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.

Highly borated dispersed aluminum: experimental evaluation of its neutron-shielding properties

By the method of mechanical alloying, compaction and thermosynthesis of a mixture of amorphous boron and aluminum powders, a prototype of highly borated (~50 wt.%) dispersed boron-aluminum was obtained. A comparative assessment of the neutron-shielding properties of borated dispersed aluminum and fibrous boron-aluminum VKM Al-B under irradiation with neutrons with a flux density of 1.4·106 n/cm²·s with a fluence of 3·109 n/cm2 was carried out. Using optical and scanning electron microscopy, a morphological analysis of samples of dispersed-borated powdered aluminum and fibrous-composite boron-aluminum was carried out. It was found that in both materials the level of absorption of neutrons with energies of 0.02-0.05 eV is up to 99.5-99.95%. It is concluded that highly borated dispersed boron-aluminum supplements the line of known boron-containing neutron-absorbing materials with the possibility of using it up to temperatures of 500-700°C.

Properties of the surface of structural materials in the area of a barcode formed under the action of laser radiation

A review of experimental investigations of changes in the structure and properties of the surface and near-surface layers of various materials (steels, metal alloys, ceramics and graphite) in the area of a barcode applied by continuous laser radiation and short (nanosecond) and ultrashort (femto- and picosecond) laser pulses.

Mechanical effect of an electric field on nanostructure elements

A computational and experimental estimation of the magnitude of forces acting in a high-intensity electric field on elements of nanoconstructions with a high surface curvature is made. Depending on the magnitude of the electric potential and vacuum conditions, these forces can vary both in magnitude and direction over a wide range. They can cause structural damage, as well as provoke unwanted electrical discharges. The possibilities of useful application of these effects are analyzed.

Non-coherent diffusion of a vacancy in a one-dimensional lattice in the quasiclassical approximation

A vacancy in a one-dimensional lattice is considered as a vacant site in a one-dimensional chain of atoms. The energy model of this system is a double potential well with two levels. Based on the relations of nonequilibrium statistical mechanics, including the Kubo formula for the transport coefficient, the frequency of vacancy jumps is calculated. In this case, two factors of the system perturbation are taken into account: lattice deformation associated with the formation of an empty site, and phonon scattering by mass fluctuations in the chain. An analysis of two high-temperature jumps is given. First, the classical limit of vacancy motion under weak coupling conditions is considered for small values of the gradient of the interaction potential of the defect with the chain. In the classical case, the transition of an atom adjacent to a vacancy occurs through a quasy-stationary excited state. Secondly, a jump under tight binding conditions, when the motion of a neighboring atom occurs through a quasistationary state of finite width, and therefore having a finite lifetime.

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.