Silicon Nitride Work Stress Discussion and Its Burning Point Calculation
The Si3N4 firing curve Mangels proposed a nitridation system with a temperature increase of 0/kWh. In this process, only the standard furnace pressure, the initial and final nitriding system, the heating rate and the gas feed rate are determined in advance, and the temperature increase is controlled by using the nitriding gas pressure in the furnace as a parameter. After nitriding begins, if the furnace pressure is less than the control pressure for a certain period of time, the nitriding reaction is ongoing and the furnace temperature should be maintained. If the furnace pressure is greater than the control pressure, the reaction basically reaches a equilibrium and it is necessary to start the temperature increase again until The next drop in furnace pressure is detected. The final nitridation temperature will be lower than the melting point of Si, the nitridation gas is quasi-static, and the entire nitridation process is essentially not vented. Nitriding speed of this process is relatively uniform, which overcomes the disadvantages of stepwise temperature rise. The growth mechanism of Si3N4 The mechanism of Si reaction to generate Si3N4 is relatively complicated. So far, there is no complete theory of nitriding mechanism that can be universally accepted by researchers. Through reasonable simplification, the general steps of Si nitriding are as follows: 1 Stage 1, The nitrogen molecules in the gas phase diffuse to the Si surface through the gas phase boundary layer and undergo a chemical reaction to generate a thin layer of Si3N4. This process is controlled by the chemical reaction. In the second stage, N2 diffuses to the Si3N4/Si surface through a thin layer of Si3N4. Si undergoes a chemical reaction. The Si3N4/Si interface extends to the inner layer over time. The rate of the nitridation reaction is controlled by chemical reaction and diffusion. In the third stage, Si3N4 has a considerable thickness, and the diffusion path of N2 is longer than that of chemical reaction. The reaction, diffusion 1 becomes the limiting part of the entire nitriding reaction, so the nitriding reaction rate is controlled by diffusion. During the reaction to produce Si3N4 bonding agent, SiC does not react with N2 and Si3N4 chemically, regardless of its influence. Nitride Kinetics of Si Gas-Solid Reaction Kinetics is a factor that discusses the gas-solid reaction rate and the rate of influence, including chemical reactions, diffusion, and adsorption. Therefore, the total reaction rate should be composed of the various reaction rates that make up it, and it should be controlled by the slowest partial velocity. There have been many studies on combustion, carbon-thermal reduction, plasma nitridation, chemical vapor deposition, and various nitridation methods using ammonia, but the study of the nitriding kinetics of Si in reaction sintering less. Since the green body contains impurities such as O and Fe, N2 contains O2 and H2O impurities, and such impurities have a greater influence on the reaction, making the kinetic laws of Si3N4 generation from Si nitrides observed by different researchers different. There is a continuous decrease in linear, parabolic, logarithmic, and dynamic (study). Li Liben et al. analyzed the high-temperature nitriding kinetics of Si from a macroscopic perspective based on the gas-solid reaction kinetics principle, and proposed a 3-segmental model (shown): 1 Initial nitriding, chemical reaction controlling speed: vW/A = 0.0023 + KCt where: vW/A is the weight gain per unit area of ​​the sample, KC is the rate constant of the nitridation reaction controlled by the chemical reaction rate, and t is the nitridation time vW/A) 2 = -0.0267 + KDt where: KD Diffusion rate control of the nitriding reaction rate constant. The relationship between nitriding amount and time According to the model, the experimental data were processed by least squares method, and the empirical relationship between the nitriding reaction rate constant and temperature T(K) at each stage was fitted, and a satisfactory correlation coefficient was obtained. Si-Nano-Nitration Depths Bu Jing-Long establishes a nitriding kinetic model for Si particles microscopically, as shown. N2 flows along the pores to the surface of the Si particles. As the pores are large, the flow resistance is negligible. Assuming that the Si particles are ideally spherical, the particle size is uniform, the radius is R, the outer ring is the product Si3N4, and the nitriding depth is X. N2 passes through the product layer and diffuses to the Si3N4/Si interface, where it reacts chemically with Si. The simulation of the temperature field of Si3N4-SiC material during the firing process of Si3N4-SiC materials at home and abroad is more research, but the temperature field of the firing process of refractory materials has not yet been reported. Since the temperature directly affects the nitridation process of the firebrick, how to effectively control the rate of temperature rise to uniformize the Si particles and strictly control the nitriding temperature below the melting point of Si is the key to improving product quality. With the help of the numerical simulation of the temperature field, it is also possible to analyze the operating conditions of the kiln, make a reasonable evaluation of its stability and economy, and further optimize the process parameters, so that the kiln can operate in a safer and more economical state, thereby prolonging the equipment. The service life, reduce the cost of conversion, provide protection for energy saving. Conclusion Increasing the research on the formation mechanism of Si3N4 can provide a more economical nitriding process. Combining with the nitriding kinetics of Si, the temperature field of the firing process of Si3N4-SiC material can be simulated, and then the quality of refractory bricks can be improved and the process parameters can be optimized to achieve the purpose of energy saving. With the deepening of research, the application of Si3N4-SiC refractories will continue to expand. Globe Valves ,Globe Valve ,Globe Valve Types,Y Pattern Globe Valve WENZHOU DIYE VALVE&FITTINGS CO.,LTD , https://www.diye-valve.com