sintering of nanoceramics (rus. спекание нанокерамики) — a method for thermal processing of nanopowders or pieces molded from them, designed to produce compact (consolidated) and, as a rule, high-density materials and items with the minimum average grain size.

Description

To ensure sintering of nanopowders and nanoceramics, traditional sintering methods and special heat treatment techniques are used. A specific problem related to sintering of nanoceramics is preserving the small size of grain and preventing their aggregation when pressed specimens are being sintered. This is possible in the case of high-density compacts (not less than 0.7 of the theoretical density of the material) when sintering takes place fairly quickly at a relatively low sintering temperature (no more than half the material's melting temperature), reduced duration of the sintering process.

High-density compact nanomaterials are produced by hot pressing under high (up to 10 GPa or more) pressure. For example, TiN powder with average particle size of 40 nm is sintered at 4 GPa and 1400-1500 K; these parameters resulted in the grain size of not more than 60 nm and a relative density of 92-93%.

The use of pulse compaction makes it possible to produce samples with a higher density compared to static compaction due to the rapid movement of the powder medium while the short time of nanopowder heating ensures low recrystallisation at high temperature to preserve small size of particles. Another promising method is sintering of ceramic nanomaterials with microwave radiation.

This method is based on microwave heating of sintered samples. Heating is achieved through radiation in the millimetre range (frequency from 24 to 84 GHz). Volumetric absorption of microwave energy provides simultaneous uniform heating of the entire sample since the heating rate is not limited by thermal conductivity as in the conventional sintering methods. This allows producing sintered ceramics with uniform microstructure. For example, microwave sintering of compact samples of Al2O3 pressed from nanopowders with an average particle size of 26 nm and a relative density of 52% makes it possible to obtain samples of Al2O3 with a density of 99% and an average crystallite size of ~ 80 nm; the sintering temperature was 1770 K. The use of microwave sintering also makes it possible to make sound bonds between different ceramic nanomaterials.

Author

  • Gusev Alexander I.

Sources

  1. Gusev A. I. Nanomaterials, Nanostructures, and Nanotechnologies (in Russian) // Fizmatlit, Moscow (2007) - 416 pp.
  2. Gusev A. I., Rempel A. A. Nanocrystalline Materials. — Cambridge: Cambridge International Science Publishing, 2004. — 351 p.

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