Nanocomposites and nanomaterials

Molybdenum carbide nanostructural coatings obtaining by electrolysis of salt melts
Malyshev V.V., Shakhin D.B., Kushchevska N.F., Luzan D.R.
University”Ukraine”, 23 Lvivska St., Kyiv-03115, Ukraine. 
E-mail: viktor.malyshev.igic@gmail.com

The goal of this study was to investigate the composition of cathode products of carbon-containing melts based on the eutectic mixture of sodium chloride and lithium fluoride and melts based on sodium tungstate depending on the electrolysis conditions, as well as to fulfill the molybdenum carbide galvanic coatings HTES.
Experiments at T = 1173 K and cathode current density ic = 8 A/dm2 showed that continuous molybdenum precipitates are formed at the Na2MoO4 concentration in the melt of ≤ 15 wt. %. At a higher molybdate content, molybdenum oxides precipitate along with molybdenum.
To investigate the influence that other parameters have on the properties and structure of the Mo and Mo2C coatings, we selected the following optimal alloys: NaCl – LiF – 5 wt % Na2MoO4, NaCl – NaF – 5 wt % Na2MoO4 – 2 wt % Na2CO3. Continuous precipitates were obtained at T = 1073-1323 K. Well-adhered continuous pore-free coatings are observed at a current density of 2–15 A/dm2 and deposition rate of 2-20 μm/h. The current yield of carbide coatings is 40-50%, and their thickness reaches 30 μm.
A coarse-crystalline structure of formed coatings was made finer using DC reverse mode during the electrolysis. The durations ratio of the cathode and anode pulses (τc/τa) varied within the limits of 30-60, the duration of the anode period was 0.5-1.5 s, and its current density was 0.15-0.50 A/dm2. As a result, we succeeded in increasing the thickness of me.tal coatings to 200 μm and that of carbide coatings to 100 μm. The optimal parameters of the reverse mode were τc = 45 s, τa = 1.5 s, 
ic = 8-10 A/dm2, and ia = 20-30 A/dm2.
Continuous coatings of molybdenum carbide were obtained from electrolyte Na2WO4 – 5 mol % MoO3 – 10 mol % Li2CO3 at T = 1073-1223 K and ic > 0.5 A/cm2. At T < 1073 K and current densities higher than 0.5 A/cm2, the precipitates are presented by highly dispersed powders of molybdenum carbide with a specific surface up to 30 m2/h. Well-adhered, uniform, continuous, and absolutely pore-free coatings at T = 1173 K are observed at cathode current densities from 0.01 to 0.10 A/cm2. The deposition rate of coatings in the range of ic under study is 5-25 μm/h; the current yield of molybdenum carbide reaches 80%. The maximum thickness of the coatings does not exceed 100 μm.