news

With the increasing demand for new materials with excellent high-temperature performance in modern industry and the continuous breakthroughs in sintering technology, the development speed of silicon nitride ceramics has significantly increased, and their applications have become more widespread.

① Substrate material

Compared to other ceramic materials, silicon nitride ceramics have many excellent characteristics, with theoretical thermal conductivity up to 200-320W/m · K. At the same time, silicon nitride has good chemical stability, high resistivity, low dielectric loss, low expansion coefficient, high bending strength, and fracture toughness. These characteristics make it considered a promising heat dissipation and packaging material for high-speed circuits and high-power devices.

② Bearing material

Rolling fatigue life is an important indicator for measuring the performance of bearing materials. Silicon nitride ceramics have the characteristics of low density, low coefficient of thermal expansion, high elastic modulus, high compressive strength, high temperature resistance, corrosion resistance, excellent chemical stability, self-lubrication, long service life, and low temperature rise. Among common structural ceramics, the rolling fatigue life of silicon nitride is significantly higher than that of materials such as zirconia, silicon carbide, and alumina, and it is also the most suitable ceramic material for bearing materials. Silicon nitride precision ceramic bearings have been increasingly applied in precision transmission systems such as electroplating equipment, high-speed machine tools, medical devices, chemical equipment, low-temperature engineering, and wind power generation.

③ Grinding materials

Silicon nitride has a high hardness, second only to a few superhard materials such as diamond and cubic boron nitride. Low friction coefficient, self-lubricating properties, similar to metal surfaces lubricated with oil. In the ultra-fine powder and food processing industries, the performance of silicon nitride ceramic grinding balls is higher in hardness and superior in wear resistance compared to traditional grinding balls. Due to its very low consumption, it reduces the grinding cost and powder pollution level.

④ Metallurgical materials

Silicon nitride ceramic materials have excellent chemical stability and mechanical properties, and can be used as components in thermal equipment such as crucibles, burners, and aluminum electrolytic cell liners in the metallurgical industry. Silicon nitride ceramics have good oxidation resistance. The antioxidant temperature can reach up to 1400 ℃. Stable in a dry oxidation atmosphere below 1400 ℃, with a usage temperature of up to 1300 ℃. And silicon nitride materials can be used in environments with rapid cooling and heating, so they are also widely used in the metallurgical industry.

⑤ Mechanical Engineering

Silicon nitride ceramics can be used as turbine blades, mechanical sealing rings, high-temperature bearings, high-speed cutting tools, permanent molds, etc. in the mechanical industry. Many equipment in the traditional mechanical industry uses metal materials. Due to the existence of defects such as high temperature resistance, wear and corrosion in metals, the reliability and service life of these equipment will be greatly affected. Silicon nitride ceramic materials have excellent wear resistance, corrosion resistance, and high-temperature thermal shock resistance, which can replace metal materials and be applied in the mechanical industry.

2、 Preparation of high-performance silicon nitride ceramics:

① Selection of Silicon Nitride Powder

Silicon nitride powder mainly includes α- Si3N4 powder and β- There are two types of Si3N4 powders. The main preparation methods for commercial silicon nitride powder on the current market are:

Silicon powder direct nitriding method. The direct nitriding method of silicon powder is relatively mature in industrial production, capable of large-scale production, and has relatively low production costs. Therefore, most domestic and foreign enterprises use this method to produce silicon nitride powder. However, the drawback of this method is that the silicon nitride powder produced by it is prone to containing impurities such as Fe, Ca, Al, etc.

● Silicone imine pyrolysis method. The silicon nitride powder prepared by this preparation method has extremely high α The phase content and excellent sintering activity are very suitable for the sintering and preparation of high-performance silicon nitride ceramics. This method has the following characteristics: the produced Si3N4 powder has good crystallinity, and through appropriate heat treatment system regulation, it can obtain Si3N4 powder with hexagonal equiaxed grains; The prepared Si3N4 powder has a high α Phase content (>95%), low oxygen content (<2.0%), and it does not contain metal impurities, resulting in high sintering activity; The produced silicon nitride powder is relatively fine, with a size distribution of 0.2-1.0 μ m. And the production is huge.

② Selection of sintering additives

Silicon nitride ceramic sintering aids are mainly divided into two categories: metal oxides and rare earth oxides. There are mainly magnesium oxide, rare earth oxides (such as yttrium oxide), and composite sintering aids (such as Y2O3-Al2O3). During the sintering process of silicon nitride ceramics, composite sintering aids Yb2O3 MgSiN2 and Yb2O3 MgO were added to prepare high thermal conductivity silicon nitride ceramics. Research has found that the thermal conductivity of silicon nitride ceramics using MgSiN2 as a sintering additive has increased by about 15%. Research has shown that adding Yb2O3 as a sintering aid during the sintering process of silicon nitride ceramics will be beneficial for the growth of silicon nitride grains, resulting in a larger aspect ratio. Moreover, with the increase of Yb2O3 addition, the coarsening phenomenon of silicon nitride grains becomes more obvious; A composite sintering aid composed of two or more additives can improve liquid viscosity, increase softening temperature, and high-temperature performance. For example, after fully mixing MgO-Al2O3-SiO2 as an additive with Si3N4 powder, at 1730 ℃ × Under normal pressure sintering for 3 hours, the room temperature bending strength of Si3N4 ceramics reached 1.06 GPa, microhardness 14.2 GPa, and fracture toughness 6.6 MPa · m1/2. Rare earth oxides Nd2O3, Sm2O3, Dy2O3, and MgO can be used as composite sintering aids to β- The particles of Si3N4 have a high aspect ratio, thereby improving the fracture toughness of the material.

③ Selection of sintering method

At present, the main sintering methods used for silicon nitride ceramics include hot press sintering, gas pressure sintering, discharge plasma sintering, etc. These sintering methods have their own advantages in the sintering application of silicon nitride ceramics.

Hot pressing sintering is a sintering method that promotes sample sintering by applying mechanical pressure. This method fills the ceramic powder into the mold cavity, applying mechanical pressure while also heating the filled powder to the firing temperature. Due to the presence of external mechanical pressure, the sintering driving force is increased, making it easier for the sample to achieve higher density. This makes it easier for hot pressing sintering technology to prepare ceramic materials that are difficult to sinter, such as many covalently bonded ceramic materials.

Gas pressure sintering is a sintering method that combines a certain gas pressure during the high-temperature sintering process of ceramics. The gas pressure is generally maintained at 1-10MPa to prevent the decomposition and weight loss of ceramic materials under increased sintering temperature conditions, thus preparing ceramic products with high density.