Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10620585 | Acta Materialia | 2011 | 9 Pages |
Abstract
The Ag-Ni system is characterized by large differences in atomic sizes (14%) and a positive heat of mixing (+23Â kJÂ molâ1). The binary equilibrium diagram for this system therefore exhibits a large miscibility gap in both solid and liquid state. This paper explores the size-dependent changes in microstructure and the suppression of the miscibility gap which occurs when free alloy particles of nanometer size are synthesized by co-reduction of Ag and Ni metal precursors. The paper reports that complete mixing between Ag and Ni atoms could be achieved for smaller nanoparticles (<7Â nm). These particles exhibit a single-phase solid solution with face-centered cubic (fcc) structure. With increase in size, the nanoparticles revealed two distinct regions. One of the regions is composed of pure Ag. This region partially surrounds a region of fcc solid solution at an early stage of decomposition. Experimental observations were compared with the results obtained from the thermodynamic calculations, which compared the free energies corresponding to a physical mixture of pure Ag and Ni phases and a fcc Ag-Ni solid solution for different particle sizes. Results from the theoretical calculations revealed that, for the Ag-Ni system, solid solution was energetically preferred over the physical mixture configuration for particle sizes of 7Â nm and below. The experimentally observed two-phase microstructure for larger particles was thus primarily due to the growth of Ag-rich regions epitaxially on initially formed small fcc Ag-Ni nanoparticles.
Related Topics
Physical Sciences and Engineering
Materials Science
Ceramics and Composites
Authors
C. Srivastava, S. Chithra, K.D. Malviya, S.K. Sinha, K. Chattopadhyay,