Phase transformation and mechanical properties of B2O3-doped cordierite derived from complex-alkoxide

Cordierite gel powders doped with up to 3 mol % B2O3 were prepared by the hydrolysis of an alkoxide complex. The effects of B2O3-doping on phase transformation were investigated for the purpose of preventing micro-cracking due to μ-α cordierite transformation. B2O3-doping retarded the crystallization from amorphous to μ-cordierite, and accelerated the crystallization of α-cordierite. High doping concentrations (e.g. 1.5 mol %) appeared to promote the direct formation of α-cordierite from the amorphous state. The development of microcracks due to the μ-α cordierite transformation was prevented by the modified crystallization characteristics. The flexural strengths of the sintered bodies reached 190 MPa. B2O3-doping also lowered the temperatures of densification and crystallization of α-cordierite to 850 and 950 °C, respectively. At the sintering temperatures of 1100 °C or above, however, glassy phase oozed out on to the surfaces and internal pores were formed in the sintered bodies, resulting in decreased flexural strength.