纳米材料和纳米结构第四讲.ppt

纳米材料和纳米结构;Bothmethodsaretechniquestoseparatemetalionsfrom

asaltsolution

Advantagesofchemicalco-precipitation

Cheaprawmaterials

Easeofhandling

Large-scaleproduction

Advantagesofforcedhydrolysis

Producingfine,sphericalnanoparticles

Improvingchemicalpurity,chemicalhomogeneity

Controllingparticlesize;Theeasiestwaytoprepareuniformcolloidalmetalhydrousoxides〔胶体状的金属氢氧化物〕isbasedonforcedhydrolysisofmetalsaltsolutions.;1-1KeyFactorsAffecttheSynthesizingProcess;EffectofAnions;Agingasolutionof0.02MFeCl3+0.001MHClat100°Cfor24hrsinasealedtesttube,wecanobtainhematite〔赤铁矿，Fe2O3〕;

BychangingtheconcentrationsofFeCl3andHCl,theagingtemperature,andtheheatingtime,theparticlesize,thecompositionandtheshapecanbechanged,suchasintheshapeofdouble-ellipsoidal,ellipsoidal,irregular,rod-like,andspherical.;Mostofthehomogeneousprecipitationprocessesinvolveionicsolutions.Mono-dispersiveparticlescanbepreparedbycarefullycontrollingthekineticsoftheprecipitation.

Thekineticsofnucleationandparticlegrowthcanbeadjustedbythespontaneousreleaseofprecipitatinganionsfromorganicmolecules.

Itisalsoessentialtofulfilltherequirementsofhomogeneityofsolution,slowprecipitationandeasycontrolofthefinalPHforhomogeneousprecipitation.;Urea((NH2)2CO)isalmostanidealreagenttobeusedinahydrolyticprocesstopreparesphericalnanoparticles:

Possessingnegligiblebasicproperties

Quitesolubleinwater

Hydrolysisratebeingeasilycontrolled;Ureahydrolysis:

H2N-CO-NH2NH4++NCO-

NCO-+2H2ONH4++CO32-;pH值在尿素和Y3+Eu3+老化过程中的变化;含有Y、Eu离子粉末的红外吸收谱

〔a〕水解产物；(b)、〔c〕500°C、700°C煅烧;1-3NucleationandGrowth;Theoryofhomogeneousnucleationandgrowth;Whentheconcentrationofsolublematerialdropsbelowthecriticallevel,nucleationstops