Труды КНЦ вып.5 (ХИМИЯ И МАТЕРИАЛОВЕДЕНИЕ вып. 5/2015(31))

As follows from XRD analysis, MoNi and MoNi 4 alloys form on the surface o f molybdenum plates during both currentless transfer and electrolysis. The alloy formation leads to the “loosening” of the molybdenum substrate surface, which increases the specific surface area of the samples during carbonization. Table 1. Phase compositions of molybdenum-nickel alloys after carbonization Alloy formation conditions Carbide formation conditions Phase composition exp # Melt NaCl-KCl- NiCl 2 -Ni, 1123 K currentless, 1 h 923 K, 0.5 h 973 K, 1 h 1023 K, 3 h 1123 K, 5 h Mo,Ni,Ni 3 Mo 3 C, Mo 0 25Ni0 75 , ^MoC Mo, Ni, Mo 2 C, Ni 3 Mo3C Mo, Ni, Mo2C Mo 2 C, Mo, Ni, p-NiMoO 4 A electrolysis, ic = 5 mA-cm-2, 1 h 923 K, 0.5 h 973 K, 1 h 1023 K, 3 h 1123 K, 5 h Mo, Ni Mo, Ni, Mo2C Mo 2 C, Mo, Ni, p-NiMoO 4 Mo, Ni, NiC, Mo2C B C Fig. 1 shows the cyclic voltammograms recorded at various reverse potentials on a molybdenum electrode in the NaCl-KCl-Li 2 CO 3 melt. These voltammetric curves have three cathodic waves (Rb R 2, R3) and four electrooxidation peaks (Oxb Ox2’, Ox2’’, Ox3). The height of wave Ri decreases monotonically with increasing polarization rate and almost vanishes at rate of 1.0 V-s-1. At the potential corresponding to wave R1, we performed potentiostatic electrolysis on the molybdenum electrode to form Mo 2 C. /, m A £\V Fig.l. Cyclic voltammograms on a molybdenum electrode in the ЫаС1-КС1-Ы2СОз melt at various reverse potentials. The electrode area is 0.238 cm2, the polarization rate is 0.1 V^s-1. T = 1023 K. Concentration o f Li 2 CO3: 2 .3710 -4 m o lcm -3. The quasi-reference electrode: platinum The electroreduction R 1 current density is very low, which is likely to be caused by a low concentration of carbon- containing particles. Wave R 1 can correspond to the reduction of carbon dioxide, since the solubility of CO 2 in the NaCl-KCl melt at the given temperature is ( 6 - 8 )T 0 mol-cm -3 and the electrode process can be described by the following reaction CO 2 + 4e- + 2Mo ^ Mo2C + 2O2-. (5) In the presence of a carbonate ion, the chemical reaction CO32- ~ CO 2 + O2- ( 6 ) precedes reaction (5). The use o f reverse at the potentials corresponding to wave R 1 (-0.77 V with respect to the platinum reference quasi-electrode) is accompanied by oxidation wave Ox 1 corresponding to the dissolution of Mo 2 C. The reverse from the base of wave R 2 (-0.850 V) does not cause a new oxidation wave, and the peak Ox 1 height increases. This behavior means that only the Mo 2 C phase forms on the molybdenum electrode in the cathodic half-cycle at these conditions and waves Ox 2 and Ox 1 had the same potential which corresponds to the dissolution of Mo 2 C. A new anodic peak Ox2’ was observed in the anodic region when a more negative potential -0.887 V vs. Pt was applied corresponding to R 2 wave. This peak can be assigned to the dissolution of the MoC phase. Therefore, the electrode processes corresponding to wave R 2 can be described by the following reactions: CO32- + 4e- + 2 Mo ^ Mo2C + 3 O2- (7) CO32- + 4e- + Mo ^ MoC + 3 O2-. ( 8 ) Waves R 3 and Ox 3 correspond to the discharge of alkali metal cations at the molybdenum cathode and the dissolution of alkali metals, respectively. Shoulder Ox 4 on the voltammograms arises from the oxidation of oxide ions at a molybdenum surface, as it was confirmed by addition of Li2O to the melt. 221