INFLUENCE OF POROSITY OF PRESSED SAMPLES OF SUPERFINE ALUMINUM POWDER ON COMBUSTION PARAMETERS

Данная статья посвящена исследованию влияния пористости прессованных таблеток из сверхтонкого порошка алюминия (СТП Al). Определен механизм горения, протекающий в две стадии: первая, медленная, включающая в себя как «кольцевое» горение боковой поверхности, так и параллельное горение концентрическими слоями, вторая стадия объемная, сопровождающаяся резким самопроизвольным увеличением температуры горения и интенсивности свечения. Показано, что увеличение плотности упаковки СТП Al позволяет замедлить процесс окисления алюминия более чем в два раза. Это обусловлено снижением газопроницаемости таблетки и затруднением доступа воздуха вглубь образца. Повышение пористости материала позволяет регулировать процесс нитридообразования за счёт увеличения содержания азота в продуктах при фильтрационном механизме горения, что открывает возможности получения тугоплавких материалов. This article is devoted to the study of the effect of porosity of compressed tablets from ultrafine aluminum powder (STP Al). The combustion mechanism was determined, which proceeds in two stages: the first, slow, which includes both "ring" combustion of the side surface and parallel combustion with concentric layers, the second stage is volumetric, accompanied by a sharp spontaneous increase in the combustion temperature and glow intensity. It has been shown that an increase in the packing density of HFC Al makes it possible to slow down the process of aluminum oxidation by more than two times. This is due to a decrease in the gas permeability of the tablet and the difficulty of air access deep into the sample. An increase in the porosity of the material makes it possible to regulate the process of nitride formation by increasing the nitrogen content in the products during the filtration mechanism of combustion, which opens up the possibility of obtaining refractory materials.

Quality assessment of AL-C-B coatings on steel surfaces obtained by electro spark alloying

Problem. As a rule, during the operation of the product, the surface layers of materials are most affected. These can be parts that work in aggressive environments, at high temperatures, various force actions, the presence of abrasive particles, etc. Under such conditions, different types of steels and alloys are used, and, most commonly, it is high-alloy, which significantly complicates the manufacturing process and increases the cost of the finished product. Diffusion coating methods are the most widespread in the industry, which is due to the best study and ease of these processes. However, there are alternative methods of surface treatment, which are devoid of the disadvantages of diffusion methods. The goal is to develop a method of obtaining boron-containing coatings of the Al-C-B system by the electro spark alloying (ESA), applying STS to the treated surface, to study the processes of structural and phase formation of surface layers depending on the energy processes of ESA and substrate material. Methology. Samples made of steel 20 and 40 were used for the study, on which a coating consisting of their sulfur ointment, aluminum powder, amorphous boron powder was applied. Without waiting for drying, the ESA surfaces of the samples were carried out with a graphite electrode on an installation with a discharge energy of 0.13, 0.55 and 4.9 J. The surface roughness after treatment was determined on a profilograph-profilometer by removing and processing profilograms. Metallographic analysis of coatings was performed using an MIM-7optical microscope, and durometric studies were made on the PMT-3 device according to standard methods. Results: the article presents the original method for obtaining boron-containing coatings of the Al-C-B system by the ESA method, which involves applying a coating consisting of sulfur ointment, aluminum powder, amorphous boron powder on the treated surface, followed by electric spark doping with a graphite electrode.

The structure and phase composition of the cermet charge in the Al‒Al2O3 system obtained using mechanical processing of aluminum powder in a planetary ball mill

The cermet charge in the Al‒Al2O3 system was obtained by mechanical processing (MP) in a planetary ball mill of aluminum powder of the industrial grade PAP-2 (GOST 5494‒95), consisting of flake particles of submicron thickness with a coating of stearin. Depending on the MP modes used, 4 types of charge were obtained, the bulk density of which varied from 0,33 to 1,1 g/cm3. For all types of charge, the synthesis of the α-Al2O3 phase was observed as a result of the exothermic reaction of the interaction of air oxygen with the surface of aluminum particles during the MP. It is also possible to form boehmite and gibbsite when the activated surface of Al particles interacts with atmospheric water vapor. The local X-ray spectral analysis (EDX) was used to detect X-ray amorphous carbon in the composition of the charge, the appearance of which is associated with the impact- shearing effect of grinding bodies, leading to the nucleation of X-ray amorphous carbon inclusions due to the termal destruction of stearin. The maximum bending strength of the sintered cermet was 550 MPa. This cermet is characterized by a discrete fracture: the formation of dimples as a result of the shear of layered packets under the action of tangential stresses. The revealed mechanisms cermet’s fractures allow us to establish the optimal modes of MP of powder compositions for obtaining various constructional elements from them.

Study and Development of the Components of Gas Generator Compositions Based on the Ammonium Nitrate to Improve Blasting Operations Safety

The article is devoted to the study and development of the components of gas generator compositions based on the ammonium nitrate to improve safety of blasting operations. This is primarily due to the low cost of ammonium nitrate, low sensitivity to mechanical and detonation effects and a significantly lower content of harmful compounds in the combustion products compared to the analogues. PA-4 aluminum powder was used as fuel, carbon black powder — as a gas-forming agent. The effect was studied concerning different amounts of aluminum powder on the combustion characteristics of a gas generator composition based on the ammonium nitrate. Calculated and experimental data showed that it is unreasonable to introduce more than 5 % of aluminum into the composition. According to the results of the conducted study, a gas generator composition based on the ammonium nitrate was developed to increase blasting operations efficiency and safety. Laboratory and polygon studies confirmed the efficiency and safety of using gas generator compositions at the destruction of stone. Destruction of the stone occurred without scattering of individual fragments, formation, and propagation of an air shock wave. Thus, the urgent task is to ensure blasting operations safety using gas generator compositions, which will allow to eliminate the formation of harmful, toxic gases and the high explosive effect.