造孔剂对多孔Si_(3)N_(4)陶瓷透气系数的影响

Influence of pore-forming agents on permeability coefficient of porous Si_(3)N_(4)ceramics

为改善多孔Si_(3)N_(4)陶瓷的透气性,以Si粉为原料,Y_(2)O_(3)和CaF_(2)为烧结助剂,粒径为5和20μm的聚甲基丙烯酸甲酯微球为造孔剂,先注凝成型再排胶,最后在氮气气氛中于1650℃保温3 h反应烧结,制备了多孔Si_(3)N_(4)陶瓷。研究了造孔剂粒径和添加量(体积分数分别为0、15%、30%、45%和60%)对多孔Si_(3)N_(4)陶瓷显气孔率、孔径分布、孔结构、透气系数等的影响。结果表明:1)添加造孔剂的试样呈堆积衍生孔和球形演化孔的二级孔结构,孔径呈双峰分布;2)在粒径相同时,随着造孔剂添加量的增加,试样的显气孔率和透气系数增大,而体积密度、弯曲强度、断裂韧性降低;3)相同添加量下,添加5μm的小粒径造孔剂的试样具有更高的显气孔率、透气系数和弯曲强度,采用较小粒径的造孔剂能减小孔壁的厚度,并扩大孔壁内堆积衍生孔的孔径,提高孔壁的渗透性;4)添加体积分数为60%的5μm造孔剂的试样综合性能最优,其显气孔率、透气系数和弯曲强度分别为55.1%、11.6×10^(-14)m^(2)和35.3 MPa。

To improve their permeability,porous Si_(3)N_(4)ceramics were prepared using Si powder as the raw material,Y_(2)O_(3)and CaF_(2)as sintering aids,and polymethyl methacrylate microspheres(5 and 20μm)as pore-forming agents,gel-casting,binder-removing,and finally reaction sintering at 1650℃for 3 h in a nitrogen atmosphere.The effects of the particle sizes and additions(volume fractions of 0,15%,30%,45%,and 60%)of the pore-forming agents on the apparent porosity,pore size distribution,pore structure and permeability coefficient of the porous Si_(3)N_(4)ceramics were studied.The results show that:(1)the samples with pore agents exhibit dual pore structures,which are composed of stacking-derived pores and spherical evolution pores,with bimodal pore size distribution;(2)with the same particle size,as the pore-forming agent addition increases,the apparent porosity and permeability coefficient of the samples increase,while the bulk density,bending strength,and fracture toughness decrease;(3)at the same addition,the samples with the smaller-sized agents(5μm)have higher apparent porosity,permeability coefficient,and bending strength;using smaller-sized pore-forming agents can reduce the thickness of the pore walls and enlarge the pore sizes of the stacking-derived pores within the pore walls,thus enhancing the permeability of the pore walls;(4)the sample with 60%pore-forming agents of 5μm has the best comprehensive performance,with the apparent porosity of 55.1%,permeability coefficient of 11.62×10^(-14)m^(2)and bending strength of 35.3 MPa.