TEXTURAL MODIFICATIONS IN NICKEL ELECTRODEPOSITION UNDER PULSE REVERSED CURRENT

Nickel electrodeposits consist of crystallites whose orientation, micr ostructure and size depend on the electrolytic conditions. Study of th e mechanism of nickel electrocrystallization has indicated that the or iented growth observed is determined by the specific inhibition exerte d by the chemical species which exist or are formed on the metal-elect rolyte interface (catholyte) and which are selectively absorbed on the continually renewed metal surface. The pulse reversed current (PRC) t echnique was used to perturb the electrocrystallization process and he nce to change the texture and the structural characteristics of nickel electrodeposits. The structural changes that occur in deposit orienta tion under PRC conditions were studied. Nickel electrodeposition was r ealized from a Watts-type bath on a rotated cathode, and the electroly sis parameters (current density, rotation velocity, electrolyte pH and temperature) were chosen in such a way that using direct current they led to the preparation of perfectly [100], [211], [210], [110]A and [ 110]B textured deposits. The deposit texture was determined by X-ray d iffractometry and the results are summarized in texture diagrams given as a function of PRC parameters: pulse frequency and duty cycle. It w as proved that the texture is directly related to PRC parameters, whic h provoke strong perturbation in the crystal growth process. This phen omenon is reinforced when both the pulse frequency and the duty cycle are small. The PRC technique affects the nickel electrocrystallization process according to a mechanism analogous to the action of organic a dditives under direct current conditions by intervening in the catholy te composition and hence in the adsorption-desorption phenomena occurr ing at the metal-solution interface during the dissolution and the dep osition time.