III International Conference

PP-III-14residual pressure of 0.67 Pa, first at room temperature and then stepwise at 473, 673, and 873K. The cell was heated using a programmable furnace and the temperature was measuredusing a Pt–Rh (10 wt.%) Pt thermocouple. The retort was then filled with high purity argon(U-grade: < 3 ppm H 2 O and < 2 ppm O 2 ) and the electrolyte was melted. Li 2 CO 3 , Na 2 MoO 4and Li 2 C 2 were added to the alkali chloride melts.Molybdenum sheets (99.99+ wt.% Mo) of 40 mm long, 8 mm width, with a thickness of100 μm were used in this study. Molybdenum samples were cleaned in xylene for 1 hour toremove organic contaminations from the surface and dried in an oven at 413 K. Themolybdenum substrates were immersed in the melt through a special hole in the top part ofthe retort under inert atmosphere. Synthesis of Mo 2 C on the molybdenum substrates wasperformed at 1123 K for 7 h with a cathodic current density of 5 mA cm -2 for molten systems(1) and (2) and with a anodic current density of 5 mA cm -2 for molten system (3). The glassycarbon crucible served as anode for systems (1) and (2). After experiments, the samples werewashed in distilled water and alcohol and weighted.The thickness of Mo 2 C samples obtained from molten systems (1) and (3) did notexceed 2μm, because carbides of refractory metals are formed a good barrier layer andinterdiffusion coefficients of molybdenum and carbon decreased on some orders ofmagnitude. Joint electroreduction of MoO 2- 4 and CO 2- 3 ions led to the formation of Mo 2 Ccoatings with the thickness ca. 50 μm. The morphology, roughness and specific surface areaof molybdenum carbides were determined for samples obtained by different methods.In all cases Mo 2 C coatings with the hexagonal lattice were obtained. At the same time abulk Mo 2 C usually has a cubic lattice. The formation of Mo 2 C with the hexagonal structure inthe processes of electrochemical synthesis is due to specific conditions (electrical field,double layer, high temperature) of electrocrystallization. It was noted in our studies thesimilarities of the effects of electrochemical crystallization and the external high pressure.A preliminary results on the catalytic activity of three types molybdenum carbidecoatings were obtained.AcknowledgementsThe financial support by the Netherlands Organization for Scientific Research (NWO),project No. 047.017.029 and by the Russian Foundation for Basic Research (RFBR), projectNo. 047.011.2005.016, is gratefully acknowledged.495