资源描述：
《Mechanism and Kinetics of the Carbothermal Nitridation Synthesis of α‐Silicon Nitride》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。
1、JournalJ.Am.Ceram.Soc.,80[11]2853±63(1997)MechanismandKineticsoftheCarbothermalNitridationSynthesisofa-SiliconNitrideAlanW.Weimer,*GlennA.Eisman,DavidW.Susnitzky,*DonaldR.Beaman,andJeffreyW.McCoyCeramicsandAdvancedMaterialsResearch,TheDowChemicalCompany,Midla
2、nd,Michigan48667Thecarbothermalnitridationsynthesisofa-Si3N4isstud-3SiO2+6C+2N2®Si3N4+6CO(1)iedusingelectronmicroscopytechniques(FEG/SEMandTEM)andchemicalcompositionanalysistocharacterizeReaction(1)ismoderatelyendothermic,requiringapproxi-thereactionatvarious
3、degreesofconversion.Thereactionmately1268kJ/molofSi3N4at1427°C.followsanucleation±growthmechanism.Without``seed''Thereactionisbelievedtoinvolvemultiplestepsandtoa-Si3N4intheprecursor,thereactionrateiscontrolledbybeginwiththereductionofSiO2bycarbon(C)indirectp
4、hysi-theformationofnucleiwhichareassociatedwithaSi±O±Ccalcontactaccordingtointermediatephase.Inthepresenceof``seed,''thelimitingC+SiO2®SiO+CO(2)stepisgrowthofa-Si3N4ontothe``seed''nuclei.Growthappearstofollowagas-phaserouteandischaracterizedbyThereductionprod
5、uctofthisfirststepisgaseoussiliconmon-anirregularporouslayerwhichgrowsontothe``seed.''oxide(SiO),avolatileintermediatewhichthenreactstoyieldTheporousstructureistheresultofreactionaroundcar-SiN.OnceCOisformed,SiOcanalsobeproducedbygas-34bonparticleswhicharecon
6、sumedduringtheprocess.Thephasecarbonreductionaccordingtothecombinationofreac-presenceofadmixed``seed''Si3N4intheprecursorformu-tions(3)and(4):lationincreasesthereactionratesincethenucleationstepiseliminated.AnactivationenergyofE=457±55kJ/molforSiO2+CO®SiO+CO2
7、(3)theoverallreactioncloselyapproximatesthatpreviouslyreportedfortheformationofSiO.Thisresult,alongwithC+CO2®2CO(4)thefindingthatresidualcrystallineSiO2ispresentatallThegas-phasecarbonreductionmechanismisbelievedtopre-stagesofthereaction,indicatesthattheovera
8、llreactiondominate5onthebasisofbothkineticandthermodynamicrateiscontrolledbythereductionofSiO2.Sincereactionatconsiderations.thecarbonandSiO2contactpointsisfast,therate-limitingstepismost
