Study On The Preparation Process Of Andalusite Modified Silicon Carbide Composite Ceramics

Silicon carbide ceramic materials are widely used in mechanical seals,metallurgical chemical industry,high temperature flue gas dust filtration,semiconductors,bulletproof armor,aerospace and other fields,because of their high hardness,good wear resistance,strong chemical corrosion resistance,low coefficient of thermal expansion,and excellent thermal shock resistance.However,due to the strong covalent bond characteristics of silicon carbide and its low diffusion rate during sintering,it is difficult to sinter at low temperatures.Therefore,this article introduces andalusite,relying on the high-temperature transformed mullite and silicon rich liquid phase of andalusite as the bonding phase between silicon carbide particles,thereby enhancing the sintering of silicon carbide ceramic particles.In this way,it does not only optimizing the process,reducing production costs,but also follows our national policy of energy conservation and emission reduction.This topic uses mold pressing to prepare silicon carbide ceramic billets,and then sinter silicon carbide ceramics under normal pressure.It studies the effects of the types of mineralizers,the amount of andalusite,different preparation parameters,and the content of graphite pore forming agent on the physical properties,mechanical properties at room and high temperatures,phase composition,and microstructure of silicon carbide ceramic samples.The main research results are as follows:（1）Through exploring the effects of three mineralizers,5wt%MgO,5wt%TiO₂,and 2.5wt%MgO+2.5wt%TiO₂,on the properties of silicon carbide ceramic samples,it was found that both single mineralizer and binary mineralizers reduced the apparent porosity of silicon carbide ceramic samples,increased bulk density,decreased flexural strength first and then,and improved thermal shock resistance.However,on the other hand,it was also found that single mineralizer made the number of thermal shock resistance of the sample got a limited increase,only 8 times,while the use of 2.5wt%MgO+2.5wt%TiO₂ made the volume density of the sample rise in a step way,and the number of thermal shock resistance that could withstand increased by 18 times.In conclusion,2.5wt%MgO+2.5wt%TiO₂ were considered as the best mineralizing agents for sintered sic composite ceramics.（2）Investigating the impact of amount of andalusite on the properties of silicon carbide ceramic samples,it was found that with the increase of the content of andalusite,the apparent porosity of the samples continued to decrease,the bulk density increased in a wavy manner,and the flexural strength and thermal shock resistance both increased first and then decreased.When the content of andalusite is small,the porosity of the sample is larger and the flexural strength is lower;When a large amount of andalusite is added,the glass phase produced by mullitization is relatively more,which will lead to greater volume expansion.Therefore,when the content of andalusite is 15wt%,the comprehensive performance of the sample is the best,with an apparent porosity of 39.45%,water absorption of 20.96%,bulk density of 2.267g/cm³,flexural strength of 43.01 MPa,and thermal shock resistance of 47 times.（3）It also studies effects of different molding pressures（80 MPa,100 MPa,120MPa,140 MPa）,different sintering temperatures（1400℃,1450℃,1500℃,1550℃）,and different holding times（1h,2h,3h,4h）on the properties of silicon carbide ceramic materials.It was found that increasing the molding pressure,sintering temperature,and holding time all contribute to the sintering of silicon carbide ceramic particles,resulting in a decrease in porosity and an increase in bulk density of the sample.However,the molding pressure should not be too large,which is not conducive to the discharge of gas during the sintering process,resulting in a rebound in the porosity of the sample.The optimum process parameters were obtained as follows:blank forming pressure 120MPa,sintering temperature 1550℃,holding time 4h.（4）with the study of the effect of graphite amount on the properties of silicon carbide ceramics,it was found that as the amount of graphite increased,the amount of pores generated increased,and large pores were formed between pores,which increased the apparent porosity of the sample to 46.32%,while the bulk density decreased to 2.154 g/cm³,and the flexural strength decreased to 23.21 MPa.When the graphite content is 6wt%,the resistance to thermal shock can reach 20 times.