If the surface of the galvanized layer adheres to a layer of condensed water, and oxygen, carbon dioxide, hydrogen carbide, sulfur dioxide and soot, dust and other chemical gases, into a corrosive aqueous solution and attached to the surface of the galvanized layer, forming an electrolyte. This electrolyte electrochemical corrosion with the less chemically stable zinc layer, resulting in a powdery corrosion product, white rust [Zn (OH)2-56%, ZnCo3-40%, H2O - 4%].
The main reasons for indoor corrosion of zinc layer are:
(1) High indoor air humidity;
(2) Finished products are stored before drying;
(3) There is a layer of condensation water film on the surface of the zinc layer. When the moisture content in the air reaches 60% or 85 ~ 95% and PH < 6, the corrosion reaction is more intense. When the water temperature is up to 70℃, the corrosion speed of zinc layer is the fastest.
Methods to prevent white rust:
(1) When the galvanized sheet is stacked, there can be no condensation water on the surface;
(2) Air circulation should be maintained in the warehouse, and the relative humidity of air should not be 60% or 85-95%;
(3) The galvanized sheet should not be stacked with harmful gases and too much dust;
(4) The surface of the galvanized layer is oiled and passivated.