Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2018 Aug 30;8(1):13114.
doi: 10.1038/s41598-018-31521-3.

Spontaneous Colloidal Metal Network Formation Driven by Molten Salt Electrolysis

Affiliations
Free PMC article

Spontaneous Colloidal Metal Network Formation Driven by Molten Salt Electrolysis

Shungo Natsui et al. Sci Rep. .
Free PMC article

Abstract

The molten salt-based direct reduction process for reactive solid metal outperforms traditional pyrometallurgical methods in energy efficiency. However, the simplity and rapidity of this process require a deeper understanding of the interfacial morphology in the vicinity of liquid metal deposited at the cathode. For the first time, here we report the time change of electrode surface on the sub-millisecond/micrometre scale in molten LiCl-CaCl2 at 823 K. When the potential was applied, liquid Li-Ca alloy droplets grew on the electrode, and the black colloidal metal moved on the electrode surface to form a network structure. The unit cell size of the network and the number density of droplets were found to depend on the applied potential. These results will provide important information about the microscale mixing action near the electrode, and accelerate the development of metallothermic reduction of oxides.

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Electrochemical characteristics of the Mo electrode in LiCl-CaCl2 eutectic melt at 823 K (a) Cyclic voltammogram at the scan rate of 10 mV/s, together with representative photographed working electrode(WE) (ϕ1.5 mm) images at different potentials captured using a single-lens reflex digital camera (D810, Nikon Co.) (b) Time change of current density and supplied charge in each potential condition derived by chronoamperometry.
Figure 2
Figure 2
Photographs of the electrodeposited melt and black colloidal metal formed on the flat Mo electrode at 823 K. The snapshots correspond to almost the same region. The corresponding current-time curves are represented in Fig. 1b. (In Supplementary Video, we reported the temporal change of the electrode surface at E = −2.55 V.)
Figure 3
Figure 3
Morphology of metal droplets electrolytically deposited on flat Mo surface (a) Potential-dependent temporal changes of the droplet number density. The number of droplets in areas of 1.28 × 10−7 m2 was counted using ImageJ, and the average value thereof was calculated (b) Representative coalescence behaviour between electrodeposited droplets (t > 1.0 s, E = −2.55 V).
Figure 4
Figure 4
Cell generation mechanism by interfacial tension gradient-induced convection. (a) Schematic diagram of Marangoni convection near electrodes. (b) Length and grow rate of cells in the colloidal network obtained from image analysis. The minimum and maximum diameters of a given cell are denoted respectively as a and b in consideration of the thickness of the network, and the mean cell diameter is given based on multiple cells. t1 is the reference time when the cell was formed.

Similar articles

See all similar articles

References

    1. Kroll W. The production of ductile titanium. Trans. Electrochem. Soc. 1940;78:35–47. doi: 10.1149/1.3071290. - DOI
    1. Chen GZ, Fray DJ, Farthing TW. Direct electrochemical reduction of titanium dioxide to titanium in molten calcium chloride. Nature. 2000;407:361. doi: 10.1038/35030069. - DOI - PubMed
    1. Bhagat R, Jackson M, Inman D, Dashwood R. The production of Ti-Mo alloys from mixed oxide precursors via the FFC Cambridge process. J. Electrochem. Soc. 2008;155:E63–E69. doi: 10.1149/1.2904454. - DOI
    1. Jiang K, et al. “Perovskitization”-assisted electrochemical reduction of solid TiO2 in molten CaCl2. Angew Chem Int Ed. 2006;45:428–432. doi: 10.1002/anie.200502318. - DOI - PubMed
    1. Xiao W, Wang D. The electrochemical reduction processes of solid compounds in high temperature molten salts. Chem. Soc. Rev. 2014;43:3215–3228. doi: 10.1039/c3cs60327j. - DOI - PubMed
Feedback