Molybdenum oxygen-containing solid-phase compounds were electrodeposited on the platinum cathode from the alkaline solutions containing sodium molybdate or ammonium molybdate under galvanostatic condition.
Bath composition and electrolytic condition were as follows:
Sodium bath: Na₂MoO₄·E₂H₂O (0.2M), NaOH (for adjusting pH10.5)
Ammonium bath:(NH₄) ₆Mo₇O₂₄·E₄H₂O (0.2M as Mo), NH₄OH (for adjusting pH10.5)
Current density: 50mA/cm², Temperature: 70°C
Black deposits were obtained from the sodium baths and black-brown deposits from the ammonium baths.
Structure of these deposits were investigated by studying the crystallization processes of the deposits. Thermal analysis curves, X-ray diffraction pattern, infra-red absorption spectra measurements and trymethyl-silylation of the deposits were carried out and following results were obtained.
As plated state, deposits were amorphous MoO₂-n (OH) _2n (n; 0-2). Deposits obtained from the sodium bath contained Mo₆+and Na+. Deposits were dehydrated to crystallize as MoO₂, Na₂Mo₃O6.5 and small amount of Na₂MoO₄ with elevating temperature.
Deposits obtained from the ammonium bath contained NH4. Differing from the deposits obtained from the sodium bath, they scarcely contained Mo₆₊. Deposits dehydrated with vapouring NH₃ to crystallize as MoO₂ by elevating temperature.