制备工艺对多孔si3n4陶瓷介电性能的影响

焦万丽：交变磁场对重力SHS制备复合管微观结构和机械性能的影响·1443·第37卷第8期制备工艺对多孔Si3N4陶瓷介电性能的影响李军奇1,2，周万城2，罗发2，朱振峰1，马建中1(1.陕西科技大学材料科学与工程学院，西安710021；2.西北工业大学，凝固技术国家重点实验室，西安710072)摘要：采用添加成孔剂和冰冻–干燥法制备具有不同气孔率(30%～60%)的多孔Si3N4陶瓷，研究了不同制备工艺对多孔Si3N4陶瓷介电性能的影响。结果表明：不同的成型工艺制备出具有不同孔分布的氮化硅多孔陶瓷，添加成孔剂制备的多孔陶瓷具有较大的孔，洞分布在致密的基体上；冰冻–干燥法制备的多孔陶瓷具有复合孔分布。对样品的介电特性的研究表明，随着样品的气孔率增加，其介电常数和介电损耗减小；添加成孔剂制备样品的介电常数小于冰冻–干燥法制备样品，而其介电损耗较大，多孔Si3N4陶瓷的介电常数和介电损耗分别在5.21～2.91和9.6×10–3～2.92×10–3范围内变化。关键词：多孔氮化硅陶瓷；成孔剂；冰冻–干燥；介电性能中图分类号：TQ174文献标志码：A文章编号：0454–5648(2009)08–1443–04INFLUENCESOFFABRICATIONPROCESSONDIELECTRICPROPERTIESOFPOROUSSILICONNITRIDECERAMICSLIJunqi1,2，ZHOUWancheng2，LUOFa2，ZHUZhenfeng1，MAJianzhong1(1.SchoolofMaterialsScienceandEngineering,ShaanxiUniversityofScience&Technology,Xi′an710021;2.StateKeyLaboratoryofSolidificationProcessing,NorthwesternPolytechnicalUniversity,Xi′an710072,China)Abstract:Twodifferentseriesofporoussiliconnitride(Si3N4)ceramicswithdifferentporositiesfrom30%to60%werefabricatedusingtwodifferentpreparationroutes:theadditionofpore-formingagentandfreeze–drying.Themicrostructuresofthesampleswereobservedindetail.Theresultsshowthatthereisabigdifferenceintheporousstructureofthesamplespreparedbythedifferentfab-ricationroutes.Thesamplespreparedusingthepore-formingagenthaveadensematrixcontainingcloseporesandcavitieswithsomeneedle-shapedandflakyβ-Si3N4grains,whilethosepreparedbythefreeze–dryingprocesscontainopenandconnectiveporeswithaflatshapescatteredalmostuniformlyintheSi3N4matrix.Theporosity,porestructureanddielectricpropertiesweremeasuredsepa-rately.Theresultsshowthatwiththeincreaseofporosity,theelectricconstantanddielectriclossoftheceramicdecrease,andtheporedistributionoftheceramicisalsoamajorfactorthatinfluencesitsdielectricproperties.Theεofthesamplespreparedbytheadditionofpore-formingagentislowerthanthatbyfreeze-drying,whileitstanδishigherunderthesameporosity.TheεandtanδoftheporousSi3N4ceramicstypicallyareintherangeof5.21–2.91and9.6×10–3–2.92×10–3,respectively.Keywords:poroussiliconnitride;pore-formingagent;freeze–drying;dielectricpropertiesSiliconnitride(Si3N4)isknownasanimportanthigh-temperaturestructuralceramicwithhighstrength,highdecompositiontemperature(1900℃),goodoxidationresistance,lowcoefficientoffriction,negligiblecreep,goodthermalshockproperties,andgoodresistancetocorrosiveenvironments.[1–2]Inaddition,ithasanaccept-abledielectricconstantandlowdielectricloss.Therefore,thesepropertiesallowsiliconnitrideceramicstobeacandidatematerialformicrowavewindowsinhightem-peratures.Recentstudiessuggestthattheporosity,porestructureanddistributionarethekeymicrostructuralelementstocontrolthecharacteristicsofamaterial,especiallythedielectricproperties.Porositycandecreasethedielectricconstantwhentheporousmicrostructureiscarefullycontrolled.[3]Nowadays,variousprocessingtechniqueshavebeendevelopedtofabricateporoussiliconnitrideceramicsforstructuralorfunctionalapplications.Forexample,porousSi3N4ceramicscanbefabricatedbyeitherusingthefugitivesubstance,orbycontrolledsin-teringofSi3N4powderwithvarioustechniquesinclud-inglow-contentsinteringadditive,freeze-drying,partialhotpressing,tapecastingandpartialsinter-forgingtechnique.[4–8]收稿日期：2009–01–04。修改稿收到日期：2009–02–16。基金项目：陕西科技大学科研启动基金(BJ08–02)资助项目。第一作者：李军奇(1978—)，男，博士。Receiveddate:2009–01–04.Approveddate:2009–02–16.Firstauthor:LIJunqi(1978–),male,Ph.D..E-mail:[e-mail]第37卷第8期2009年8月硅酸盐学报JOURNALOFTHECHINESECERAMICSOCIETYVol.37，No.8August，2009硅酸盐学报·1444·2009年Inthiswork,poroussiliconnitrideceramicswerefab-ricatedusingtwodifferentpreparationroutes:(1)theadditionofpore-formingagent,and(2)thefreeze-dryingprocessing,inordertoachievematerialswithdifferentporosities,poresizeandgeometry.Thedielectricproper-tiesoftheceramicshavebeenevaluated,andtherela-tionshipsbetweenthedielectricpropertiesandmicro-structuralfeaturesarediscussed.1Experimentalprocedure1.1PreparationofsamplesPorousmaterialspreparedwiththeadditionofpore-formingagentcontainedSi3N4powderwith96%inmass(thesamebelow)α-phase,andanaverageparti-clesizeof0.5μm,andY2O3(99.99%purity)andAl2O3(chemicallypure)asthesinteringadditivesandusingbenzoicacidasthepore-formingagent.Thebenzoicacidwasaddedinvariousvolumesfrom10%to40%totheSi3N4mixedpowderlistedinTable1.Theresultingpow-dermixtureswereuniaxiallypressedat100MPaintodiskswithadiameterof80mmandathicknessof5mm.Thepressedgreenbodieswereplacedinanoventode-composethepore-formingagents.Theresultantporousgreenbodiesweresintered.Table1ProcessconditionsofsamplesSampleBenzoicacidcontentinvolume/%Watercontentinvolume/%A110A220A330A440B130B240B350TherawmaterialwasSi3N4mixedpowderwith5%Y2O3and5%Al2O3,andsinteredat1800℃for1hunder0.1MPanitrogen.Poroussiliconnitridematerialswerepreparedwithfreeze-dryingwiththeSi3N4mixedpowderlistedinTable1.Themixedpowderwasball-milledindistilledwaterfor20h.Theslurrywithdifferentwatercontentswasdeairedbystirringinavacuumdesiccator.There-sultantslurrywaspouredintothemold,andthemoldwasputinrefrigeratorandstoredatatemperatureof–10℃.Theicewasstimulatedtogrowmacroscopicallyinaverticaldirection,resultingin