Srinivasan, K.N. (1988) Studies on the influence of addition agents in electroplating solutions with special reference to zinc plating baths. PhD thesis, Madurai-Kamaraj University.

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Zinc plating is mostly carried out on steel articles for protection from atmospheric corrosion. Electrodeposited zinc coatings have some special characteristics which cannot be achieved by any other at such a low cost. Zinc can be plated from alkaline cyanide, sulphate, chloride, fluoborate, pyrophosphate and non-cyanide zinc electrolytes. Cyanide based electrolytes pose serious problems in effluent disposal due to their inherent toxicity. Recent trend is to deposit zinc from alkaline zincate baths because of the stringent pollution control measures enforced all over the world. The success of the zincate electrolytes mainly depends on the incorporation of organic additives. In their absence the deposit obtained from alkaline zincate baths are powdery and dark. Generally the addition agents employed are organic in nature. Sixteen addition agents are chosen and studied their influence on deposit characteristics, hydrogen permeation cathode efficiency, cathodic polarization adsorption behavior and corrosion resistance in acid sulphate and non-cyanide zincate electrolytes. The techniques employed for the study are Hull cell, electro permeation measurements, capillary electrometer, impedance measurements, galvanostatic polarization, Tafel extrapolation technique, and SEM studies. Addition agents selected are thiourea and its derivatives, gelatin, dextrin, p-naphthol benzaldehyde, glucose, cetyltrimethylammonium bromide, tetraethylene pentammine and pyridine. It is found from the above studies that in acid bath glucose, dextrin, tetraethylene pentammine and pyridine produce bright deposits and in alkaline bath only CTAB and gelatin are capable of producing white adherent deposits. Additives which produce low permeation of hydrogen during deposition in acid baths are dextrin and pyridine. In alkaline bath gelatin gives low permeation current of good correlation has been obtained between hydrogen permeation and porosity of the deposit and also between hydrogen permeation and current efficiency. Thiourea and its derivatives decrease the cathodic polarization and other additives increase it in acid bath. Adsorption behavior of the additives clearly prove that there is a definite correlation between adsorption and polarization correlation has also been obtained with charge transfer resistance and polarization behavior of additives in acid and alkaline zincate bath. Among the additives studied in acid bath only dextrin is found to give corrosion resistant uniform fine grained deposits with low uptake of hydrogen. In alkaline bath successful additives which give white adherent deposits at higher c.d. are CTAB and gelatin. The study has brought out the effect of substituent groups in thiourea in acid zinc and alkaline non-cyanide zincate baths

Item Type: Thesis (PhD)
Uncontrolled Keywords: Zinc plating
Subjects: Industrial Metal Finishing
Depositing User: Dr. N Meyyappan
Date Deposited: 13 Jun 2012 04:04
Last Modified: 13 Jun 2012 04:04

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