Voprosy khimii i khimicheskoi tekhnologii (Issues of Chemistry and Chemical Technology)

11-16

Authors: A.A. Kityk, Y.D. Rublova, N.G. Bannyk, K.M. Shcherbakova, V.V. Malaya

The effect of water on the corrosion rate of mild steel in deep eutectic solvent, Ethaline, was investigated by electrochemical impedance spectroscopy technique. Quantitative characteristics of the process of corrosive destruction of metallic samples have been obtained, the peculiarities of this process have been determined and its mechanism has been established by selecting an equivalent electrical circuit. It was shown that increasing of water content in this ionic liquid leads to an appreciable increase in the corrosion rate. It was stated that the growth of corrosion activity of Ethaline mixture can be associated with the appearance of water in its composition and it is chiefly connected with the changes of physicochemical properties of this mixture. With increasing the water content in the investigated liquid mixture, decreasing of viscosity and density are observed. These changes in physicochemical properties of Ethaline can be resulted from the destruction of hydrogen bonds, existing between the components of the mixture, that leads to an increase in depolarizer transport to the surface of the samples and, as a consequence, to the acceleration of the corrosion.

23-31

Authors: O.Yu. Mariichak, G.M. Rozantsev, S.V. Radio

We determined the conditions for the synthesis of a normal salt of sodium heteropoly decatungstosamarate(III) Na9[Sm(W5O18)2]•30H2O (Z=0.80) and acid salts with heteropoly decatungstosamarate(III)-anion Na7H2[Sm(W5O18)2]•24H2O (Z=0.90), and Na5Н4[Sm(W5O18)2]•17H2O (Z=1.00) from aqueous solutions of sodium tungstate acidified to Z=ν(H+)/ν(WO42–)=0.80–1.20, having the ratio of ν(Sm):ν(W)=1:10 and with addition of acetone. By means of FTIR spectroscopy, we showed that heteropoly anion contained in the isolated salts belongs to Peacock-Weakly structural type. In this anion, two lacunar tetradentate pentatungstate-anions [W5O18]6– are coordinated to Sm(III)-heteroatom, thus forming a coordination polyhedron in the shape of a square antiprism. Using scanning electron microscopy, the surface morphology of Na9[Sm(W5O18)2]•30H2O was studied, and it was found out that the grain size is within the range of 250–550 nm. Single-phase condition of the synthesized salt was confirmed by the surface uniform contrast in backscattered electron mode. There are no regions with different surface morphology on the micrographs of Na9[Sm(W5O18)2]•30H2O powder in characteristic X–ray emission, and there is an even distribution of Sm, Na, W, O, without segregation and eliquation. DTA method was used to study thermal decomposition of the Na9[Sm(W5O18)2]•30H2O, while powder XRD analysis revealed the formation of sodium ditungstate Na2W2O7 and double sodium–samarium orthotungstate Na0.5Sm0.5WO4 as a result of thermolysis. Powder XRD analysis of products obtained during the thermolysis of Na9[Sm(W5O18)2]•30H2O, Na7H2[Sm(W5O18)2]•24H2O and Na5Н4[Sm(W5O18)2]•17H2O was used to confirm the decrease of Na(I) in the composition of the synthesized salts (as shown by a decrease in relative intensity of the lines indicating a Na2W2O7 phase). It was established that maximum acidity, at which the isolation of salts with Peacock-Weakley heteropoly anion and Sm–heteroatom occurs, is Z=1.10.

39-43

Authors: O.S. Pogrebnyak, O.А. Zaporozhets, A.N. Pavlenko

The purpose of the study was to suggest a simple, expressive and, at the same time, sensitive method of the determination of bromide ion in water. The spectrophotometric method of bromide determination in the range of 0.1−4.0 mg dm-3 has been proposed. The method is based on bromide oxidation by the known excess of bromate in sulfate acidic medium in the presence of N,N-dietylaniline followed by the registration of light absorption (at 222 nm) of 4-bromo-N,N-diethylaniline formed under these conditions. The effects of reagents and manifold variables on the sensitivity have been determined and the optimum conditions have been established. The detection limit (blank + 3) for bromide is 0.064 mg dm-3 where  is the standard deviation of blank estimation. The effect of foreign ions in bromide determination (3.110−5 mol dm-3) has been studied. It was established that such components of natural water as dihydrophosphate, dihydropirophosphate, fluoride, chloride and NH4+-ions do not interfere with the determination of bromide. The presence of sulfide, thiocyanate, Cu2+ and Fe3+ ions in comparable amounts impedes the determination of Br− ions. The proposed techniques have been tested by determination of bromide in standard solutions and waters of various categories. The relative error of bromide determination did not exceed 0.12. The reagents are accessible and resistant over time. The proposed procedure is simple and suitable for bromide determination in various objects.

50-56

Authors: Yu.E. Sknar, I.V. Sknar, A.A. Savchuk, A.A. Bezik, F.I. Danilov

The photocatalytic activity of Ni–TiO2 composites obtained from a methanesulfonate electrolyte was studied. The photodegradation of methyl orange in the presence of Ni–TiO2 composite resulted in a partial poisoning of the photocatalyst, which is manifested in a decrease of its activity over time. The photodegradation of methyl orange dye was stated to follow the pseudo-first order kinetics. The observed rate constant of the photodegradation reaction is proportional to the surface area of the photocatalyst. The dependences of the composite composition on the dispersed phase concentration in the solution and current density showed only a limited possibility of increasing the content of photocatalytically active TiO2 particles in the coating. This paper presents a new method for increasing the photocatalytic activity of the Ni–TiO2 composite. The authors have proposed to deposit a photocatalyst on a preformed nickel developed surface matrix. The effect of increasing the specific surface area of the matrix is achieved by nickel electrodeposition from a suspension electrolyte containing carbonyl nickel powder as a dispersed phase. The inspection of the voltammograms of hydrogen evolution reaction on smooth and developed nickel surfaces revealed that the incorporation of nickel particles into the coating leads to a significant increase in the specific surface area of the matrix. The composite Ni–TiO2 coatings deposited on a developed surface matrix have a four times higher photocatalytic activity than those obtained on a smooth sample.

63-67

Authors: A.V. Zaychuk, A.A. Amelina

The effects of the gaseous atmosphere and the burning temperature of quartz ceramics on its phase composition and physical and technical parameters are investigated. Sintering the investigated ceramic in the air was stated to result in considerable crystallization of quartz glass at temperatures of above 1250C. The formation of crystalline cristobalite phase causes a significant increase in the temperature coefficient of linear expansion to 64.310-796.6•10-7 deg-1, which negatively affects the ability of glass ceramics to resist thermal stresses. The expediency of carrying out the thermal activation of sintering of quartz ceramics in a reducing medium is shown, which allows shifting the process of its appreciable crystallization to a temperature range of above 1350C and achieving a better sintering effect without significantly deterioration of the thermophysical properties (the temperature coefficient of linear expansion is (13.710-719.4•10-7 deg-1). The structure of the investigated quartz ceramics predominantly contains the glass phase and only a small amount of crystalline new formations in the form of β-cristobalite. The material obtained in this case is characterized by a complex of improved physical and technical properties, in particular, by low values of open porosity (3.7–7.2%) and water absorption (1.85–3.77%), which determines its high apparent density (1.92–2.00 g cm-3) and mechanical compressive strength (72.3–104.1 MPa).

75-81

Authors: I.V. Parsadanov, N.D. Sakhnenko, M.V. Ved', I.V. Rykova, V.A. Khyzhniak, A.V. Karakurkchi, A.S. Gorokhivskiy

The paper is devoted to the search for the rational ways of increasing the efficiency of intra-cylinder catalysis in diesel engines. The use of base metal oxides and composite oxides of transition metals as the coatings for the piston combustion chamber has been justified. This allows controlling the chemical reaction rates and reducing the formation of toxic substances. When selecting the scientific fields and rational practical ways of increasing the efficiency of intra-cylinder catalysis in diesel engines, a number of chemical, physical and technological factors were taken into consideration. The formation of catalytic coatings based on the oxides of transition metals (Mn, Co) was provided using the plasma-electrolytic oxidizing on the Al25 alloy. The coatings included both individual manganese and cobalt oxides and the mixed oxides of both metals. The catalytic coatings of the combustion chamber in the diesel engine piston on the basis of manganese and cobalt oxides and mixed oxides were tested. A maximum catalytic effect was achieved when cobalt oxides were used. The data on testing the prototype diesel showed that the fuel rate in this case was decreased by 4-6%, the emission of NOx was reduced by 14-15% and the emissions of carbon oxide were reduced by 20-25%.

89-96

Authors: O.V. Savvova, V.L. Topchyi, Yu.O. Smyrnova, D.V. Petrov

Current transparent high-strength materials used for transparent armor are considered; the importance of creating new, less expensive and more manufacturable materials based on glass-ceramics is emphasized in the article. The examination of literature data allows selecting transparent glass-ceramic materials based on lithium disilicate as promising ones because of their high operational and technological properties. It is shown that the known transparent glass-ceramics have either a quite long-continued mode of their production or an insufficient strength and heat resistance values. Therefore, the aim of this work was to establish the relationship between viscosity and crystallization ability in the course of the heat treatment and to determine the optimum conditions of the heat treatment and the formation of a required structure of material based on lithium disilicate. It has been found that the emergence and growth of lithium metasilicate crystals in experimental lithium silicate glasses of the selected chemical composition near the value of the viscosity of 109.5 Pas result in fine-dispersed volume-crystallized structure containing lithium disilicate and β-spodumene in the amount of 50 vol.% under conditions of a two-stage low-temperature short-term heat treatment. The formation of the ceramized structure of the developed glass-ceramic materials provides high mechanical properties (HV=8740 MPa and K1C=3.1 MPa•m1/2), and enhanced thermal and optical properties (transmittance of 72%) of transparent glass-ceramic on their basis. The obtained results can be used in the design and development of transparent high-strength glass-ceramic materials for the protection of special vehicles.

104-109

Authors: I.M. Trus, H.Y. Fleisher, V.V. Tokarchuk, M.D. Gomelya, V.I. Vorobyova

The efficiency of water desulphatization during the lime softening process with aluminium coagulant was estimated in the article. The joint use of sodium aluminate and aluminium hydroxychloride as complex coagulants was stated to be efficient for the purpose of water purification. Water treated with chemical reagent has a lower level of the residual alkalinity and minimal level of the secondary chloride contaminants. The efficiency of water desulphatization and softening increases with an increase in the sodium aluminate dosage and at constant dosages of lime and aluminium hydroxychloride. The efficiency of desulphatization reached 76–92% and water softening was 95–97% at optimal contents of the reagents. The treatment of water with carbon dioxide does not result in a significant increase in the efficiency of water desulphatization. The waste product of the chemical water softening process is a precipitate which contains calcium sulphate, calcium sulphohydroxoaluminate and magnesium hydroxide. Due to a high content of calcium sulphate, it is expedient to use the residue as an expansive admixture and a sulphate activator for cements. Cement expansion results from the hydration of calcium sulphate and its transformation into gypsum. In addition, calcium sulphate reacts partially with tricalcium aluminate in a highly alkaline medium forming calcium hydrosulphoaluminate. It is determined that the optimal dosage of the residue is up to 5 wt.%, the magnitude of the expansion being up to 2.9%. The dependence of the expansion on residue concentration is extreme. The presence of 2.5% residue accelerates the hardening of slag blended cement and increases its strength on the twenty-eighth day.