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•Combination of SHS and HP use to obtain ceramics in the ZrSi2-MoSi2-ZrB2 system.•Kinetics of oxidation at 1400 °C described using a power function with index n > 2.•Mostly the ZrSi2 ...phase were oxidized.•Two-layer film formed during oxidation consist of silicate glass and ZrSiO4 sublayer.•ZrSiO4 with scheelite-type structure encapsulate the ZrB2 and MoSi2.
The results of a study of the kinetics and mechanism of heterogeneous and compact ceramics oxidation in the ZrSi2-MoSi2-ZrB2 system at air temperature of 1400 °C are presented. The ceramics were obtained by the hot-pressing of composite powders that were manufactured by self-propagating high-temperature synthesis following the magnesiothermal recovery approach. Oxidation kinetics are described using a power function with index n>2, confirming the significant influence on the evolution process in the structure of the formed oxidation coating. The oxidation mechanism includes the formation of a two-layer structure consisting of a continuous silicate film, of which the outer part contains magnesium and a sublayer based on the ZrSiO4 phase, with the scheelite structure encapsulating the ZrB2 and MoSi2 grains. The influence of the ZrSi2, MoSi2 and ZrB2 phases on the structural-morphological peculiarities of the appearing oxide films and the effectiveness of its protective action are revealed.
The investigation results on development and testing of heat-resistant coating with experimental composition of Si–TiSi
2
–MoSi
2
–TiB
2
–CaSi
2
for protection of C
f
/SiC composites from oxidation ...and high-speed erosion in high-speed gas flows are presented. This coating was formed by slip firing technology out of slip compositions with filler based on heterophase powder of the system of interest. The results of fire bench tests of samples with coating under conditions of flow-around and off balance heating by air plasma streams with M = 5.5–6.0 and enthalpy of 40–45 MJ/kg. The effectiveness of the protective action of coating at surface temperature
T
w
= 1810–1820°C is kept not less than 920–930 s, at
T
w
≥ 1850–1860°C—not less than 420–430 s. It was found that the effectiveness of coating is provided by structural-phase state of the base coating and formation of heterogeneous oxide film on its surface formed by borosilicate glass with titanium and calcium segregation heterogeneity and TiO
2
reinforce micro-needles in the form of rutile. The decrease in saturated steam pressure level in oxide film–coating system induced by increase in the level of external layer heterogeneity was experimentally confirmed.
Monitoring of the level of different flammable liquids is examined, including that of petroleum products in high capacity tanks, as well as during pumping, at oil storage depots. The operating ...characteristics of most level measurement devices do not meet customer specifications in practice. Commercial accounting for petroleum products requires more precise measurements and more stable operation of the liquid level gauges set up for factory conditions and spark-explosion safe operation. The development of a spark-explosion-safe device with a hydrostatic fiber-optic liquid level sensor and a position-sensitive detector is validated. For continuous monitoring of liquid level, it is proposed that measurements be made of the displacement of the bottom of a bellows under the influence of the hydrostatic pressure created by a column of the liquid with automatic compensation of the change in the density of the liquid. Compensation is carried out with a small buoy with an optical triangulation sensor for small displacements installed in it with a position-sensitive detector. The use of a bellows for suspension of the buoy is justified theoretically. The operating principle of the fiber-optic liquid level sensor is described. The calculated absolute measurement error for the level of a petroleum product is less than ±1 mm. The spark-explosion hazard of the device is reduced because there are no wires in the measurement zone, so the proposed device can be used in different fi re-hazardous media with a corresponding spark safety level confirmed by certification.
Modern nuclear physics is impossible without the implementation of projects of the megascience class, for the creation of which the efforts of many organizations and countries are consolidated. The ...level and complexity of experiments carried out with the use of such facilities is provided by scientific researchers with a wide range of competencies. The education of such researchers is an important task for scientific and educational organizations. These issues were discussed at the 2nd conference "Personnel training and legal support for the implementation of scientific projects of the Mega-science class" organized by National Research Nuclear University MEPhI and Kutafin Moscow State Law University on June 25, 2020. The aim of the Conference was to discuss the policy management issues of implementation of the Mega-science class research projects.
This article contains the results of research on the development of a Cf/C-UHTC carbon fabric composite based on a viscose precursor and a combined matrix consisting of partially sintered ceramics in ...a system consisting of HfC–HfB2–NbC–NbB2–TiC–TiB2–B4C–SiC, amorphous carbon, and pyrocarbon. The SiC fraction does not exceed 8.5–9.0 wt%. In its initial state, the composite has open porosity, with apparent and true densities of 18–22%, 2.25–2.29 g/cm3 and 2.79–2.91 g/cm3, respectively. The bending strength and the elasticity modulus are 27.8 ± 0.7 MPa and 7.8 ± 0.2 GPa, respectively, and the fracture strain is 0.85 ± 0.05%. The tests for resistance to oxidation and ablation were carried out in a gas dynamic flow regime and non-equilibrium air plasma heating at flow rates of 4.5–4.8 km/s and breaking enthalpy of 45–50 MJ/kg. Heating was performed in the temperature range Tw = 1400–2700 °C at the critical point on the front surface of the samples. The average linear ablation rate and mass loss rate of the composite are 6.3 ± 0.3 μm/s and 6.22 ± 0.44 mg/s. The estimated value of the conductivity factor is 0.280–0.285 W/(m K). The performance ability of the composite arises from the formation and evolution of a passivating heterogeneous oxide film consisting mainly of titanium niobate Ti2Nb10O29, mixed solutions of Hf1−xTixO2, (Ti1−xHfx)1−yNbyOz and (Ti1−xHfx)NbO4 with broad homogeneity ranges, and also encapsulated carbide and boride particles. It is shown that the oxidation resistance of the composite increases as a result of the transition through a number of phases into a liquid state as the working temperature increases.
•Dense heterophase HfB2–SiC ceramics produced by hot pressing of SHS powders.•The best heat resistance was observed for the ceramics with 8 % SiC under gas-dynamic conditions.•A dense protective ...layer consisting of HfO2/HfSiO4 grains is formed on the surface during oxidation.•Ceramics exhibits: heat capacity - 0.38 J/(g × K), thermal diffusivity - 40.9 mm2/s, and thermal conductivity - 89.7 W/(m × K).
The kinetics and the mechanism of oxidation of ceramics based on HfB2 and SiC, manufactured by elemental self-propagating high-temperature synthesis followed by hot pressing were investigated. The synthesis product contained HfC(x) and HfO2 as impurity phases. Depending on the ratio between the main components, the samples were characterized by high structural and chemical homogeneity, porosity of 3–6 vol%, hardness up to 29 GPa, bending strength of 500–600 MPa, fracture toughness of 5.6–8.9 MPa × m1/2, and thermal conductivity of 86.0–89.7 W/(m × K). The oxidation was performed under static conditions at 1650 °C and upon exposure to a high-enthalpy gas flow. A dense layer consisting of HfO2/HfSiO4 grains formed on the surface of the ceramics during both oxidation conditions; the space between the grains was filled with amorphous SiO2–B2O3. The best heat resistance was observed for the ceramics with 16 wt% SiC for static conditions and 8 wt% SiC for gas-dynamic conditions.
MoSi
2
-based coatings on a CSC substrate are formed by reaction synthesis using slurry painting of powder compositions at 1500°C and a pressure of 8–9 mPa. Mechanisms are proposed for the reaction ...interaction in the Mo–Si–C and Mo–Si–C–HfB
2
systems, which determine the synthesis of the secondary phases MoSi
2
, Mo
4.8
Si
3
С
0.6
, MoB, and HfC. Possible chemical reactions are thermodynamically calculated. Possible causes of the high porosity of the synthesized coatings are analyzed.
Composites MoSi2–ZrB2–SiC and MoSi2–HfB2–SiC were investigated in this study as the prospective materials for high-temperature industrial heaters. The composites with relative density 97–98% were ...produced by combustion synthesis followed by hot pressing. The macrokinetic features of combustion, as well as phase and structure formation mechanisms in the combustion waves, were analyzed and their influence on the structure, mechanical properties, and performance of heaters were ascertained. The mechanical and electrical properties of the heating elements produced in this work are considerably higher as compared to conventional MoSi2 counterparts. Among the investigated compositions, the MoSi2–HfB2–SiC demonstrated the highest resistance to high-temperature oxidation. Both compositions featured the formation of a stable continuous oxide layer consisting of crystalline α-quartz (high-temperature modification of SiO2) reinforced by ZrO2, ZrSiO4, HfO2, and HfSiO4 precipitates.
The authors analyze the results of tree taxation of different apple trees varieties on the territory of I V Budagovsky research and development center at Michurinsk State Agrarian University. The ...plantation valuation and the establishment of locality class were carried out using the methodology of Michurinsk State Agrarian University. Studies have shown that class quality of the garden can be characterized as high - from 85 to 100 points, which corresponds to the first class of quality. Thus, all graft-rootstock combinations are normally developed, while it was found that within the studied population for a number of graft-rootstock combinations the percentage of normally developed trees is on the verge of transition to a lower quality class. The authors proposed a method for developing a program to automatically determine the state of each tree based on using digital recognition technology, the proposed technology will significantly reduce time and labor costs and exclude the subjective assessment factor.
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