Nanocrystalline Oxides and Carbides of Transition Metals
Nanocrystalline Oxides and Carbides of Transition Metals. Synthesis, Properties and Application
Tech Area / Field
- ENV-RWT/Radioactive Waste Treatment/Environment
- MAT-SYN/Materials Synthesis and Processing/Materials
- PHY-SSP/Solid State Physics/Physics
3 Approved without Funding
VNIIEF, Russia, N. Novgorod reg., Sarov
- Institute of Solid State Chemistry, Russia, Sverdlovsk reg., Ekaterinburg
- Tohoku University / Graduate School of Engineering, Japan, Sendai\nUniversity of Tsukuba / Institute of Materials Science, Japan, Ibaraki\nUniversität Stuttgart / Institut für Theoretische und Angewandte Physik, Germany, Stuttgart\nNational Institute for the Physics of Matter, Italy, Bologna\nUniversity of Bologna/Department of Physics, Italy, Bologna\nSCK-CEN, Belgium, Mol
Project summaryThe problem of production, examination and use of nanocrystalline materials becomes progressively more urgent in recent years. Generally, properties of nanocrystalline materials differ from those of coarse-grained, monocrystalline or amorphous materials having similar chemical compositions. This circumstance explains the interest paid to nanosized materials both in basic and applied research. A large number of nanomaterials based on pure metallic and nonmetallic elements have been prepared today. Great attention has been attached to production of two- and multicomponent alloys, which are used in practice as soft or hard magnetic materials. The work on production of nanocrystalline metal compounds has been started. In particular, successful studies concerned with synthesis of stoichiometric sulfides and oxides deserve mentioning. However, synthesis of nonstoichiometric nanocrystalline compounds, such as oxides and carbides of transition metals, has received little attention. But these materials in the nanocrystalline state can acquire practically significant properties, which will considerably extend their applications.
The study and the use of nonstoichiometric oxides and carbides of transition metals, for example, ZrO2-y, TiO2-y, TiCy, VCy, and NbCy, are due to their unique physical and chemical properties, including superior conductivity, radiation resistance, high hardness, and refractoriness. In addition to these practically significant properties, the said materials are nonstoichiometric and, hence, their properties can be changed by varying their chemical composition, while these materials still remain binary compounds. Numerous studies of these compounds, which were performed almost all over the world, showed that nonstoichiometry is due to appearance of structural vacancies both in the nonmetal and metal sublattices. The vacancy concentration may be as large as several tens of atomic percent. For example, cubic titanium carbide TiCy contains 50 at.% of carbon vacancies at the lower limit of the homogeneity region, while the concentration of titanium vacancies in cubic titanium monoxide may be as large as 23 at.%. The Springer-Verlag Publishers have recently published a book, in which the authors of this Project considered in detail the cause of nonstoichiometry and its effect on properties of oxides and carbides.
In terms of this Project, it is planned to prepare oxides and carbides of such transition metals as Ti, Zr, V and Nb in the nanocrystalline state. The synthesis method will be high-energy ball milling of coarse-grained oxides and carbides having different nonstoichiometric compositions. Also, transition-metal carbides will be prepared from powders of the corresponding metals and carbon. Two processes, namely refinement of particles and mechanical synthesis of carbides, will take place simultaneously during high-energy milling of the mixture of metal powders and carbon. High-energy milling will also be used to dope zirconium dioxide ZrO2 with yttrium oxide Y2O3. This technology will provide stabilization of the cubic phase in zirconium dioxide and ensure a nanometer size of grains. Powders prepared by the first and second methods will be compacted using low-temperature axial and hot pressing techniques, and also the method of high-temperature isostatic pressing so as to obtain compact samples having a minimum porosity. The prepared powders and compact samples will be subject to full chemical certification. The microstructure, the crystal structure and nonstoichiometry will be examined using optical and electron microscopic methods and the X-ray diffraction analysis. Mechanical, electrokinetic, thermodynamic and magnetic properties of the powders and the compact samples will be studied. Experiments will be accompanied by a theoretical analysis and generalization of obtained results. The research results will be used to formulate recommendations on production and practical use of nanocrystalline oxides and carbides of transition metals taking into account environmental safety. Fuel cells and containers for radioactive waste disposal will be considered as the main applications.
The research will make the best use of capabilities and professional skills of defense-oriented scientists and scientists working at the Russian Academy of Sciences.
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