200
6 Nanocrystalline Deposits
Fig. 6.6 Hall–Petch relationship for electrodeposited Ni samples produced from Watts-type baths
of various saccharin concentrations (3 and 5 g dm −3 for No. 1 and 2, respectively) and with various
deposition conditions. Reprinted from [81]. Copyright (2009), with permission from Elsevier
the decrease in grain size was rated as being either beneficial [78] or harmful [84]
for the corrosion resistance. The good corrosion resistance of nc-Ni was associated
with its grain boundary structure [106].
6.2.4 Miscellaneous Transition Metals
The electrodeposition of nanocrystalline cobalt [98, 107–110] is similar to nickel,
so much that they are often mentioned in comparative studies. The generally applied
electrodeposition method is pulse plating from a Watts-type bath, occasionally
containing also saccharin as stress reliever and grain refiner. The resulting mean grain
size falls in the 12–20 nm range. The mean grain size decreases with the increase in
the pulse current density [98]. As it is common for Co electrodeposited from low-pH
solutions, the nc-Co samples were reported to be of the hcp structure in all abovementioned studies. (From solutions of higher pH, fcc-Co is occasionally obtained
that exhibits nearly the same atomic distances and whose free energy differs from
hcp-Co marginally. The fcc structure is favourable for Co at higher temperature.)
During the annealing of nc-Co, a relaxation process takes place around 500 K
(with a wide exothermic wave in the DSC curve) followed with a recrystallization
at around 625 K (narrow peak) [107, 109]. The recrystallization is complete before
the hcp–fcc transformation temperature (695 K) is achieved. The thermal behaviour
of electrodeposited nc-Co is influenced by the sulphur content that originates from
the S-containing additive in the bath (saccharin). The higher the sulphur content, the
larger the activation energy of the grain growth and the higher the peak temperature
related to recrystallization in the DSC curves [109]. This behaviour was attributed to
6 Nanocrystalline Deposits
Fig. 6.6 Hall–Petch relationship for electrodeposited Ni samples produced from Watts-type baths
of various saccharin concentrations (3 and 5 g dm −3 for No. 1 and 2, respectively) and with various
deposition conditions. Reprinted from [81]. Copyright (2009), with permission from Elsevier
the decrease in grain size was rated as being either beneficial [78] or harmful [84]
for the corrosion resistance. The good corrosion resistance of nc-Ni was associated
with its grain boundary structure [106].
6.2.4 Miscellaneous Transition Metals
The electrodeposition of nanocrystalline cobalt [98, 107–110] is similar to nickel,
so much that they are often mentioned in comparative studies. The generally applied
electrodeposition method is pulse plating from a Watts-type bath, occasionally
containing also saccharin as stress reliever and grain refiner. The resulting mean grain
size falls in the 12–20 nm range. The mean grain size decreases with the increase in
the pulse current density [98]. As it is common for Co electrodeposited from low-pH
solutions, the nc-Co samples were reported to be of the hcp structure in all abovementioned studies. (From solutions of higher pH, fcc-Co is occasionally obtained
that exhibits nearly the same atomic distances and whose free energy differs from
hcp-Co marginally. The fcc structure is favourable for Co at higher temperature.)
During the annealing of nc-Co, a relaxation process takes place around 500 K
(with a wide exothermic wave in the DSC curve) followed with a recrystallization
at around 625 K (narrow peak) [107, 109]. The recrystallization is complete before
the hcp–fcc transformation temperature (695 K) is achieved. The thermal behaviour
of electrodeposited nc-Co is influenced by the sulphur content that originates from
the S-containing additive in the bath (saccharin). The higher the sulphur content, the
larger the activation energy of the grain growth and the higher the peak temperature
related to recrystallization in the DSC curves [109]. This behaviour was attributed to