Determining the influence of ultra-dispersed aluminum nitride impurities on the structure and physical-mechanical properties of tool ceramics

This paper considers features related to manufacturing the chromium oxide-based tool material. The process involved ultra-dispersed powders made of aluminum nitride. It has been established that the destruction of chromium oxide at high sintering temperatures is prevented through the reaction sintering of chromium oxide (Cr2O3) and aluminum nitride (AlN). It was established that the structure of the composite depends both on the temperature and the duration of hot pressing. Thermodynamic calculations of the interaction between Cr2O3 and AlN showed that this interaction begins at a temperature of 1,300 °C. In contrast to hot pressing in the air, no СrN and Сr2N compounds were formed in a vacuum. With increasing temperature, the content of Al2O3 in solid solution becomes maximum at a temperature of 1,700 °C in the case of hot pressing in the air while in vacuum the content of Al2O3 remains unchanged within the entire temperature range of 1,300–1,700 °C. When increasing the time of hot pressing to 30 minutes, the size of individual grains reaches 10 μm. It has been shown that in the sintering process involving Cr2O3 and AlN, the plasma-chemical synthesis produces the solid solution (Cr, Al)2O3 at the interphase boundary, which improves the mechanical properties of the material. The influence exerted on the quality of the machined surface of tempered hard steel when machining by the devised tool material based on chromium oxide with an optimal admixture of 15 wt % of ultra-dispersed aluminum nitride powder was investigated. It was determined that the quality of the machined hard steel surface improved compared to standard imported tool plates. It was established that the resulting tool material, in addition to relatively high strength and crack resistance, also demonstrates high thermal conductivity, which favorably affects the quality of the machined steel surface, given that lubricants and coolants are not used during the cutting process.

Modeling the Structure and Processes of Heat Transfer in Beds of Aluminum Micro- and Nanopowders

A model of the structure and a method for calculating (forecasting) the thermal conductivity of beds from coarse to nano-dispersed aluminum powders are developed. A significant change in the thermal conductivity of the particles themselves was taken into account during the transition from the micro-meter to the nanometer-sized range of particle sizes. The thermal conductivity was calculated over a wide range of particle sizes, granular structure skeleton porosity, and total porosity of the beds.

Determining the effect of dispersed aluminum particles on the functional properties of polymeric composites based on polyvinylidene fluoride

Polymeric materials that contain inorganic fillers demonstrate a unique set of physical properties due to the combination of matrix elasticity and filler strength. This paper reports determining the effect of dispersed aluminum particles on the properties of polyvinylidene fluoride-based materials. This study result is the fabrication of a series of composite materials using a piston extruder. Their functional characteristics have been explored using the methods of thermophysical and mechanical analysis, dilatometry, and acoustic spectroscopy. It was established that the introduction of dispersed aluminum particles leads to the loosening of the matrix, which may indicate the transition of macro macromolecules from the crystalline phase to the boundary layer around the filler. This feature of structure formation and the uniform distribution of filler particles ensured the improvement of the functional characteristics of the materials obtained. It has been shown that with an increase in the content of filler in the system to 5 % the thermal conductivity increases from 0.17 W/(m·K) to 1.55 W/(m·K). The introduction of the filler leads to an improvement in the heat resistance of the materials obtained, by 17 K. The increase in both melting point and destructiveness is explained by the formation of a more perfect polymer structure with a higher degree of crystallinity. An increase in the speed of ultrasound propagation was identified, by 67 %, as well as in the tensile strength, by 36 %, in the materials obtained, which can be explained by contributions from the filler, which has greater sound conductivity and mechanical strength than the polymer matrix. Such systems show the reinforcing effect of aluminum particles on the polymer matrix, so they could be used as structural materials with improved functional characteristics

Adhesive properties of aluminum-containing functionalized polymer composites obtained in the process of mechano-chemical modification

The influence of the concentration of finely dispersed aluminum and compatibilizer on the resistance to peeling of aluminum foil from the surface of a composite based on low density polyethylene and high density polyethylene is considered. To improve the compatibility of the filler with the polymer matrix, a compatibilizer was used, which is a graft copolymer of polyethylene of various grades with methacrylic acid and maleic anhydride. Copper and aluminum foil was used as a substrate. It is shown that the introduction of a compatibilizer into the composition of aluminum-filled composites improves their peeling resistance. It has been found that if an aluminum filled compatibilizer is used directly as an adhesive, then the peeling resistance of copper and aluminum foil is significantly increased. Graft copolymers of polyethylene with maleic anhydride have the highest peel resistance values. The results of the study of the influence of the pressing temperature on the type of adhesive failure are presented. It is shown that with an increase in the pressing temperature, a mixed type of adhesive destruction is observed. It has been experimentally proved that, in percentage terms, the cohesive type of fracture prevails in composites where graft copolymers are used as a polymer matrix. It was found that a 100 % cohesive type of fracture is observed in foil-clad composites pressed at a temperature of 190 °C, where a graft copolymer of polyethylene with methacrylic acid or maleic anhydride is used as an adhesive.

Highly borated dispersed aluminum: experimental evaluation of its neutron-shielding properties

By the method of mechanical alloying, compaction and thermosynthesis of a mixture of amorphous boron and aluminum powders, a prototype of highly borated (~50 wt.%) dispersed boron-aluminum was obtained. A comparative assessment of the neutron-shielding properties of borated dispersed aluminum and fibrous boron-aluminum VKM Al-B under irradiation with neutrons with a flux density of 1.4·106 n/cm²·s with a fluence of 3·109 n/cm2 was carried out. Using optical and scanning electron microscopy, a morphological analysis of samples of dispersed-borated powdered aluminum and fibrous-composite boron-aluminum was carried out. It was found that in both materials the level of absorption of neutrons with energies of 0.02-0.05 eV is up to 99.5-99.95%. It is concluded that highly borated dispersed boron-aluminum supplements the line of known boron-containing neutron-absorbing materials with the possibility of using it up to temperatures of 500-700°C.

Synthesis of preceramic precursor based on organic aluminum salts for stereolithographic 3D printing of corundum ceramics

Various options for the synthesis of aluminum acrylates, including substituted hydroxoacrylates, as well as an adduct of aluminum isopropylate with allylamine, have been tested in order to develop a mixture that can be formed by photopolymerization, followed by annealing while maintaining the shape of the ceramics, meaning further molding using stereolithographic 3D printing. By photopolymerization of a polymer precursor based on an acrylate suspension of in situ synthesized alumoxane of the Al(OH)2(ООСН2СН=СН2), corundum ceramics of a given shape were prepared. The inhomogeneity of the polymer precursor is not an obstacle to its use in technology. A significant percentage of weight loss during heat treatment of a polymer precursor suggests its possible use as a binder when filled with dispersed aluminum oxide powder. The strongest shrinkage of a ceramic product occurs in the range of 200 – 400 °C; it is necessary to develop a special program for heating the product to the sintering temperature in order to minimize the consequences of severe shrinkage. When a molded product is heat treated in an inert atmosphere, the shrinkage is less than when annealed in air, since a large amount of amorphous carbon remains during pyrolysis. Annealing such ceramics with amorphous carbon in a nitrogen atmosphere is promising for carrying out the carbonitridization process in the preparation of aluminum nitride and oxynitride.

COMPOSITION AND STRUCTURE OF COMPOSITE COATINGS BASED ON METAL OXIDES AND POLYTETRAFLUOROETHYLENEDEPOSITED UNDER CONDITIONS OF ELECTRON-INITIATED ENDOTHERMIC PROCESSES

In this article features of physicochemical processes initiated by the low-energy electron flow between the components of the target based on nitrates of metals and metals, their influence on the kinetics of the formation of volatile products, the chemical composition and structure of the deposited coatings are established. When electrons act on a mixture of aluminum nitrate and dispersed aluminum, zinc oxide coatings containing zinc nanorods are formed. The impact of the electron flow on a mechanical mixture of powders of iron nitrate and dispersed aluminum is accompanied by explosive evaporation of the target, and a large number of microdroplet formations deposited at the final stage of exothermic reactions in the surface layers of the target are fixed on the surface of the coating containing oxides and metal nanoparticles. The features of the structure and chemical composition of coatings deposited from the volatile products of electron beam dispersion of a mechanical mixture of polytetrafluoroethylene, iron nitrate, and aluminum are determined. It is shown that under such conditions of generation of the gas phase, coatings are formed consisting of a polymer matrix and containing particles of oxide, a free metal, and a certain amount of the initial undecomposed salt. The result of exothermic reactions in the crucible is partial defluorination and increased defectiveness of the molecular structure of the fluoroplastic matrix.