The Morphological Evolution and Growth Trend of the Tantalum Layers in the Molten Salt Electrodeposition
摘要
The electrodeposition of tantalum from the LiF-NaF-7 wt.% K2TaF7 molten salt on tungsten matrix was investigated. The effects of current density and deposition time on the morphology and texture of tantalum deposited layers were studied. The crystalline phase and its optimal growth direction of tantalum deposited layers were determined. The results showed that with the increase in current density, the surface structure of the tantalum deposition layer changes from a pyramid-shaped cluster structure to a closely arranged prismatic cluster structure. Finally, the cluster boundaries gradually disappear and the surface tends to be flat. With the extension of deposition time, the surface structure of tantalum deposits undergoes a sequential transformation from spherical cluster structure to pyramid structure and then to prismatic structure. Eventually, the cluster structure disappears, forming a flat and dense surface. Under the conditions of 60 mA/cm2and 4 h, the deposition efficiency and deposition rate of tantalum reached maximum values of 80.13% and 38.91 μm/h, respectively; the current density had no significant effect on the preferred orientation of tantalum grains, as TC(200) remained greater than 1 with increasing current density. In contrast, deposition time exerted a significant influence, with TC(200) reaching a maximum of 3.53 at 4 h, indicating that the (200) crystal plane was the main preferred orientation plane. In addition, the corrosion behavior of the Ta coatings prepared under different deposition parameters was evaluated by potentiodynamic polarization tests in 0.1 M H2SO4 solution, using the corrosion current density as the assessment criterion. The coating deposited at 60 mA/cm2 for 4 h exhibited the lowest corrosion current density, indicating superior corrosion resistance, which is attributed to its dense and compact microstructure.