【作者】 窦建鹏；

【导师】 刘晓林；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2012， 硕士

【摘要】 本研究采用冷等静压和凝胶注模两种成型工艺制备了多孔氮化硅复相透波陶瓷（Si₃N₄-SiO₂-BN），研究了成型与烧结工艺条件对材料性能的影响，获得了合理的工艺参数和原料组成，制备了介电常数低于3.0，损耗角正切值小于0.01，且抗弯强度高于50.0MPa的多孔Si₃N₄-SiO₂-BN复相透波陶瓷。系统研究了冷等静压成型后多孔Si₃N₄-SiO₂-BN复相陶瓷的无压烧结温度和烧结助剂对材料介电和力学性能的影响，获得了材料性能与微观结构和原料组成的关系。在4wt%Yb₂O₃烧结助剂的作用下，1750℃保温2小时无压烧结后含10.6wt%BN的多孔Si₃N₄-SiO₂-BN复相透波陶瓷材料的抗弯强度达到65.1MPa，微观结构显示，孔壁致密，β-Si₃N₄晶粒呈明显的棒状结构，优于其它烧结助剂的作用；当多孔Si₃N₄-SiO₂-BN复相陶瓷的孔隙率为50%时，随着造孔剂粒径的减小，抗弯强度由27.6MPa增大至57.1MPa，这是由于材料的孔径从20μm减小至1.8μm，从结构上给予增强；BN的引入显著改善了多孔陶瓷的介电性能，当BN含量由4.6wt%增加到12.5wt%时，材料的介电常数由3.9降低至3.0，抗弯强度均大于50.0MPa。最终，选择在1750℃保温2小时无压烧结、添加4wt%的Yb₂O₃烧结助剂、粒径为1.8μm的造孔剂和12.5wt%的BN作为制备多孔Si₃N₄-SiO₂-BN复相陶瓷的较优工艺条件和原料组成，制备材料的介电常数为3.0，损耗角正切值小于0.002，抗弯强度为54.5MPa，满足制备天线罩透波材料的要求。为了克服冷等静压法制备的复杂形状（如抛物线形）的坯体时出现的滑移现象，本研究还采用凝胶注模成型法制备了多孔Si₃N₄-SiO₂-BN复相透波陶瓷。研究了预配液中单体浓度以及单体与交联剂的比例、凝胶温度、坯体干燥环境和脱模顺序等因素对成型性的影响，结果表明，当单体浓度为3.50mol/L、单体与交联剂比例为20:1时，并将制得坯体浸泡在聚乙二醇中进行干燥后，获得了表面光滑、变形率低的坯体、坯体收缩率低于6%、抗弯强度大于30.0MPa，经无压烧结后，制得的含6wt%BN的多孔Si₃N₄-SiO₂-BN复相透波陶瓷的介电常数达到2.9，抗弯强度为50.5MPa，满足制备天线罩透波材料的要求。更多还原

【Abstract】 In this paper, porous Si₃N₄-SiO₂-BN wave-transmitting ceramiccomposites were prepared by gelcasting and cold isostatic pressing. In order toacquire the ceramic composites with dielectric constant less than3.0,dielectric loss less than0.01and flexural strength higher than50.0MPa, theinfluence of processing parameters, material composition and structure onperformance of wave-transmitting ceramic composites were researched, themain contents of this paper were summarized as follows:Porous Si₃N₄-SiO₂-BN ceramic composites were prepared by coldisostatic pressing, and PMMA was added as pore-forming agent, the factorsthat affect the dielectric properties and mechanical properties were studied.And found that ceramic composites were manufactured by pressurelesssintering, experimental results show that the flexural strength of ceramiccomposites was as high as65.1MPa by adding4wt%Yb₂O₃,10.6wt%BN andsintering at1750℃for2h. Using scanning electron microscope, the resultswere obtained that Yb₂O₃was a better sintering aid and more β-Si₃N₄was produced in the ceramic. Ceramic composites with50%porosity have beenprepared, the flexural strength increased from27.6MPa to57.1MPa withchanging of PMMA size, the reason was that the size of pore was smaller, thestructure was stronger. BN greatly improved the dielectric properties, whenBN content increased from4.6wt%to12.5wt%, the dielectric constant ofceramic composites reduced from3.9to3.0, but also the flexural strengthwere more than50.0MPa. Finally, the ceramic composites with4wt%Yb₂O₃,12.5wt%BN were sintered at1750℃for2h, the diameter of pore was about1.8μm, dielectric constant was3.0, dielectric loss less than0.002and flexuralstrength was54.5MPa, meet the requirement of wave-transmitting radome.Porous Si₃N₄-SiO₂-BN ceramic composites were prepared by gelcasting.In the preparation process, crack and deformation has been found on the greenbody. The process was improved in this paper: Firstly, green bodies weresteeped in polyethylene glycol to dry instead of drying in air; Secondly,demould process was improved, demoulding follow a particular order insteadof demoulding directly. And these improvements have greatly improved thequality of green body. The influences of monomer content and rate ofmonomers on quality of green bodies were studied, and found that whenmonomer content was3.5mol/L and rate of monomers was20:1, green bodieshad low shrinkage rate and warpage rate （all less than6%）, but also had veryhigh flexural strength （more than30MPa）. Ceramic composites with6wt%BNwere manufactured by pressureless sintering, the dielectric constant of ceramic composites was2.8, but also the flexural strength was about50.5MPa, meetthe requirement of wave-transmitting radome.更多还原