MECHANISM OF FORMATION OF NI-SC INTERMETALLIC COMPOUND LAYERS ON A NICKEL SURFACE IN MOLTEN HALIDES

The use of intermetallic compounds (IMC) based on rare-earth metals enables the problem of precision alloying to be solved. During investigation of the electrochemical synthesis of nickel-scandium IMC, the mechanism of formation was determined. Scandium cations with highest oxidation state and subions of alkaline metals were shown to take part in transfer of the electronegative component of the alloy onto the nickel substrate. Both the amount of scandium incorporated into nickel and the phase composition of the layers formed depend on temperature, process duration, current density, mass ratio of scandium metal and molten salts, and the initial concentration of scandium ions. Thermodynamic properties of the IMC were calculated using chronopotentiometric data. Six plateaux with constant potentials were recorded on the discharge curve, which is in agreement with the number of two-phase regions in the nickel-scandium phase diagram. From the results of the calculation it was concluded that in all compounds the bonds are predominantly covalent.