Preparation Of High-energy Ball Milling Mg TiO Research 2 4, MgO Nano Powder And Ceramic Microwave Dielectric Properties

Nowadays, the communication technique developed rapidly, mobile communications, intelligent transportation system and wireless applications have been promoted. Meanwhile, it is necessary to lower the sintering temperature of the dielectric ceramics, because the dielectric ceramics and electrode metals with high conductivity metals such as Ag and Cu should be co-fired in the case of multilayer microwave devices. How to prepare nanometer powder, obtain pure phase and sinter the ceramics at lower temperatures is still a challenging issue.High energy ball milling (HEBM) has been successful in preparing some compounds which is effective in lowing the sintering temperature of ceramics, because HEBM powders have nanometer particle size and very high homogeneity. During mechanical activation, powder particles are subjected to severe plastic deformation resulting the formation of high defects concentration. This induces enhanced atomic mobility, promote different phenomena depending on the materials being milled. HEBM is useful to get the nanopowders and improve to lower ceramics’sintering temperature.Using MgO, TiO2as start materials and nanopowders were obtained by HEBM. Mg2Ti04nanopowders ware investigated and it had a good influence of the grain size, phase structure, synthesis temperatures for Mg2TiO4ceramics. Usually, solid state reaction method for preparing Mg2TiO4ceramics needs high temperature (more than1400℃). In this paper, we synthesized pure Mg2TiO4phase powders at1000℃via the HEBM method milled30h, and the magnesium-titanate Mg2TiO4ceramics sintered at1175℃. Meanwhile, the nano MgO powders were obtained by this method, and the MgO ceramics sintered at a low temperature about900℃. Our experiment results were shown as follows:(1) Commercially available MgO (99.99%purity) and TiO2(99.99%purity) powders were used as the starting materials with the nominal composition of Mg2Ti04. After milling5～30h, MgO disappeared and Mg(OH)2was detected. With increasing milling time, magnesium-titanate Mg2TiO4phase with relatively weak diffraction intensity vaguely appeared at20h and increased at30h. The powders fired at550℃ are composed of the mixed phases of MgO, TiO2, MgTiO3, and Mg2TiO4compounds. Increasing the calcined temperatures from600℃to85O℃, MgTiO3gradually becomes a dominant phase mixed with Mg2TiO4.The Mg2TiO4phase became the predominant at900℃, and a single phase of the Mg2Ti04was obtained at1000℃. Thus, the pure Mg2TiO4phase was obtained at the calcinations temperature of1000℃. HEBM process applied to the mixtures of MgO and TiO2for the preparation of Mg2TiO4nanopowders about163nm. Crystallization and chemical reaction were enhanced by an increase of clcination temperatures and milling time. The Mg2TiO4ceramics from30h powders sintered at1175℃showed dense microstructures (increased up to95.8%)(εr=13.9, Q×f=98,600GHz, τf=-50.9ppm/℃).(2) MgO nanopowders were prepared by HEBM method for5to25h. Tungsten carbide vial with diameter of80mm and tungsten carbide balls with diameter of10mm were used as milling medium. The ball-to-powder weight ratio was20:1. The vial rotation speed was360rpm. After drying process, the milled powders were calcined at500℃for4h, nanocrystalline MgO with different particle diameters of425nm,267nm,186nm,114nm. The calcined powders mixed with a nominal composition of (1-x)MgO-xLiF (x=0.01～0.08) were ball-milled for10h under the solid phase method. The powders were compacted into cylindrical pellets of10mm diameter and6mm thickness, then these pellets were sintered at900℃for4h in air. HEBM and LiF addition reduced MgO ceramics sintering temperature at900℃. The MgO (milled25h) powders with0.05mol%LiF addition sintered at900℃showed excellent microwave dielectric properties (εr=12.3,Q×f=67000GHz, σf=-56.1ppm/℃).