Effect of structure on the electrochemical oxidation rate of copper and nickel sulfides

Nuevamente se utiliza la voltamperometría para el estudio de una oxidación electroquímica, pero esta vez para los sulfuros de Cu y Ni.

Synthesized samples were crystd. at 10-1000 K/s (νcooling) to study the effect of sulfides structure on the electrochem. oxidn. rates.  The methods of x-ray, optical and electronic microscopy were used to analyze the phase compn., and the methods of voltamperometry and chronoamperometry were used to study the laws of electrochem. oxidn.  Slow cooling of the samples with sulfide phase (Cu1,96S, Ni3S2) leads to crystn. of the metal (Ni, Cu).  High cooling rate leads to crystn. of nonequil. phases, increasing of proportion of the sulfide phase and decreasing of metallic component up to complete disappearance.  Electrochem. oxidn. of Cu and Ni sulfides proceeds stepwise: Me2S → Me2-XS → Me1 + XS → MeS → Me2+ + S.  Expts. revealed the rates of electrochem. oxidn. of granular sulfides that exceed the rates established for the slowly cooled samples.  The rates of the electrochem. oxidn. of Ni3S2 at potential of 1500 mV are 8.8 × 10-8 g/s·mm2 (at νcooling = 10 K/s) and 1.3 × 10-7 g/s·mm2 (at νcooling = 1000 K/s).  The rates of the electrochem. oxidn. of Cu2S at potential of 1000 mV are 2.8 × 10-8 g/s·mm2 (at νcooling = 10 K/s) and 4.3 × 10-8 g/s·mm2 (at νcooling = 1000 K/s).  The forming of a passivation layer effects the rate of the electrochem. oxidn. of Cu sulfide and Ni sulfide.  Nonequil. phase compn. and refinement provide greater reactivity of sulfides in the conditions of anodic polarization.  The oxidn. and passivation of metallic phase along with sulfide phases proceed from the surface of Me2S - Me alloys.  As for the samples crystd. at 1000 K/s only anodic oxidn. of sulfides occurs due to a lack of metallic phase.  The compns. of passivation films and potentials providing the extn. of S in the elemental state from the sulfides crystd. at high rates were detd.

 Diffusion and Defect Data--Solid State Data, Pt. A: Defect and Diffusion Forum (2012), 326-328(Diffusion in Solids and Liquids VII), 383-387

 Nechvoglod, O. V.; Selivanov, E. N.; Mamyachenkov, S. V