K. Murase et al., Determination of Mo(VI) species and composition in Ni-Mo alloy elating baths by Raman spectra factor analysis, J ELCHEM SO, 147(6), 2000, pp. 2210-2217
The equilibrium constants of the formation of isopolymolybdates HrMo7O24(6-
x)- (x = 0-2), heteropolymolybdate NiMo6O24H64- and Mo(VI)-citrate complexe
s H-r(MoO4)(2)Cit((7-r)-) and H(r)MoO(4)Cit((5-r)-) (Cit(3-) = C6H5O73-) we
re determined from factor analysis of Raman spectra and visible absorption
spectra to calculate the chemical species present in acidic Ni-Mo alloy pla
ting baths. On the addition of citrate to a Ni(II)-Mo(VI) bath, (i) the pol
ymolybdates were decomposed by the formation of H-r(MoO4)(2)Cit((7-r)-) com
plex, and then (ii) H(r)MoO(4)Cit((5-r)-) and NiCit(-) complexes formed. Th
is complex formation was necessary for the alloy deposition, but an excess
addition of citrate, which results in the formation of NiCit(2)(4-) complex
, lowered the current efficiency. The deposition behavior of Ni-Mo alloy fr
om Ni(II)-Mo(VI)-citrate baths was compared with that of pure Ni from Ni(II
)-citrate baths, in which concentrations of Ni(II)-species are identical to
those in the corresponding Ni(II)-Mo(VI)-citrate baths. The alloy depositi
on behavior is strongly governed by the ease of Ni deposition, indicating t
hat the electrodeposited nickel induces the deposition of molybdenum. (C) 2
000 The Electrochemical Society. S0013-4651(99)08-032-5. All rights reserve
d.