Additive And Impurity Effects During Plating In Tin Methanesulfonate Electrolytes

Methyl sulfonic acid (MSA) tinplating is paid more and more attention to because it is friendly to the environment and completely biodegradability, and treatment of electroplating wastewater is simple. In this paper, based mainly on existing methyl sulfonate tinplating process, different kinds and contents of antioxidant, auxiliary agent and brightener were determined with Hull Cell experiment, and different kinds and contents of antioxidants, auxiliary agents and brightener were studied by electrochemical test. Bath properties including current efficiency, dispersive and covering power were tested through Cu-coulometer, far and near cathode and inner bore methods, moreover corrosion resistance, porosity and microstructure of coating were tested.Experiment results showed that in MSA tinplating bath the best contents of antioxidants, auxiliary agents and brightener were antioxidant (HXY) 20mL/L, auxiliary agent (HXY) 20mL/L and brightener 2mL/L. Electrochemical test results showed that antioxidant could obviously improve the stability of bath, auxiliary agent and brightener could increase the cathode polarization, suppress reducing of hydrogen and make the refined grains. Current efficiency was 98.47%, electrodeposition rate was 0.0445g/s·cm2 dispersive and covering power were 97.7% and 83.1%. Porosity decreased, corrosion resistance improved and crystallization diminished on the layer.This paper also studied the source of Fe²⁺ and Fe²⁺ effect for coating porosity and corrosion resistance and discussed removal methods of in tinplating bath. Results showed that not thoroughly with water-washing after washing with a pickling and plating dissolved in acidic tinplating bath were the main source of Fe²⁺, Allowing content of Fe²⁺ in tinplating bath was determined as 10g/L. Coating corrosion resistance was worse with the concentration of Fe²⁺ increasing, while the producing rate of sludge was accelerated with the concentration of Fe²⁺ increasing, too. Removing Fe²⁺ by freezing method, the removal rate could achieve more than 80% in this method.