C. Kollia et N. Spyrellis, TEXTURAL MODIFICATIONS IN NICKEL ELECTRODEPOSITION UNDER PULSE REVERSED CURRENT, Surface & coatings technology, 57(1), 1993, pp. 71-75
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.