Formation of coloured coating on zinc (alloys) - by treating with water vapour at a defined pressure and temperature

摘要

Zn and Zn alloys are given a coloured coating by exposing the Zn or Zn alloy article to an atmos. contg. steam or water vapour at a pressure of 0.1-40 atm. and temp. 105-250 degrees C, which produces a Zn oxide and Zn hydroxide layer. The Zn and Zn alloy substrate is coated by treating with steam or water vapour and a portion of the water vapour may be replaced by CO2 whereby a Zn hydrocarbonate coating is formed. Oxidising substances are pref. added such as NO2, HNO3 or H2O2, which accelerate oxidn. of the surface. Method is economical as a pretreatment of the substrate is not required. Grease, oil or emulsions present on rolled sheet need not be removed prior to coating and castings exhibit a greater dimensional stability.