Comparison of solving algorithms for a mathematical model of filtration-diffusion transfer in the medium of spherical moisture-saturated microporous particles

The article considers the use an analytical and numerical approaches for finding solutions of mathematical model of diffusion mass transfer in the medium of particles of microporous structure. The special software developed based on both approaches and these software were used for computer simulation of pressures in particles and interparticle space for spatial and temporal parameters of the filtration process, and the results were compared taking into account their accuracy and speed of production. Considered algorithms showed approximately the same accuracy in finding the pressure profiles. Analytical solution-based software has demonstrated the higher efficiency for calculating unit pressure values at given parameters, in turn, numerical techniques have been found to be convenient for building high-resolution profiles.

Effect of energy mechanical pre-treatment on the structural-mechanical properties of (Co – Cr – Mo) alloys obtained by spark plasma sintering

We studied the effect of energy mechanical pre-treatment (EMT) of the initial (Co – Cr – Mo) alloy powders in a vortex layer of ferromagnetic bodies on the structural-mechanical properties of products obtained by spark plasma sintering (SPS). To study the properties of powder and compact samples, the methods of scanning electron microscopy (SEM), optical microscopy, determining the bending strength and microhardness on the Vickers scale were used. It was shown that the EMT of powders for a short time (1 – 3 min) leads to intense plastic deformation of a large part of the initial rounded particles, forming irregular- and plate-shaped particles with high surface roughness. As a result, EMT has a positive effect on spark plasma sintering process of powder, makes it possible to obtain a densely sintered material with a low-porous structure. It was found that the sample pre-treated under EMT for 3 min is compacted during sintering process to a high level (relative density reached 98.3 %) and its mechanical properties has greatly improved (microhardness and bending strength are 16 % and 14 % respectively higher than the sample without pre-treatment). The improvement of structural and mechanical properties of sintered specimens pre-treated under EMT is a result of intensification of diffusion mass transfer processes during sintering due to the plastic deformation of material, change in the shape, surface state of the powder particles and an increase in the total contact area between them. High surface roughness and deviation of particles from the round form lead to a decrease in the radii of curvature of their contact surfaces and, consequently, to an increase in the Laplace forces value, which play a dominant role in the diffusion mass transfer processes during sintering.

Interfacial Crystallization within Liquid Marbles

We report interfacial crystallization in the droplets of saline solutions placed on superhydrophobic surfaces and liquid marbles filled with the saline. Evaporation of saline droplets deposited on superhydrophobic surface resulted in the formation of cup-shaped millimeter-scaled residues. The formation of the cup-like deposit is reasonably explained within the framework of the theory of the coffee-stain effect, namely, the rate of heterogeneous crystallization along the contact line of the droplet is significantly higher than in the droplet bulk. Crystallization within evaporated saline marbles coated with lycopodium particles depends strongly on the evaporation rate. Rapidly evaporated saline marbles yielded dented shells built of a mixture of colloidal particles and NaCl crystals. We relate the formation of these shells to the interfacial crystallization promoted by hydrophobic particles coating the marbles, accompanied with the upward convection flows supplying the saline to the particles, serving as the centers of interfacial crystallization. Convective flows prevail over the diffusion mass transport for the saline marbles heated from below.

Interfacial Crystallization within Liquid Marbles

We report interfacial crystallization in droplets of saline solutions placed on superhydrophobic surfaces and liquid marbles filled with the saline. Evaporation of saline droplets deposited on superhydrophobic surface resulted in the formation of cup-shaped millimeter-scaled residues. The formation of the cup-like deposit is reasonably explained within the framework of the theory of the coffee-stain effect, namely, the rate of heterogeneous crystallization along the contact line of the droplet is many times higher than in the droplet bulk. Crystallization within evaporated saline marbles, coated with lycopodium particles, depends strongly on the evaporation rate. Rapidly evaporated saline marbles yielded dented shells built of a mixture of colloidal particles and NaCl crystals. We relate the formation of these shells to the interfacial crystallization promoted by hydrophobic particles coating the marbles, accompanied with the upward convection flows supplying the saline to the particles, serving as the centers of interfacial crystallization. Convective flows prevail over the diffusion mass transport for the saline marbles heated from below.

Boron Diffusion in Steel 20

As is known, boriding is carried out to increase the wear resistance and corrosion resistance of iron-carbon alloys. Along with high hardness, borides, unfortunately, have very high fragility and high refractoriness. An effective way to counter the fragility of boride layers is to form a composite structure consisting of inclusions of solid borides in a more plastic matrix. Such coatings can be obtained by volumetric heating in a muffle furnace using a boron paste that besides a mixture of iron and boron powders contained ammonium hydroxide and activated carbon with or without liquid glass. Boriding of a surface is carried out at high temperatures =1000 °С for 5 minutes. It is experimentally found that the microhardness of the surface layer increased by about 30% compared with the microhardness of the substrate, and that the thickness of the boride layer depends on the presence of liquid glass in the coating. It has been established that specially calculated proportions of ammonia, liquid glass, and charcoal contribute to the formation of an extensive diffusion zone of iron borides, the formation of which is due to the anomalously high diffusion mass transfer of boron into the matrix.

Modeling and automation processes of water purification from multicomponent pollution

Mathematical models of the processes of cleaning liquids from multicomponent contamination by filtration, as well as diffusion-mass transfer perturbations and the development of numerical-asymptotic methods for solving the corresponding nonlinear regularly and singularly perturbed boundary value problems are shown. The construction of automation systems of corresponding treatment systems and complexes on the basis of solving model problems is presented.