18. What are the causes of zinc coating corrosion in indoor environments? What are the corrosion products?

Zinc coating corrosion indoors is significantly less severe than outdoors due to the absence of rainwater erosion, typically reducing corrosion by about 80%. The primary indoor corrosion causes include high humidity or un-dried finished products entering storage, which form a water film on the zinc surface. Studies show that corrosion becomes most intense when air moisture content reaches 60% or 85-95%. Warehouses are most prone to corrosion during winter.
Corrosion occurs under a thin layer of oxygen-rich liquid, so the corrosion rate is mainly determined by the diffusion of oxygen in the wet corrosion layer.
The corrosion products of zinc coating in indoor are not washed away by rainwater as those in outdoor, but form deposits in the place of corrosion and gradually expand, so the structure is loose and porous, the volume and weight increase, and the corrosion products are strongly alkaline.
The corrosion rate of the air in the kitchen is about 3 times higher than that of the general situation because of the cooking and combustion gases.
The corrosion products of zinc coating in the room are mainly zinc hydroxide and zinc carbonate.