Degassing of a cordierite glass melt during nucleation and crystallization

The crystallization of coarse cordierite glass particles (0.4-0.63 mm in diameter) was studied by means of evolved gas analysis during constant heating. It was observed that crystallization is accompanied by complex degassing phenomena of H2O, CO, CO2, O-2 and Ar. The evolution process gradually appears at temperatures above the glass transition temperature. At higher temperatures two distinct degassing maxima are evident which can be attributed to the formation of the primary high-quartz solid-solution phase (''mu-cordierite'') and its subsequent transformation into the hexagonal high-temperature polymorph of cordierite (''indialite''). In respect of these two crystallization steps, characteristic differences in the evolution behaviour between (a) CO and (b) H2O, CO2, O-2 and Ar are detectable. The results are discussed in relation to the different chemical properties and the ''porosity'' of both crystalline structures.