Study of structural and morphological changes during acсelerated oxidative degradation of mixtures of polyoxybutyrate with polycaprolactane

Structural and morphological changes in the films of poly(oxybirutyrate-co-oxyvalerate) (P(OB-OV)) with poly-e-caprolactone (PCL) were studied by IR spectroscopy, DSC, and scanning electron microscopy during accelerated oxidative degradation under tests in Fenton reagent. It is shown by the DSC method that the phase separation of the P(OB-OV) and PCL components is observed in the initial mixture. The melting of various phases of P(OB-OV) is observed at temperatures of 147 °C and 157 °C, and PCL melts at a temperature of 61 °C. The degree of crystallinity of P(OB-OV) and PCL in the mixture is 67 % and 50 %, respectively. It was found that the degradation of poly(oxybirutyrate-co-oxyvalerate) prevails during incubation of composite samples in Fenton solution for 2 to 12 weeks. By changing the ratio of the components, it is possible to significantly change the rate of oxidative degradation, the molecular weight and the degree of crystallinity of the polymer composite material P(OB-OV):PCL.

Experimental study on tensile deformation process of graphitized high carbon steel sheet

As the object for the study, graphitized high-carbon steel sheet with a carbon content of 0.66 % was used, the tensile test of this sheet using a universal testing (breaking) machine was performed; as well as in-situ observation of the microstructure in the process of tensile deformation of this sheet using in-situ technology of scanning electron microscopy (SEM) was made. The test results show that the main mechanical properties in different directions of tested graphitized high-carbon steel sheet are relatively the same, that is, for a tensile sample of different directions, the ratio of the yield strength σ0,2 to the tensile strength σв is approximately 0.73; the strain hardening index n is approximately 0.24; the plastic deformation coefficient r is approximately 0.83. This indicates that this sheet did not exhibit significant anisotropy. In the process of tensile, deformation of the specimen is mainly developed from local plastic deformation of the graphite inclusions to the total deformation in the deformation zone of the sample; with the increase of displacement, micro-gap between the graphite inclusion and ferrite grain along the direction of the axis of tensile gradually formed and propagated along the direction perpendicular to the axis of tensile; number of slip lines in the ferrite matrix gradually increased, and the distance between them gradually decreases; when the sample breaks, in the fracture large dimple with the core of graphite inclusion and small dimples in the ferrite appears. And the ferrite matrix near the fracture is covered with slip lines, this shows that the ferritic matrix underwent severe plastic deformation before breaking.

The effect of long-term annealing simulating the parameters of dry storage of VVER-1000 fuel rods on the mechanical properties of E110 alloy shells in the longitudinal direction

Presented are the results of mechanical tensile tests of longitudinal (segmental) samples cut from the midsection of claddings spent as VVER-1000 FA during one- and six-year campaigns and subject to thermal tests in helium at 480 °С during 468 full days. An average burnup of these fuel rods achieved ~ 20 and ~ 70 (MW·day)/kg U, respectively. The tests followed the examinations for cladding mechanical properties performed using the tests results for ring samples cut from the specified fuel rods. These fuel rods were tested in the experiments to determine impact of long-term thermal tests that model dry storage conditions on mechanical properties of Zr E110 claddings. Based on mechanical tests results at room temperature and at 380 °С there was determined as follows: ultimate strength sв, yield strength s0,2 and total relative elongation d0 of claddings length-wise on the fuel rod segments at the fuel column midsection. The obtained characteristics were compared to corresponding values for initial (unirradiated) cladding tubes and mechanical test results of the ring samples in the transverse direction. Long-term thermal tests have led to partial return to initial (before operation) values sв, s0,2 and d0 of radiation-hardened claddings; this return was more prominent in the longitudinal direction than in the transverse one. A radiation hardening decrease was accompanied with an increase in total relative elongation values in both cladding directions. Anisotropy of yield strength has changed as well. These changes can be explained by partial annealing of radiation defects, which are obstacles to dislocation movements during cladding strain. The morphology of above radiation defects is different in various sliding planes in texturized grains of cladding material.

Some features of the analysis of water, soil and ground in mass spectrometers with inductively coupled plasma (ICP-MS)

The paper discusses the possibilities and limitations of the method of mass spectrometry with inductively coupled plasma on the example of elemental analysis of natural and drinking waters, soils and grounds. It is shown that the combination of this method with the simpler atomic emission method makes it possible to expand the range of determined elements, simplify the mass-spectral analysis and increase its reliability. It is shown that the use of the ICP-MS method in the analysis of various objects makes it possible to determine the majority of elements with extremely low detection limits. The reason for the manifestation of matrix effects is the positive space charge formed between the interface and the extractor, the composition of which is determined by the composition of singly charged argon ions. The increase in the concentration of ions in this region is the appearance of a matrix element, which facilitates the scattering of ions from this region. It was found that the heavier the ions of the matrix element, the more the space charge density increases and the scattering occurs. A serious limitation of the method is associated with interferences due to the presence of a certain amount of two and three-charged ions in the plasma. These ions, which have approximately the same mass as the isotopes of the element being determined, are formed as a result of various plasma-chemical reactions and interfere with the determination.

Changes in the structure of a thermal protective aluminum-nickel coating under the influence of a single thermal laser pulse

The regularities of changes in the structure and phase composition of the thermal protective aluminide-nickel coating (Ni — 45 %; Al — 14 %; Co — 22 %; Cr — 18.9 %; Fe — 0.15 %; Nb — 0.14 %; Y — 0.09 %; Ca — 0.06 %; Mn — 0.01 %; C — 0.15 %; Si — 0.15 %; S — 0.006 %) after exposure to short-term pulsed heat fluxes of various power, created by the radiation of a pulse-periodic laser LRS-150A with a radiation wavelength λ = 1.06 µm and a pulse duration τ = 12·10–3 s. The radiation energy was E = 5, 10, and 15 J. Microstructural analysis and the elemental composition of the resulting coating were carried out as well as analysis of the phase composition. X-ray microanalysis of the coating was also carried out. In the initial state and after irradiation of the coating with a heat flux of power P = 7·103 W/cm2, light microregions are observed in the micrographs of the surface. These regions do not have clearly defined external boundaries and consist of the NiAl phase and a small amount of the Ni3Al phase with the presence of inclusions of particles containing a solid solution of Ni – Co – Cr. After irradiation of the coating with heat fluxes of higher power (P = 1.7·104 W/cm2 and P = 2.2·104 W/cm2), large convex formations appeared on its surface, consisting mainly of Ni3Al and NiAl phases. On micrographs of the surface, they appear as white areas with well-defined outer boundaries. The content of the Ni3Al phase in them in comparison with the initial state increased, and the content of the NiAl phase decreased, while the particles of inclusions of Ni, Co, and Cr disappeared. It can be assumed that an increase in the Ni3Al content is associated with the dissolution of particles of a solid solution of Ni – Co and Cr in the melt and the subsequent diffusion of nickel into the NiAl phase. When exposed to a heat flux of power P = 2.2·104 W/cm2, microcracks appear on the areas of the coating surface covered with aluminum oxide.

Study of operational properties of steel friction pairs with antifriction coating from copper alloys produced by electric spark alloying

Improving the reliability, durability and safety of operation of heavily loaded friction units is an urgent problem in physics, chemistry and surface mechanics. The tribotechnical characteristics of coatings made of bronzes BrAZhMts10-3-1.5 and BrMtsF3-6, applied by electrospark alloying on bushings made of structural steel 30KhGSN2A for operation under conditions of high contact pressure under friction without lubrication, have been investigated. Modes of coating deposition from the standpoint of tribology (the value of the electric discharge current in a pulse, the value of the longitudinal electrode feed per one rotation of the part, the rotation speed of the workpiece, the number of passes during processing, finishing of the coating) have been developed. It was found that when applying bronze BrMtsF3-6 to obtain a high-quality coating, the process must be performed in a protective atmosphere of argon to prevent phosphorus burnout. The tribotechnical efficiency of coatings when working under dry friction conditions is shown. For the steady-state wear mode, the friction coefficient is 0.10 – 0.13 at a pressure of 200 – 250 MPa, the wear resistance of coated steel is doubled. Steel with a bronze coating BrAZhMts10-3-1.5 has a higher bearing capacity, with BrMtsF3-6 coating — a higher antifriction. The ways of increasing the service life of steel-coated steel friction pair are analyzed.

Synthesis of Al – Fe/SiO2 and Al – Co/SiO2 catalysts by solid-phase method

Powders of catalysts from aluminides Fe and Co on a SiO2 support (33.3 wt. %) were obtained by mechano-thermal synthesis. The formation of large powder fractions (> 100 μm) was experimentally established. The fractions of these fractions for Fe – Al – SiO2 and Co – Al – SiO2 respectively amounted to ~ 43 % and ~ 55 %, which is a positive result for further catalytic studies. After annealing the powders at 700 and 900 °C in vacuum, the SiO2 support and compounds: Co27Al73 (close in composition to CoAl3, Co4Al13 type intermetallic compounds), Fe3Al intermetallic compound with iron silicide type Fe0.9Si0.1 and compound Al0,3Fe3Si0.7 in small volumes. On the synthesis of cobalt aluminides, a conclusion has been made about more efficient annealing at 900 °C than at 700 °C. For Fe – Al – SiO2 powders, it is advisable to anneal in the temperature range 700 – 750 °C with the assumption that the SiO2 support influences the thermosynthesis of iron aluminides. An experimental analysis of the morphology and elemental composition of the surface of the obtained samples is presented. It was found that the catalyst powders have medium sphericity and angularity. Fe – Al – SiO2 powders have a more developed surface than Co – Al – SiO2. Lower intermetallics are predominantly formed on the surface of the Co – Al – SiO2 sample. The correction of the mechanical alloying modes by means of the fragmentation of the process, changes in the intensity of its parameters, and various annealing conditions for Co – Al – SiO2 and Fe – Al – SiO2 are proposed.

Formation of bulk samples from the Ti3AlC2 MAX-phase powder by selective laser sintering

Bulk samples from the powder of the MAX-phase Ti3AlC2 were obtained by selective laser sintering (SLS). A complex structural-phase study was carried out using optical and electron microscopy, as well as X-ray phase analysis, the elemental and phase composition of the samples was determined, and the morphology of the initial powders and bulk SLS samples was described. This study allowed to describe the elemental and phase composition, as well as the morphology of both the initial powders and bulk SLS samples. Modes of selective laser sintering are established at which the maximum presence of the MAX-phase in the samples after SLS is observed.

Simulation of crystallization of the melt modified by nanoscale particles during laser treatment of a metal surface

A 2D mathematical model is proposed for the modification of an iron-based alloy with refractory nanosized particles. Numerical simulation of the processes during the modification of the surface layer of the substrate metal using the energy of a laser pulse has been carried out. Within the framework of the proposed model, the processes of heating and melting of metal on a substrate covered with a layer of nanosized refractory particles penetrating into the molten metal, convective heat transfer in the melt, and solidification after the end of the pulse are considered. Metal melting is considered in the Stefan approximation, and when the melt is cooled, the model of heterogeneous nucleation and subsequent crystallization is used. The fluid flow is described by the Navier-Stokes equations in the Boussinesq approximation. The distribution of nanoparticles in the melt is modeled by moving markers. Based on the results of calculations, the mode of pulsed laser action is determined, in which a flow is formed for a homogeneous distribution of particles of the modifying substance in the presence of a surfactant in the metal. The volume of the solid phase formed around the nucleus determines the size of the grain structure in the solidified alloy. The liquidus temperature changes depending on the concentration of dissolved carbon in the melt. In the numerical simulation of the solidification of the surface layer of the metal, it was found that the conditions of nucleation and crystallization differ significantly in the volume of the melt. It is determined that the duration of nucleation in a supercooled melt is several tens of microseconds. The maximum number of crystallization centers occurs in areas where heat removal occurs most rapidly. With the growth of the solid phase in the melt and the release of the latent heat of crystallization, the value of supercooling decreases, the nucleation stops and the number of formed crystallization centers does not change further. The distribution of the dispersion of the crystal structure over the volume of the melted metal is estimated. It was found that as the melt cools, sequential-volume crystallization occurs.

Effect of oxygen and bismuth impurities on the structural and physicochemical properties of nickel melts

There are practically no data in the literature on the combined effect of oxygen and bismuth impurities on the structural and physicochemical properties of nickel melts or heat-resistant alloys based on it. In the presented work, the state of pure nickel and nickel melts containing (0.005-0.01) bismuth and oxygen is considered in the process of refining from oxygen and bismuth impurities. The influence of these impurities on the structural and physicochemical properties was studied, which was evaluated by the parameters of the density and surface tension of the melts. In nickel melts with bismuth and oxygen, a compression effect and a negative deviation from Raoult’s law were observed. The effect of an increase in the surface tension of a nickel melt containing oxygen with an increase in the concentration of bismuth is found, which corresponds to the isotherm of desorption of excess substance from the surface into the bulk.