X-RAY AND ELECTRON-DIFFRACTION STUDIES ON CRYSTALLIZATION OF 2 CORDIERITE PRECURSORS PREPARED BY ATOMIZATION OR SOL-GEL PROCESS

The crystallization paths of two cordierites, a sol-gel cordierite and an industrial cordierite obtained by the atomization process, are com pared by using XRD, EDS and TEM techniques. The sol-gel precursor crys tallizes following a simple path from mu-cordierite to alpha-cordierit e. On the contrary, the precursor obtained by the atomization process presents more intricated crystallization paths with various phases. Fi rst, a partial demixing in mu'-cordierite and spinel phases occurs, fo llowed by a total demixing in alpha-quartz and spinel phases. Then a m ixing of alpha-cordierite, sapphirine, spinel, mullite and alpha-quart z phases is produced. Moreover, a double cell is pointed out by TEM fo r the mu'-cordierite and several multiple cells for alpha-cordierite. A method is given in order to distinguish, by electron diffraction, be tween alpha and beta phases.