基础材料和有机材料 (23).pdf

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1、.SiO2 system phase diagram.ZrO2system phase diagramApplications of One-component Diagrams1.Seven Crystal Forms of SiO2quartzPeer transformation(slow)tridymite cristobalitefused silicaMelt(1600)quartz87017231470573Melt(1670)163117tridymitetridymite180270cristobaliteQuartz glass.SiO2 System Phase Diag

2、ramsplat coolingSimilar transformation(quick)Displacement transition:The speed of transition is fast.Reconstruction transition：The speed of transition is slow.2.Two Forms of Polycrystalline Transitionreconstruction transitiondisplacement transition3.Volume Effect of SiO2Polycrystalline Transition-qu

3、artz -tridymite VMAX16The volume change of cristobalite is the largest VMAX=2.8The volume change of tridymite is the smallest VMIN=0.2%The speed of displacement transformation is fast,so the harm of displacement transformation is great.4.SiO2System Phase Diagram Equilibrium diagram for SiO2The vapor

4、 pressure of all SiO2variants inmetastable state is higher than that of variantsin thermodynamic stable state in the sametemperature range.Example:Refractory silicon brick Raw material：Natural quartz(-quartz)Requirement：more tridymite and less cristobaliteActual situation：When heated to 870,it will

5、not be transformed into tridymite.Under production conditions,it is often overheated to 1200 1350 to directly transform into metastable-cristobalite.5.Applications of SiO2phase diagram(1)Properinsulationat870topromotethegeneration of tridymite.（2）Carefully accelerate the temperature rise at 1200-135

6、0 to avoid the appearance of cristobalite.(3)Adding appropriate mineralizers such as Fe2O3,MnO2,CaO or Ca(OH)2to the formula,there willproduce a certain amount of liquid phase at about 1000.-tridymite is continuously crystalized from the liquidphase.Measures taken:（1）ZrO2 is the main raw material of

7、 special ceramics.Cubic crystal solid solution is formed at 1500,called stabilized cubic ZrO2.1.Applications of ZrO2.ZrO2System Phase Diagram（2）High melting point(2680),used as refractory.（3）Oxygen conductivity,used as oxygen sensitive sensor element.（4）Volume effect,used to toughen other ceramic materials with phase transformation.Three crystal forms of ZrO2:monoclinic ZrO2,tetragonal ZrO2,and cubic ZrO2.Monoclinic ZrO2 tetragonal ZrO2 cubic ZrO21200237010002.ZrO2System Phase Diagram Equilibrium diagram for ZrO2