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 const ant heating. It was observed that crystallization is accompanied by co mplex degassing phenomena of H2O, CO, CO2, O-2 and Ar. The evolution p rocess gradually appears at temperatures above the glass transition te mperature. At higher temperatures two distinct degassing maxima are ev ident which can be attributed to the formation of the primary high-qua rtz solid-solution phase (''mu-cordierite'') and its subsequent transf ormation into the hexagonal high-temperature polymorph of cordierite ( ''indialite''). In respect of these two crystallization steps, charact eristic differences in the evolution behaviour between (a) CO and (b) H2O, CO2, O-2 and Ar are detectable. The results are discussed in rela tion to the different chemical properties and the ''porosity'' of both crystalline structures.