Influence of bismuth on cordierite polymorphism

Synthesis of Cordierite was carried out by solid state reaction sintering of oxides and Andean mineral precursors. Strong mechanic mixing was employed, with and without bismuth oxide added as a flux. Powder x-ray diffraction patterns were taken after sintering at different temperatures, in the range from 900 °C to 1400 °C. A comparative analysis was performed to investigate the phase formation dynamics for compositions with bismuth contents of 0, 5 and 13 %wt Bi 2 O 3 . Hexagonal α-Cordierite was obtained after sintering at 930°C under the appropriate conditions. The behavior of the distortion index Δ with the sintering temperature reveals how the cordierite order-disorder polymorphism is affected by the bismuth addition. The resultant structure became more ordered with increasing sintering temperature. From the distortion index behavior and DTA measurements it can be observed that all the thermal events are shifted to lower temperatures for increasing bismuth contents. A preliminary study on sintering kinetics is presented from dilatometric measurements. The addition of bismuth would act as a catalyzer, through a liquid phase sintering process, by increasing the reaction rate and lowering the diffusion barriers.