Добірка наукової літератури з теми "Nanodispersed powder mixture"

Properties of nanodispersed powder copper oxide, synthesized during arc sputtering of copper in a gas mixture of low pressure oxygen, were studied. It was shown that the particles possess nanometer size and narrow size distribution. The issue of reduction, recrystallization and sintering of nanodispersed powder were discussed.

The article is devoted to the analysis of the possibilities to obtain gradient materials by the method of spark plasma sintering. Pure copper powders consisting of particles with the average particle size 100 microns and the nanodispersed powder of aluminum oxide were used in this study. Two powder compositions - pure copper powder and a mixture of copper powder and aluminum oxide powder were sintered:. As a result of the sintering process a sample with a double-area structure has been formed with a well-defined boundary between these areas. After sintering the copper powder porosity remained at the initial level. But having been mixed and sintered, the aluminum oxide powder particles agglomerated up to the average particle size of 80 – 100 microns.

The article is devoted to the analysis of the possibilities to obtain gradient materials by the method of spark plasma sintering. Pure copper powders consisting of particles with the average particle size 100 microns and the nanodispersed powder of aluminum oxide were used in this study. Two powder compositions - pure copper powder and a mixture of copper powder and aluminum oxide powder were sintered:. As a result of the sintering process a sample with a double-area structure has been formed with a well-defined boundary between these areas. After sintering the copper powder porosity remained at the initial level. But having been mixed and sintered, the aluminum oxide powder particles agglomerated up to the average particle size of 80 – 100 microns.

Introduction. One of the methods for improving the properties of sintered materials is mechanical activation of powders. It ensures milling the powders, changing its energy state, intensifying the sintering of powder materials, and forming a fine-grained structure in it. When tungsten powders are mechanically activated in planetary centrifugal mills, nanoparticles can be formed, which have a high reactive power. The objective of the paper is to study the effect of mechanical activation of tungsten particles on the structure and properties of the sintered Sn-Cu-Co-W powder material. Research technique: Mechanical activation of W16,5 grade tungsten powder is carried out in a planetary centrifugal ball mill AGO-2U for 5…120 minutes with carrier speeds of 400…1,000 rpm. The mixture of tungsten, tin, copper, and cobalt powders are compacted by static pressing in molds and then sintered in vacuum at 820 °C. The morphology and size of powder particles, as well as the structure of the sintered samples, are studied by scanning electronic microscopy, X-ray microanalysis, and optical metallography. Porosity of the sintered samples is identified by the gravimetric method. Microhardness of the structural constituents and macrohardness of the sintered materials are measured, too. Results: in the modes under study, mechanical activation is accompanied by the formation of tungsten nanoparticles with the minimum size of 25 nm. Alongside this, the powder is exposed to cold working, which hinders further milling. Tungsten nanoparticles, characterized by high surface energy, have a significant effect on the dissolution-precipitation of cobalt during liquid-phase sintering of Sn-Cu-Co-W powder material. Addition of nanodispersed tungsten into the material slows down the growth of cobalt particles during sintering and contributes to the formation of a fine-grained structure. The sintered Sn-Cu-Co-W material, containing mechanically activated tungsten, features higher hardness of 105…107 HRB, which is explained by cold working of tungsten particles and dispersion hardening. The results can be applied for improving mechanical properties of Sn-Cu-Co-W alloys used as metallic binders in diamond abrasive tools.

Effect of activating the sintering process of powder steel alloyed with nickel or chromium by grinding the initial powders and introducing alkali metal compounds was investigated. The kinetics of grinding the initial iron powders, Cr30, and a mixture of iron powders with 4 % nickel was studied. It is shown that, depending on the hardness of the powder, it is grinded in three or two stages. When grinding more hard powders, there is no stage of intensive deformation of particles and an increase in their size. Crystalline lattice defects resulting from grinding of powders accelerate diffusion processes. This reduces sintering temperature by 100–200 °С compared to the sintering temperature of steels from the initial powders, contributes to a homogeneous structure, reduces porosity by 4–17 %, and increase strength of powder steels by 1.5–1.6 times. The mechanism of the effect of sodium bicarbonate on the acceleration of diffusion of carbon, nickel and chromium into iron has been established. With the introduction of sodium bicarbonate under the action of water vapor, formed upon its decomposition to carbonate, thin oxide films are formed on iron particles, which are actively recovered in a protective-recovering atmosphere during sintering. This leads to formation of a metal contact between the particles, acceleration of the self-diffusion of iron atoms and the diffusion of alloying additives into iron by 5–7 times, depending on the sintering temperature and the amount of added additive. Sodium forms nanodispersed complex compounds of the ferritic type Na3Fe5O9 along the grain boundaries of the iron base, which provide grain refinement and the formation of a homogeneous structure. Changes in the structure of powder steel with the introduction of sodium bicarbonate cause an increase in its strength by 1.5–1.7 times. The results can be used to obtain structural products from alloyed powder steels.

The results of an experimental study of laser pulsed modification of the surface of stainless steel 12CR18NI10T in a layer of alloying compound made of graphite paste and nanodispersed titanium dioxide powder (anatase) and without coating are presented. A comparative analysis of the effect of the coating on the elemental and phase compositions, morphological characteristics and microhardness of the modified surface is carried out. It was found that as a result of the treatment, the processes of cementation and oxidation of the surface occur, which made it possible to obtain a mixture of iron carbide and high-strength oxides in the surface layer of steel. In the samples that underwent laser treatment in the coating layer, an increase in the intensity of the diffraction peaks of the graphite phase and the formation of iron oxides Fe3O4 and chromium Cr2O3 with the presence of titanium dioxide TiO2 were revealed, which created a mixed heterophase metal oxide structure with increased mechanical strength. An increase in the microhardness of the modified surface after laser pulsed scanning in the layer of the experimental alloying compound is established.

The polycondensation of 5,5-methylene bis(2-aminophenol) and the mixture of diamines 5,5-methylene bis(2-aminophenol) and 4,4-(hexafluoroisopropylidene)dianiline (molar ratio 0.8:0.2) with isophthaloyl dichloride was used to synthesize a new heat resistant binder of the composites for microelectronics: poly(o-hydroxyamide) (POA) and poly(amido-o-hydroxy amide) (POA-F). The thermal stability of synthesized polymer coatings, as well as based on them photosensitive compositions with a naphthoquinondiazide photosensitive component were studied in the temperature range from 100 to 500 °C. Ferroelectric composites with nanodispersed lead titanate zirconate powder filler were formed based on these polymer matrices. By manipulating the conditions of the polymer formation, we obtained matrices with different stiffnesses, which reflected on the properties of the composite. The electrophysical parameters of the synthesized polymer and ferroelectric composite coatings were measured in the frequency range from 0.1 Hz to 1.5 GHz and the temperature range from 0 to 300 °C. The frequency and temperature stability of the dielectric constant of ferroelectric composite coatings up to 10 MHz and 300 °C, respectively, are noted. The influence of the composition and structure of the polymer matrix and the grain/matrix interfaces on the thermal stability of the dielectric parameters of composite films is estimated. The shift of the phase transition region toward higher temperatures in the composite structure, as well as the sufficient rigidity of the poly(benzoxazole) matrix, provide high temperature and frequency stability of the dielectric constant of the studied composites.

This paper presents the results of work on the application of plasma-chemical technology for producing uranium and plutonium oxides and their homogeneous mixtures from nitrate solutions of a given composition for the purpose of manufacturing fuel element cores. The technology is based on the process of high-temperature decomposition of aqueous solutions of salts by spraying them into a flow of the heat-transfer gas (air) heated to 5000 – 6000 K in a plasma torch. It is a highly productive short-stage process. No reagents are required for salt precipitation; there are no filtration and high-temperature treatment precipitation operations; the resulting powders are chemically active. It was found that the transformation time of salt solution drops to oxides is 0.05 – 0.10 s for the length of 0.5 – 0.7 m. The temperature in the reactor varies in the range of 1200 – 1800 K; no sintering and fusion of particles occurs. The apparatus-technological scheme of the plant has been developed. The technological equipment is made in a nuclear-safe design and installed in the exhaust boxes. The scheme includes a high-frequency induction plasmatron (plasma torch) with coaxial gas inlet into the discharge chamber. The high-frequency induction discharge is excited by inserting a grounded ignition electrode into the plasmatron discharge chamber. The plasmatron design provides the possibility of long continuous operation at high plasma temperatures with the creation of intensive plasma-jet processes for processing radioactive solutions. The reactor provides ways to prevent product accumulation on the walls (gas curtain method, electric pulse cleaning of cylindrical surfaces, vortex tangential gas supply at the level of the outlet holes of the injectors). Equipment for the separation of nanodispersed oxide powders from high-temperature steam- and powder-gas flows (vortex precipitators, filters with a metal-woven partition) has been developed and applied. The degree of oxide recovery in vortex precipitators is 88 – 92 % per stage, in filters with a metal-cloth partition the degree of purification reaches 105 – 108. Plasma-chemical oxides are nanocrystalline and nanoscale materials represented by crystalline and amorphous structures. Mixed powders are a homogeneous mixture of oxides in the form of solid solutions. The particle size does not exceed 3 μm; the crystallite size is about 10 nm. Fuel elements were manufactured from mixed powders at FGUP “Mayak”, which passed successful tests in the “Bor-60” reactor. Seven industrial fuel elements were manufactured for the BN-600 reactor, six of which were loaded into the reactor.

Possibilities of receiving ceramics from the nanodisperse ferric oxide (II, III) powder are investigated. In a hot pressing facility (by Spark Plasma Sintering method) the ceramics with fine-grained (about 1 micron and less) structure made. Structure of the received ceramics is investigated by the method of scanning electronic microscopy. Radiographic examination of initial nanopowder and the received ceramics is also carried out. If in the phase relation the initial powder and the ceramics sintered at 800 о С are magnetite Fe3O4 (75-1610), the ceramics sintered at 900 о С – Fe3O4 (75-33), and at 1200о С the diffraction picture of a mixture of two phases – a iron protoxide FeO (46-1312) phase and a metal Fe (6-696) phase – took place. Microhardness of the ceramics was 8 GPa, ultimate compression strength – 0,8 GPa. Thereby availability of use of the SPS method is shown

Дисертація на здобуття наукового ступеня доктора технічних наук за спеціальністю 05.02.08 – технологія машинобудування (13 – механічна інженерія). – Національний технічний університет «Харківський політехнічний інститут», Харків, 2019. У дисертаційній роботі проведено комплекс досліджень, спрямованих на вирішення важливої науково-технічної проблеми в області технології машинобудування: розробка інноваційних та короткотривалих технологій поверхневого зміцнення деталей машин порошковими сумішами керованого складу для забезпечення експлуатаційних властивостей виробів на високому рівні при значному зниженні затрат на їх виготовлення. Розроблено загальний методологічний підхід керування технологічними процесами поверхневого зміцнення деталей порошковими сумішами керованого складу при насиченні поверхневих шарів азотом, вуглецем і бором на основі використання інноваційних технологій і системного аналізу при мінімальних витратах, що дозволило підвищити експлуатаційні властивості виробів при значному скороченні тривалості ХТО. Розроблено комплексні ХТО, які значно знижують крихкість борованих шарів за рахунок більш плавного зниження твердості від поверхні до серцевини виробів зі сталей для підвищення експлуатаційних властивостей виробів та терміну служби деталей машин та інструменту. Удосконалено технологію борування з паст титанових сплавів за рахунок використання нанодисперсного насичувального середовища, що дозволило скоротити процес борування у 2-3 рази та скоротити технологічний процес виготовлення деталей за рахунок поєднання двох операцій: борування і гартування титанового сплаву. Інтенсифіковано процеси ХТО методами нагрівання струмами високої частоти та за рахунок попередньої лазерної обробки деталей, що дозволило отримати високі експлуатаційні властивості поверхневих шарів при значному скороченні тривалості обробок.
The thesis for the scientific degree of doctor of technical sciences, specialty 05.02.08 – technology of mechanical engineering (13 – mechanical engineering). – National Technical University "Kharkiv Polytechnic Institute", Kharkiv, 2019. In the thesis a set of studies was aimed at solving an important scientific and technical problem in the field of engineering technology: the development of innovative and short-term technologies of machine parts surface hardening with controlled composition powder mixtures to ensure the performance properties of products at a high level with a significant reduction in the cost of their production. Mathematical models and nomograms of existing technologies of steels surface hardening were created to determine the specific conditions of ChTT (temperature and duration) based on a given depth of the diffusion layer or the surface hardness of steels, which significantly affects the efficiency of the strengthening processes. The general methodological approach of management of technological processes of details surface hardening by powder mixes of the controlled structure at saturation of surface layers with nitrogen, carbon and boron on the basis of use of innovative technologies and the system analysis at the minimum expenses was developed that allowed to increase operational properties of products at considerable reduction of ChTT duration. ChTT was designed the complex, which significantly reduces the fragility of boriding layers due to a more gradual decrease in hardness from surface to core products from steels to improve the operational properties of the goods and service life of machine parts and tools. It was created a mathematical model of the temperature distribution in the depth of the diffusion layer to determine the nature of the dependencies and obtain data on the temperature distribution in the depth of the product under different processing conditions. It was improved boriding pastes technology of titanium alloys through the use of nanodispersed environment, thereby reducing the boriding process 2-3 times and to shorten the manufacturing process of components by combining two operations: boriding and titanium alloy hardening. The solutions of boundary value diffusion problems by the boundary element method were proposed, which allowed to create a mathematical model of the distribution of boron concentration over the thickness of the hardened titanium alloy. The processes of heating by high-frequency currents and due to the preliminary laser treatment of parts were intensified, which allowed to obtain high performance properties of the surface layers with a significant reduction in the duration of treatments. A comparative analysis of the influence of existing and developed hardening treatments on the change in the depth of the layer, the surface hardness and wear resistance of the surface layer of steel 38Ch2MoAl was done. It was established that the developed complex hardening treatment based on the process of diffusion saturation with boron can provide wear resistance of the surface layers at a high level with abrasive wear.

This paper provides a mathematical model of combustion of a nanodispersed aluminum-air suspension (NAAS). The main feature of the model is the local approach for oxidant diffusion which implies the diffusion of oxidizer through alumina layer on the particle surface and its reaction with aluminum. The oxidation rate of aluminum particles and the rate of heat release for the whole assembly of particles are determined from the solution of local combustion problems for each Al nanoparticle. The parameters of the NAAS are determined from the solution of the system of equations which include the energy conservation equations for gas and particles and the mass conservation equations for the components of the gas-dispersion mixture. The developed model does not require setting the ignition temperature of Al nanoparticles. The system of equations is solved numerically. The problem of combustion front propagation is solved with the following formulation: NAAS is placed in a tube of large diameter and length with a closed left end and open right end. The initial mass concentration of Al powder in the air is uniform and less than the stoichiometric value. Since a high-temperature ignition source on the left end of the tube ignites the NAAS, a combustion wave occurs and starts propagating along the tube. In the present study, the dependences of the combustion-front propagation velocity on the Al mass concentration and initial temperature of the NAAS have been determined. With increasing the initial temperature and mass concentration of Al powder, the propagation velocity of the combustion front increases.