Cordierite Ceramics with Near-zero Expansion

Cordierite ceramic has been used as square mirror materials for the lithography machine successfully due to its low thermal expansion coefficient, good mechanical properties and low density. At present, few researches have been reported on the cordierite ceramic for square mirror in China, so it is of great significance to carry out relevant research for promoting domestic substitution of the advanced cordierite ceramic parts. Cordierite ceramics (Mg_(2-x)La_xAl₄Si₅O_(18+0.5x)) were prepared by using a sol-gel process with La³⁺ as dopant. The effects of La³⁺ doping on structure, thermal expansion and mechanical properties of the samples were studied. It is found that thermal expansion coefficients of the cordierite ceramic samples were varied from negative to positive gradually with increasing content of La³⁺. As the content of La³⁺ (x) was 0.15, absolute thermal expansion coefficients of the samples were not greater than 0.02×10^-6 K^-1 at (22.0±0.5) ℃. Meanwhile, the samples had bending strength of 211.44 MPa and elastic modulus of 145.77 GPa, meeting the requirements for square mirror applications.During the sintering process, La³⁺ would replace Mg²⁺ in the cordierite structure, leading to the six-membered ring distortion. In addition, densification sintering also occurred because of the liquid formation. The properties of cordierite ceramic could be adjusted effectively through above two aspects interaction.