Reactive growth of niobium silicides in bulk diffusion couples

Silicide characterization at alumina–niobium interfaces

“…At the processing temperature employed in this study, NbSi 2 , with a hexagonal crystal structure (space group P6 2 22) and lattice parameters a = 4.819 Å , c = 6.592 Å , and c = 120°, is also stable [66]. In diffusion couples involving bulk Nb/Si and bulk Nb/NbSi 2 phases in the temperature range from 1200-1350°C, only NbSi 2 and Nb 5 Si 3 formed [22]. Similarly, in samples prepared by field-activated pressure-assisted combustion synthesis of elemental Nb and Si powders at 1400°C, either Nb 5 Si 3 or a combination of Nb 5 Si 3 and NbSi 2 were formed [46].…”

“…In parallel, one can also compare the findings to those of prior studies of niobium-silicide nucleation and growth involving Nb/Si planar reaction couples [11], bulk diffusion couples of Nb/Si and Nb/NbSi 2 [22], or the deposition of thin Nb films onto single-crystal substrates [9], followed by annealing at various temperatures. As discussed by Milanese et al [22], thin-film studies can provide limited amounts of one or more components, phases may form sequentially rather than simultaneously, and interfaces may affect growth and diffusion.…”

“…The silicides found include NbSi 2 [17,18], Nb 5 Si 3 [17][18][19], Nb 3 Si [17][18][19][20], amorphous Nb silicides of varying composition [17,18], and a body-centered orthorhombic Nb 11 Si 4 phase [21]. In thin-film (and other periodic) systems, interpretation can be difficult due to limited amounts of one or more components, phases forming sequentially rather than simultaneously, and the effects of interfaces on growth and diffusion [22]. To avoid these complications, bulk diffusion couples of Nb-Si and Nb-NbSi 2 were used to study diffusion-controlled reactive growth of NbSi 2 and Nb 5 Si 3 [22].…”

“…In thin-film (and other periodic) systems, interpretation can be difficult due to limited amounts of one or more components, phases forming sequentially rather than simultaneously, and the effects of interfaces on growth and diffusion [22]. To avoid these complications, bulk diffusion couples of Nb-Si and Nb-NbSi 2 were used to study diffusion-controlled reactive growth of NbSi 2 and Nb 5 Si 3 [22]. In Nb-Si couples, NbSi 2 nucleated first and grew much faster than the Nb 5 Si 3 layer that developed (the NbSi 2 layer was &1 order of magnitude thicker than the Nb 5 Si 3 layer).…”

Preparation of Niobium Disilicide Coating by Heating Niobium in a Sodium–Silicon Melt

“…No formation of Nb 5 Si 3 on Nb plates has been reported for NbSi 2 coating prepared by pack cementation at 1327 1373 K 8,9) and by electroless plating using molten salt at 1173 K. 12) On the other hand, formation of Nb 5 Si 3 was confirmed in the experiments of NbSi diffusion couples at higher temperatures (14731773 K) under an ambient pressure 22,23) and under high pressure (40 MPa) with SPS equipment.…”