Fabrication of cordierite powder from magnesium–aluminum hydroxide and sodium silicate: its characteristics and sintering

Cordierite as-precipitated powder was prepared by coating magnesium aluminum hydroxide powder with an amorphous coating layer from the reaction between magnesium chloride and sodium silicate. The coated powder transformed to amorphous in the range of 500–600°C, and then amorphous silicate crystallized to cristobalite and an intermediate phase appeared at 850°C. α-Cordierite formation in this system is attributed to the reaction between amorphous silicate and a metastable phase of sapphirine, which resulted from the reaction between the crystalline cristobalite and an intermediate phase. The densification of green compacts was not affected by the crystallization of amorphous silicate and intermediate phase because some amorphous silicate remained in the matrix till the temperature of α-cordierite formation.