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:Al2O3:2SiO(2) were inves tigated to obtain dense cordierite ceramics at temperatures <1000 degrees C . While heating the mixture of kaolinite and Mg(OH), with the equivalent of 2 mass % of boron oxide (B2O3) (in the form of magnesium berate, 2MgO B2O3 ), an amorphous phase formed at a temperature of similar to 850 degrees C a fter thermal decomposition. Firing the mixture at a temperature of 900 degr ees C yielded dense ceramics with an apparent porosity of almost zero. The addition of B2O3 promoted the densification at 850 degrees-900 degrees C an d accelerated the crystallization of alpha-cordierite. The specimen with 3 mass % of B2O3 that was fired at a temperature of 950 degrees C showed a li near thermal expansion coefficient of similar to 3 x 10(-6) K-1, a bending strength of >200 MPa, and a relative dielectric constant of 5.5 at 1 MHz. T hese cordierite ceramics may be used as substrate materials for semiconduct or interconnection applications.