Structural Characterization of Silver Doped Silica Prepared by Two Different Wet Chemical Methods

摘要

Two sets of silver doped silica samples were prepared,one using the traditional sol-gel method and the other from colloidal silica.In samples prepared by the lirst method,the addition of Ag promotes crystallization of the SiO_2 matrix when annealed at temperatures below those marked by the phase diagram.Before crystallization of the silica glass into the alpha-cristobalite phase occurs,the silver diffuses throughout the amorphous network to form silver colloidal particles at annealing temperatures that depend on the silver concentration.In samples obtained from the colloidal silica,larger Ag particles are formed at lower annealing temperatures.Further annealing at higher temperatures crystallizes the glass into the already mentioned phase.The reason of having larger Ag particles at lower temperatures in the latter set of samples is probably because they have a more open structure,produced by a wider distribution in the Si-O-Si bridging angle.