Effects of metals on the structure of heat-treated sol-gel SiO2 glasses

The crystallization of amorphous SiO2 sol-gel made samples, containing diff erent metals has been studied after heat treatments in air at temperatures in the range 100 to 800 degreesC. Two types of samples were investigated, b ulk and thin coatings. In bulk samples the SiO2 matrix crystallizes during treatments at low temperature (500 degreesC) when certain metals, such as A g or Ag + Cu, are added. The phase in which the glass crystallizes, quartz or cristobalite, depends on the metal or metals added. Other metals such as Cu, Fe and Co form metal oxide aggregates, but the amorphous SiO2 structur e does not crystallize after thermal treatments at temperatures up to 800 d egreesC. In coating samples, crystallization of the SiO2 matrix is not obse rved, regardless of the incorporated metal and of the annealing treatment a t temperatures up to 800 degreesC. This result indicates that the amorphous structures of the coatings and bulk samples are different. (C) 2001 Elsevi er Science Ltd. All rights reserved.