Reseach On Particle Size Distribution During The Molding Of Reaction Sintered Silicon Nitride Bonding Silicon Carbide

Reaction bonded silicon nitride/silicon carbide is a kind of refractory with high qualities widely used in ceramics, metallurgy, and so on. This paper investigated the molding of ceramic crucibles and conveying pipes of melted metal which are produced with reaction bonded silicon nitride/silicon carbide. Varying the particle size distribution and cool isostatic pressing, the bulk density of the green body of SIC/Si would rise, and then the bulk density of the sintered material would be increased, while the void volume be reduced. The major contents and conclusions are as follows: 1. The effect of particle size distribution on packing density of silicon carbide with two main sizes was studied. The size of fine particles is between 0.1 and 0.4 mm, while that of the coarse is between 0.5 and 1.2 mm. It was discovered that the packing density is optimized when particle size ratio is greater than 3 and the content of coarse particles is in 60?0%. The optimized packing density rises with the increasing of the size of coarse particles. 2. The results of computer simulation of particle packing phenomena carried by Dennis R. Dinger was applied to study the effect of particle size distribution on packing density of silicon carbide with several main sizes. It was found that the packing of this system is relatively dense when the content of coarse particles (12, 24, and 46 meshes) is about 70%. The relative density of packed, axial pressed, and isostatic pressed is 54%, 69%, and 70% respectively. 3. The content of Si is so high in the particle system of SiC/Si that the effect of the particle size distribution on packing density is decreased. Varying of the contents of different size SiC particles has little effect on the density of packed, pressed, and isostatic pressed. It was discovered that the SiC/Si system would pack relative dense when the content ratio of coarse particles (12, 24, and 46 meshes) to fine particles (90 and 180 meshes) is about 6:4. When the content of Si powder in that system is 25%, the bulk density of the green body isostatic pressed would be increased by about 5% compared with that of axial pressed only, and the relative bulk density of the green body isostatic pressed is about 76%. 4. The samples were analyzed with XRD and SEM after nitrified. It was found that the microstructure of the reaction bonded silicon nitride/silicon carbide is that the coarse SIC II Abstract particles are surrounded by the matrix composed of the fine SiC particle and the reaction produced Si3N4, forming strong physical combination. 5. The radial basis function neural net (RBFNN) was used to simulate the packing of the SiC/Si system with the results of the experimentation and some forecast was made. The width of the basis function is 0.555, and there are 21 nerve cell in the hidden layer. The training error is 0.22%, and the controlling error is 3.58%. This RBFNN can forecast the bulk density of the pressed with relative accuracy and the error between the forecasted and measured is less than ?%. But it can not forecast the packing density of the SiC/Si system credibly, mainly because of the large system error during the measurement. 6. The geometric shape of SiC and Si particles is an important factor affecting the packing. The fractal dimension analysis was made on the two-dimensional silhouette of SiC particles, an...