Microstructural Development on Crystallizing Hot‐Pressed Pellets of Cordierite Melt‐derived Glass Containing B 2 O 3 and P 2 O 5

Comparing the crystallization mechanism of stoichiometric and B 2 O 3 and P 2 O 5 containing glass reveals that the additives extend the gap between the glass transition and crystallization temperatures and suppress formation of μ, cordierite while promoting direct crystallization of α cordierite. Detailed TEM analysis of nucleation and growth of crystals in hot‐pressed pellets of B 2 O 3 /P 2 O 5 ‐containing glass particles shows that nucleation occurs on unidentified heterogeneous nuclei at the sites of the previous particle surfaces. Growth of α cordierite with a cellular morphology or μ cordierite with a dendritic morphology is most likely controlled by the glass composition directly ahead of the growth front.