Post-treatment by Sodium Silicate after Zinc Phosphating on Cold-Rolled Steel
Supunsa Dech-oup, Sirinee Thaiwatthana and Torranin Chairaungsri* Author for corresponding; e-mail address: chato@chiangmai.ac.th
Volume: Vol.39 No.1 (JANUARY 2012)
Research Article
DOI:
Received: 3 August 2010, Revised: -, Accepted: 14 June 2011, Published: -
Citation: Dech-oup S., Thaiwatthana S. and Chairaungsri T., Post-treatment by Sodium Silicate after Zinc Phosphating on Cold-Rolled Steel, Chiang Mai Journal of Science, 2012; 39(1): 30-40.
Abstract
Post-treatment by sodium silicate after zinc phosphating on cold-rolled steel was studied. The steel substrates were firstly phosphate in a zinc-phosphating bath containing ZnO, NaF, H3PO4 and Ni(NO3)2·6H2O under controlled conditions. Post-treatment by sodium silicate was consequently performed by varying the sodium silicate concentration and immersing time in the range of 33.3-100 wt% and 1-10 minutes, respectively. The coating layers before and after post-treatment were characterized by X-ray diffractometry and scanning electron microscopy-energy dispersive X-ray microanalysis. The phosphated layer was formed to be mainly amorphous sodium silicate. The optimum post-treatment condition was using the 33.3wt% sodium silicate solution at 5 minutes immersing time, by which an increase in corrosion resistance can be adequately obtained after post-treatment.