Nanocomposites and nanomaterials

Electrochemical behavior of dielectrics and semiconductors in ionic melts
Malyshev V.V.1, Gab A.I.1, Shakhnin D.B.1, Talavira Ye.S.1
1 Institute of Engineering & Technology, Open International University of Human Development “Ukraine”, 23 Lvivska St., Kyiv-03115, Ukraine. 
E-mail: viktor.malyshev.igic@gmail.com

The grains of diamond, boron nitride, and silicon and boron carbides in contact with the melt can be used as a cathode material for the high-temperature electrochemical synthesis (HTES) of molybdenum carbide. To electrochemically coat the high-resistance dielectrics (HRD) and semiconductors (SC) grains, they were held in the melts of the following compositions: Na2WO4 - 5 mol % of MoO3 - 10 mol % of Li2CO3 or KCl - NaCl (1 : 1) - 5 mol % of Na2MoO4 - 7.5 mol % of Na2CO3 at 1073-1173 K and the cathode current densities 10-100 A·m-2. Under such conditions, the HRD and SC surfaces become conducting and play the role of an active substrate for the HTES of molybdenum carbide.
The rate of coating diamond grains with Mo2C substantially depends on both the electrolysis temperature and the cathode current density. As these parameters increase, the rate of deposition increases at the equal testing duration. For ASK 125/100 diamond grains, the coefficient of breaking load was found as the ratio of the breaking loads of coated and uncoated grains. Molybdenum carbide coatings deposited under certain operation conditions allows the initial breaking load of the diamonds to be elevated by the factor 1.3-1.9, depending on the electrolysis mode.
For AS-32 500/400 diamond grains, coating with molybdenum carbide enhances the breaking load by a factor of 1.1-1.3. In this case, the load increases as the mass or thickness of the coating increases.
The serveability of pilot lots of tools made from diamonds electroplated with molybdenum carbide at high temperature increased by the factor 1.5-2.0. Similar results were also obtained in the case of molybdenum carbide deposition on the boron nitride grains.
Mo2C coatings were deposited onto the 400/320 sized silicon carbide grains and onto the 160/125 sized boron carbide grains at 1173 K and cathode current densities 50-200 A·m-2 during 15-90 min. The coating degree substantially depends directly on the cathode current density and the electrolysis duration. Upon coating deposition, the breaking load coefficient of the boron and silicon carbides grains was 1.5-2.5, and the capillarity of the boron and silicon carbides grains increased by the factors of 3.4-4.0 and 2.3-2.5, respectively.