RESUMEN
Objects of modern technology located in the rain zone experience additional loads and can be destroyed due to water droplet erosion. With a significant number of successive impacts in a certain period of time, rain causes damage to the surface of materials or structures. It should be noted that supersonic water droplet impact has a low probability of occurrence; however, the peak pressure impulse of the water hammer (up to GPa level) far exceeds the strength of many materials, and a small number of impacts are enough to damage the material or structure. Therefore, it is very interesting to determine the external load caused by a water droplet's impact and its response to various obstacles. In this work, the external load is determined on the basis of experimental studies. To carry out such tests, a single-jet generator is most widely used, which, with a certain ease of operation, makes it possible to investigate the mechanisms of damage to materials and the effect of water droplet impact erosion on structural elements. Based on the obtained research results, mathematical modeling of the droplet impact with an obstacle is provided. The examples are considered.
RESUMEN
The results of a study on the development and testing of a heat-resistant coating in a Si-TiSi2-MoSi2-TiB2-CaSi2 system to protect Cf/C-SiC composites from oxidation and erosional entrainment in high-speed flows are presented here. The coating was formed using firing fusion technology on the powder composition. Oxidation resistance tests were carried out under static conditions in air at 1650 °C and under conditions of interaction with high-speed air plasma flows, with Mach numbers M = 5.5-6.0 and enthalpy 40-50 MJ/kg. The effectiveness of the protective action of the coating was confirmed at surface temperatures of Tw = 1810-1820 °C for at least 920-930 s, at Tw = 1850-1860 °C for not less than 510-520 s, at Tw = 1900-1920 °C for not less than 280-290 s, and at Tw = 1940-1960 °C for not less than 100-110 s. The values of the rate of loss of the coating mass and the rate constant of heterogeneous recombination of atoms and ions of air plasma on its surface were estimated. The performance of the coating was ensured by the structural-phase state of its main layer, and the formation and evolution on its surface during operation of a passivating heterogeneous oxide film. This film, in turn, is composed of borosilicate glass with titanium and calcium liquation inhomogeneities, reinforcing TiO2 microneedles and in situ Si2ON2 fibers. It was shown that at Tw ≥ 1850-1860 °C, the generation of volatile silicon monoxide was observed at the "oxide layer-coating" interface, followed by the effects of boiling and breakdown degradation of the oxide film, which significantly reduced the lifespan of the protective action of the coating.
RESUMEN
Nowadays, numerous researches are being performed to formulate nontoxic multifunctional magnetic materials possessing both high colloidal stability and magnetization, but there is a demand in the prediction of chemical and colloidal stability in water solutions. Herein, a series of silica-coated magnetite nanoparticles (MNPs) has been synthesized via the sol-gel method with and without establishing an inert atmosphere, and then it was tested in terms of humic acids (HA) loading applied as a multifunctional coating agent. The influence of ambient conditions on the microstructure, colloidal stability and HA loading of different silica-coated MNPs has been established. The XRD patterns show that the content of stoichiometric Fe3O4 decreases from 78.8% to 42.4% at inert and ambient atmosphere synthesis, respectively. The most striking observation was the shift of the MNPs isoelectric point from pH ~7 to 3, with an increasing HA reaching up to the reversal of the zeta potential sign as it was covered completely by HA molecules. The zeta potential data of MNPs can be used to predict the loading capacity for HA polyanions. The data help to understand the way for materials' development with the complexation ability of humic acids and with the insolubility of silica gel to pave the way to develop a novel, efficient and magnetically separable adsorbent for contaminant removal.