Solid particle erosion (SPE) behaviour of materials applied in different industries, including a widespread titanium Ti6Al4V alloy remains a subject to study. At the same time, resistance of microarc coatings, well known for their anti-corrosion properties, to erosive wear is yet understudied. Here, in order to estimate the wear resistance behavior and its character, experimental and numerical studies of Ti6Al4V alloy and aluminium-based MAO coating erosion by solid Al 2 O 3 particles (~30 m/sec) have been carried out. The experiment resulted in intensive wear of the MAO coating, which cuts its scope to short-term or indirect anti-erosion protection. Reynolds-averaged Navier – Stokes simulations of heterogenous abrasive-air mixture showed high influence of particle initial velocities and shape on the resulting impact velocity, while good agreement with the experiment was observed. Finite element explicit simulations of the impact, resulting in the deformation and the fracture of the particle and the surface were conducted using the Johnson – Cook model for titanium alloy and the Johnson – Holmquist model for the brittle particle. High influence of the particle orientation and the choice of the material model coefficients for both the particle and the sample was observed. Also, a satisfactory agreement with the experimental surface wear area was noted. Additionally, significant dependence of wear depth on the damage and fracture coefficient in the Johnson – Holmquist model for the Al 2 O 3 brittle particle and surface scenario has been found. Future studies should be addressed to a more detailed survey of the particle rotation, relative angle and position of the impact. Also, additional sensitivity studies are needed to determine the effect of brittle material model coefficients for solid particle erosion simulation cases.
The results of a comparative analysis of methods for immobilization of carbon quantum dots (CQDs) on the surface of a carbon-containing electrode and the development of an electrochemical sensor for voltammetric determination of prednisone in blood serum are presented. The effectiveness of the electrochemical approach for depositing quantum dots has been demonstrated using various electrochemical, optical, and microscopic methods. Using cyclic voltammetry and electrochemical impedance spectroscopy, it has been proven that immobilization of quantum dots on an electrode pre-modified with carbon nanotubes increases the electroactive surface area from 0.24 to 9.76 mm 2 and reduces the charge transfer resistance by more than 1300 times compared to an unmodified electrode. Using the solid-state luminescence method, the luminescent properties of quantum dots on different surfaces were compared, and the decrease in signal intensity on an electrode modified with nanotubes was demonstrated. Using transmission and scanning electron microscopy, the nanoscale dimensions of the studied quantum dots were demonstrated, which can penetrate deep into the developed network of nanotubes with numerous pores, cavities, and intertubular spaces. The working conditions for the voltammetric determination of prednisone using the modified electrode were chosen, and the mechanism of the hormone’s electroreduction involving two electrons and two protons was proposed. The hormone was determined in blood serum using differential pulse voltammetry. The accuracy of the method was confirmed by the recovery test and by comparison with the high-performance liquid chromatography. The developed sensor based on CQDs and carbon nanotubes can be recommended for rapid monitoring of prednisone in biological fluids, including in anti-doping practice.
Products intended for use in coastal and marine environments are constantly exposed to a harsh environment. The aim of this study is to investigate the microstructure of pipe metal after 15 years of use in a salt-mist removal system (5% NaCl, pH 6.5 – 7.2, 35°C). The chemical composition of the metal in different parts of the pipe was analyzed using optical emission spectroscopy. It was found that the chemical composition corresponds to austenitic steel AISI 304. When measuring the microhardness with a load of 9.81 N, a 34% increase was observed in the curved parts of the pipe compared to the straight parts due to riveting and the formation of deformation twins. To identify the microstructure of the metal, chemical etching was performed using a boiling solution of acids (HNO 3 and HCl) and a Marble reagent. The results showed that intercrystalline corrosion was the most common type, observed on both the inner and outer surfaces of the pipe, near the welding joint. Additionally, there were pockets of knife-shaped corrosion. The maximum depth of corrosion damage, which was 55% of the wall thickness, was detected at the intersection of factory and installation welds. These results can be used to improve the method of non-destructive testing for critical sections of stainless steel pipes.
Description of the proposed approach for the probability assessment of composite material properties based on the known properties of components included in the material is given in this paper. Difference from a classical micromechanic models is accounting for the stochastic law of fiber and matrix properties distribution, fiber orientation in the longitudinal direction. Problem of effective characteristic calculation is solved numerically with implementation of the finite element method in ANSYS. User subroutine is written on APDL in order to realize the proposed approach and Monte Carlo method, which allows performing the necessary calculations and outputting the required results automatically. Results validity is based on good agreement with the analytical approach and experimental data. The approach proposed in this paper allows us to get all the necessary elastic properties of composite material while material costs saving. The sensitivity analysis of elastic properties in composite fibrous material with polymer matrix was carried out by the Monte Carlo method. It is shown that some number of parameters involved in the formation of elastic properties of the entire composition have an insignificant effect on them. In particular, it is noted that the deviation of the fiber axis from the longitudinal arrangement has an insignificant effect on the shear modulus in the plane of the fibers, the transverse modulus of elasticity and Poisson’s ratios. On the other hand, the matrix elasticity modulus has a significant effect on the shear moduli of the material and the transverse modulus of elasticity. The proposed approach for effective characteristic assessment can be implemented at the design stage of composite structure elements in the aviation and rocket and space industries, as well as in the development of new materials for comparative assessment when changes occur in material type of component, volume content, fiber package type, and fiber shape.
A series of silica-based stationary phases with a covalently bonded, spatially distant layer of branched polyethyleneimine (PEI) is studied. The polymer was used in amounts of 0.001 – 1.0 g per 1 g of the amino phase substrate, providing different functional layer thickness and conformation. Model mixtures of polar compounds with various properties were used to determine the chromatographic properties of the adsorbents, namely, neutral carbohydrates, nitrogenous bases and nucleosides, zwitterionic amino acids, and a group of water-soluble vitamins, including acidic analytes. The low efficiency of the B-PEI-0.001 adsorbent toward amino acids may indicate an uneven distribution of the PEI functional layer on the substrate surface. An increase in the hydroxyl selectivity parameter from the Tanaka HILIC test with increasing PEI content indicates an increased thickness of the surface layer of adsorbed water contained in the stationary phase. Increasing PEI content led to increased both retention times and selectivity for amino acids, but followed by a deterioration in the symmetry of their peaks. Adsorbent B-PEI-0.01 provided optimal characteristics in the set of phases in selectivity, peak symmetry, high efficiency of up to 40,000 tp/m and a decrease in the separation time for amino acids, allowing the resolution of 7 acids in 9 min. Maintenance of retention times and selectivity for carbohydrates and uridine and an increased both retention factors and selectivity for water-soluble vitamins with increasing the PEI content were established for the set of phases. For reducing sugars, increased efficiency of up to 40,000 tp/m was registered for B-PEI-1.0 phase. For vitamins, high efficiency of up to 40,000 tp/m was achieved on adsorbent B-PEI-0.01, whereas increasing PEI content led to increased selectivity and decreased efficiency by almost 2 times on phase B-PEI-0.6. The optimal mass ratio of substrate: PEI in a series of HILIC stationary phases is recommended to be 1:0.01 for amino acids or vitamins separation, and 1:1 for sugars.
