Journal
CERAMICS INTERNATIONAL
Volume 48, Issue 1, Pages 32-41Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.ceramint.2021.08.088
Keywords
DIW; Low-temperature sintering; Si2N2O-Si3N4 ceramics; Dielectric properties; Si-SiO2 slurry
Categories
Funding
- National Key R&D program of China [2017YFB0310701]
- Science and Technology Innovation Fund of Henan for Outstanding Talents [17420051001]
- Young top-notch talent of Zhengzhou University [125/32310189]
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Direct ink writing (DIW) and low-temperature sintering were used to prepare Si2N2O-Si3N4 ceramics, with HPMC addition and silica fume proportion optimized for stable and pseudoplastic slurry. By controlling temperature and additives, high-quality Si2N2O-Si3N4 ceramics with good dielectric properties can be obtained.
Direct ink writing (DIW) and low-temperature sintering methods were applied to prepare Si2N2O-Si3N4 ceramics for radome materials. Lattices of Si-SiO2 green body were printed by DIW with 78 wt % solid portion of waterbased Si-SiO2 slurry, in which silicon particles and silica fume were used as the solid portion and Methylcellulose (HPMC) was used as the dispersant. Effects of HPMC addition on stability and silica fume content on rheological properties of the slurry were studied, respectively. The pseudoplastic mechanism of the slurry was analyzed. The Si-SiO2 green bodies were sintered at 1250 degrees C-1400 degrees C in nitrogen. The effect of temperature on phase composition, microstructure, mechanical and dielectric properties of samples was investigated. With the HPMC addition of 0.12 wt% and the silica fume proportion of 30 wt% in solid portion, a stable and pseudoplastic slurry with the yield stress of 110.9 Pa was obtained, which is suitable for DIW. With the decrease of initial holding temperature, more N2 enters the sample and reacts with silicon and silica fume, promoting the generation of Si2N2O and Si3N4. The optimal condition yields Si2N2O-Si3N4 ceramics with apparent porosity of 42.73%, compressive strength of 24.7 MPa, dielectric constant of 4.89 and loss tangent of 0.0054. It is found that columnar Si3N4 comes from a direct reaction between silicon and N2, and fibrous Si2N2O is mainly generated by the reaction between silicon, SiO(g), and N2 through the chemical vapor deposition mechanism. Good dielectric properties are achieved due to high porosity, high proportion of Si2N2O phase and no residual silicon.
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