基础材料和有机材料 (13).pdf

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1、1.Definition of the viscosityLecture 2 The properties of the melt:viscosityUnit:PasFluidity:1/When liquid flows,the shear velocity dv/dx is proportional to the shear stress when shear stress is applied to the liquid.The proportional coefficient is named as viscosity,which is represented by.dv/dx2.Re

2、lationship between temperature and viscosityFluidityViscosityE:the activation energy of particle movement,which is also called as potential barrier.)exp()exp(kTEkTEoo The activation energy of the melt is different in different temperature ranges.The activation energy is related to the composition st

3、ructure of the melt.ln=A+B/T A=ln0；B=E/kln1/T in Na2O-CaO-SiO2 meltA.The effect of O/SiThe higher value of oxygen-to-silicon ratio,the larger amount of non-bridge oxygen and oligomers.This results in the lower viscosity.2.Relationships between composition and viscosityB.The effect of R+The content o

4、f R2O 25mol%,O/Si is high.SiO4 tetrahedrons are close to the isolated islands in these melts,which are connected by the alkali metal ions.The attraction force between Li+and SiO4 is larger so that the viscosity of the melt containing Li2O is much higher.OKON aOL i222C.The effect of R2The effect of d

5、ivalent cations on viscosity is the same as that of monovalent cations,which also reduce the viscosity.But the effect of ion polarization on viscosity should be considered.Pb2+Ba2+Cd2+Zn2+Ca2+(sometimes)Mg2+Ion polarizationD.The effect of Al2O3Al2O3can mend the broken network of silicate melt.E.The

6、effect of B2O3(boron anomaly)1)The addition of Na2O to B2O3-SiO2BO343B OOB On b 3)R2O-B2O3-SiO2systemIf(RO+R2O)/B2O3 1,BO4 will be decomposed with the adding R2O,resulting the decrease of the viscosity.2)The addition of B2O3to Na2O-SiO2ViscosityF.Mixed alkali effect If more than one R2O or RO are introduced into the melt,the viscosity of the melt is larger,compared with the same amount addition of one kind of alkaline oxide.The various ions may restrict each other when there are multiple cations in the system,making the effect of reducing viscosity insufficient.C aOM gOC aOM gO3.03.02.01.0