Glass nano metal matrix

Nanoparticles of metals and semiconductors in glass matrix are commonly formed by homogeneous nucleation in solid state. 'First the desired metal or semiconductor precursors are introduced and homogeneously distributed in the liquid glass melt at high temperatures during glass making, before quenching to room temperature. Then the glass is annealed by heating to a temperature to about the glass transition point and then held for a pre-designed period of time. During annealing, metal or semiconductor precursors are converted to metals and semiconductors. As a result, supersaturated metals or semiconductors form nanoparticles through nucleation and subsequent growth via solid-state diffusion.
Homogeneous glasses are made by dissolving metals, in the form of ions, in the glass melts and then rapidly cooled to room temperature. In such glasses metals remain as ions. Upon reheating to an intermediate temperature, metallic ions are reduced to metallic atoms by certain reduction agents such as antimony oxide which is also added into the glass. Metallic nanoparticles can also be nucleated by ultraviolet, X-ray, or gamma-ray radiation if a radiation-sensitive ion such as cerium is present. The subsequent growth of the nuclei takes place by solid-state diffusion. For example, glasses with nanoparticles of gold, silver, and copper can be prepared with such an approach. Although metallic ions may be highly soluble in the glass melts or glasses, metallic atoms are not soluble in glasses. When heated to elevated temperatures, metallic atoms diffuse and migrate through the glasses and subsequently form nuclei. These nuclei grow further to form nanoparticles of various sizes. Since solid-state diffusion is relatively slow, it is relatively easy to have a diffusion-controlled growth for the formation of monosized particles.
Nanoparticles dispersed in glass matrix can be synthesized through sol-gel processing as well. There are two approaches: (i) mixing presynthesized colloidal dispersion with matrix sol before gelation, and (ii) making a homogeneous sol containing desired ions for the formation of nanoparticles first and annealing the solid product at elevated temperatures.


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