Nickel electroplating is widely used for decorative thin films, for better abrasion resistance and increased corrosion protection. The properties of the nickel deposit, such as its structure and morphology, can be varied by adding different organic additives to the nickel electrolyte. For example, additives such as coumarin and saccharin are used in nickel plating to generate a nickel film with uniform thickness on rough substrates.

Levelling is referred to as a process of progressive reduction of surface roughness during electrodeposition. In this case, scratches or non-uniform structures on the cathode represent the initial roughness, and the result of cathodic deposition is a smooth levelled layer with reduced roughness. In this type of levelling, more metal is deposited in the grooves than on the elevated surface features. This is due to the fact that metal deposition is less inhibited in the recessed features. True levelling requires the presence of appropriate levelling agents and brighteners. A wide variety of organic compounds are used as brighteners e.g. olefinic, acetylenic and sulphur and nitrogen containing compounds.

The singular and synergistic effect of the following additives on Ni electroplating was investigated and discussed in this work, such as the 1,1-dimethylpropargylamine (MPA:5 to 20 mg/L), sulfopropylated butynediol (HBOPS: 7.5 or 75 mg/L), 1-(3-sulfopropyl)-pyridinium betaine (PPS: 1.6, 3.2 or 150 mg/L), saccharin (1.5 g/L) and sodium allyl sulfonate (ALS: 1.5 g/L).

Reflectance and colour measurements showed that the samples coated from nickel electrolyte containing 5mg/L MPA and 7.5 mg/L HBOPS exhibited better uniformity, gloss and good throwing power in the low current density regime when compared to the electrolytes containing other additives or without MPA. Cross section analyses of the deposits indicate that the MPA is not only acting as a strong brighter, but it also helps in levelling (Fig. 1). XRD measurements indicated the effect of the different additives on the structure of the nickel deposits.

Fig. 1. Cross section of a sample deposited for 72 minutes at 2 A/dm² and 50 °C from a Ni electrolyte containing 240 g/L NiSO₄ x 7 H₂O, 40 g/L NiCl₂ x 6 H₂O, 30 g/L H₃BO₃, 0.5 g/L SDS, 1.5 g/L saccharin, 1.5 g/L ALS, 1.6 mg/L PPS, 7.5 mg/L HPOPS und 5 mg/L MPA