简介:采用HSiCl3—NH3—N2(稀释气体)体系在石英陶瓷基板上通过低压化学气相沉积(LPCVD)法沉积出了Si3N4涂层,研究了工艺条件对涂层沉积速率的影响。结果表明,在没有稀释气体的情况下,随着沉积温度升高,Si3N4涂层的沉积速率逐渐增加,在850℃附近达到最大值,随着反应温度的进一步升高,涂层沉积速率下降。当存在稀释气体时,在所选温度范围内随着沉积温度的升高,Si3N4涂层的沉积速率一直增大,反应的表观活化能约为222kJ/mol。随着原料中NH3/HSiCl3流量比值的增大,Si3N4涂层的沉积速率逐渐增加,随后稳定,但稍有下降趋势。在所选稀释气体流量范围内,Si3N4涂层的沉积速率随着稀释气体流量的增加而增大。
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简介:Theyolk-shellLaMnO3perovskitemicrosphereswerefabricatedbyanovel,simpleandmildsofttemplateapproach.Aseriesoftemplate-P123concentrations(0-6.12mmol·L^-1)wereemployedtooptimizethemostcompletespheres.WhentheconcentrationofP123is3.0mmol·L^-1,theobtainedyolk-shellmicrosphereswithadiameterof200-700nmwereconstructedbynanoparticles.Thepossibleformationmechanismoftheyolk-shellmicrosphereswasrevealedstepbystepviaXRD,SEM,TEM,EDSandHRTEM.MoleculesofP123weresuitablymixedwithsolventsfordoubleshelledvesiclesthroughself-assembly,whichinteractedwithmetalcomplexestoformP123-metalvesicles.AftertheremovalofP123andcitricacidbycalcinationat700℃,theyolk-shellLaMnO3microsphereswiththrough-channelswereobtained.Through-channelsonthesurfacewereduetocitricacidandthesolidcorewasattributedtotheshrinkofinnervesicles.Preparedyolk-shellmicrospheresamplespossessedalargersurfaceareaandahighermaximumNOconversionvalueof78%at314℃forNOoxidation,comparedwithsampleswithouttheyolk-shellstructure.
简介:Thewidthandspacingofadiabaticshearbands(ASBs)intheserratedchipsgeneratedduringhighspeedorthogonalcuttingof30CrNi3MoVstructuralsteelweremeasuredbyopticalmicroscopy(OM),thetemperatureriseintheshearbandwasestimated.ThemicrostructuresoftheASBswerealsocharacterizedbySEMandTEM.TheresultsshowthatthewidthandspacingofASBsdecreasewiththeincreaseofthecuttingspeed.ThefurtherobservationsshowthatthemicrostructurebetweenthematrixandthecenteroftheASBgraduallychanges,andthatthemartensiticphasetransformation,carbideprecipitationandrecrystallizationmayoccurintheASB.
简介:60%whitecorundumusedforaggregate,5%aluminiumpowderforfixedadditionsand35%variousadditivesformatrixwerepreparedforspecimens1#,2#,3#.Theyweremixeduniformlywiththesuitableresinasabinderandpressedunderpressureof315tonforgingpress,thendriedat200℃for24h.Effectsofvariousadditiveson1500℃×2hcreeppropertiesofAl3CONreinforcedcorundumcompositewereresearched.Theexperimenalresultsshowthatcreepcoeffi-cientsofspecimens1#,2#,3#at1500℃×2hare1.4×10-4,-9.4×10-4,-22.6×10-4,respectively.CrushingstrengthoftheslideplateaddedwithsuitableadditiveAafterfiredat1500℃×3hreachesto225MPa,thecreeprateispositiveallthetimefrom0%to0.014%at1500℃for2h.Themicro-structureresultanalysisshowsthatreinforcedphasesofAl3CONfibercompositehavebeenformedafterfiredwithAlpowderincokeathightemperaturesforspecimen1#,andthestrengthofthecompositeisincreased.Thehotmodulusofruptureisupto59MPaat1400℃andtheRULisobvi-ouslyhigherthanthatat1700℃.ItsservicelifeistwotimesasthatofAl2O3?Cslideplatewhenusedintheprocessofpouringsteel.Themechanismofcreeprateresistanceofthecompositescanbedis-coveredbymeansofSEMandEDAXanalysis.ItisconcludedthattheactiveAl3CONandAl2O3multiphasesthatwereformedbyN2ingas,C,AlandAl2O3insidethematrixofthecompositesduringin-situreaction,whichgivesthecompositesoutstandingcreeprateresistanceforthedensezonere-sultingfromAl3CONoxidationthatinhibitscontractionatthehightemperature.Besides,thematrixwillturnintothemultiphasewithhighrefractoriness,NcontentanditsAl3CONreinforcedfiberwillfurtherincreaseaccordingly.Inaddition,Al3CONformedbyAl2O3andC,AlinthematrixwithN2ingaswillinhibitthecreeprateandalsogreatlyimprovethecreeprateresistanceofthecomposites.