Additives containing carboxyl and amino groups increase the overpotential of a copper cathode during electrolysis in an acid sulfate electrolyte, the amino group being more effective than the carboxyl. At a given additive concentration the overpotential increment apparently depends on the adsorptivity and size of the additive molecule. The adsorptivity in turn depends on the number and kind of polar functional groups, the structural relation between electron‐donating atoms, and the lattice dimensions of the copper deposit. It is suggested that the behavior of a chemisorbed additive can be understood in terms of two effects, (i) the complete blockage of growth sites by chemisorption bonds and (ii) the partial blockage of adjacent sites by the physical bulk of the adsorbed molecule.
In the electrolysis of an acidified copper sulfate solution with a copper wire cathode located vertically along the axis of a cylindrical copper anode, addition of a small amount of norvaline to the solution causes a disklike deposit of copper to grow outwardly from the cathode and along the air‐solution interface. Experiments show that this phenomenon is due mainly to a solid reaction product arising from air oxidation of the norvaline along the line of contact between the copper anode, air, and solution. This solid, presumably present in a highly subdivided state, migrates by surface diffusion from the anode to the cathode along the air‐liquid interface, giving rise to nucleation sites that lead to the interfacial cathode growth. The mechanism is thought to involve a conductive surface film containing copper powder as a conducting medium. The rate of disk formation depends on the concentration of the norvaline, the area of anode surface along the air‐solution interface, the acidity of the solution, the partial pressure of oxygen above the solution, and the rate of current flow. It does not depend very markedly on the concentration of the copper sulfate.
Bei der Elektrolyse einer angesäuerten Cu‐sulfatlösung mit einer Cu‐Drahtkathode , die von einer zylindrischen Cu‐Anode umgeben ist, bildet sich bei Zugabe geringer Mengen Norvalin zu der Lösung eine scheibenförmige Cu‐Abscheidung außen an der Kathode längs der Grenzfläche Luft‐Lösung.
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