Research On The Crystallization And Microstructure Control Of The R₂O-MgO-CaO-SiO₂Glass-ceramic

R2O-MgO-CaO-SiO2glass-ceramic is used to manufacture Fluoramphiboleglass-ceramic, when CaF2is added to the batch glass. This kind of glass-ceramic hasoutstanding mechanical properties and good processability. Since the crystal structureof fluoramphibole is quite complex and the chemical composition is also complex, itis very difficult to crystallize directly from the matrix and it should crystallize withthe help of some transition phases. In this paper, the flouramphibole glass-ceramicsare prepeared by reaction-crystallization method. The phase transition、the strengthand the chemical stability of R2O-MgO-CaO-SiO2glass-ceramics was investigated byDTA, XRD and EPMA-microstructure analysis.The influence of composition ofglass-ceramic and heat-treatment temperature on the crystallization and themicrostructure was also investigated.In this paper, the two main phases of glass-ceramic are K-Fluorrichterite andDiopside. The crystallization of K-Fluorrichterite was the product of a chemicalreaction of metastable phases such as residual glass phase and diopside. The phaseseparation occurred between650~660℃,when treated the glass at this temperaturewill lead to nucleartion. At higher temperatures(750℃~800℃), diopside wasprecipitated as a nucleation. At about950℃the dipside and metastable phasesreacted to form K-Fluorrichterite and the speed of reaction comes to the top at about1030℃~1050℃. With the increase of temperature, more sheet like K-Fluorrichteritecrystallized and had a tendency to gather other, which is helpful for improvement offlexural strength.The increase of CaO promoted the crystallization of diopside. crystal, With theincrease of CaO, more diopside crystallized around the K-Fluorrichterite, it helps toblock the growth of microcracks and it is helpful for improvement of flexural strength.Crystallization activation energy decreased, with the copmsition of CaO increased.The increase of Na2O, increased the nucleation temperature slightly. It is exactlythat increase of Na2O is good for crystallization of K-Fluorrichterite. Althoughincreased the composition of Na2O could decrease the crystallization activationenergy, but too much Na2O led to the increase of crystallization activation energy. On the other hand the percent of Na2O composition must not be more than6~8wt%,otherwise, a metastable phases whose composition is close to that of KMgLi2Si4O10F2will easily crystallized and it is not good for crystallization of K-Fluorrichterite.It is found that with the increase of the composition of SiO2, the proportion ofcrystals became less and crystallization became more diffcult, but resistance ability toerosion was improved. When the composition of SiO2increased, the weight losscaused by acid and alkali solution erosion reduced about10~25%.