Low-temperature Synthesis Of Magnesium Titanate Nanopowders By Sol-gel Method

The devices and components of mobile communication, wireless LAN and GPS systems were developed to miniaturization, high frequency and integration, which required excellent performance of microwave dielectric ceramics. Therefore, the studies on microwave dielectric ceramics were focused on nano-powders, low sintering temperature and high frequency.MgTiO₃ ceramics is an excellent microwave dielectric ceramics to fabricate components working at high frequency such as resonators, filters and antennas. However, it has some disadvantages such as high sintering temperature (over 1400℃), narrow sintering temperature range and large powder particles. Therefore, it is difficult to prepare multilayer microwave components of miniaturization and low cost. Based on requirements of components for miniaturization and low cost, and on current development and existing problems of MgTiO₃ ceramics, Ti(OC₄H₉)₄ and Mg(NO₃)₂.6H₂O (low cost, instead of organic salt) were used as precursors. MgTiO₃ nano-powders with good dispersivity were synthesized using sol-gel method by controlling the conditions of the sol and the gel, and the surface characteristics of powders. The nano-powders can meet the requirements of ultra-thin tapecasting green sheet to fabricate miniaturization microwave components. The main results are as follows:The study on the conditions of low temperature synthesis of MgTiO₃ nano-powders. The characteristics of sol and gel were influenced by the concentrations and adding sequences of absolute ethyl alcohol, Ti(OC₄H₉)₄ and Mg(NO₃)₂.6H₂O, glacial acetic acid. On condition that the mol proportions of Ti(OC₄H₉)₄ to CH₃CH₂OH and Mg(NO₃)₂.6H₂O to CH₃CH₂OH were both 8, glacial acetic acid was added the same volume as absolute ethyl alcohol to adjust PH value, steady sol was abtained. When the dried gel was calcined at 600℃ for 1 hour, the main crystal phase was MgTiO₃ and the average size of the nano-powders was between 10nm and 30nm with heavy agglomeration.The study on the improvement of MgTiC>3 sol characteristics. In order to solve the agglomeration of MgTiC>3 nano-powders, surface modification mechanism, different PEG modifiers and content of surface modifiers were investigated. Surface modifiers increased decomposing temperature of organic materials from 370°C to 410°C, and the crystallization temperature of MgTiO3 was increased from 625°C to 700 °C. When adding 4wt% PEG1000 and heat-treated at 700 °C for 1 hour, MgTiO3 nano- powders of 20nm with perfect dispersivity were synthesized , and the agglomeration problem was solved.The study on sintering characteristics and dielectric properties of MgTiO3 nanopowders. The sintering characteristics and dielectric properties of MgTiC>3 were improved because of the large specific surface of nano-powders. Homogenous and dense MgTiC>3 ceramics was obtained when sintered at 1200 °C (Compared to the solid state method, the sintering temperature was decreased by 200 °C) with good microwave dielectric properties of 8r=16.6> Qf=42600GHzo...