Heat-resistant Materials Research Articles

Synthesis and Properties of 1,2,4-Triazol-3-one-Based Energetic Compounds

1,2,4-Triazol-3-one (TO) is an important nitrogen-rich heterocycle in synthesis chemistry. In the field of energetic materials, some synthesis strategies are applied to prepare TO-derived energetic materials. However, none of them can be used as a heat-resistant energetic material due to their lower decomposition temperatures. In this paper, a series of energetic TO derivatives 4–13 were prepared from 5-oxo-4,5-dihydro-1H-1,2,4-triazole-3-carboxylic acid. These compounds were fully characterized by using elemental analysis, 1H and 13C NMR spectroscopy, IR analysis, and MS. The crystal structures of fused-ring compound 6 and perchlorate 8 were further identified using single-crystal X-ray diffraction. Most compounds exhibit good thermostability (Td = 166.5–324.5 °C), low sensitivities (impact sensitivity IS ≥ 20 J; friction sensitivity FS ≥ 360 N), good detonation performance (Dv = 7905–8753 m s–1), and positive heats of formation (ΔHf = 295.9–1121.1 kJ mol–1), except compound 9 (Td = 92 °C; IS = 15 J; FS = 240 N). Among these target molecules, compound 6 with a high decomposition temperature (Td = 324.5 °C), a high density (ρ = 1.859 g cm–3), low sensitivities (IS > 40 J; FS > 360 N), and a decent detonation performance (Dv = 8406 m s–1; P = 29.2 GPa) is superior to the traditional heat-resistant explosive hexanitrostilbene (Td = 318 °C; ρ = 1.750 g cm–3; IS = 5 J; FS = 240 N; Dv = 7612 m s–1; P = 26.3 GPa) and can be used as an insensitive and thermostable energetic material.

Measuring the burnout rate of flammable liquids

The article discusses the express method proposed by the authors for experimental measurement of the mass burnout rate of liquid combustible substances. Describes the experiments carried out with various liquids, which impregnated products made of porous heat-resistant material in the form of spheres or flat cylindrical "tablets" of different diameters. These products were placed on digital scales and set on fire. A video camera connected to a computer recorded the readings of the scales and simultaneously monitored the combustion process, fixing the value of the current time t. When processing the video file, the dependence of the mass of the liquid burning on the sample on time M = f(t) was plotted. On this graph, a linear section was allocated to measure the mass loss rate, and the specific mass burnout rate of the liquid ṁ was calculated from it. The results were compared with data obtained by other researchers in experiments using various methods for determining ṁ: in particular, with the methods of "stationary sphere", "suspended drop", burnout in a tubular burner, and also from a flat free surface.

In-situ laser-ultrasonic visualization with the use of regenerated fiber Bragg grating sensors at elevated temperatures

The authors have developed a high-temperature ultrasonic sensing system with a regenerated fiber Bragg grating (RFBG) sensor, that was fabricated by annealing a fiber-optic Bragg grating (FBG). Different from the common FBG, the RFBG ultrasonic sensor is resistant to temperature as high as 900 °C. In this study, taking advantage of the RFBG sensor, we attempted to establish a laser-ultrasonic visualization method for in-situ damage diagnosis in heat-resistant materials at elevated temperatures. In the first part of this paper, after reporting the fabrication of the RFBG in detail, we validated that the RFBG sensor has reasonable sensitivity to ultrasonic measurement over a broad frequency range at high temperatures. The RFBG was then incorporated into a laser-ultrasonic visualizing inspector to visualize the ultrasonic wave propagating in a SiC plate with an artificial defect at 800 °C. An improved data processing method was employed to verify the reliability of the visualization result. In the processing method, the visualization result was transformed to the spectrum in the wavenumber-frequency domain with the help of three-dimensional fast Fourier transform. Referring to theoretically calculated dispersion curves of the Lamb wave propagating in the SiC plate, we identified S0 and A0 modes from the spectral results. In addition, the agreement between the theoretical results and the experimental results also verified the feasibility of our proposed system to visualize the ultrasonic wavefield in high-temperature environment. Moreover, we developed a window function to extract the wave modes from the visualization result based on the dispersion curves. The artificial defect in the SiC plate could be then clearly localized from the visualization results for the separated individual modes.

Gradient microstructure response in different phases of Ti2AlNb alloy with laser shock peening

Ti2AlNb alloy is a new type of lightweight and heat-resistant structural material that has been an active research topic with multi-phases due to its improved mechanical properties. However, the phase response under severe plastic deformation (SPD) at high strain rates is unclear, which limits the understanding of its strengthening mechanism. Here, laser shock peening (LSP) was employed to investigate the microstructure response of α2, O, and B2/β phases in Ti2AlNb alloy. After LSP, the highest density dislocations were generated in the B2/β phases, followed by the O phases, and the least dislocations were observed in the α2 phases. In the B2/β phases, only dislocation tangles (DTs) were observed. Dislocation lines (DLs) and DTs were mainly distributed in the O phases. As for the α2 phases, DLs were generated while a small number of DTs were piled up at the grain boundaries. In addition, parallel dislocations (PDs) with a spacing of about 135 nm can be observed on the surface of the α2 phases, and the dislocations interspersed between PDs were composed of screw dislocations with long segments. In addition to dislocation structures, stacking faults (SFs) were observed in both α2 phases and O phases, and mechanical twins were formed in the O phases, which were generated to coordinate the SPD induced on the surface. These dislocation structures formed dislocation cells (DCs) and sub-grain boundaries which further developed into high-angle grain boundaries (HAGBs) together with mechanical twins, dividing the coarse grains and refining the microstructure. As the depth increased, the responses of the three kinds of phases decreased. The PDs in the α2 phases have widened spacing and could not penetrate the grains. The mechanical twins were gradually reduced until no obvious twin structure could be observed. Finally, dislocations, grain size, microhardness, and residual stress presented a gradient distribution. The improved microhardness (maximum 470 HV) and compressive residual stress (maximum −600 MPa) which were consistent with the refined grains and high-density dislocations gradually decreased to that of the base metal (BM).

Distributed Fiber-Optic Calorimetric Dosimeter

A novel distributed fiber-optic calorimetric dosimeter is presented. The dosimeter sensors are thermally insulated spherical beads (calorimetric sensors) made of lead mounted on an optical fiber in constant steps. Under gamma radiation exposure, due to the calorimetric effect, the temperature of the beads increases proportional to the dose rate of the radiation. The temperature of the sensor is measured using a stimulated Brillouin scattering analyzer, which makes it possible to obtain the dose rate distribution over the entire length of the optical fiber at distances of up to several tens of kilometers. The results of the experiment confirm the linear nature of the dependence of the sensor temperature on the dose rate with a factor of 0.0027 °C h/Gy. The working range of the experimental sample of the dosimeter is shown to be limited to approximately 315 Gy/h–81 kGy/h. The upper limit of the working range is determined by the melting point of the polystyrene foam which is used to insulate the point sensors. This could be improved by utilizing more heat-resistant materials.

Micro-, Meso- and Macrostructural Design of Bulk Metallic and Polymetallic Materials by Wire-Feed Electron-Beam Additive Manufacturing

Abstract Additive manufacturing of metal materials is one of the most promising technologies in modern industry. A wide variety of current additive manufacturing techniques allow rapid prototyping and industrial production of different-sized products from various structural and functional materials. The structure and physical-mechanical properties of the metal products fabricated by electron-beam additive manufacturing (EBAM) within nonstationary metallurgy in a local molten pool often differ from those of the products fabricated by conventional metallurgy due to different crystallization mechanisms, sequence and completeness of phase transformations, and heterogeneous/homogeneous chemical composition of the resulting material. The possibility to control local metallurgical processes in the molten pool is the key advantage of the EBAM technology. It allows one to control the structure, composition, and properties of mono- and polymetallic, graded, composite and heat-resistant materials in order to obtain products with the desired chemical composition, macroscopic architecture, and microscopic structural parameters. As any new industrial technology, the EBAM method requires the development of scientifically based approaches to the choice of materials and production conditions. Here we provide an overview of the scientific approaches developed for electron-beam additive manufacturing of products from metals and alloys using wire or rods as a feedstock. The range of the studied materials includes additive materials based on copper, bronze, aluminum, nickel, titanium alloys, and different steels, as well as aluminum-based functionally graded materials and copper-based graded materials. The most important research findings are summarized.

A Simple, Low-Cost, and Green Method for Preparing Strong, Tough, and Ductile Poly(lactic acid) Materials with Good Transparency and Heat Resistance

Notwithstanding that unprecedented progress has been achieved in strengthening and toughening PLA materials, it is still a challenge to find a facile and low-cost way to improve poly(lactic acid) (PLA) strength, toughness, and ductility while maintaining transparency and biodegradability. Herein, strong, tough, transparent, and highly heat-resistant PLA materials with a nacre-like lamellar structure were fabricated via a simple, low-cost and additive-free pressure-driven flow process. PLA powders with a size under 500 μm and heterogeneous size distribution obtained from ball milling and size sieving were used to yield a PLA material with a dense and ordered crystalline structure after pressure-driven flow treatment. The newly formed structured PLA material exhibited exceptional mechanical properties, with tensile strength, elongation at break, impact strength, and tensile toughness reaching 88.9 MPa, 102.5%, 45.1 KJ/m2, and 81.2 MJ/m3, respectively. The refined strength, toughness, and ductility were attributed to more particles undergoing uniform plastic deformation during the pressure-driven flow treatment. The interface between particles in the powder was much larger and more tortuous, and the particles were firmer. Additionally, the newly formed tightly stacked crystal structure consisting of densely and orderly arranged nanosized crystals played an important role in improving the mechanical properties of PLA. Moreover, the newly formed structured PLA materials exhibited enhanced heat resistance and retained good transparency, with a visible light transmission of over 80%. Overall, this work presents a simple and efficient method for fabricating high-performance PLA materials that are strong, tough, ductile, transparent, heat-resistant, and easily recyclable.

Mathematical modeling to estimate machining time during milling of Inconel 718 workpiece using ANN

For the manufacturing of thin walled-complex shape components used in complex dies and moulds it is important to manufacture these kinds of components with hard, tough and heat resistant material such as Income 718. During the end milling of such type of components there are many challenges related to machine time, surface roughness, tool wear etc identified in the recent past. Therefore, in this study a prediction model for machining time with respect to the input parameters such as cutting speed, Depth of Cut, Feed rate and nose radius has been developed. The prediction model with high accuracy is very important for the optimization problems usually faced during machining. For prediction of machining time many of the researchers have applied Statistical, Analytical as well as artificial network (AI) techniques and as per the recent literature review it has been observed that the AI techniques are most accurate and reliable. Inconel 718 used for making components in aerospace, marine, automobile, steam turbines etc is difficult to machine due to its physical and chemical properties. Therefore, in the present work an attempt has been made to develop a prediction model of machine time during milling of Inconel 718 with the help of BBD-RSM-Regression (statistical techniques) as well as Artificial Neural network (AI techniques). Beside this a comparative analysis has been made among these techniques and it has been observed that AI technique provide better prediction as compare to the BBD-RSM-Regression. The ANOVA technique is also applied to find the estimate the percentage contribution of each machine parameter with respect to machine time.

Модернизация системы управления капельным поливом сельскохозяйственных культур

The study solves the problem of modernizing the control system for automatic watering of plants. There is pre-sented a modernization project based on a flowchart, the operation of which does not require constant monitoring, since it functions in a set automatic mode and, if necessary, can be programmed for a certain period (week, month), while the setting is performed remotely. The advantages of the proposed system are the regulation of irrigation cycles with the choice of water consumption rate, time and duration of irrigation; regulation of the irrigation sector (irrigation angle); the possibility of carrying out different watering cycles within one day; the ability to switch irrigation control to manual mode; no dependence on power failures; aesthetic design. Mechanical damage to the pipelines included in the system is not possible, since the components are made of moisture- and heat-resistant polymeric materials. The project implementation provides for the modernization of the automatic control system for watering plants through the introduction of a modernized soil moisture control device. A diagram of the developed soil moisture sensor on an autogenerator is presented. The principle of operation of the sand filter included in the automatic irrigation system is considered.

The Effect of Room Temperature on the Spread of the Covid-19 Virus by Creating a Special Isolation Room with a Hot Temperature for Those Indicated as Medical Service Facilities

During the Covid-19 pandemic, there were many alternatives to anticipate or anticipate through certain tools and media with less effectiveness and endanger the users, for example, a device that can be called a disinfecting chamber or "disinfection chamber". Quoted from CNN Indonesia, sourced from the WHO Indonesia Twitter account that not to spray alcohol or chlorine directly on the body, spraying such chemicals can be dangerous if exposed to clothing or mucous membranes (example: eyes, mouth) . Alcohol and chlorine can be used on the surface of the body with instructions or user guides. With an official statement from the world health organization directly that it can endanger health, there must be a breakthrough in new media that is safer for users . According to scientists from Aix-Marseille University in France, if the corona virus is exposed to high temperatures it can reduce the life span of the virus itself or can kill the virus itself at 92 degrees Celsius within 15 minutes (quoted from DetikHealt.com) . Giving heat to the room itself using heating by providing steam as in the sauna room and the interior elements are also applied special heat-resistant materials without compromising the safety and health of the users of the room . Then this room will be in health centers that move to handle patients who are examined and also useful for medical practitioners who treat patients . With a room that has a high temperature is expected to minimize the spread of the virus on an ongoing basis and neutralized our bodies outside of the virus in a safe way , because reported by various news , the specialists in internal medicine provide a statement that the virus that is outside the host or can be called a part of our body can last within 3 hours without handling such as washing hands using a handsanitizer or other treatments . The output of the research itself is a room with a hot temperature with wood material and the shape of the room adapts to the needs and existing literature, Then the benefits of this research can be realized a tool to inhibit the spread of the Covid-19 virus and can be used as much as possible for health workers and people who need it.
 Key Word : Covid-19, Disinfection Chamber , Isolation Room

Development of a Novel Spiral Duct Particulate Matter Separator for Internal Combustion Engines

In compliance with the stringent BS-VI emission norms, control of particulate matter in diesel engine exhaust emission is currently achieved through diesel particulate filters, catalytic convertors, and baffle filters of various designs. In the present study a device comprised of a spiral duct with an increasing cross-sectional area over the length is designed and developed. The duct has a lining of heat-resistant and porous material fixed along the inside walls. The inlet of the devices is connected to the outlet of the tailpipe of the exhaust system. The device will collect the particulate matter in the heat-resistant porous lining along the walls of the spiral. The developed device is simple, economical and easily serviceable. The developed spiral duct particulate matter separator was tested on diesel vehicles, and the smoke density of tailpipe emission was measured in terms of the light absorption coefficient. During the analysis it was found that there is a reduction in light absorption coefficient by 25.37%. The developed design also overcomes the clogging problem of the exhaust system, which is a cause of backpressure in the case of conventional particulate filters. The design of the device is such that it can be easily retrofitted in the existing fleet of vehicles, making them compliant with stringent statuary emission norms.

Surface modification of a Mo-substrate to form an oxidation-resistant MoSi2 layer using a Si-saturated tin bath

Molybdenum disilicide (MoSi2) is one of the most heat and oxidation resistant materials used in high-temperature applications. In this work, the feasibility of forming an oxidation-resistant MoSi2 coating using a low-temperature Sn-Si bath by the hot dipping method was evaluated. It was found that a smooth and dense MoSi2 layer can be successfully synthesized on the surface of a Mo-substrate at 700 °C to 1000 °C. Using this method, MoSi2 can be synthesized more rapidly than using conventional methods and at much low operating temperatures. The diffusion through the product layer controlled the growth of the formed MoSi2 layer, and the growth rate was fastest at 800 °C. This was due to the replacement by the larger tin atoms that led to the expansion of the lattice, allowing the faster diffusion of silicon through the silicide layer towards the unreacted Mo-substrate. Oxidation resistance test at 1150 °C for 2 h confirmed that the MoSi2 layer formed by the present method protects the Mo-substrate from rapid oxidation at elevated temperatures.

The skeleton of 5,7-fused bicyclic imidazole-diazepine for heat-resistant energetic materials

In light of the low yields and complex reaction routes of some well-known 5,5-fused and 5,6-fused bicyclic compounds, a series of 5,7-fused bicyclic imidazole-diazepine compounds were developed with high yields by only two efficient steps. Significantly, the seven-membered heterocyclic ring has a stable energetic skeleton with multiple modifiable sites. However, the 5,7-fused bicyclic energetic compounds were rarely reported in the area of energetic materials. Three neutral compounds 1, 2 and 4 were synthesized in this work. To improve the detonation performances of the 5,7-fused neutral compounds, corresponding perchlorate 1a and 2a were further developed. The physicochemical and energetic performances of all newly developed compounds were experimentally determined. All newly prepared energetic compounds exhibit high decomposition temperatures (Td: 243.8–336 °C) and low mechanical sensitivities (IS: >15 J, FS: >280 N). Among them, the velocities performances of 1a (Dv = 7651 m/s) and 4 (Dv = 7600 m/s) are comparable to that of typical heat-resistant energetic material HNS (Dv = 7612 m/s). Meanwhile, the high decomposition temperature and low mechanical sensitivities (Td = 336 °C; IS = 32 J; FS > 353 N) of 4 are superior to that of HNS (Td = 318 °C; IS = 5 J; FS = 250 N). Hence, the 5,7-fused bicyclic compounds with high thermostability, low sensitivities and adjustable detonation performance have a clear tendency to open up a new space for the development of heat-resistant energetic materials.

Self-toughening of epoxy resin by introduction of highly crosslinked thermoset epoxy microspheres

The theories and technologies concerning polyolefin toughening with rubber or inorganic rigid particle have been studied comprehensively, the results indicated that the toughening with rubber always lowers the modulus and heat resistance of materials. Also, toughening with inorganic rigid particle is not good because of its low dispersion and miscibility with epoxy resin. Monodisperse epoxy microspheres (EMs) with high crosslinking density were prepared with Polypropylene glycol with molecular weight of 600 as the reaction solvent and trifunctional epoxy resin (TDE-85) and aromatic diamine (DETDA) as the precursors. The formation of EMs was investigated in detail. The crosslinked microspheres were used as toughening agent to realize DGEBA/DDS system self- toughening. When adding 5wt% epoxy microspheres, the impact strength improved by 87% and Tg increased more than 6 °C. The results show that the prepared epoxy microspheres with high crosslinking density can not only greatly improve the toughness of epoxy resin, but also improve its heat resistance.

Experimental investigations of electrical discharge micro-drilling for Mg-alloy and multi-response optimization using MOGA-ANN

Electric Discharge Drilling (EDD), a spark erosion drilling process, is designed to produce small to large size holes in high-strength and heat-resistant materials with the greatest precision. Magnesium (Mg) based alloy is potential material for biodegradable medical implants, and EDD can be employed to create perforated implants for tissue engineering. The present study was carried out to investigate the EDD process for Mg-alloy using a face-centered central composite design (FCCD) and the effect of input process variables such as discharge current (I p ), spark-on time (T on ), spark-off time (T off ) and work height (WH) have been evaluated on response characteristics; drilling rate (DR), tool wear ratio (TWR) and hole overcut (HO). Analysis of Variance (ANOVA) suggests that Ip, T on , T off and WH are the most significant factor affecting the response characteristics under 95% confidence level. Based on the response surface methodology (RSM), regression equations have been developed between the input process variables and response characteristics. Further, an artificial neural network (ANN) model is developed, and a multi-objective genetic algorithm (MOGA) was utilized to optimize the multi-response objectives. It has been found that the best combination of input parameters while using RSM is: Ip; 4 amp, T on ; 30 µs, T off ; 48 µs, WH: 10 mm, and the predicted values of DR, TWR and HO were Ip; 129.22 mm/min, TWR; 0.142 and HO; 87.26 µm respectively whereas in the Multi-objective Genetic algorithm artificial neural network (MOGA-ANN) hybrid technique, optimal balance results achieved are DR of 142.527 mm/min, with TWR and HO 0.168, 98.258 µm respectively at optimal input parameters. The optimal results obtained with MOGA-ANN are validated experimentally.

Microstructure design to achieve optimal strength, thermal stability, and electrical conductivity of Al-7.5wt.%Y alloy

Aluminum-rare earth (Al-RE) alloys are being increasingly evaluated as new generation heat resistant conductor materials owing to their superior thermal stability, which is attributed primarily to the limited solubility of RE elements in the Al matrix and resulting RE-containing eutectic intermetallic compounds formed in their microstructure. This paper describes the main results from an experimental investigation into tailoring the contrasting strength-electrical conductivity characteristics of an Al–Y eutectic alloy by manipulating several microstructural features using multi-passes cold drawing and annealing processes. High strength of the alloy was achieved not only owing to substantial grain refinement, high dislocation density, and β-Al3Y intermetallic phases but also by forming stacking faults and inducing <111> fiber texture via cold drawing. The alloy was found to preserve fine grains in its annealed state, which is attributed to the β-Al3Y intermetallic phases at grain boundaries stimulating nucleation but also preventing grain growth. Moreover, <111> fiber texture and some stacking faults remained stable during annealing, while the β-Al3Y intermetallic phases spheroidized. As a result, the alloy exhibited extraordinary thermal stability with some loss of strength originating mainly from the reduction in dislocation density upon annealing. Importantly, the novel Al–Y wires exhibit superior heat resistance over the commercial Al–Zr wires. Finally, electrical conductivity of the Al–Y wires improved with annealing, which is primarily due to the release of interfacial energy accompanying spheroidization of β-Al3Y phases and underlying decrease in interfacial scattering at β-Al3Y/α-Al interfaces.

ANALYSIS OF DESIGN OF THE ROLLERS OF THROUGH FURNACES OF ROLLING MILLS

Furnace rollers are the most expensive part of the through-type furnaces, which determine the efficiency of the whole furnace unit. The features of design of rollers that are used at different temperatures of the working space of the furnace were considered. At temperature up to 1000 °C the rollers are used without water cooling (“dry”) or with cooling only of trunnions. With increase in temperature in the furnace up to 1250 °C the rollers with cooled shaft are used. It is shown that the operating costs of the through-type furnaces of rolling mills depend on the durability of the rollers and the costs associated with their cooling. Application of modern heat-resistant materials for manufacturing of furnace rollers enable to eliminate the necessity of their cooling in the furnaces with the temperature of working space up to 1250 °С and to reduce operating costs at the expense of saving of technological fuel for furnace heating. It is noted that the use of “dry” furnace rollers at furnace temperatures up to 1250 °C would require more expensive refractory materials, which will increase their cost. Therefore, it is important to select the correct material strength criteria for the barrel rollers in the design, taking into account the demanding operating conditions of the rollers. Based on the analysis of the process loads on the furnace rollers, the strength criterion is the conditional yield strength of the barrel material at the operating temperature and a safety margin of 3.5.

High-temperature flexible WSe2 photodetectors with ultrahigh photoresponsivity

The development of high-temperature photodetectors can be beneficial for numerous applications, such as aerospace engineering, military defence and harsh-environments robotics. However, current high-temperature photodetectors are characterized by low photoresponsivity (<10 A/W) due to the poor optical sensitivity of commonly used heat-resistant materials. Here, we report the realization of h-BN-encapsulated graphite/WSe2 photodetectors which can endure temperatures up to 700 °C in air (1000 °C in vacuum) and exhibit unconventional negative photoconductivity (NPC) at high temperatures. Operated in NPC mode, the devices show a photoresponsivity up to 2.2 × 106 A/W, which is ~5 orders of magnitude higher than that of state-of-the-art high-temperature photodetectors. Furthermore, our devices demonstrate good flexibility, making it highly adaptive to various shaped surfaces. Our approach can be extended to other 2D materials and may stimulate further developments of 2D optoelectronic devices operating in harsh environments.

Increasing the efficiency and reliability of gas turbine power plants through the use of additive technologies

The article is dedicated to the study of the feasibility of increasing the efficiency, reliability and manufacturability of existing gas turbine power plants with additive technologies that allow creating recuperators with regeneration degrees of 90...95%. The characteristics are presented for the following gas turbine power plants: TEEDA (Iran) 3.13 MW, ODK Perm Motors GTU-4P (Russia) 4.13 MW, Siemens SGT-100 (Germany) 5.1 MW, Solar Turbines Taurus 60 (USA) 5.67 MW. The research was carried out using the methods and programs of the Higher School of Power Engineering for the calculation of thermal circuits of GTPP. The dependences of effective efficiency, work ratio, effective specific work and specific consumption of conventional fuel of GTPPs under examination on compressor pressure ratio and regeneration factor are obtained. Solving the problem of increasing the regeneration factor in GTPP (above 0.9) requires the development of special designs of heat exchanger matrices of the recuperator, which is only possible with the use of additive technologies and new heat-resistant materials. Promising recuperators have a more complex design of heat exchange matrices, which ensures their being very compact. Such technical solutions can ensure the development and creation of fundamentally new designs of GTPP heat exchangers and significantly improve their technical characteristics.

Study of the structural changes in oxide ceramics using polarization microscopy

The mechanical and thermal properties of heat-resistant ceramic materials based on refractory oxides largely depend on the defect-free nature of their crystal structure, the presence of extraneous phases, the size and orientation of the grains. We present the results of studying the structure of ceramic fibers of mullite-corundum composition during high-temperature heating using optical polarization microscopy. The structural features of a continuous fiber of Al2O3 – SiO2 system heat-treated in a free state and under tension, as well as the structure of short fibers of a similar composition obtained by injecting a solution with subsequent heat treatment of the fiber mass at different temperatures were studied. It is shown that the structure of a continuous fiber after heat treatment in the free state has a multidirectional orientation of the grains, whereas heat treatment at the same temperatures under tension leads to the formation of an oriented uniaxial structure. Thus, the fibers obtained from the same solution and heat-treated at the same temperatures are characterized by different strength values. Moreover, the strength of a fiber with an oriented uniaxial structure is one and a half times higher than that of a fiber with a multidirectional grain orientation, which greatly facilitates its further processing. It is also revealed that structural defects like incomplete crystallization, collective recrystallization, and inhomogeneous inclusions of the second phase, characteristic of short fibers obtained by nozzle spraying, negatively affect the thermal properties of thermal insulation made of such fibers. The results obtained can be used to improve the methods of analyzing the microstructure of aluminum oxide fibers using the method of optical polarization microscopy.