Low‐Temperature Fabrication of Cordierite Ceramics from Kaolinite and Magnesium Hydroxide Mixtures with Boron Oxide Additions

Thermal reactions of mixtures of ultrafine particles of magnesium hydroxide (Mg(OH) 2 ) and kaolinite in a composition of MgO:Al 2 O 3 :2SiO 2 were investigated to obtain dense cordierite ceramics at temperatures <1000°C. While heating the mixture of kaolinite and Mg(OH) 2 with the equivalent of 2 mass% of boron oxide (B 2 O 3 ) (in the form of magnesium borate, 2MgOB 2 O 3 ), an amorphous phase formed at a temperature of ∼850°C after thermal decomposition. Firing the mixture at a temperature of 900°C yielded dense ceramics with an apparent porosity of almost zero. The addition of B 2 O 3 promoted the densification at 850°‐900°C and accelerated the crystallization of alpha‐cordierite. The specimen with 3 mass% of B 2 O 3 that was fired at a temperature of 950°C showed a linear thermal expansion coefficient of ∼3 × 10 −6 K −1 , a bending strength of >200 MPa, and a relative dielectric constant of 5.5 at 1 MHz. These cordierite ceramics may be used as substrate materials for semiconductor interconnection applications.