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| SHI C.X., YE H.Q. |
| A GENERAL SURVEY OF INSTITUTE OF METAL RESEARCH, CHINESE ACADEMY OF SCIENCES |
Abstract
The objective of this work was to obtain the nanocrystalline Cu - 5 vol.% Al2O3 powder material by modification of the original mechanical-chemical preparation procedure of nanocrystalline Cu powder. This procedure is based on the combination of milling of powders and reduction of CuO during preparation process.
The initial raw material was a prehomogenized CuO powder with the corresponding amount of aqueous solution of Al(NO3)3 . 9 H2O and addition of ammonia. The initial mixture was annealed at the temperature of 400°C for 1 h. In the annealing process, the ? Al2O3 secondary phase, was formed from aluminium nitrate directly in the CuO matrix. The formation of ? Al2O3 by phase transformation of Al(NO3)3.9H2O was confirmed by infrared spectroscopy (IR) of samples, thermogravimetric analysis (TG) and differential thermal analysis (DTA). The reduction of CuO to Cu took place subsequently in hydrogen at the temperature of 300°C for 2 h.
The crystallite size of the CuO and Cu matrix were evaluated on the base of X-ray measurements. The linear dimensions of Cu crystallites in the individual crystallographic directions after reduction are in range from 37 to 55 nm. Since Cu particles retained their nanocrystallic structure even at relatively high temperatures during reduction, it can be stated that fine and uniformly distributed Al2O3 particles inhibited the interface migration.
The Cu - 5 vol.% Al2O3 mixture was then wet-milled in the attritor for 8 h. The purpose of the wet-milling was to refine the structure of Cu matrix and make a distribution of the Al2O3 secondary particles more homogeneous. The most significant refinement of the structure of Cu particles was achieved after the first 4.5 hours of milling. When milling is further prolonged, the refinement of the structure of Cu particles is insignificant. After 8 hours of milling the average Cu crystallite size was 17 nm. The final nanocrystalline structure of Cu particles was achieved under the given conditions after 8 hours of milling.
The particles of Al2O3 secondary phase, formed by the "in situ" reaction directly in the matrix, efficiently inhibit the grain boundary migration and maintain the nanocrystalline structure of the matrix particles in the individual stages of preparation of the nanocrystalline Cu - 5 vol.% Al2O3 mixture.
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| No 1 (2001), p. 105-114 |
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