Chromate passivation of zinc

The paper describes the results obtained on chromate films formed on zinc, zinc plated steel and galvanised steel, by dipping in acidified composition and time of immersion etc. on the weight of the film formed and metal attacked and also on the characteristics of the film formed. The protective property of the film has been determined by salt spray test and humidity test. The results indicate that the acid content of the solution primarily affects the properties of the film formed in solution containing 200gm/1 of sodium dichromate. Acid content above 12.5 c.c/1 was found to give loose film, which had lower protective property. Of the three types of zinc, zinc plated steel possessed maximum resistance and galvanised steel the least. (Mr. S. Rao Addanki, Senior Scientific Assistant; Mr. A.K. Lahiri, Senior Scientific Officer; National Metallurgical Laboratory, Jamshedpur)