Developing of chemical sensors is relevant for solving environmental problems of monitoring the atmosphere of cities and industrial zones. Semiconductor sensors based on metal oxides are a promising type of chemical gas sensors due to their high sensitivity, low cost, small size, and low energy consumption. First attempts of pilot operation of atmospheric air monitoring systems based on such sensors revealed an insufficient stability of their response. Doping silicon in the basic material can solve the problem. At the same time, data on the amount and distribution of the dopant in the material are necessary to determine the relationship «synthesis conditions – composition – properties». We propose an approach to the determination of the composition of novel semiconductor materials based on β-Ga₂O₃ with a silicon dopant content from 0.5 to 2 %at. The approach included grinding of samples using a planetary mill and preparation of suspensions in ethylene glycol, followed by TXRF determination of the analytes on sapphire substrates using the method of absolute contents (Si) with S_r 0.08 and the method of external standard (Ga) with S_r 0.04. X-ray fluorescence analysis of the samples was performed on a S2 PICOFOX spectrometer (Bruker Nano GmbH, Germany). MoKα radiation was used to excite X-ray fluorescence. The spectrum acquisition time is 250 sec. It is shown that the homogeneity of the dopant distribution in the material can be estimated using the suspension analysis. The studied materials demonstrate an irreproducible sensory response which we associated with the revealed inhomogeneity of the silicon distribution over the surface of β-Ga₂O₃.

The piezosensors modified with a molecularly imprinted polymer (MIP) with potassium sorbate (MIP-E202) and sodium benzoate (MIP-E211) imprints are tested and implemented in the determination of preservatives in soft drinks. Molecularly imprinted polymers were synthesized by noncovalent imprinting on the base of copolymer of 1,2,4,5-benzene tetracarboxylic acid dianhydride and 4,4’-diaminodiphenyl oxide in N,N-dimethylformamide (DMF) in the presence of templates. Piezoelectric sensors based on MIP and non-imprinted polymer (polyimide) were compared. High values of the imprinting factor (IF) and selectivity coefficient (k) obtained for MIP-E202 (IF = 5.4) and MIP-E211 (IF = 6.0) sensors indicated better selectivity and ability of MIP-based sensors to recognize target molecules than piezosensors modified with a reference polymer. The detectable concentrations range within 5 – 500 mg/liter, the detection limits for potassium sorbate and sodium benzoate are 1.6 and 2.0 mg/liter, respectively. Correctness of the preservative determination in model solutions was verified using the spike test. MIP-based sensors appeared sensitive to the preservative determination and insensitive to interfering substances. The matrix composition of the non-alcoholic drinks did not affect the value of the analytical signal of the piezoelectric sensor. High performance liquid chromatography (HPLC) was used as a reference method. The results of potassium sorbate and sodium benzoate determination in non-alcoholic drinks using piezosensors match the HPLC data rather well, their content in the studied soft drinks being 130 – 176 and 129 – 146 mg/liter, respectively.

A simple spectrophotometric method for the determination of bismuth potassium ammonium citrate in the cleaning wastes of industrial equipment using 4-(2’-pyridylazo)-resorcinol is proposed. The method is based on displacement of bismuth from its potassium ammonium citrate by 4-(2’-pyridylazo)-resorcinol, formation of the colored complex, and the colorimetric determination of the resulting product. The calibration curve is linear within the range from 4 to 20 mg/L of bismuth potassium ammonium citrate, the molar attenuation coefficient is 10,100 m²/mol, the detection limit is 2.7 mg/L, the quantification limit is 8.2 mg/L. The method is selective with respect to the common excipients, exhibits a good accuracy (the relative uncertainty does not exceed 10%) and precision (the relative standard deviation does not exceed 5%), does not require lengthy sample preparation and sophisticated laboratory equipment and is suitable for the routine analysis of the cleaning wastes of industrial equipment.

The development of methodological tools for studying the most possible range of the objects of dielectric nature is an urgent task. We present the results of studying dielectric objects by the method of electret-thermal analysis (ETA). Electrophysical changes in dielectric objects were studied taking into account polarization effects and electret state. The ETA data of ultrahigh molecular polyethylene, polyvinyl alcohol, human blood, synovial fluid, starch-containing polymer biodegradable compositions, chitosan, and vegetable oils are presented. Analysis of the spectra of thermally stimulated currents obtained during tests revealed that ETA method is characterized by high information content regarding various dielectric objects.

Thermally stimulated current response makes it possible to identify and interpret phase phenomena occurring upon heating of the objects, including those accompanied by electrophysical processes of transfer and relaxation of the electret charge. The results obtained can be used to improve the methodology for analyzing electrophysical changes in dielectric objects.

Organic semiconductors and novel carbon forms (fullerene, carbon nanotubes, carbon foam, graphene) promote synthesis of carbon nanocomposites with modified properties based on thermally treated polyacrylonitrile (TPAN) that comprises curved (spherical, ring-like, and tube-like) carbon planes. Here we present a review of the studies regarding the properties of TPAN-based nanocomposites. The features of the IR irradiation procedure with a synergetic effect and the mechanism of polyacrylonitrile (PAN) transformation into carbon nanocrystalline material (CNM) have been analyzed. The developed method is promising for the synthesis of luminescent carbon nanostructures and biocompatible carbon nanostructures with high sensitivity to pH medium; metal-polymer nanocomposites (Ag/PAN, Cu/PAN, Fe₃O₄/TPAN), which can be used in electronics, catalysis, and in water purification from heavy metals, etc. The results obtained may be used to synthesize TPAN-based novel nanocomposites with modified properties.

Improving the efficiency of assessing the results of low-cycle fatigue (LCF) test in the course of interlaboratory comparison tests (ICT) requires a reduction of the uncertainty associated with a number of random factors independent on the quality of testing and qualification of testing laboratories. Those factors are attributed to a random nature of the initiation and development of the fatigue fracture due to the inhomogeneity of the macro- and microstructure of the material, the state of the sample surface, stress concentrator, etc. A method for evaluating the results of LCF tests at ICT is presented. The method is implemented on the basis of linear regression analysis of experimental values of the mean and standard deviation of the logarithm of the durability at a given stress level. The features of evaluating the results of experimental data of interlaboratory comparison tests for low-cycle fatigue are presented. We propose to use the median estimate of the logarithm of fatigue life (corresponding to a given level (amplitude) of stresses obtained from the median fatigue curve constructed from the results of statistical analysis including regression analysis of the variances of experimental data) as an assigned value for assessing the characteristics of functioning of the laboratories participating in the ICT. The assigned value and estimates of the performance of laboratories is obtained using the median fatigue curve, which is plotted depending on the number of participants in the ICT. With a small number of participants, the median low-cycle fatigue curve is plotted according to the test results obtained by the expert laboratory, whereas for a sufficiently large number of participants according to the test results combined for all laboratories participating in the ICT.

The basic aspects of the J-A concept of elastic-plastic two-parameter fracture mechanics, based on a three-term asymptotic description of the stress field at the crack tip are presented. It is noted that the field of elastic-plastic stresses at the crack tip is controlled by two parameters of fracture mechanics, namely, J-integral and parameter A. Parameter A is a measure of the deviation of the stress field from the HRR-stress field and can be considered a parameter of elastic-plastic constraint at the crack tip both under conditions of small- and large-scale yielding. The results of studying the influence of the exponent of the strain hardening of the material, crack aspect ratio and the thickness of standard specimens with a crack on the elastic-plastic stress intensity factor and parameter A are presented. A two-parameter elastic-plastic J-A fracture criterion based on the relationship between J-integral and strain(stress) on the surface of the crack-notch and the principle of linear summation of damage is formulated. To reflect the crack-tip constraint, the parameter A is introduced into the criterion equation as a function of applied failure stresses. The elastic-plastic fracture toughness as a function of the crack-tip constraint in the fracture criterion is interpreted as the corrected elastic-plastic fracture toughness of a specimen with the corresponding constraint parameters A. The results of studying the normalized corrected fracture toughness as a function of failure stresses, crack aspect ratio and strain hardening exponent of the material are presented.

Studying the vibration strength of various structures, parts and load-bearing elements used in aviation engineering, oil-and-gas and metallurgical industry at elevated temperatures suggests using of special heating appliances. We present the heating appliance developed to study the vibration strength of the structures used as part of vibration stands capable of sustaining the temperature mode close to 1300°C during long periods of time. A framed structure of the heating appliance is presented, having neither bottom, side or end walls nor cover, all of them substituted with a roll heat-retaining material. The frame design of the heating appliance provides for rather quick manufacture of a frame of the desired dimensions. The use of heat-retaining material makes it possible to remove temperature sensors from the heating appliance, as well as pipelines for conducting gas-dynamic studies. The analysis of frequently used heat-resistant alloys (superalloys) is carried out. A wire made of Kh23Yu5T-N alloy was used as a material for heating elements to maintain the desired temperature conditions. The design, shape, mode of fixing the heating elements in the heating device, as well as the method of connection to the power supply and measuring systems are proposed. The results of experimental study are presented to confirm the long-term operability of the appliance with heating elements made of the wire 6 and 7 mm in diameter at a temperature up to 1300°C. The results obtained revealed the necessity of replacing the heating elements after each long-term high-temperature exposure. The proposed designs and material of the heating elements provide the possibility of their rapid manufacture and replacement. It should be noted that all the components of the heating device are economically efficient. The developed heating appliance was used in studying the strength of various structures under the effect of vibration and gas-dynamic loads at temperatures close to 1300°C.