Microstructures developed in solid-liquid reactions: using Cu-Sn reaction, Ni-Bi reaction, and Cu-In reaction as examples

In this study Cu was reacted with pure liquid Sn and liquid Sn saturated with Cu at 240 °, 250 °, and 275 °C. Different microstructures were observed for different liquid Sn baths. For reaction in the Sn bath saturated with Cu, Cu6Sn5 and Cu3Sn with the layered structure formed. The growth follows the parabolic kinetics, suggesting the growth is diffusion-controlled. The apparent activation energy for the parabolic growth constant is 29 kJ mol−1. For reaction in pure Sn, the reaction produced a very thin and irregular Cu3Sn layer and a thicker Cu6Sn5 region with long protrusions into the Sn region. In addition to the diffusional reaction, Cu dissolved very rapidly into the pure liquid Sn bath. It is proposed that the formation of the non-planar structure is due to the rapid dissolution of Cu6Sn5 into the liquid Sn. Similar behaviors were observed for the reaction between Ni and liquid Bi as well as between Cu and liquid In. For Ni reacted in liquid Bi saturated with Ni at 300 °C, NiBi3 formed with the layered structure. For Ni reacted in pure liquid Bi. NiBi3 formed with an irregular structure. For Cu reacted in liquid In saturated with Cu at 200 °C, Cu11In9 formed with the layered structure. For Cu reacted in pure liquid In. Cu11In9 formed with an irregular structure; Cu7In3 and Cu2In also formed but were very thin, only a few microns in thickness.