THE INFLUENCE OF ELEMENTAL POWDER RAW MATERIAL ON THE FORMATION OF THE POROUS FRAME OF TI3ALC2 MAX-PHASE WHEN OBTAINING BY THE SHS METHOD

The ternary carbide compound Ti3AlC2 belongs to the so-called MAX-phases – a new type of ceramic materials with unique properties. A simple energy-saving method of self-propagating high-temperature synthesis (SHS) based on combustion is one of the promising methods for the production of this MAX-phase. The application of the SHS technology is to produce a Ti3AlC2 MAX-phase porous frame with the homogeneous porous structure without such defects as large pores, laminations, and cracks is of great interest. The paper investigates the possibility of producing such a porous frame with the maximum content of the Ti3AlC2 MAX-phase using powders of Ti, Al, and C elements of various grades different in particle sizes and carbon forms (soot or graphite) as initial components. Porous frame samples were produced by the open-air burning of pressed briquettes of charge of the initial powders of the selected grades without applying external pressure. The authors studied the macro- and microstructure of the obtained samples, their density, and phase composition. The study shows that using the finest titanium and carbon powders leads to the excessively active combustion with gas evolution and the synthesis of the defective porous samples with the charge briquette shape distortion, large pores, laminations, and cracks. Besides the titanium carbide by-phase, the highest values for the MAX-phase amount in the SHS-product were obtained using the titanium powder of the largest-size fraction together with the graphite powder, rather than soot. The excess aluminum powder addition to the stoichiometric ratio to the initial charge leads to an increase in the MAX-phase amount in the SHS product, compensating for the loss of aluminum due to evaporation. An increase in the sample volume (scale factor) also leads to an increase in the MAX-phase amount in the SHS product due to the slower cooling of the product after the reaction.

Frame Polymerbetons Based on Fillers of Different Nature

Recently, the frame composite materials have been developed greatly at the production introduction level. The manufacturing technology of these materials is carried out in two stages: first, large aggregates are glued into the frame, and second, the porous frame voids are impregnated with the matrix component. In this article, we studied the various aggregates’ effect on the polymer concrete frame structures properties using epoxy binders. The materials based on the quenched cullet, brickbats, granite and limestone crushed stone, and the polymer granules were considered as large aggregates. The studied properties were the strength and elastic modulus. Quantitative dependences of compressive and bending strength, elastic modulus of frame composites on the aggregate type and other prescription factors are obtained. Using the methods of mathematical experimental planning, the optimal particle size distribution for the composites with grains from quenched cullet was selected. Particular attention should be paid to the possibility of using industrial wastes in polymer concrete compositions: polymer granules, quenched cullet and brickbats. Used glass makes up about 10% of the household waste. Its reuse is usually associated with high capital costs allocated for sorting glass by color, removing stones and other impurities. Glass grinding allows to get a fine-grained filler and aggregate. Strength and deformation characteristics of the matrix compositions, frameworks and composites as a whole are determined.

MORE DETAILSABOUT IMPREGNATION OF CARBON GRAPHITE WITH ALUMINUM

The process of forming a composite material carbon - graphite-aluminum alloy by impregnation of a porous frame AG-1500 is studied. The technology of filling the open porosity of carbon graphite with a metal melt in a device for impregnation in the mode of constant heating of the furnace is described. The method of applying a protective coating to the inner surface of the pores is shown. It is possible to seal the matrix alloy AK12 in the pores of AG-1500 with lead. It is shown that such processing allows to compact the aluminum alloy and modify it due to the comprehensive pressure of the lead alloy.

FEATURES OF CARBON GRAPHITE IMPREGNATION WITH ALUMINUM ALLOY

The process of forming a composite material carbon-graphite-aluminum by impregnating a porous frame AG-1500 with aluminum melt at a temperature of 650С is studied. The redistribution of elements of the impregnating alloy is established. it is shown that the transition of silicon, Nickel, chromium, and iron from the aluminum melt to the «melt - pore surface of carbon graphite» is determined not by the mechanism of chemical localization of conduction electrons, but by the rearrangement of the electronic structure of components during crystallization. In this case, it is possible to change the solubility of the melt elements in aluminum, as a result of the combined action of pressure and temperature on it during the impregnation process.

Development of effective compositions of concrete for the construction of slabs of the roadway of steel concrete span structures

Structural concrete spans of various systems and structures with modular and monolithic roadways were used in the construction of bridges. The article presents the results of a survey of such bridge structures at 3 sites: across the Suju River (Grozny), across the Vologda River (Vologodsk), across the Tsna River in the town of Shatsk, Ryazan Region. Defects and damage to the plates of the carriageway are given. It was found that the most dangerous factors affecting the early failure of the roadway steel-reinforced concrete structures, is used to combat glaze and ice sleet aggressive in relation to reinforced concrete sand-salt mixtures. In addition, the lack of durability of structures due to other factors: vulnerability to carbonization processes; lack of reliability of the mounting joints and connections, the heterogeneity of the plate on the transverse and longitudinal bending. An algorithm for determining the parameters of the safe operation of the elements of bridge structures has been compiled; on the basis of the results of the study, the need to solve two urgent problems has been identified: urgent repairs; development and implementation of new solutions for construction and repair. It is shown that in world practice various types of concretes are developed: powder-activated, frame, etc. as well as protective materials – fine polymer concretes. Provides data on the cyclic strength of these materials, as well as the technology of their installation. In the study of the degree of influence of factors of temperature and humidity of the environment on the amount of short-term creep of polymer concrete, the method of experiment planning with the construction of an orthogonal composition plan was used and a methodical model was obtained relating these values. The main stages of the device of the polymer concrete slab instead of the collapsed one are given. The prospects of polymer-concrete coatings produced by frame technology, consisting in the first stage of gluing the aggregate grains with each other in the form of a future product, and the second, filling the voids of the porous frame with a highly mobile polymer composition is shown.

Quasi-Liquid Layer on Ice and Its Effect on the Confined Freezing of Porous Materials

Freezing of the water confined in thin pores can be destructive to the porous frame, but the effect of the quasi-liquid layer (QLL) between the confined ice and the pore walls remains still far from being fully understood. In the present study, the physical origins of the intermediate phase of QLL were discussed by thermodynamic analyses. Different interactions on QLL bring different models to estimate its thickness, which generally decays with temperature decreasing. Four representative models of QLL thickness were selected to unveil its effect on the growing rates and extents of ice in a concrete. The engineering consequences of the confined freezing were then discussed in the aspects of effective pore pressures built from the confined ice growth and deformations framed by a poro-elastic model. Overall, thickening QLL depresses ice growing rates and contents and, consequentially, decreases pore pressures and material deformations during freezing. The QLL corrections also narrow the gaps between the predicted and measured freezing deformations. The findings of this study contribute to profound understandings of confined freezing that may bridge over physical principles and engineering observations.

Solid viscosity of fluid-saturated porous rock with squirt flows at seismic frequencies

We have developed a macroscopic model for a two-phase medium (solid porous rock frame plus saturating pore fluid) with squirt flows based on Lagrangian continuum mechanics. The model focuses on improved physics of rock deformation, including explicit differential equations in time domain, causality, linearity, frequency-independent parameters with clear physical meanings, and an absence of mathematical internal or memory variables. The approach shows that all existing squirt-flow models can be viewed as microscopic models of viscosity for solid rock. As in existing models, the pore space is differentiated into compliant and relatively stiff pores. At lower frequencies, the effects of fluid flows within compliant pores are described by bulk and shear solid viscosities of the effective porous frame. Squirt-flow effects are “Biot consistent,” which means that there exists a viscous coupling between the rock frame and the fluid in stiff pores. Biot’s poroelastic effects associated with stiff porosity and global flows are also fully included in the model. Comparisons with several squirt-flow models show good agreement in predicting wave attenuation to approximately 1 kHz frequencies. The squirt-flow viscosity for sandstone is estimated in the range of [Formula: see text], which is close to field observations. Because of its origins in rigorous mechanics, the model can be used to describe any wavelike and transient deformations of heterogeneous porous media or finite bodies encountered in many field and laboratory experiments. The model also leads to new numerical algorithms for wavefield modeling, which are illustrated by 1D finite-difference waveform modeling.