基础材料和有机材料 (15).pdf

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1、1.Glass is anisotropicThe properties of glass in all directions are the same such as refractive index,hardness,elastic modulus,thermal expansion coefficient,thermal conductivity,etc.Of course,this is only for homogeneous glass.The particles in the glass are randomly arranged,so the arrangement of pa

2、rticles in all directions is the same statistically,leading to the same properties at different directions.Lecture 3 The characteristics of glass2.Glass is metastableThermodynamicsGlass has high energy and has the tendency of crystallizationKineticsThe rate of crystallization of the glass is very sl

3、ow,so it will be in the glass state for a long time.Supercooled liquidTgTMDCBAKFMEV QCrystalGlassLiquidFast coolingSlow coolingThe glass transition temperature is higher at faster cooling rate.The transition from melt to glass occurs in a temperature range.Glass has no melting point which is differe

4、nt with crystals.3.The transition from melt to glass is a continuous and gradual changeThe structure,energy,and volume of the system change continuously from the melt state to the glass state without any jump,which is different from the crystallization.I:Electric conductivity,specific volume,etc.II:

5、Specific heat,density,expansion coefficient,etc.III:Thermal conductivity,and elastic coefficient,etc.4.Physical and chemical properties change continuous with the temperature during the transition from the melt to the glass.Tg:Glass transition temperature,is also called the brittle temperature,which

6、 is the highest temperature that the glass is still brittle.At this temperature,the internal stress of glass can be relaxed,so it is also called as the upper limit of annealing temperature.Tf:Glass softening temperature.Tfis the temperature at which the glass begins to show the typical properties of the liquid state,and the viscosity is low.