Characteristics and Structure of Silicon Carbide Ceramic Tubes and Performance Characteristics of Silicon Carbide Ceramic Matrix Composites
Time:2019-09-20
Views:4151
The silicon carbide ceramic tube is high in temperature and high in high temperature environment, and is widely used in the field of national economy and people‘s livelihood. The silicon carbide ceramic tube is a compound with strong covalent bond, and the ion type of the Si--C bond is only about 12%. It also has excellent mechanical properties, excellent oxidation resistance, high abrasion resistance and low friction coefficient.
The biggest characteristic of SiC ceramic tube is high temperature strength. The strength of ordinary ceramic materials will be significantly reduced at 1200 ~ 1400 ° C, while the flexural strength of silicon carbide at 1400 ° C is still maintained at a high level of 500 ~ 600 MPa, so its work The temperature can reach 1600 ~ 1700 degrees Celsius.
The silicon carbide ceramic tube has excellent mechanical properties, excellent oxidation resistance, high abrasion resistance and low friction coefficient.
Crystal structure of silicon carbide ceramic tube:
Silicon carbide has two main crystal structures, namely cubic β-SiC and hexagonal-SiC.
The basic structural unit of a silicon carbide crystal is a SiC and CSi tetrahedron interpenetrated with each other. The tetrahedrons form a planar layer with a common edge and are connected to the next stacked tetrahedron to form a three-dimensional structure. Hundreds of variants have been discovered due to the different order in which the tetrahedral stacking order can be formed. Generally, the letters C (cubic), H (hexagonal), and R (Rhombic) meters are used to indicate the lattice type, and the number of layers included in the unit cell is used to distinguish, for example, nH indicates that there are n layers of repetition along the c-axis. The hexagonal crystal structure, and mR represents a rhombohedral structure having a m-layer repetition period along the c-axis.
Silicon carbide is synthesized at high temperatures, so silicon carbide ceramic tubes are often prepared at high temperatures or used at high temperatures.
If only a rough calculation is made, the average thermal expansion coefficient of silicon carbide can be 4.4×10-6/°C in the range of 25 to 1400 °C. The measurement results of the thermal expansion coefficient of silicon carbide show that the amount is much smaller than that of other abrasives and high temperature materials. For example, the thermal expansion coefficient of corundum can be as high as (7~8)×10-6/°C. SiC has a high thermal conductivity, which is another important feature of the physical properties of SiC ceramic tubes.
Its thermal conductivity is much larger than other refractory materials and abrasives, about four times the thermal conductivity of corundum. Therefore, silicon carbide has a low coefficient of thermal expansion and a high thermal conductivity, so the thermal stress of the silicon carbide ceramic tube during heating and cooling is small, which is why the silicon carbide ceramic tube is particularly good in thermal shock resistance.
The silicon carbide ceramic-based composite material refers to a silicon carbide fiber introduced into a silicon carbide ceramic matrix as a reinforcing material, and a composite material in which the silicon carbide reinforcing fiber is introduced as a dispersed phase and the silicon carbide ceramic substrate is a continuous phase is formed. What are its performance characteristics?
The silicon carbide ceramic matrix composite retains the advantages of high temperature resistance, high strength, oxidation resistance, corrosion resistance and impact resistance of the silicon carbide ceramic. At the same time, it has the reinforcing and toughening effect of the silicon carbide fiber, and overcomes the low fracture toughness and external resistance of the silicon carbide ceramic. Congenital defects with poor impact load performance. This material can be kept at a high temperature of 1316 ° C without deterioration of its physical and chemical properties. When the surface of the silicon carbide material is sprayed with a thermal barrier coating, its maximum operating temperature can continue to increase to 1480 °C.
Although the temperature of the modern commercial engine turbine can reach 1650 ° C, the additional 170 ° C temperature difference needs to be compensated by the compressor bleed air cooling, but this air volume is greatly reduced compared with the blade using the traditional high temperature alloy material. According to preliminary calculations, high-pressure turbine blades with CMC materials with a temperature resistance of 1480 °C can reduce engine fuel consumption by 6%. At the same time, the amount of cooling gas required for the high temperature gasket of the combustion chamber made of CMC material is also greatly reduced, thereby reducing the chance of incomplete combustion of nitrogen oxides after the cooling air is mixed with the fuel, and the NOx emission reduction potential can be Up to 33%.
Silicon carbide ceramic matrix composites are widely used, their temperature can reach 1450 °C, high temperature strength, light weight, corrosion resistance, and many advantages can improve the performance of the engine, so it can be used in the field of aero engines. Silicon carbide ceramic matrix composites have the potential to replace metals as a new generation of high temperature structural materials.
Founded in 2006, Shenzhen Haorui Industrial Technology Co., Ltd. is a professional enterprise engaged in R&D, manufacturing and sales of non-standard industrial ceramics, hard alloys (tungsten steel) and various metal and non-metal precision machinery parts.
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