Initial stages of nucleation of molybdenum and tungsten carbide phases in tungstate–molybdate–carbonate melts

Abstract

The electrochemical nucleation of Mo 2 C and W 2 C crystals for tungstate-molybdate-carbonate melts of specific compositions on Ag, Au, Cu, Pt, and Ni substrates was studied by the electrodeposition method. The influence of electrocrystallization conditions (temperature, deposition time, initial current pulse, and current density) was investigated. Experimental measurements indicate that crystallization overvoltage is associated with threedimensional nucleation. Carbide deposition onto the substrates prepared from the same solid materials was not associated with crystallization overvoltage. The maximum value of the initial overvoltage, g max , which includes crystallization and electrolysis overvoltages, is proportional to the electrode surface area. Under these conditions, surface diffusion limits the electrode process rate. An increase in carbide deposition rate leads to an increase in the number of crystallization centers. This reduces the duration of surface diffusion. A rise in the melt temperature complicates the crystallization process by alloy-formation phenomena. Overvoltage maximum height for metals, which do not form alloys, is proportional to the reciprocal of their formation time. Melt temperature increase promotes interdiffusion of refractory metal, carbon, and substrate, and also intensifies their chemical interaction. Structural mismatch is observed during molybdenum and tungsten carbide electrodeposition onto different singlecrystal substrates.

Electrodeposition of tungsten and molybdenum carbide onto the surfaces of disperse dielectric and semiconductor materials

“…, curve 1. The resulting potential of the diamond electrode is practically equal to the stationary electrochemical potential –1.32 …–1.38 V of graphite electrode, which was measured earlier .…”

Management of composition cathodic products in the electrolysis of molybdenum‐, tungsten‐ and carbon‐ bearing halogenide‐oxide and oxide melts

“…Current output of carbide coatings is up to 40 … 50%, their thickness – 30 micrometres. Low current output in the case of carbide coatings is caused the deposit growth front violation as a result of its passivation by the lithium oxide formed during the electrode reaction . Subsequently carbides are deposited in powder form.…”