Features of phase transformations under low temperature synthesis of refractory compounds from mechanically activated powder mixtures
|Iryna V. Uvarova|
Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, Krzizanovsky, Kyiv 38(044), Ukraine
Decrease in the temperature of synthesis of refractory compounds can be achieved at the expense of acceleration of nuclei formation and diffusion processes via increasing the defectiveness of the structure of the interacting solids.
Different techniques for mechanical action on solid phase reagents which lead, on the one hand, to proceeding of mechanosynthesis reactions and, on the other hand, to decrease in the synthesis temperature and acceleration of all the process thanks to activation of diffusion processes in solid phases are considered in the present work.
In the case of proceeding of the mechanosynthesis reaction, under mechanical action formation of higher phases of refractory compounds with no intermediate products is preferable. As shown for a number of silicide and carbide systems, the mechanism of such reactions is interpreted in terms of acceleration of chemical interaction and formation of nuclei of the phase whose thermodynamic stability is determining under the process conditions.
Reduction in the tenseness (the mass ratio balls/powder) of processes of mechanical activation of reagents results only in increasing their specific surface area and defectiveness, which promotes a shift of the reaction of chemical interaction (in the case of further heat treatment) towards lower temperatures. The mechanism of these reactions is related to the determining role of diffusion processes.
Mechanical activation of a number of powder mixtures leads to activation of those reactions of solid solution formation that are not typical under usual conditions. This has been shown on the systems of solid solutions on the basis of titanium nitride in the Ti-Al-N system.
The decrease in the temperature of chemical interaction and possibility of production of refractory compounds with a particle size of about 100 nm are important results of intense mechanical action on reagents.
Presentation: Invited oral at E-MRS Fall Meeting 2008, Symposium I, by Iryna V. Uvarova
See On-line Journal of E-MRS Fall Meeting 2008
Submitted: 2008-04-10 15:08 Revised: 2009-06-07 00:48