This is another old article I wrote in a technical Chinese magazine. The following is a short summary of the content.
Aluminium metal will rust with oxygen in air to form white rust of aluminium oxide. However this oxide can be artificially formed to serve as a protective layer on top of the metal. The process is called anodizing where aluminum is put as anode and gone through electrolysis in certain solutions. This oxide layer will then grow up to desired thickness. As this oxide layer is hollow in shape, they require an additional final process we call it Sealing to close up the hollow ends to make the metal more corrosion resistant.
I remember over a decade ago that our company competed with a foreign supplier to supply this sealing product to a customer. Their product contains hydrazine (carcinogenic) and works at over 90 deg. C. I formulated a flouride (found in toothpaste) based solution works at room temperature with even better corrosion resistance and won the transaction.
