| Prepared by special processes,glass-ceramics is a new kind of inorganic nonmetallic material with a mass of microcrystalline phase dispersing in its glass matrix.Except for excellent mechanical and electric properties,glass-ceramics has lots of other special properties.For example,it has some special optical,thermal and biological properties.Therefore,glass-ceramics has been widely used in such fields as optical and electronic fields,mechanical engineering and biomedicine fields.As a member of glass-ceramics family,cordierite glass-ceramics has a lot of excellent properties.The most important one is its electric property which has made it develop rapidly in electronic field.A lot of researches have been made by specialists and scholars and numerous significant results have been achieved in recent years.However,more researches about crystallization property,especially about crystallization kinetics are needed.The reason is that when cordierite glass-ceramics is prepared,the most important thing is to get high a-cordierite content at a low temperature.MgO-Al2O3-SiO2 glass-ceramics samples were prepared by melting method with some chemical reagents as main raw materials,TiO2,ZrO2,and Cr2O3 as nucleation agents,B2O3 as fluxing agent,CaF2 as clarifying and fluxing agent.The effects of basic composition oxides contents,the ratio of MgO and Al2O3,nucleation agents and their contents on crystallization property were investigated by differential scanning calorimetry(DSC),X-ray powder diffraction(XRD)and scanning electron microscope(SEM).And the heat treatment system was optimized by the use of orthogonal experimental design.The results showed that with the increasing of MgO content(13%?27%),?T and Kgl decreased,which meant that the stability of base glass was worse and it was more easy for base glass to crystallize.However,when the contents of Al2O3 and SiO2 changed,there was an opposite effect;With the increasing of the ratio of MgO and Al2O3(0.84?1.19),crystallization activation energy decreased firstly and then increased,while frequency factor and crystallization kinetic parameter K had an opposite change.When the ratio of MgO and Al2O3 was 1:1,the glass samples were the least stable and the most easily crystallized;According to the range analysis of research about nucleation agents,the primary and secondary sequence of influencing factors was Ti02>ZrO2>Cr2O3,and the optimum contents of three nucleation agents were D3E3F3,that was Ti02 6%,Cr2O3 2.5%and ZrO2 3%.According to the variance analysis of research about nucleation agents,nucleation agent TiO2 had significant influence on crystallization activation energy and crystallization kinetic parameter K of glass samples and nucleation agent Zr02 only had significant influence on crystallization activation energy,while nucleation agent Cr2O3 had significant influence on neither of them.The crystallization mechanism stayed the bulk crystallization when the contents of nucleation agents changed;According to the range analysis of research on heat treatment system,the primary and secondary sequence of influencing factors on coefficient of thermal expansion of glass-ceramics was nucleation temperature>crystallization time>nucleation time>crystallization temperature.The optimal process parameters were A1B1C3D3,that was nucleation temperature 780 ?,nucleation time 60min,crystallization temperature 1025? and crystallization time 120 min.According to the variance analysis of research on heat treatment system,nucleation temperature had very significant influence on coefficient of thermal expansion of glass-ceramics,and crystallization time and nucleation time had a significant influence,while the influence of crystallization temperature was not significant.In this paper,the main crystal phase and sub-phase of all samples were a-cordierite and magnesium titanate. |
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