It is known that pieces with nanocrystalline structure condition have much higher performance than those with an ordinary structure. There are number of techniques for manufacturing nanocrystalline materials in powder condition however a question of manufacturing bulk material in the same nanocrystalline state is still a problem. One of the main reasons for the above-mentioned is that compaction and sintering of nanocrystalline powders are accompanied with intensive growth of particles – a process which promotes to formation of bulk material in an ordinary crystalline state instead of being crystallized in the desirable nanocrystalline state. A number of new techniques for powder consolidation aimed at fully dense bulk nanocrystalline materials have been proposed in recent years. Preparation of bulk pieces requires compaction and sintering of the obtained nanocrystalline powders. This process is connected with lots of problems, namely, it is very difficult to preserve nanocrystalline structure of powders in the bulk. Standard methods for manufacturing of bulk material are: cold compaction with further sintering, hot pressing, sintering under high pressure, electric discharge synthesis, shock-wave sintering and gasostate sintering. Basing on these methods by different companies there were designed and built various installations. Using of these methods and of an appropriate installation is not effective because of intensive growth of grains which stimulates formation of an ordinary structure instead of the desired nanostructure. One way to prevent the processes of grain growth is adding of inhibitors to the powders. However this route is not the best one because composition of the material will possibly be changed due to contaminations brought in the powders: nanocrystallinity may improve properties of the material; however adding of inhibitors may reduce these properties. Therefore improving of characteristics induced by preservation of nanocrystallinity is not as efficient as expected. Another way to prevent the processes of grain growth is: guiding of sintering processes in the time limited to a certain extent. This route is realizable in the installation based on using SPS method which is considerably new and it can be used to conduct in situ preparation and synthesis of composites with superfine microstructures. In spite of the fact that there are already designed and constructed the SPS method-based industrial installations, physical essence of the provided processes are not yet clarified to final extent. Therefore, upon fabrication of any new material by using this installation the scientists continue to study the provided processes of sintering.
Journal: TechConnect Briefs
Volume: 1, Nanotechnology 2009: Fabrication, Particles, Characterization, MEMS, Electronics and Photonics
Published: May 3, 2009
Pages: 67 - 70
Industry sector: Advanced Materials & Manufacturing
Topics: Advanced Manufacturing, Nanoelectronics