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The article considered the solution of the inverse problem of chemical kinetics of the analysis of experimental data of a thermogravimetric experiment at a constant sample heating rate. The fitting method for identifying the parameters of a kinetic triplet using the integral method for a model of a solid-state reaction based on the modified Arrhenius equation is described. The effectiveness of the proposed approach was confirmed by solving test cases for low, medium, and high rates of material conversion. Unlike other methods, setting the parameters of the reaction mechanism is not required, as they are determined by the solution. Solutions for real data of TGA studies with high and low sample heating rates were compared with the results obtained by other authors and experimental data. A description of the full cycle of calculations used to identify kinetic parameters from thermogravimetric experimental data is given, from the derivation of calculated relationships to the implementation of a short (three to five formulas) program code for MS Excel spreadsheets. The presented code is easy to verify and reproduce and can be modified to solve various problems.
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Calefação , Cinética , TermogravimetriaRESUMO
In this work, Al-Mg intermetallic powders were characterized and obtained by melting, casting into a steel chill and subsequent mechanical activation in a planetary mill. The method for producing Al12Mg17 intermetallic powder is presented. The dispersity, morphology, chemical composition, and phase composition of the obtained powder materials were investigated. Certain thermodynamic properties of high-energy materials containing the Al-Mg powder after mechanical activation of various durations were investigated. The addition of the Al-Mg powders to the high-energy composition (synthetic rubber SKDM-80 + ammonium perchlorate AP + boron B) can significantly increase the burning rate by approximately 47% and the combustion heat by approximately 23% compared with the high-energy compositions without the Al-Mg powder. The addition of the Al12Mg17 powder obtained after 6 h of mechanical activation provides an increase in the burning rate by 8% (2.5 ± 0.1 mm/s for the mechanically activated Al12Mg17 powder and 2.3 ± 0.1 mm/s for the commercially available powder) and an increase in the combustion heat by 3% (7.4 ± 0.2 MJ/kg for the mechanically activated Al-Mg powder and 7.1 ± 0.2 MJ/kg for the commercially available powder). The possibility of using the Al-Mg intermetallic powders as the main component of pyrotechnic and special compositions is shown.
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Ligas/química , Alumínio/química , Magnésio/química , Pós/química , Dureza , Teste de Materiais , Tamanho da PartículaRESUMO
The dynamic sorption concentration of explosive vapours on concentrators made of a metal mesh, and the transportation of explosive vapours through the extended metal channels are considered. The efficiency of the concentration and transportation is determined by the breakthrough of the substance's molecules through the channels. The research methods we used were breakthrough calculation theory and experiment. When calculating the breakthrough, a mesh was presented as a set of parallel identical channels. Wire mesh and extended channels were made of stainless steel. The breakthrough is determined through the specific frequency of the collisions between the molecules and the channel's surface. This is presented as a function of the ratio of the substance diffusion flow to the channel's surface to the airflow through the channel. The conditions for high-speed concentration, complete capture of explosive vapours, and low vapour losses during their transportation through the extended channels were determined theoretically and experimentally. For a concentrator made of a mesh, the condition of a high concentration rate at a high breakthrough (up to 80%) was determined. The described sorption concentration is used in portable gas chromatographic detectors of explosive vapours of the EKHO series.
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Cromatografia Gasosa/instrumentação , Substâncias Explosivas/análise , Monitoramento Ambiental/instrumentação , Gases , CinéticaRESUMO
When developing neutralization systems for harmful agents, it is necessary to understand the mechanisms of the formation and evolution of an aerosol cloud in a closed or open space. Effective decontamination with aerosol clouds is provided by a rather high particle concentration and dispersion in an open space or on contaminated surfaces. This paper considers neutralization systems based on pulsed powder aerosol generators. It is shown that an aerosol cloud consisting of micron- and submicron-sized particles appears for several seconds after spraying. A further evolution of the aerosol cloud in a room is associated with the gravitational settling, diffusion, and coagulation of particles and their settling on the walls and ceiling. In the case of an open space or a ventilation system in a room, the evolution of the aerosol cloud is affected by the airflow. The main purpose of this paper is to determine the most important parameters and critical conditions of pulsed aerosol generation. A mathematical model is, thus, proposed for pulsed aerosol generation, and its parametric study is conducted in the most typical conditions. The purpose performance predicted by the model is the mass concentration of aerosol particles in the air and on surfaces, depending on the time of particle spraying and dispersion.
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In this paper, a mathematical model of the extrusion process in 3D printing of high-energy composites is studied. These composites are formed from polymer binder and powder with bimodal particles obtained by electric explosion technique. The main difficulty of extrusion 3D printing method is primarily linked to the high viscosity of utilized material, especially one with high concentration of particles. In this case, the viscosity of the initial mixture depends on the pressure, temperature and concentration of the filler, as well as on the particle dispersion. Under certain conditions the ignition of high-energy material in the nozzle is possible, thus the search for optimal printing parameters based on the mathematical modeling and the following experimental verification are the main purposes of the current work.
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This paper presents the results of studies on AlMgB14-based ceramic coatings deposited on WC-Co hard alloy substrates using RF plasma sputtering. The aim of this work is to study the structure, phase composition, and mechanical properties of AlMgB14-based coatings depending on the sputtering mode. According to the results of the microstructural study, the bias voltage applied to the substrate during the sputtering process significantly contributed to the formation of the coating morphology. Based on the results of compositional and structural studies by energy dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy, it was found that the coatings are composed of nanocrystalline B12 icosahedrons distributed in an amorphous matrix consisting of Al, Mg, B, and O elements. The nanohardness of the coatings varied from 24 GPa to 37 GPa. The maximum value of the hardness together with the lowest coefficient of friction (COF) equal to 0.12 and wear resistance of 7.5 × 10-5 mm3/N·m were obtained for the coating sputtered at a bias voltage of 100 V. Compared with the COF of the original hard alloy substrate, which is equal to 0.31, it can be concluded that the AlMgB14-based coatings could reduce the COF of WC-based hard alloys by more than two times. The hardness and tribological properties of the coatings obtained in this study are in good agreement with the properties of AlMgB14-based materials obtained by other methods reported in the literature.
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Digital light processing (DLP) or stereolithography is the most promising method of additive manufacturing (3D printing) of products based on high-energy materials due to, first of all, the absence of a high-temperature impact on the material. This paper presents research results of an ultraviolet (UV)-cured urethane methacrylate polymer containing 70 wt.% of high-energy solid powder based on ammonium salts, which is intended for digital light processing. Polymerization of the initial slurry is studied herein. It is shown that the addition of coarse powder transparency for the UV radiation to resin increases its curing depth. The thickness of the layer, which can polymerize, varies from 600 µm to 2 mm when the light power density ranges from 20 to 400 mJ/cm2, respectively. In DLP-based 3D printing, the obtained material density is 92% of the full density, while the compressive strength is 29 ± 3 MPa, and the ultimate tensile strength is 13 ± 1.3 MPa. The thermogravimetric analysis shows the decrease in the thermal decomposition temperature of UV-cured resin with high-energy additives compared to the thermal decomposition temperatures of the initial components separately. Thermal decomposition is accompanied by intensive heat generation. The burning rate of obtained samples grows from 0.74 to 3.68 mm/s, respectively, at the pressure growth from 0.1 to 4 MPa. Based on the results, it can be concluded that DLP-based 3D printing with the proposed UV photocurable resin is rather promising for the fabrication of multicomponent high-energy systems and complex profile parts produced therefrom.
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A mathematical model of the pulse generation of decontaminating aerosols utilizing the energy of high-energy materials (HEM) is proposed with account for the physical and chemical properties of the atomized substance, HEM characteristics, and gas generator parameters. Such a model is needed to counter the environmental hazards, process emissions, and terrorist attacks with hazardous and dangerous aerosols. Another aspect of the problem is the danger of biological aerosols carrying viral or microbial particles that are spread naturally or induced using biological weapons. In many cases, the mission is not only to neutralize aerosol particles in indoor air and on surfaces but also to do it quickly. In this regard, an attractive option is the pulse method for generating special aerosols aimed at quickly, within a few seconds, creating a cloud of particles that will interact with hazardous aerosol particles and decontaminate them. HEM energy is proposed to be used for the pulse generation of such aerosols. It is important not only to atomize the decontaminating aerosol quickly and evenly in space but also to preserve the useful physical and chemical properties of the particles. To test the regimes and methods of pulse generation, an adequate mathematical model of the process is required, which is proposed in this manuscript.
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In this work, the structure, phase composition, hardness and tensile strength of the AlMgB14-based material obtained by spark plasma sintering (SPS) were investigated. According to the XRD results, the spark plasma sintered material contains 94 wt% AlMgB14 phase and 6 wt% spinel MgAl2O4. Analysis of the SEM images showed that the obtained AlMgB14 sample has a dense structure; the relative density of the sample is 98.6%. The average microhardness of the spark plasma sintered (SPSed) sample is 29 ± 0.88 GPa. According to the results of the Brazilian test, the tensile strength of AlMgB14 is 56 MPa. The fracture is characterized by a single straight tensile crack that divides the sample along the compression line into two halves. The type of fracture in the AlMgB14 sample can be characterized as a cleavage fracture due to crack growth occurring in accordance with the transcrystalline fracture. The tensile strength of the obtained material is in good agreement with the tensile strength of boride and oxide ceramics studied in other works.
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For the first time, we performed functionalization of the surface of porous titanium nickelide alloys with bambusuril[6]-based macrocyclic compounds by different methods in order to provide the basis for saturation with therapeutic agents to impart antibacterial activity and accelerate its osteogenesis. It has been shown for the first time that the vacuum modification method is preferable for bambusuril deposition, since it provides a uniform deposition of organic matter on both the outer and inner surfaces of the pores. The effect of bambusuril deposition methods on the continuity, structure, and cytocompatibility of the porous titanium nickelide surface was evaluated. In vitro tests proved high biocompatibility and low toxicity of porous TiNi treated with BU[6] under vacuum. The SEM study of the structure of the surface layer of TiNi modified with BU[6] under the vacuum method showed that BU[6] agglomerates are uniformly deposited on the inner and outer surfaces of TiNi pores, which will provide an even saturation of BU[6] cavities with various pharmaceuticals, including antibiotics and inhibitors.
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In this study, we successfully obtained Al-TiB2 composite materials using self-propagating high-temperature synthesis and preliminary mechanical activation of the initial Al-(Ti + 2B) powder mixture with a high aluminum content (70 wt.%). We investigated the possibility of controlling the structure of synthesis products, in particular, the size and shape of ceramic particles. We examined the effects of the mechanical activation of the initial powder mixture on the structure and particle size of titanium diboride in the synthesis products. We proposed a mechanism of structure formation in the synthesis products obtained by SHS using the method of preliminary mechanical activation of the initial mixture. We found that mechanical activation for 60-180 s led to the formation of isolated TiB2 particles of prolate and irregular shape. The average particle size of TiB2 in the synthesis products was 0.77 (after 60 s of mechanical activation) and 1.5 µm (after 180 s of mechanical activation), respectively. An increase in the duration of mechanical activation to 900 s led to the formation of an island (skeletal) structure, in which there were interconnected aggregates and isolated particles of titanium diboride. The average size of these particles was 4.3 µm.
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The phase composition, microstructure, and multiple shape memory effect of TiNi50-xVx alloys were studied in this work. The phase composition of the TiNi50-xVx system is the TiNi matrix, spherical particles of TiNiV, the secondary phase Ti2Ni(V). Doping of TiNi alloys with vanadium atoms leads to an increase in the stability of high-temperature B2 and rhombohedral R-phases. An increase in the atomic volume with an increase in the concentration of the alloying element V from 1 to 4 at.% was established. Vanadium doping of the Ti-Ni-V system alloys leads to an increase in the temperature interval for the manifestation of the multiple shape memory effect. It has been established that the value of the reversible deformation of the multiple shape memory effect both during heating and during cooling increases linearly from 2 to 4% with an increase in the vanadium concentration.
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It is known that the presence of oxygen phases in hard materials leads to an undesirable decrease in the mechanical properties. In materials based on AlMgB14, the main oxygen impurity is spinel MgAl2O4; it significantly reduces the hardness of AlMgB14 and its formation during sintering is inevitable. In this work, the ultra-hard spark plasma sintered (SPSed) AlMgB14-TiB2 composite material was fabricated from the AlMgB14-TiB2 precursor obtained by self-propagating high-temperature synthesis (SHS). Due to the high synthesis temperatures, the main oxygen phase in the obtained composite was Al4B2O9 instead of spinel MgAl2O4. It was found that the obtained composite has excellent mechanical properties. The maximum hardness of the sample is 44.1 GPa. The presence of oxygen in the form of the Al4B2O9 phase led to unexpected results: the friction coefficient of the obtained AlMgB14-TiB2 composite under dry conditions against the Al2O3 counter-specimen is approximately four times lower than the friction coefficient of pure ceramic AlMgB14 (0.18 against 0.7, respectively). Based on the observed results, it was found that the Al4B2O9 particles formed during the SHS are responsible for the low friction coefficient. The quantum chemical calculations showed that the elastic moduli of Al4B2O9 are significantly smaller than the elastic moduli of AlMgB14 and TiB2. Thus, during sliding, Al4B2O9 particles are squeezed out onto the composite surface, form the lubricating layer and reduce the friction coefficient.
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In this work, composite materials were obtained by spark plasma sintering of an Al12Mg17-B-Si powder mixture. The structure, phase composition, and mechanical properties of the obtained composites were studied. It was found that various compounds based on B12 icosahedrons, such as AlB12, B4Si, and B6Si, are formed during spark plasma sintering. Based on the SEM images and results of XRD analysis of the obtained specimens, a probable scheme for the formation of the phase composition of composite materials during spark plasma sintering was proposed. An increase in the Al12Mg17-B powder content in the initial mixture from 30 to 70 wt% leads to an increase in hardness from 16.55 to 21.24 GPa and a decrease in the friction coefficient and wear rate from 0.56 to 0.32 and 13.60 to 5.60 10-5 mm-3/(N/m), respectively.
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This paper studies the impact of the mass fraction of NiTi-TiB2 particles obtained by the method of self-propagating high-temperature synthesis (SHS) on the phase composition, structure, and mechanical properties of composites made by direct laser deposition from an Inconel 625-NiTiz-TiB2 powder mixture. Composites were obtained from a powder mixture with the mass fraction of particles at 5-10 wt%, and they consisted of an Inconel 625 metal matrix wherein ceramic inclusions of titanium diboride TiB2 were distributed. Increasing the mass fraction of SHS-produced NiTi particles from 30 to 95 wt% led to the emergence of a NiTi intermetallide phase in the matrix material as well as an increase in the average TiB2 particle size and formation of their agglomerates. In addition, an increase in the microhardness of the materials was observed. The graph of tensile strength of Inconel 625-NiTi-TiB2 samples has a parabolic shape with a maximum at 1000 MPa (when the mass fraction of SHS-produced NiTi-TiB2 particles is at 30 wt%). A further increase in the mass fraction of NiTi-TiB2 led to a decrease in the tensile strength down to 400 MPa. Here the deformation of samples decreases linearly as the ratio of composite particles in the initial mixture increases. From a comparative analysis of the results obtained, the optimal mass fraction of composite NiTi-TiB2 particles in the Inconel 625-NiTi-TiB2 powder mixture was found to be 5 wt%.
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This article considers issues pertinent to the research of the phase composition, structure and mechanical properties of materials obtained from powders of composite (Ni-Ti)-TiB2, which have prospective applications in aerospace and automotive industry and engine construction. The starting powder materials (Ni-Ti)-TiB2 were obtained by self-propagating high-temperature synthesis (SHS). Research samples were produced using high-temperature vacuum sintering. It was shown that the use of such materials increases the wettability of the particles and allows the production of composites, the density of which is 95% of the theoretical one. Average particle size was 1.54 µm, average microhardness was 8 GPa, which is an order of magnitude higher than the average microhardness of pure nickel-based and titanium-based alloys, and the ultimate strength values were comparable to those of tungsten-based heavy alloys.
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Photoactive, optically transparent heterostructures from silver nanowires and titanium dioxide were obtained by the sol-gel method on the surface of a polyethylene terephthalate film. The characteristics of optical transmission on the wavelength and those of dielectric permittivity, conductivity and dissipation on frequency in the range of 25-1,000,000 Hz were investigated.
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The manuscript describes the phase composition, microstructure, some physical and mechanical properties of the Ti-Al system with addition of 2 at. % Dy (TAD) and Ho (TAH) obtained by "hydride technology". Phase diagrams for Ti-Al-Dy and Ti-Al-Ho at a temperature of 1150 °C and basic properties for ternary phases Dy6Ti4Al43 and Ho6Ti4Al43 were calculated. A crystallographic database of stable and quasistable structures of the known elemental composition was created in the USPEX-SIESTA software by means of an evolutionary code. The calculations show that adding REM leads to a significant stabilizing effect in each Ti-Al-Me (Me = Dy, Ho) system without exception. It has been established that the lattice energies of AlTi3Ho and AlTi3Dy are, respectively, equal to: EAl4Ti12Dy3 = -32,877.825 eV and EAl4Ti12Dy3 = -31,227.561 eV. In the synthesized Ti49Al49Ho2 compound, the main phases include Al-Ti, Al3Ti3 and Al4Ti12Ho3 and the contributions to the theoretical intensity are equal to 44.83, 44.43 and 5.55%, respectively. Ti49Al49Dy2 is dominated by the Al-Ti, Al3Ti3 and Al4Ti12Dy phases, whose contributions are equal to 65.04, 16.88 and 11.2%, respectively. The microhardness of TAD and TAN specimens is 1.61 ± 0.08 and 1.47 ± 0.07 GPa, respectively.
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The novelty of this work consists of obtaining original fundamental data on the laws of synthesis of new metal matrix composite materials for additive technologies. CrN + TiNi composites were obtained using the method of self-propagating high-temperature synthesis. In this work, analysis of the parameters of the synthesis of composite materials as well as their structure and phase composition were carried out. A scheme for the formation of a composite structure is established; it is shown that the phase composition is represented by 54.6 wt.% CrN and 45.4 wt.% TiNi. It was shown that composites based on the system are suitable for machines that make use of direct laser deposition to grow layers of materials. Sample structure and phase parameters were studied. It is shown that titanium nitride particles are uniformly distributed in the CrNi intermetallic matrix, the TiN particle size ranges from 0.3 to 9 µm and the average particle size is 2.8 µm. The results obtained indicate the possibility of synthesizing promising metal matrix composite materials for additive technologies. Such materials may have increased hardness, operating temperature and strength.
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This article dwells upon the additive manufacturing of high-energy materials (HEM) with regards to the problems of this technology's development. This work is aimed at identifying and describing the main problems currently arising in the use of AM for nanostructured high-energy materials and gives an idea of the valuable opportunities that it provides in the hope of promoting further development in this area. Original approaches are proposed for solving one of the main problems in the production of nanostructured HEM-safety and viscosity reduction of the polymer-nanopowder system. Studies have shown an almost complete degree of deagglomeration of microencapsulated aluminum powders. Such powders have the potential to create new systems for safe 3D printing using high-energy materials.