Ultra-fine Treatment Of SiC Powder, Addition Of Sintering Additive And Their Effects On Preparation Of Siclicon Carbide Ceramic

Silicon carbide (SiC) has been recognised as an important structural ceramic with high hardness, high strength, high-temperature resistance, chemical and high thermal conduction and low thermal expansion, and many advantages, and widely applied in many industries. The sintering, structure and properties of silicon carbide ceramic are related to raw materials sysnthesization, moulding methods, sintering processes and additions and so on. At present, the improvement of silicon carbide ceramics' performances are limited by raw materials with big granularity, wide particle-size distribution, seriour reuniting, more impurties, worse moulding and sintering behaviours, which are disadvantageous for the application of silicon carbide materials.On the basis of reviewing the present statu of SiC powder preparation and ceramic sintering, ultr-fine treatment of SiC powder was carried out by new jet mill to obtain fine powder with small size, narrow particle-size distribution and no reuniting. With the synthesization of YAG (Y3Al5O12) fine powder, YAG sintering additives was added into SiC powder by sol gel method to prepare SiC/YAG composite powder with homogeneous phase distribution, which decreased the sintering temperature and enhanced the sintering properties. The researches were important for offering the reference for the production of silicon carbide ceramic.The super-fine treatment of SiC powder was carried out by fluidized bed opposed jet mill (QLM-100K), and the results showed that the effects of super-fine treatment increased with the increase of sorter frequency and crushing pressure. A better grinding effects was achieved by using a higher sorter frequency (40 Hz), a higher crushing pressure (0.7 MPa) and few milling tims (only once); compared with these before treatment, the average particle size of SiC powder decreased from 3.01 μm to 0.75 μm, two peaks of particle-size distribution (0.4~1.5μm and 8~23 μ m) became one peak (0.4-1.2 μm), distribution width decreased from 25.125 to 0.833, and the super-fine treatment had a better effect for SiC powder. The compacts had relatively high density and microstructure homogeneity; the sintering temperature of the compact decreased; and the surface microstructure, densification and mechanical properties of the sintered body could be ameliorated obviously. Compared with these before treatment, hardnessof silicon carbide ceramics increased from 2.05GPa to 2.60Gpa, and fracture toughness from 3.1 MPa·m1/2 to 3.8 MPa·m1/2, and bending strength 353 MPa to 420 MPa.Yttrium aluminum garnet (Y3Al5O12, YAG) and SiC/YAG composite powder were synthesized by sol-gel method with inexpensive aluminum nitrate and yttrium nitrate as starting materials. The results showed that the YAG gel assumed network structure, the formation procedure of YAG was amorphism—YAM—YAP—YAG; the complete YAG phase could be attained after the dried gel being heat-treated at 920°C, the atom ratio of Al and Y was about 3:5; and YAG fine powder with small granularity (200nm) and narrow particle size distribution was prepared. During the preparation process of YAG, SiC powder were added into the sol, the SiC particles were embedded in the gel network, which form the thin film on the surface of SiC particle. The additives could be uniformly distributed into SiC powder after drying and calcining to prepared SiC/YAG composite powder uniform distribution of fine YAG phase.The densification of SiC composite powders was carried out by vacuum pressureless sintering. The results showed that the sintering and mechamical properties of silicon carbide ceamic with 10wt% additive were superior and decreased with increase of sintering temperature. The suitable sintering parameters were: 10wt% of YAG conent, 1860℃ of sintering temperature and 45min of sintering time; under above parameters, silicon carbide ceramic had higher sintering and mechanical properties, its relative density was 98.23%, fracture toughness property was 5.03 MPa·m1/2 and bending strengh reachs 486 MPa. The grain of ceramic was fine with 0.5-2 μ...