Preparation of diboride coatings by electrophoretic deposition in nanoparticle-containing molten inorganic salts

Abstract

Molten inorganic salts containing solid nanoparticles with a stable and uniform dispersion have attracted great attention as efficient heat transfer and storage materials 1,2 and for catalysis for chemical reactions [3][4][5] . Electrophoretic deposition in molten inorganic salts containing nanoparticles, have not been reported in the literature, compared with the related wide investigations in aqueous and organic suspensions 6,7 . Here we report the possibility of electrophoretic deposition of nanoparticles in high-temperature molten salts. In molten fluorides and chlorides, cell voltages of 1.2-1.5 V below the decomposition voltage of the electrolytes, were applied to perform the electrophoretic deposition of nanoparticles (e.g., TiB2 and ZrB2) on different cathode substrates, resulting in compact and adhesive coatings with high hardness. These findings should present opportunities to synthesize additional coatings and films via the proposed process.

Synthesis of a (Ti, Mo)B2 coating by electro‐codeposition in NaCl–KCl–AlCl3–MoO3 melt containing TiB2 nanoparticles

“…With higher magnification (Figure 2D), it seems that these micron-sized particles consist of a large number of nano-sized particles, which is similar to the results reported for EPD of ZrB 2 nanoparticles in NaCl-KCl-AlCl 3 melt. 12 Therefore, it can be concluded that in NaCl-KCl-AlCl 3 molten salts the EPD of TiB 2 nanoparticles could be achieved successfully, resulting in fabricating a dense and adhesive TiB 2 coating.…”

“…To avoid the decomposition of components of the electrolyte, we employed cell voltages below this value. So the applied cell voltage is selected in the range of 1.2–1.5 V. The detailed procedures could be referred to our previous studies 12 …”

“…Since 2017, it has been reported that nanoparticles could exist in the form of stable colloids in molten inorganic salts 8–11 . Motivated by this, the present authors have investigated the availability of electrophoretic deposition (EPD) of nanoparticles in molten halides (700–1000°C) and prepared dense TiB 2 and ZrB 2 coatings by EPD under constant cell voltages of 0.4–1.5 V, which are below the theoretical deposition voltages of components of the molten electrolyte 12,13 …”

“…[8][9][10][11] Motivated by this, the present authors have investigated the availability of electrophoretic deposition (EPD) of nanoparticles in molten halides (700-1000 • C) and prepared dense TiB 2 and ZrB 2 coatings by EPD under constant cell voltages of 0.4-1.5 V, which are below the theoretical deposition voltages of components of the molten electrolyte. 12,13 Thus, we are curious about that if we continue to add electroactive species into the bath, without any imposed stirring of the system, could the electro-codeposition of nanoparticles and metal ions (i.e., simultaneously occurrence of EPD of nanoparticles and electrochemical deposition of metal ions) happen under proper cell voltages? If so, it could provide a novel method for producing composite coatings.…”

“…So the applied cell voltage is selected in the range of 1.2-1.5 V. The detailed procedures could be referred to our previous studies. 12…”