| WP 1. NETWORK "HIGH PRESSURE TECHNOLOGIES OF NANO-CRYSTALLINE MATERIALS" (NANO) |
| Objectives:
Develop new high-pressure technologies of sintering covalent nano-crystalline powders. Investigate the transformations of grain boundary structure in nanomaterials under high pressure. Link Unipress research in nano-materials with European industry and scientific networks. |
| Description of the contents, the
workplan, the steps, the approach or the methodology:
Nanocrystalline materials are materials with crystallite size of the order of 100 nm or less. In materials with several nanometer grains up to 50% of the atoms are in interfaces between the very small crystallites. Both the small size of the crystallites and the large fraction of atoms in grain boundaries are the reasons for their special properties compared to micrometer size polycrystals with a potential for a break through in many imortant applications. The market of nanomaterials and the range of their practical applications increases very rapidly. However, most applications concern nano-powders. The technology of bulk nanocrystalline materials is less developed. The reason is that bulk materials with high density of interfaces are thermodynamically metastable and have a strong tendency to grain growth. We have been producing bulk nanocrystalline covalent materials: diamond and silicon carbide, under high pressure, high temperature conditions. Our solution to the problem is to use liquid silicon pressed between the grains of diamond by a very high pressure (5 GPa). Silicon wetts perfectly the diamond crystallites and simultaneously reacts with diamond creating silicon carbide. The resulting silicon carbide - diamond nanocrystalline composite is very hard and dense. For the first time with use of this unique method nanocrystalline diamond could be sintered without grain growth. However, the nature of the cohesive forces responsible for the strong adhesion between the nano-crystallites is not known. To understand physics of the processes at grain boundaries we need to settle co-operation with specialists in the thermodynamics of grain boundaries. Visits of the network partners to UNIPRESS and UNIPRESS scientific staff members to the network partners will be supported to carry out experiments, prepare papers for publication and discuss the interpretation of the results. Small workshops will be held bringing together the network partners to share the results on a multilateral basis. It is expected that the coordinated research will lead to progress in the following areas:
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