Inorganic Materials最新文献

The piezoelectric sensors 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 piezoelectric sensors modified with a reference polymer. The detectable concentrations range within 5–500 mg/L; the detection limits for potassium sorbate and sodium benzoate are 1.6 and 2.0 mg/L, respectively. The correctness of the determination of preservatives in model solutions was verified using the spike test. MIP-based sensors appeared sensitive to the determination of preservatives and insensitive to interfering substances. The matrix composition of the nonalcoholic 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 nonalcoholic drinks using piezoelectric sensors match the HPLC data rather well, their content in the studied soft drinks being 130–176 and 129–146 mg/L, respectively.

This article discusses the possibilities of estimation of safe sizes of integrity defects on the basis of risk criteria. Such defects occur at all stages of the lifetime of structures. In most cases the estimation of their hazard and determination of allowable sizes attract attention when the defects can lead to brittle or quasi-brittle fractures. In this case, the models of linear and nonlinear destruction mechanics are applied, when the defects are considered as internal elliptical or surface semielliptical cracks. The stochastic variety of shapes, sizes, locations, and orientations of defects has a significant influence on the failure mechanisms. Therefore, the probabilistic problem of estimating allowable sizes of defects according to the criteria of risk of failure is relevant. This paper examines a general approach to estimation of the hazards of defects according to risk criteria. Two formulations of the probabilistic problem of risk estimation are presented: on the basis of single-parameter and two-parameter failure criteria. The risk function is used as the calculated characteristic, represented as the probability of failure according to a given criterion. An equation of the risk function based on single-parameter failure criteria is presented. The main focus is on the probabilistic model based on the two-parameter Morozov failure criterion. This criterion provides a wide range of opportunities for analyzing various failure mechanisms with variations in the size of defects. An expression for the risk function based on the family of two-dimensional Lu–Bhattacharya probability distributions of Weibull type is derived. It is shown that correlations between failure mechanisms can significantly influence the probabilities of failure and, consequently, the allowable size of defects.

It is noted that, in the general case, diagrams of cyclic elastoplastic deformation of a material characterize its resistance to low-cycle loading and display the relationship between current stress values and deformation during deformation. Such diagrams in the mechanics of deformation and fracture are described by complex equations of state that depend nonlinearly on the conditions and loading modes, including temperatures, strain rates, cycle shapes, types of stress state, absolute dimensions of sections, types of working media, types of structural material, etc. The mentioned factors in their entire complex influence the shape of curves (diagrams) of material deformation and the main parameters of the equations of state describing them, for example, such basic characteristics of mechanical properties as the modulus of elasticity, yield stress and ultimate strength, and indicators of static and cyclic hardening. As exemplified by experimentally obtained data on the kinetics of cyclic and one-sided accumulated plastic deformations in each of the half-cycles (cycles) of loading during static and low-cycle tests of specimens from a heat-resistant nickel alloy, it is shown that, under conditions of cyclic elastoplastic deformation, these deformation characteristics have an essentially nonlinear pattern of change, which is described on the basis of power equations and the parameters of cyclic deformation diagrams included in them. Here, the parameters of these equations depend on the type of cyclically hardening, softening, or stable material during its deformation in the elastoplastic region. It is noted that the resistance to cyclic elastoplastic deformations of a material can be described by a set of analytical expressions with a kinetic function included in them, which varies over the number of loading half cycles, in the form of power or exponential expressions depending on the cyclic properties of the material and data on the characteristics of the mechanical properties of specific structural materials. The obtained computational and experimental data on the kinetics of deformations of the alloy under study during its cyclic elastoplastic loading and on the parameters of the deformation diagrams, which are the basic characteristics for the corresponding equations of state, make it possible to fully apply the deformation-kinetic criterion for the accumulation of damage under the considered loading conditions for calculating the durability of structural elements made from it, which are operated, as a rule, under complex temperature and power conditions. The results of the performed experiments and calculations are presented in the form of diagrams of the cycle-by-cycle kinetics of cyclic and accumulated plastic deformations of the studied material under soft and hard loading conditions and in a wide range of test temperatures.

Microporosity is a dangerous defect observed in single-crystal gas turbine blades cast from nickel-based superalloys (NBSs). The volume fraction of porosity in single-crystal alloys does not exceed several tenths of a percent; however, it can result in shortening of the lifetime of the material of gas turbine blades under fatigue loading by many times. This work presents the results of determination of the volume fraction of porosity in single-crystal NBSs. Single crystals of a CMSX-4 NBS obtained according to the industrial technology of manufacturing of single-crystal blades are used as a test object. It is found that the methods applied, except for optical microscopy, have accuracy sufficient for measuring the volume fraction of microporosity of about 0.2 vol %. The highest accuracy with a statistical error of ±0.01 vol % is demonstrated by the Archimedes method with the use of distilled water as a liquid. The method makes it possible to measure small (up to several hundredths of a percent by volume) increases in porosity in the process of high-temperature creep. The results obtained can be used for precise determination of porosity in single-crystal NBSs before and after operation. Moreover, the process of high-temperature creep can be modeled using a correlation relationship between the increase in the porosity of a single-crystal material and the accumulated creep strain.

A serious problem in computer simulation of a stress state of polymer structures is to validate the mathematical description of the mechanical properties of materials. The structural model of a viscoelastic material has a number of advantages in describing both the rheology of a material and strain curves of it. In this model, a material is described as a structure consisting of several elements with relatively simple rheological properties. Reproduction of a complex behavior of a material under alternating non-isothermal loading is provided through the interaction of these simple elements. A technique developed in this work for modeling a viscoelastic material is intended for strength calculations of structures made of materials operating under conditions of a long-term repetitive thermomechanical impact using the finite element method. The application of the developed procedure to a polymeric material, polymethyl methacrylate (PMMA), is considered. The results of testing this material under uniaxial compression at a constant temperature are presented. The methodology and results of identification of the developed structural model using a specialized software code are described. Formulas are obtained for the approximation of the deformation characteristics of the material at a constant strain rate and for the time dependence of the deformation of the material during its holding at a constant stress level. Approximation is an important stage in the validation of the material model, which facilitates the systematization of the initial experimental data and their further mathematical processing. The best approximation of the deformation characteristics of a viscoelastic material is provided by a hyperbolic tangent function, whereas a logarithmic function provides the best results for the deformation upon holding. Further construction of the structural model was performed by selecting sequential parameters of bilinear rheological functions of the separate elements of the model and by iterative refinement of these parameters. The simulation results are compared with the experiments performed at different strain rates and with holding at different stress levels. In this work, the results of the initial stage of the performed experimental and theoretical studies are presented.

Methods of qualitative analysis are widely used in various spheres of public activity, including forensic examination. Making the right decisions based on the results of qualitative analysis necessitates confirmation of the reliability (uncertainty) of the methods which can be provided by the validation procedure. However, the issues related to the validation of qualitative forensic methods are debatable in the absence general regulatory requirements for qualitative analysis methods. We consider a validation procedure of the qualitative forensic technique called microscopic examination of textile fibers, which consists in determining a complex of characteristic external features of natural and chemical textile fibers (color, color features, morphological features) using a microscope, as well as thickness and presence/absence of a matting agent for chemical fibers. These generic characteristics are used to differentiate the fibers under study in the forensic examination of fibrous materials. The reliability of the methodology and the competence of the performers were selected as validation parameters. The parameters were determined numerically by the likelihood ratio and by the values of the rate of false and true results in the total number of tests. Ten samples of natural and chemical textile fibers from the comparative collection of the Laboratory of Forensic Examination of Fibrous Materials of the RFCSE were used for validation. Three experts participating in the experiment independently identified the presence/absence of ten external signs in each of ten samples in the period of a week. Each expert tested a set of one hundred different external features, 39 of which were present in the samples and 61 were absent. When comparing the test results obtained by the expert with the corresponding regulated (known) external features, a conclusion was made about the level of true or false result for each sample. A low (1.7%) level of false results was revealed in relation to the total number of tests, and a low (2.6%) level of false results for each of the experts indicated the reliability of the technique and competence of the experts. The calculation of the likelihood ratio (LR) showed that the probability of true results in the assessment of a set of features is about 60 times (significantly more than one) higher than the probability of false results, which also indicates the reliability of the technique. The results of the validation experiment allowed us to conclude that the method is suitable for use in solving expert problems in the forensic examination of fibrous materials.

Chloride–oxide melts used in electrosynthesis of calcium and rare-earth borides have been studied by Raman and IR spectroscopies. The results, in combination with analysis of data in the literature, have been used to identify the mechanism underlying the sequential transition of solid lanthanide oxides to an ionic form in molten calcium chloride. Using chronopotentiometry and cyclic voltammetry, we have demonstrated that the boride formation is a two-step process. An overall reaction has been proposed that describes the electrochemical boride synthesis process. The proposed mechanism is consistent with the laws of chemical thermodynamics and allows one to describe the exchange and electrode reactions involved.

We have studied general trends in the formation of nanostructured sodium aluminosilicates with a Si/Al ratio from 1 to 5 in a multicomponent aqueous system. Data are presented on the elemental composition, morphology, and thermal behavior of the synthesized compounds and their Cs⁺ sorption performance under static conditions. The results demonstrate that the sorption capacity of the sodium aluminosilicates (89.3–328.2 mg/g) exceeds that of some reported sorbents, which opens up the possibility of employing such aluminosilicates for Cs⁺ removal from aqueous solutions.

Single crystals of Pb_0.75Sn_0.25Te solid solutions containing up to 1.0 at % excess Pb have been grown by the Bridgman method, and their thermoelectric properties have been studied in the range ~90–300 K before and after heat treatment at 673 and 773 K. The results demonstrate that excess Pb and heat treatment conditions have a significant effect on the electrical conductivity, thermoelectric power, and thermal conductivity of the material and their temperature variation. The highest 300-K thermoelectric figure of merit is offered by the material containing 1.0 at % excess Pb and annealed at 773 K, which is due to its rather high thermoelectric power (~160.1 μV/K) and low lattice thermal conductivity (∼1.04 × 10^–2 W/(cm K)).