Periodic precipitation of metal compound in agar gel mixed with glass powder

Abstract

Within the scope of a long-term research effort to make novel composite materials, the preparation of suitable precursors (pre-forms) was studied in this thesis. The long-term objective is a glass matrix containing a spatially periodic arrangement of metallic inclusions. The immediate objective of the presented thesis is the preparation of a glass powder pre-form containing metal compound precipitates of the desired arrangement. The metal compound chosen is copper oxalate. The initial pre-form is a glass powder dispersed in an agar gel. The method to produce the spatial arrangement of precipitates is the so-called periodic precipitation (Liesegang phenomenon). The agar gel phase serves as diffusion and precipitation medium only and is completely removed in a later stage. The approximate ratio is 30 ml agar gel per 100 g glass. An appropriate system is copper nitrate counter-diffusing with ammonium oxalate contained in the agar gel. The suitable concentration ratio is 0.3 : 0.1 M. The surface of the glass had to be made hydrophobic to prevent heterogenerous nucleation, which otherwise spoils the precipitation process. Chemical coating with dimethyldichloro-silane and consecutive physical coating 9dip coating) with paraffin wax allows suitable precipitation patterns to form. This type of coating can be removed completely by heat treatment at temperatures below the viscous sintering temperature of the glass powder, and the copper oxalate can be partially reduced to metallic Cu.