基础材料和有机材料 (16).pdf

1.Tamman theoryCrystallization:Nucleation(Iv)Grain growth(u)Influencing factor:Undercooling T=TMTLecture 4 The formation of glass:kinetics conditionsIv=PDP the formation rate of embryo D the transition rate of atomsDPIvIv TRateConclusionA maximum value on the Iv curve T kinetic energy of particles attraction between particles P T viscosity D A.The rate of nucleationU=Bexp(-Ga/kT)1-Bexp(-Gv/kT)Influenced by the atomic diffusion Influenced by Gv,which is the energy change between the crystal and melt.Gv H T/Te TURateB.The rate of grain growthConclusionA maximum value on the UcurveIn the overlapping region of Iv and u curves,the melt has a larger crystallization rate.This region is called as the crystallization region.The melt is easier to crystallization than the formation of glass if the crystallization region is larger.C.The total crystallization rate2.Uhlmann TheoryAs long as the volume of crystals in the system is less than the lower detection limit of the instrument,the product can be defined as glass.The lower limit of detection is generally considered to be 10-6.(V/V106)；Volume fraction of the crystals V/V can be described by the Johnson-Mehl-Avrami formula.The critical cooling rate can be determined by the 3T curve.3T:Time-Temperature-TransformationThe smaller the critical cooling rate(dT/dt)c,the easier it is for the melt to form glass.Which one is easier to crystallize or form glass?Undercooling(K)Time(s)ABC10-31107806040100120103The critical cooling rate is also determined by the composition of the melt.2251030.6510-3Se13800.010.3107Ni6130.020.3108LiCl320300.5810-1ZnCl25401060.6710-6BeF22801050.7510-5As2O320500.60.5103Al2O34501050.7210-6B2O311151060.6710-2GeO2SiO217101070.7410-6TM()(TM)(dPa.s)Tg/TmdT/dt(/s)CompoundsPropertiesThe melt with high viscosity at the melting point is easy to form glass.it is easy to form glass if the ratio of glass transition temperature to melting point temperature is greater than 2/3.Kinetic conditionsConclusion:2/3 rule(TM)