Nanoceramics Fabrication by Microwave Sintering with Application of Pressure
Investigation of Nanostructured Ceramic and Composite Materials Fabrication by Combined Effect of Microwave Radiation and External Pressure
Tech Area / Field
- MAT-SYN/Materials Synthesis and Processing/Materials
3 Approved without Funding
Kyrgyz-Russian Slavonic University, Kyrgyzstan, Bishkek
- Russian Academy of Sciences / Institute of Applied Physics, Russia, N. Novgorod reg., N. Novgorod\nVNIIEF, Russia, N. Novgorod reg., Sarov
- Kinki University / Liaison Center, Japan, Hiroshima\nOsaka University / Joining & Welding Research Institute, Japan, Osaka\nLoughborough University, UK, Loughborough\nUniversitat Bayreuth / Lehrstuhl für Werkstoffverarbeitung, Germany, Bayreuth\nPennsylvania State University / Materials Research Institute, USA, PA, University Park\nForschungszentrum Karlsruhe Technik und Umwelt / Institut für Hochleistungsimpuls und Mikrowellentechnik, Germany, Karlsruhe\nDepartment of the Navy / Naval Research Laboratory, USA, DC, Washington
Project summaryFabrication of structural and functional ceramics with dimensions of the structure on the order of 100 nm and below is a topical scientific and technological problem. Nanostructured materials feature enhanced plasticity, improved hardness, fracture toughness and wear resistance. The mastering of the production technology of volumetric articles from nanostructured materials will broaden considerably the application range of ceramic and composite parts in such industries as automobile, aircraft, mechanical engineering, energy production, etc. The enhanced plasticity of nanostructured materials facilitates net shape production, which is especially important in the fabrication of ceramic parts.
The efforts aiming on creating nanocrystalline ceramic and composite materials are actively undertaken in virtually all developed countries. By today’s date, numerous methods of producing a broad range of nanosize powders have been developed. The main difficulties in the fabrication of ceramic and composite parts from nanosize powders are caused by the absence of an adequate method that would ensure obtaining high-density materials while retaining a close-to-initial grain size. The currently existing densification methods either do not ensure achieving the necessary densities and performance (cold pressing), or lead to significant grain growth (high-temperature sintering). Although high potential of the use of nanostructured ceramic and composite materials to fabricate a broad range of products for perse applications is commonly recognized, no technology of their industrial fabrication exists to date.
The approach to the problem of nanostructured ceramics fabrication suggested by the authors of this project is to enhance the sinterability of nanopowder compacts by precisely controlled, combined effect of microwave field and external pressure. In the proposed method the microwave activation of the mass transport processes leading to enhanced sintering is accompanied by efficient porosity removal due to the applied pressure. To further enhance mass transport rates and reduce the agglomeration of the powders, methods of mechanical activation will be also utilized.
The team of authors of this project has a long-term experience not only in the field of materials science and fabrication of new materials, but also in the development of purposely designed equipment for microwave processing of materials. The implementation of this project will be based on the knowledge and experience gained during previous ISTC projects. The research methods successfully tested in these activities will be adapted to the problems of nanostructured ceramics and composites fabrication, with due regard to the specific requirements imposed by the work with nanomaterials.
At the first stage of project implementation, components of the gyrotron system for microwave processing of materials with application of external pressure will be designed and manufactured. As a prototype, the existing supermultimode applicator will be used. A hydraulic press will be integrated into the applicator to exert automatically regulated pressure on the samples. The pressing fixtures of special configuration will be fabricated from refractory ceramic and crystalline materials with low microwave absorptivity (alumina, silicon nitride, and sapphire). To reduce the time and labor consumption, the construction of the pressing fixture will be preceded by development of a model and computer simulation of the thermoelastic stresses in the dielectric press forms and the samples undergoing sintering under volumetric microwave heating.
The research will be aimed primarily on the fabrication of nanostructured ceramics based on metal oxide powders. In parallel with the development of the specialized equipment, an investigation into powder de-agglomeration and compaction methods leading to maximum and uniform density of the compacts will be undertaken. Based on the obtained experimental data, algorithms of automatic two-parameter control over the microwave heating and the pressure applied to the sample will be developed for each of the materials studied, to ensure sintering with a controlled densification rate. This will be a generalization of the rate-controlled sintering method onto the combined effect of the microwave field and the applied pressure on the material undergoing sintering.
The two-stage method of sintering nanopowder compacts tested in recent years for conventional heating methods will be developed for the case of a combined effect of the microwave field and external pressure. In the two-stage sintering method the grain growth at densification is depressed due to different kinetics of the grain-boundary diffusion and the grain boundary migration processes. The second stage of the densification process is carried out at a reduced temperature, so that densification continues but grain growth is limited since the activation energy for grain boundary migration is higher than the activation energy for grain-boundary diffusion. An additional method that will be used to enhance sinterability of the powders is their mechanical activation.
Along with the experimental investigation of the sintering process under a combined influence of the electromagnetic field and external pressure, sintering by the hot pressing method will also be studied. To obtain the materials with the highest possible density, the microwave-sintered samples will be further densified by hot pressing. After the microwave sintering stage, the sample will have closed porosity and density on the order of 90 % of the theoretical value. The samples will retain nanometer structure, since the grain growth rate at densities below 90 % is insignificant. The subsequent hot pressing of the samples at reduced temperatures, compared to conventional sintering, will make it possible to avoid grain growth and obtain materials with a close-to-theoretical density.
The expected results of the project implementation regarding the influence of
- two-parameter (temperature + pressure) control over the sintering process with the controlled densification rate,
- two-stage heating regime,
- mechanical activation of nanopowders,
- high-frequency ponderomotive force
on the sintering process will form a physical basis for obtaining high-density nanoceramics under a combined effect of the microwave field and applied pressure. The laws found in the studies of oxide materials as model structures will be of a general nature and will be applicable to the solid-phase sintering processes of all nanostructured ceramic and composite materials. The experimental and theoretical results obtained under the project will equally be applicable to such processes as joining of ceramic parts, development of ceramic and composite materials, since they are primarily based on the same mass transport phenomena as sintering. Therefore, the final result of the project implementation will be not only the scientific basis of nanostructured materials fabrication by sintering, but also general physical laws of the processes based on mass transport in polycrystalline materials.
The International Science and Technology Center (ISTC) is an intergovernmental organization connecting scientists from Kazakhstan, Armenia, Tajikistan, Kyrgyzstan, and Georgia with their peers and research organizations in the EU, Japan, Republic of Korea, Norway and the United States.
ISTC facilitates international science projects and assists the global scientific and business community to source and engage with CIS and Georgian institutes that develop or possess an excellence of scientific know-how.