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Heat-treatment on Crystallization and Dielecty Property of Mg-Al-Si-Ti-B Glass-ceramics

QU Jing-Jing;WEI Xing;LIU Fei;YUAN Chang-Lai;CHEN Guo-Hua;HUANG Xian-Pei;School of Mechanical and Electrical Engineering, Guilin University of Electronic Technology;Department of Science and technology, Guilin University of Aerospace Technology;Guangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology;  
Effects of different heat-treatment process on the crystallization,phase composition and content,and microstructure of 19MgO-23Al_2O_3-53SiO_2-4TiO_2-2.5B_2O_3(wt%,M-A-S-T-B)were studied by means of differential scanning calorimeter(DSC),X-ray diffraction(XRD)and scanning electron microscope(SEM)techniques.The influence of different nucleation and crystallization time on the microwave dielectric properties were discussed as well.The results showed that,based on the controlled crystallization mechanism of glass,MgSiO_3 phase was precipitated adequately for M-A-S-T-B samples heat-treated at 850℃/2 h+950℃/2 h,and also,theα-cordierite,x MgO-y Al_2O_3-z SiO_2 andα-SiO_2phases could be precipitated from matrix phase.Additionally,with the increase of nucleation time,types of crystalline and phase content were found no discernible changes in the M-A-S-T-B glass-ceramics.While crystallization time increased to20 h,the crystallized volume fraction of the glass increased,leading to the improvement of the quality factor(Q×f)and the obvious precipitation of granular grains.However,the dielectric loss slightly increased and the relative density of specimens decreased with further increase of crystallization time(30 h).Wherein,the M-A-S-T-B glass-ceramic sample heat-treated at 850℃/2 h+950℃/20 h exhibited the excellent microwave dielectric properties ofε_r~3.85,Q×f~12740 GHz(at 13.973 GHz)andτ_f~–5.37×10~(–6)/℃.
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