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Nano-sized metal inclusions in ceramic matrixes are of great interest for many technological applications, and great efforts have been made to develop synthetic routes to materials containing small and homogeneously dispersed metal particles in ceramic matrixes. There are many interesting and important properties that can be obtained from enclosed or supported nano-sized metal particles of narrow size distributions in the range 1-20 nm, such as optical absorption tunable by particle size, catalytic properties, magnetic properties where the ferromagnetism of bulk-metal changes to less ordered states more typical of molecules, and hardness/toughness optimised combinations of tough metal and brittle ceramic.
We have developed a route to Ni metal inclusions of sizes down to 2-5 nm, homogenously loaded in amorphous Al2O3. The composites could be obtained as films or very porous structures with any Ni:AlO1.5 ratio between 1 to ca 90 mol%. Other mono- and hetero-metallic inclusions have also been prepared, such as CuNi alloy particles in Al2O3.
The films have shown to be highly efficient and durable spectrally selective solar heat absorbers, and the materials have shown to sustainably catalyse the industrially important syngas reaction of CO2 and CH4 to yield CO and H2. We have also used the films as substrates for growth of carbon nanotubes, and are now investigating the magnetic properties; ZFC and FC magnetization measurements showed that the blocking temperatures (TB) increased with Ni concentration, and that the irreversibility temperatures (Tirr) are close to TB for samples with less than 80% Ni, indicating a narrow size distribution of the particles. In contrast, for 90% Ni Tirr is much higher than TB, probably due to clustering of Ni particles.
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