The synthesis, characterization and sintering of sol-gel derived cordierite ceramics for electronic applications

Abstract

Cordierite ceramics were synthesized by sol-gel processing using alkoxides and acetate with an aim to use the material as substrate and packaging material. Preparation conditions were optimized by varying the amount and pH of water added and the amount of acetic acid as chelating agent. The powders were characterized by different analytical techniques such as thermogravimetric analysis, differential thermal analysis, surface area by BET, X-ray diffraction, transmission and scanning electron microscopies and infrared spectroscopy. The best product was obtained using 19.6 mol water and 0.34 mol acetic acid with respect to silicon ethoxide. The pH of the water added did not make any significant difference. Sintered materials were characterized by measuring different physical properties such as density, electrical and dielectric properties, thermal expansion, microstructure and composition. Well-sintered bodies could be achieved at 1000 °C in air with a soaking time of 2 h having a density of ∼ 99% theoretical, electrical resistivity of ∼10¹⁴ Ωcm, dielectric constant of 5, dielectric loss ∼0.008 and thermal expansion coefficient of 28.5 × 10⁻⁷ °C⁻¹, 25–200 °C. X-ray diffraction studies show the phase evolution in these materials is predominantly μ-cordierite (hexagonal high cordierite) and some β-quartz. SEM reveals a uniformly dense microstructure with crystals of granular habit. X-ray photoelectron spectroscopy indicates that the surface composition of the sintered material is slightly enriched with aluminium and deficient in silicon.