Research Of Microstructure And Dielectric Properties Of CLST/PTFE Composites

With the rapid development of information technology and materials, a higherrequirements of information processing and transmission were put forward, andinformation functional product is rapidly growing in shrinking, multi-functioning,high-frequency and other fields. Compared with the conventional dielectric ceramicmaterials, polymer-based dielectric composites have been widely used due to itsbetter flexibility and machinability as well as excellent designability. Because of theunique properties of polytetrafluoroethylene (PTFE), PTFE based composites havereceived widespread concern. However, PTFE has a high value of linear expansioncoefficient and a low value of dielectric constant. and PTFE based composites have ahigh value of dielectric loss and poor temperature stability of dielectric propertiesafter filling modification, which limits its application to some extent.PTFE attracts widespread attention since it has advantages on good corrosionresistance, high temperature resistance and a low value of dielectric loss over a widefrequency range. CaO-Li2O-Sm2O3-TiO2(CLST) has a high value of dielectricconstant, a low value of dielectric loss and good thermal stability. Compositespossessing a good mechanical property and continuously tunable dielectric propertiescould be prepared by CLST filling modification. In this paper, PTFE was chosen asthe matrix and CLST was chosen as the filler. The effects of preparation process,including the filler content, the usage of coupling agent, mixing methods and particlesize distribution of filler on microstructure and dielectric properties of PTFE-basedcomposite were studied. The main purpose is to optimize and determine processparameters and prepare composites which have a continuously adjustable dielectricconstant, a low dielectric loss, good temperature stability of dielectric properties andexcellent corrosion resistance as well as high temperature stability.1. An active surface of ceramic particles were created by H2O2hydroxylationtreatment, which made it better to combine with the coupling agent and enhanceinterfacial bonding between filler and matrix. Moreover, it promoted uniformdispersion of filler in the matrix. The result indicated that the optimal addition ofcoupling agent is0.8wt%with respect to the filler.2. The effect of preparation process on microstructure and dielectric properties of CLST/PTFE composite were investigated. The results showed that when takenapproach of dry mixing process and the sintering temperature is390°C, ceramicparticles were uniformly dispersed in PTFE matrix, and higher density as well asbetter dielectric properties of the composites were obtained.3. The effect of filler content and particle size distribution on microstructure anddielectric properties of CLST/PTFE composite were studied. The results indicatedthat a smaller average particle size and narrow particle size distribution range had anegative effect on uniform dispersion of filler in PTFE matrix. A jet milling speed of3000r/min was more proper to fill in PTFE matrix.4. When use the modified EMT model and taken the third phase of air intoconsideration for analysis, the measured values of dielectric constant agreed well withthe calculated ones.