In this paper, we present the development of new types of boron carbide-based ceramics. Boron carbide is applied in the electronics and nuclear industries as well as for production of the grinding and abrasive materials, protective plates for body armor. The interaction of boron carbide with chromium nano-oxide additives (1-5 wt.%) during sintering was studied by mass spectrometry. It is shown that the formation of chromium nano-boride takes place at the stages of formation of metallic chromium, the lowest chromium boride and chromium carbide. The maximum solubility of chromium in the boron carbide lattice was found to be 0.5 wt.%. A composite material based on boron carbide, В4С with CrB2 nano-inclusions, was prepared. The bending strength and modulus of normal elasticity were equal to 44.6 MPa and 449.5 GPa, respectively. Micro-hardness and residual porosity were determined to be 40 GPa and 5-7 %.
The optimal modes (temperature, time, pressure force) of spark plasma sintering (SPS) and hot pressing of boron carbide obtained by various methods are determined. The initial powders were obtained from soot and amorphous boron by the mechanochemical synthesis method, by the high-temperature synthesis (SHS) method and by the carbon reduction method. The structure and the properties of SPS sintered and hot-pressed boron carbide blanks were determined. The highest value of the relative density was achieved during SPS sintering of blanks from B4C powders obtained by mechanosynthesis and SHS methods. It was found out the optimal conditions for sintering blanks from B4C powder obtained by mechanosynthesis. The density value reaches 99.0 rel.% at 1500 °C/25 MPa and sintering time of 45 min. For powders obtained by the SHS method, the density of sintered blanks is 98.5 rel.%. at 1800 °C/30 MPa with sintering time of 45 min. The highest value of the relative density was achieved during the hot pressing of blanks from B4C powders obtained by mechanosynthesis.
Today there are numerous research works meant to improve nuclear fuel element performance in order to ensure reliable operation under increased burn-up conditions. In this context the pellet microstructure seems to be a very important parameter. An increase in the grain size diminishes the branching of boundaries and reduces the migration speed of gas-filled pores to the grain boundaries which are the routes of accelerated diffusion. The problem can be solved by introducing nano additives to uranium dioxide considering the influence of small addition agents upon the grain growth activation and microstructure evolution. The addition of nano particles of different powders should stimulate agglomeration process. This is one of modern tendencies in the development of new material technologies for fast reactors. In the research process the mechanical activation with simultaneous size reduction of gadolinium oxide and aluminum and gadolinium hydroxide powders (Gd2O3 №1, Gd2O3 №2, Al(OH)3 and Gd(OH)3) was done in planetary centrifugal mill "Pulverisette 5" made by Fritsch GmbH company (Germany). The technology of UO2 nuclear fuel manufacture has been developed in several variants including the agglomeration with pre-pressing or extruding, isostatic and hot pressing, rotary swaging, vibratory compacting, slip casting, etc. Today the main UO2 fuel element manufacturing technologies are cold pressing and agglomeration considering their simplicity and affordability. The conducted research permitted to ascertain some specific features of initial TiO2, Al(OH)3, Gd2O3, and Gd(OH)3 additives and determine their basic properties. The authors determined the most optimal modes of fine-grained additives production and proposed and optimal method of their introduction into UO2 mixtures. The paper also considers possible mechanisms of fine-grained additives influence on the fuel pellet production.
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