简介:La15Fe77B8hydrogenstoragealloyswerepreparedusingavacuuminduction-quenchingfurnace.TheresultsofX-raydiffraction(XRD)andscanningelectronmicroscopy(SEM)suggestedthatLa15–xSmxFe2Ni76Mn5B2(x=0,2,4,6)alloyshadmultiphasestructureincludingthemainLaNi5phase,La3Ni13B2phaseand(Fe,Ni)phase.WiththeincreasingsubstitutionofSmforLa,themainphasestructureofalloysdidnotchange,whiletheunitcellvolumesdecreased,thecyclestabilitywasimprovedandthemaximumdischargecapacitydecreased,butthelowtemperaturemaximumdischargecapacityofthesamesubstitutionalloywasgraduallyapproachingthemaximumdischargecapacityatroomtemperature,whichshowedthatLa15Fe77B8hydrogenstoragealloysofthepartialsubstitutionofSmforLahadbetterlow-temperaturedischargeability(LTD).Forthesamesubstitutionalloys,self-dischargecharacteristicsandcyclestabilityatlowtemperaturewerebetterthanthatatroomtemperature.Furthermore,thehigh-ratedischargeability(HRD)andtheexchangecurrentdensityI0firstincreasedandthendecreasedwiththeincreasingofSmcontent,whereasthehydrogendiffusioncoefficientDinalloybulkdecreasedgradually,whichindicatedthatappropriatesubstitutionofSmforLaimprovedtheelectrochemicalkineticspropertiesofthealloys.TheHRDwasmainlydominatedbythecharge-transferrateonthealloysurface.
简介:Eu2+andDy3+codoped(Ca,Sr)7(SiO3)6Cl2yellowphosphorsweresuccessfullysynthesizedbyself-fluxmethod.Thestructure,morphologyandphotoluminescencepropertieswereinvestigatedbyX-raydiffraction(XRD),scanningelectronmicroscopy(SEM)andphotoluminescencespectra.Theas-preparedphosphorshowedabroademissionspectrumcenteredat550nmforEu2+single-dopedphosphor,whilelocatedat548–544nmfortheEu2+,Dy3+codopedsamplesunderexcitationat380nmlight.TheemissionintensitywasgreatlyimprovedwhenDy3+wasdopedintothe(Ca,Sr)7(SiO3)6Cl2:Eu2+system.Thecomposition-optimizedsamplewith3mol.%ofDy3+andconstant10mol.%ofEu2+exhibiteda220%PLenhancementcomparedtothephosphorwith10mol.%Eu2+single-doped.Meanwhile,itwasfoundthatthequantumefficiencyofphosphornamely(Ca,Sr)7(SiO3)6Cl2:3mol.%Dy3+,10mol.%Eu2+couldgetupto24.6%.Thesynthesizedyellow-emitting(Ca,Sr)7(SiO3)6Cl2:Dy3+,Eu2+isapromisingcandidateashigh-efficiencyyellowphosphorforNUV-excitedwhiteLEDs.
简介:基于轻质、高强和耐磨等诸多优势,铝基碳化硼复合材料已成为集结构/功能一体化的新型材料。本文采用粉末冶金及轧制方法,制备出厚度3.5mm、碳化硼质量分数为33%的B4C/Al复合材料板材,并对其疲劳性能和断裂机制进行分析。在1×107循环次数下,铝基碳化硼复合材料板材的疲劳强度达到110MPa。采用SEM对疲劳断口进行观察,结果表明B4C/Al复合材料疲劳断口可清楚的看到裂纹的萌生、扩展和失稳断裂的典型特征,但存在多种形式的疲劳启裂源。疲劳裂纹扩展路径取决于裂纹尖端塑性区的半径和B4C颗粒的间距大小,当增强颗粒的间距小于塑性区半径时,裂纹主要沿着颗粒的连接界面或断裂的碳化硼颗粒扩展,当增强颗粒的间距大于塑性区半径时,有利于裂纹尖端钝化,减缓裂纹的扩展和方向改变。
简介:Themicrostructuresandprecipitatesinbasemetalsandheataffectedzones(HAZs)oftwoZr-Bmicroalloyedsteelswerecharacterizedbymeansofopticalmicroscopy(OM),transmissionelectronmicroscopy(TEM)andenergydispersivespectrum(EDS).Ithasbeenfoundthatprecipitatesoftensofnanometersinsizearepresentinthebasemetalsofbothsteels.Theaverageparticlesize,however,intheZr-BsteelwithTiislargerthanthatinthesteelwithoutTi.Afterthermalsimulations,inbothcases,theMnSsulfidescannucleateoncubic(Nb,Ti)(C,N)carbonitridesandnearlysphericalZr-bearingcompounds.TheprecipitatesintheHAZsofbothsteelsarecoarserthanthoseinthebasemetals,intherangesof150-200nmand50-100nmforTiaddedandTi-freesteels,respectively.
简介:15%Ag-addedcubicperovskitesSr0.9La0.1TiO3andRuddlesden-Popper(RP)phasesSr2.7La0.3Ti2O7werefabricatedviahydrothermalsynthesis,coldpressingandhigh-temperaturesintering.Thestructureandthermoelectricpropertieswerealsoinvestigatedforallsamples.TheresultsindicatedthatAgprecipitatedasasecondphase.AgadditionmadeelectricalconductivityandabsoluteSeebeckcoefficientenhanced,asaresult,theZTvalueswereenhancedbothfortwoseries.Comparedwithcubicperovskite,RPphasewassubjectedtosmallerimpactbyAgaddition.ThereasonsforenhancingZTvalueandthedifferentimpactfortwoseriesbyAgadditionwerealsodiscussed.
简介:采用电磁悬浮方法,通过原位观察再辉曲线进行过冷Ti-46Al-7Nb亚包晶合金的快速凝固研究,获得的最大过冷度为240K。在一定过冷度下对悬浮的熔体进行铜基底悬淬,进而对凝固合金的微观组织进行分析。超过一定的临界过冷度(ΔT*=205K),凝固模式将从具有包晶转变特征向包晶转变被抑制转化。当熔体初始过冷度ΔT≤ΔT*时,遵循包晶合金的典型凝固规律,β相作为初生相析出,在随后的冷却过程中包晶相α以包晶反应、包晶转变的方式析出。当ΔT〉ΔT*时,β相直接凝固,包晶相α的析出被抑制。包晶反应能否发生取决于包晶相α的孕育时间τP与再辉后熔体完全β相凝固所需的时间tβ的相对大小。当过冷度相差不大时,通过改变凝固过程的冷速,组织中获得β相向α"相的马氏体转变。
简介:通过电化学分析与测试,研究B4C体积分数分别为20%、30%、40%的B4C/Al基复合材料及其基体合金(6061铝合金)在不同浓度及不同温度的硫酸溶液中的腐蚀行为。由动态极化曲线和阻抗谱得到相应的电化学参数,并利用阻抗分析软件对该复合材料和基体合金腐蚀过程的等效电路进行模拟,分析腐蚀机理,通过Arrhenius方程计算腐蚀过程中B4C/Al基复合材料与6061铝合金的反应活化能,并分析两者的焓变与熵变,对腐蚀前后2种材料界面的微观结构进行观察。结果表明:B4C/Al基复合材料在硫酸溶液中的腐蚀速率随B4C颗粒含量增加而增大,基体铝合金在硫酸中的耐腐蚀性能高于B4C/Al基复合材料。B4C/Al基复合材料和基体铝合金在硫酸中的腐蚀速率都随硫酸溶液浓度增加而增大;当溶液温度升高时,二者的腐蚀速率都快速增加。B4C/Al基复合材料和Al基体合金在硫酸溶液中的腐蚀都表现为明显的点蚀。铝基体材料在硫酸溶液中的反应活化能大于B4C/Al基复合材料,计算所得活化焓与活化熵的值均表明复合材料的腐蚀反应比基体合金更容易进行,因而遭受腐蚀更严重。
简介:ThecompoundSm0.98Fe9.02–xGaxNδ(x=0,0.25,0.5,0.75,1)werepreparedbymelt-spunmethodandsubsequentannealingandnitriding.TheRietveldanalysisshowedthatthelatticeexpansionplayedanimportantroleinimprovingtheCurietemperature.AnobviousdevelopmentoftheCurietemperaturewasobtainedwiththeincreasedGacontentfromx=0–1(ΔTc=90oC).Theoptimumcoercivityofnitrideswasobtainedatx=0.25withthevalueHcj=652kA/m(8.15kOe)afterannealing,whichcorrespondedtoareasonabledistributionofgrainsizesofbothTbCu7-typeSmFe9Nδandα-Fe.However,anexcessofGadopingmightleadtoanabnormalgrowthofα-Fe,whichinturndeterioratedthemagneticproperties.ItwasconcludedthatamoderateGacontentwasveryeffectiveinraisingthecoercivityandCurietemperamentintheTbCu7-typeSm-Fe-N.