study, the surface morphology of Ni–P–SiO₂ composite coating was investigated by field emission scanning electron microscopy (FESEM). The amount of SiO₂ in the coating was examined by energy dispersive analysis of X-ray (EDX) and the Corrosion behavior of coating was evaluated by electrochemical impedance spectroscopy (EIS) and polarization techniques, showing the corrosion resistance of Ni–P–SiO₂ diminished after heat treatment. The results showed that in the coating with 12.5 g/L SiO₂, the coating hardness enhanced from 453VH to 980 VH before and after heat treatment. Furthermore, the wear behavior of the coating was analyzed before and after heat treatment.

Effort to improve the hardness and thermal resilient properties of coating for advanced engineering applications has necessitated this study. Zn sulphate electrolyte was induced with ZrO₂-SiC composite particulate at varied current density of 1.5 and 2.0 A/cm² for 10 minutes. The incorporated composite particles of ZrO₂/SiC were varied in other to examine their mechanical responses on zinc electrolyte. The coated films were characterised with scanning electron microscope with attached electron dispersion spectroscopy (SEM/EDS) and atomic force microscopy (AFM). The micro-hardness properties of the coated and thermal aged alloy were determined with high diamond micro-hardness tester. The anti-corrosion progression was examined using linear polarization technique in 3.65% NaCl. From the results, the incorporation of the composite matrix was found to impact significantly on the surface and microhardness properties. The co-deposition of composite submicron on the zinc electrolyte revealed that homogenous grain structure was obtained. To this end, a boost in the performance characteristics was attained due to effective co-deposition parameters in the electrolyte.

We report a comparative study of single-layer (TiAlCrSiY)N and multilayer (TiAl-CrSiY)N/(TiAlCr)N PVD coatings on cutting tools during the break-in stage of high-speed dry cutting. Phase and chemical composition of tribooxides forming in the coating wear area were studied by X-ray photoelectron spectroscopy. It is shown that amorphous oxide films with a thickness of several dozen angstroms contain phases with a chemical composition close to mullite, sapphire, rutile, and chromium oxide. As a result of selective wear, the contact surface of the coatings retains the most durable tribooxides carrying out protective functions. Low-cycle fatigue resistance is studied using the cyclic microindentation technique. Fractal analysis of time-resolved indenter penetration depth curves combined with scanning electron microscopy (SEM) demonstrates phenomenological regularities of coatings’ damageability at the early stage of wear. It is shown that, in comparison with single-layer (TiAlCrSiY)N, the nucleation and growth of microcracks in a multilayer (TiAlCrSiY)N/(TiAlCr)N coating is accompanied by acts of microplastic deformation providing a higher fracture toughness of the (TiAlCrSiY)N/(TiAlCr)N multilayer nanocomposite.

The process of electrodeposition of an iron–titania composite electrochemical coating from methanesulfonate electrolyte is studied. TiO₂ Degussa P 25 nanopowder (a mixture of crystalline modifications of rutile and anatase, with the latter prevailing) is used for preparation of suspension electrolyte. The dispersed phase content in the composition coating increases at a decrease in current density and increase in TiO₂ in the suspension. It is shown that kinetics of codeposition is adequately described by the improved Guglielmi model. It is shown that inclusion of TiO₂ particles into an iron matrix results in an increase in microhardness of the coating due to dispersion strengthening. Fe–TiO₂ (anatase+rutile) coatings manifest photocatalytic activity with respect to the reaction of destruction of the methyl orange dye in aqueous solutions under exposure to UV radiation, and this activity is higher than in the case of similar coatings containing TiO₂–rutile particles.

Scanning electrochemical microscopy (SECM) was used to sense the concentration of ions in 0.1M NaCl aqueous solution at the iron-aluminium couple. The SECM measured the concentration of ions relevant to the corrosion processes. The electrochemical behaviour of galvanic Fe/Al coupling was investigated as a function of time using SECM microelectrode tip. SECM amperometric line scan curves were obtained over the Fe/Al at a constant distance. In the first case the chemical species participating in the corrosion reactions at the sample are detected at the SECM-tip by applying appropriate potential values to the microelectrode. The release of Al³⁺ into the solution from local anodic surface, as well as the consumption of dissolved oxygen at the corresponding cathodic surface was successfully monitored. The results revealed that the galvanic couple where Fe/Al is close to each other will show lower corrosion rate due to the formation of corrosion products on the metal surface with further increase in exposure times.

In this work, the inhibitive effect of some antibacterial drugs against the corrosion of 316 stainless steel in 1M HCl has been studied by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The inhibiting effect explained by adsorption of the additives on steel surface. The inhibition efficiency increases with increasing the inhibitors concentrations and decreases with increasing the temperature. The data obtained fit well to Langmuir adsorption isotherm and the kinetic-thermodynamic model. The results of polarization studies indicate that the investigated antibacterial drugs are mixed type inhibitors. Increasing the inhibition efficiency of the investigated inhibitors with the addition of iodide ions indicates that iodide ions play important role in the adsorption process. The efficiencies obtained from the different electrochemical techniques were in good agreement which prove the validity of these tools in the measurements of the tested inhibitors.