Investigation of the Thermal Dissociation, Reassociation, and Synthesis of Zircon

The amount of dissociation present in zircon after 2‐hour heating periods at temperatures between 2800° and 3600°F. was determined by X‐ray analysis of quenched specimens. The course of dissociation was followed in the same manner during 8‐ to 10‐hour heating periods at temperatures of 2800°, 3000°, and 3200°F., respectively. Data are included that pertain to the synthesis of zircon from its constituent oxides at temperatures from 2100° to 2800°F. The results indicate that zircon is the stable phase up to about 2800°F.; above that temperature it becomes unstable, the degree of instability increasing with temperature, especially above 3200°F. On the basis of the results obtained from this investigation, a revision of the present phase diagram of the system zirconia–silica is proposed.