At present, the heat-resistant parts of automobile internal combustion engines are made of nickel-based heat-resistant materials, and the working temperature is around 1000 °C. If ceramic materials are used, the working temperature can be increased to 1300 °C, which increases the engine efficiency by about 30%. Ceramics have high high temperature strength and thermal conductivity to extend the life of the engine.
Silicon nitride ceramic features
Silicon nitride is a new type of ceramic material with high strength, high hardness, corrosion resistance, high temperature resistance and other characteristics. These properties are mainly derived from the chemical bonding of ceramics. Ceramics can be divided into two categories: oxides and non-oxides. Non-oxides are mainly bonded by covalent bonds, while oxides are mostly bonded by ionic bonds and covalent bonds. Metals formed by free electrons Compared with bonding, ionic bonds, especially covalent bonds, are strong, and are not easily deformed and cut. Substances with strong covalent bonds generally have the characteristics of low density, high hardness, high elastic coefficient and fracture stress. In addition, covalent bonds are affected by temperature. The effect is small, so the high temperature resistance of non-oxide ceramics is good.
Silicon nitride ceramics have good chemical stability because they are covalent compounds with high bond strength and can form an oxide protective film in the air. further oxidation.
Silicon nitride ceramic process
In order to ensure the quality of bad parts in hot press injection molding, attention should be paid to controlling the temperature of wax slurry, slurry feeding pressure, pressure time and mold temperature during molding. The feeding pressure is generally 0.3-0.5MPa. The pressure affects the feeding speed. The pressure value can be determined according to the viscosity of the wax slurry and the size of the blank. The appropriate pressure time can ensure that the slurry is fully filled. The mold cavity can also supplement the volume shrinkage generated by the condensation process to obtain a complete and dense bad body. Usually, the small body is pressurized at 0.3-0.4MPa for 5-15s, and the large body is pressurized at 0.4-0. .5MPa under pressure for about 60s. The mold temperature directly affects the speed and quality of condensation. It is also related to the size of the blank. Usually, the thick-walled and simple-shaped blanks are injected, and the mold temperature is lower, while the complex-shaped and thin-walled blanks are injected. The temperature can be higher, and the general mold temperature is between 20 and 30. Extrusion is suitable for the production of long-sized rod-shaped and tubular products and the shapers with the same cross-section (for the production of honeycomb ceramics). This forming method is efficient, easy to operate, and can continuously produce * The surface of the green body is smooth and regular. The extruded billets with good quality can be used as porcelain materials mainly made of chemical raw materials after being shrunk and stale, and organic binders (such as methyl cellulose, flour, dextrin, etc.) should be added for plasticization.
