Crystallization and transformation of amorphous GeO2 derived from hydrolysis of germanium isopropoxide

Abstract

The cristobalite and α-quartz forms of GeO₂ crystallize on prolonged heating at 675–770 °C of amorphous GeO₂ prepared by hydrolysis of Ge(OC₃H₇)₄. The cristobalite is transformed into α-quartz in the later stages of heating. On heating at a rate of 10 °C min^–1, only the α-quartz crystallizes above 810 °C. The kinetics of crystallization of α-quartz from an amorphous phase has been studied by means of X-ray diffraction. The crystallization isotherms are described by the Avrami equation ln(1–f)=–ktⁿ with n= 4, the activation energy being 276 kJ mol^–1. A mixture of the cristobalite and α-quartz forms has been ground in air. The cristobalite is transformed into rutile. The transformation mechanism is discussed. On grinding, α-quartz is converted into the amorphous form. The rutile form, prepared by grinding, is transformed into α-quartz at 1 010–1 050 °C on heating at 10 °C min^–1.