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Controlled Preparation And Dielectric Properties Of Porous BN/SiO2/Si3N4Composites

Posted on:2013-06-29Degree:MasterType:Thesis
Country:ChinaCandidate:N N LongFull Text:PDF
GTID:2231330374983151Subject:Materials science
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With the rapid development of aerospace technology in recent years, the study of antenna and electromagnetic interference system research has increasingly deepened. At present, Ceramics and ceramic matrix composites possessing excellent mechanical and dielectrical properties get a lot of attention at home and abroad. Porous Si3N4composites are outstanding candidate wave material due to their mechanical properties, thermal shock resistance, fire resistance performance and low dielectric constant.The paper was based on excellent mechanical and dielectric performance of Si3N4, BN and SiO2. Porous Si3N4matrix composites doped BN and SiO2nanoparticles were fabricated by pressureless-sintering at a relatively low temperature of1500℃. Flexure strength at room and high temperature, thermal shock resistance, fracture toughness, elastic modulus and porosity were investigated with the sintering temperature, content of stearic acid or content of BN and SiO2.Porous Si3N4matrix composites were fabricated by pressureless-sintering at1500℃, using stearic acid as pore-making agent and Al2O3-Y2O3as sintering additives. The results showed that the bending strength became higher and higher with sintering temperature rose. Porous Si3N4composites sintered at1500℃had a high porosity of26%, and the bending strength was200MPa. Porous Si3N4composites fabricated with stearic acid possessed higher porosity of35%, and the bending strength was207MPa. The microstructure was analyzed by X-ray diffraction and thermal field emission scanning electron microscopy. It was discovered that the pores were mainly composed of Si3N4grains. With the increase of sintering temperature, the porosity decreased and the pore size became smaller. With the increase of stearic acid content, the porosity increased and the distribution of pore size became uniform.To improve the dielectric properties and thermal properties of porous Si3N4, BN and SiO2nanoparticles were doped. Porous BN/SiO2-Si3N4composites were successfully fabricated. BN/SiO2-Si3N4composites had good resistance to heat shock and high temperature strength and low dielectric constant. The dielectric constant of porous BN-SiO2-Si3N4composites was about3.This work was supported by the National Natural Science Foundation of China (Nos. 50872072and51042005), Science and Technology Development Project of Shandong Province (Nos.2011GGX10205and2009GG10003003), and Independent Innovation Foundation of Shandong University (2009TS001and2012TS213).
Keywords/Search Tags:Porous, Si3N4, BN, SiO2, Dielectric properties
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