Phosphate Conversion Coating as a Base for Nickel Electrodeposition on Plain Carbon Steel

摘要

Zinc phosphate as a pre-treatment operation for electrodepositon of nickel on plain carbon steel substrate was evaluated on medium carbon steel. Zinc phosphating bath was formulated using zinc oxide (ZnO), phosphoric acid (H_3PO_4), nitric acid (HNO_3), sodium nitrate (NaNO_3), distilled water (H2O), and iron wool. Phosphating operations were carried out at temperature ranges of 85 °C to 95 °C at varied concentrations of phosphoric acid for 20 to 60 minutes. Nickel was electrodeposited on the phosphated and on as received steel substrates at 3 Volts for 30 minutes. The samples were later exposed to atmospheric air at room temperature for over 150 days. The film adhesion and continuity were observed under metallurgical microscope as the parameters for assessing the quality of nickel electrodeposited on the phosphated substrates. The result obtained showed that the nickel film was well adhere to the phosphated medium carbon steel substrate. It was observed that the nickel film of the sample without prior phosphating peel-off while the films of samples phosphated before nickel electroplating remained well adhered. Zinc phosphate could serve as alternative to copper cyanide bath as pretreatment for nickel electrodeposition on plain carbon steel with improved adhesion.