Theoretical justification of increase of productivity of galvanic sedimentation of coverings on the restored surfaces of details of cars
Abstract
Theoretical justification of increase of productivity of galvanic sedimentation of coverings on the restored surfaces of details of cars
Incoming article date: 13.03.2015Increase of productivity of processes of sedimentation of coverings on the restored surfaces of details of cars without decline in quality of the received deposit is a main objective on the way of improvement of galvanic processes. Productivity of galvanic sedimentation depends on the size of potential of the cathode and the anode; from concentration of components of electrolyte about a surface of sedimentation (cathode); from uniformity of delivery and dispersal of ions of metal on a sedimentation surface; from quantity of active sites of the cathode; from nature of passivation of the cathode; from temperature of electrolyte and from the speed of the movement of electrolyte in prikatodny space. Very strongly passivating of a cathodic surface limits the possible growth of productivity of galvanic sedimentation. Passivating consists in education on a surface of the cathode of the continuous passive film consisting of hydrogen, products of reaction of metal with electrolyte components, oxygen of air and foreign inclusions. The passive film is almost insoluble and disturbs electrocrystallization process, shielding a cathodic surface. And cathode covering speed a passive film directly depends on density of cathodic current. It is possible to assume that at achievement of some value of density of cathodic current the speed of formation of a passive film will exceed, the speed of delivery of ions of metal to a cathodic surface and origin of crystals of the besieged metal will become impossible. And on the remained active sites of the cathode where the passive film is absent or has the smallest thickness and growth rate, there will be centers of growth of crystals of metal (dendrites) on which there will be a concentration of the main processes of electrocrystallization. That is the cathodic surface of the restored detail will become covered by the local centers of sedimentation of metal – dendrites. The passive film interferes with growth of limit density of cathodic current at which receiving qualitative electroplated coating is possible. Mechanical elimination of a passive film during sedimentation of a covering considerably facilitates process of electrocrystallization and formation of a layer of metal on the processed detail surface, provides increase of uniformity of the received layer of metal and its microhardness, and also will prevent active formation of local sites of growth of dendrites at the high density of current.
Keywords: passive film, adsorption, sedimentation productivity, electrocrystallization, mechanical activation, crystal lattice