Abstract
Phosphating practice has been much improved in the bath composition. Heretofore some nitrates have been used as accelerator by adding to the conventional phosphating bath, however, there have appeared the chlorate-acceleraters in the recent literatures and patents. The result of investigation on this new method of chlorate-accelerated phosphating bath is reported in the present paper.
Some of the behaviours of the bath in solution and the properties of the phosphate coatings were observed. In summary, the followings are proposed:
1) The suitable compositions of the bath are
Zinc powder 5-8g/l Acetic acid 3-8g/l
Phosphoric acid 30-45g/l Potassium chlorate 1-3g/l
Caustic soda 3-4g/l
2) This solution exhibits a milky turbid colour followed by development of colloidal suspension, which hardly appears in the solution of composition range under 0.3% KClO3.
3) The deposition of fine grained phosphate-coating on the steel surface dipped in the bath's, completed in 15min. at 50-60°C.
4) The thickness of coating is about 17μ and the spontaneous electrode potential in 3% NaCl solution of the coating formed by this method, is nobler than that of the coating formed by the conventional method. Therefore, the coating of the former seems to be more anticorrosive than the later.
