Materials Science Forum Vol. 1036

Abstract: Graphite is a strategically scarce resource, and the preparation of high-purity graphite is the prerequisite and basis for the application of graphite. In order to determine the optimal purification technology parameters of an ultra-large flake graphite mine pneumatic separation ore with a fixed carbon content of 77.69%, a particle size of mainly 10 to 40 mesh, and main impurities of calcium carbonate, iron oxide and silica , two additional experiments of acid method and alkali method were added on the basis of alkali-acid method, to investigate the purification effect of different technological processes and acid leaching times on graphite raw materials, as well as to analyze the retention extent of different methods and alkali fusion temperature on graphite ultra-large flake structure. The results show that all three methods can increase the fixed carbon content of graphite to above 99%. However, compared with the acid method and the alkali method, the alkali-acid method can obtain high-purity graphite while also better protecting the graphite's ultra-large flake structure. The optimal fusion temperature is 400 °C, the optimal acid leaching time is 30% sulfuric acid thrice and 5% hydrofluoric acid once. After purification, the fixed carbon content of the product exceeds 99.97%.

Abstract: It is usually necessary to first perform temperature reduction treatment to enable the catalyst to exert its catalytic activity in the subsequent process of preparing carbon nanotubes by chemical vapor deposition. In this experiment, Fe-Mo/Al₂O₃ catalyst was prepared based on microreactor, and the effect of reduction temperature on the microstructure of the catalyst and the morphology of carbon nanotubes was investigated. The results show that the reduction temperature has a significant effect on the microstructure of the catalyst, which in turn affects its catalytic activity and the yield and quality of carbon nanotubes. Moderately reducing the reduction temperature during the catalyst reduction process is beneficial to increase the catalytic activity of the catalyst. However, although its sintering degree could be weakened when the catalyst was reduced at an excessively low temperature of 350 °C, its catalytic efficiency was greatly reduced and the degree of defects of the catalyzed carbon nanotubes was increased. When the catalysts calcined at 450 °C and reduced at 600 °C, the catalysts show excellent catalytic activity, and catalytic efficiency can reach 74.76%. In addition, the reduction temperature also has a certain effect on carbon nanotubes. As the reduction temperature increases, the span of carbon nanotubes is relatively concentrated, but the specific gravity of the thicker outer diameter gradually increases. As for the defect degree of carbon nanotubes, the carbon nanotubes M_600-600 is better and the defects are fewer when the reduction temperature is reduced from 670 °C to 600 °C.

Abstract: Straw fiber (SF)/polylactic acid (PLA) composites were prepared from SF and PLA. The effects of the composite SF/PLA mass ratio investigated in terms of mechanical properties, water resistance, crystal structure, and thermal properties were investigated. These composites were characterized by scanning electron microscopic (SEM), X-ray diffractometric (XRD), differential scanning calorimetric (DSC), and thermogravimetric analyses (TGA). The results showed that, when the SF/PLA mass ratio was 3/7, the mechanical properties and water resistance of these composites were the best. When the mass ratio exceeded 3/7, the interface compatibility in the composites decreased. As the SF/PLA mass ratio increased, the crystallinity and the heat resistance of the composites were decreased.

Abstract: In order to prepare carbon nanotubes with high specific surface area, small diameter, low resistivity, high purity and high catalytic activity, the Fe-Mo/Al₂O₃ catalyst was prepared based on the microreactor. The influence of different Fe/Al molar ratios on the catalyst and the carbon nanotubes prepared was studied through BET, SEM, TEM and other detection methods. Studies have shown that the pore structure of the catalyst is dominated by slit pores at a lower Fe/Al molar ratio. The catalytic activity is the highest when the Fe/Al molar ratio is 1:1, reaching 74.1%. When the Fe/Al molar ratio is 1:2, the catalyst has a higher specific surface area, the maximum pore size is 8.63 nm, and the four-probe resistivity and ash content of the corresponding carbon nanotubes are the lowest. The higher the proportion of aluminum, the higher the specific surface area of the catalyst and the carbon nanotubes, and the finer the diameter of the carbon nanotubes, which gradually tends to relax. The results show that when the Fe/Al molar ratio is 1:2, although the catalytic activity of the catalyst is not the highest, the carbon nanotubes prepared have the best performance.

Abstract: The graphene-based composites was prepared by the oxidation of graphene nano-platelets. The characterization results of thermogravimetric analysis (TGA) and Fourier transform infrared spectrum (FT-IR) indicated that acid treatment can generate abundant functional groups on the surface of graphene. The determined equilibrium adsorption capacity of FGN for lead was 57.765 mg/g, which is higher than that of many currently reports. The adsorption process was completed within 40 min and the adsorption isotherms confirmed to Langmuir classical isotherms models.

Abstract: A new type of water-soluble coal dust suppressant (later called MA) with excellent performance was prepared by modified starch, styrene, methyl methacrylate, Butyl acrylate (as the main monomers) and acrylic acid (as the functional monomer) via mixed the emulsifiers of Sodium dodecyl sulfate (SDS)/octylphenol polyoxyethylene(10)ether (OP-10) and ammonium persulfate served as initiator. The properties of anti-wind erosion, water retention and coal quality impact were investigated. The MA was characterized by viscosity measurements and scanning electron microscopy. The results show that the spraying of MA has no effect on coal quality, and the water loss rate of MA is slightly lower than that of water, which has certain moisture retention. After spraying MA on the surface of coal sample for 120 hours, the coal sample is swept by six-stage wind (wind speed is 10.8-13.8 m/s), and the erosion rate is only 1.8%. The MA and coal samples are closely bonded to form a dense soft film, which has a excellent dust suppression effect.

Abstract: Ceramic particle reinforced iron-based alloys have been widely used in aerospace, land transportation and other aspects, so it has attracted tremendous attention. Aiming at the preparation and interfacial reaction of ceramic particle reinforced iron-based alloys, the preparation methods for interfacial reactions, reinforcement selection and design of ceramic particle reinforced iron-based alloys are introduced in this paper. Combined with the recent studies on ceramic particle reinforced iron-based alloys, this paper focuses on the ceramic particle reinforced iron-based interface and strengthening models/mechanisms, based on existing research, prospects for further ceramic particle reinforced iron-based alloys were studied.

Abstract: Be aimed at the development and application of aerospace high-temperature resistant ceramic fiber felt, in this paper, as the common ceramic fiber felt in the field of high temperature resistance, quartz fiber felt, high silica fiber felt and mullite fiber felt were compared. The microstructure, thermal insulation, temperature resistance and mechanical properties were analyzed respectively, the performance advantages and disadvantages of three kinds of ceramic fiber felt were given, and its internal causes were studied. The results show that, the temperature resistance of mullite fiber felt is better than that of quartz fiber felt and high silica fiber felt, mainly due to its polycrystalline mullite structure, the thermal insulation performance of mullite fiber felt and high silica fiber felt is better than quartz fiber felt at high temperature, mainly due to the thermal reflection of polycrystalline mullite and the small pore structure of high silica fiber felt, the compressibility of quartz fiber felt is better than high silica fiber felt and mullite fiber felt.

Abstract: Aiming at the thermocapillary convection stability of sapphire crystal grown by liquid-encapsulated Czochralski method, by non-linear numerical simulation, obtained the flow function and temperature distribution of R-Z cross section, as well as the velocity and temperature distribution at liquid-liquid interface and monitoring point of B₂O₃/sapphire melt in annular two liquid system, covered with solid upper wall and in microgravity. By means of linear stability analysis, obtained the neutral stability curve and critical stability parameters of the system, and revealed the temperature fluctuation of the liquid-liquid interface. The calculated results of B₂O₃/sapphire melt were compared with 5cSt silicone oil/HT-70. The results show that under the same geometrical conditions, the flow of B₂O₃/sapphire melt system is more unstable than 5cSt silicone oil/HT-70, there are two unstable flow patterns, radial three-dimensional steady flow cell and hydrothermal waves near the hot wall. The larger the ratio of Pr number of upper and lower fluid layers is, the better the effect of restraining the flow of lower fluid layers is.

Abstract: Compared with traditional ceramics, Si₃N₄ ceramics have the characteristics of high theoretical thermal conductivity, high thermal shock resistance, high oxidation resistance, high strength, and strong current carrying capacity. It is a potential high-speed circuit and high-power device for heat dissipation and heat dissipation. Sealing material. For applications in 5these fields, β-Si₃N₄ with a relatively stable structure and high thermal conductivity is an ideal material. However, β-Si₃N₄ powder is difficult to sinter as a raw material. Therefore, the prepared Si₃N₄ generally has a low density, and there are various defects in the crystal. The existence of these defects will cause interference and scattering of heat in the transfer process. Limits the application of β-Si₃N₄ ceramics. Studies have shown that the introduction of different additives can form a liquid phase at high temperatures, which can effectively reduce the firing temperature of the sample and increase the density. At the same time, it can also remove lattice oxygen, weaken the intercrystalline phase, and promote the α→β phase transition. Thereby improving the thermal conductivity and sintering performance of Si3N4 ceramics. Therefore, this article reviews the types of additives and their effects on the properties of Si₃N₄ ceramics and their mechanism. Trying to find an additive system for the preparation of high thermal conductivity Si₃N₄ ceramics with excellent comprehensive performance, hoping to provide help for the work and researchers engaged in the research on the thermal conductivity of Si₃N₄ ceramics.