Formation of anodic gel of aluminum

Aluminum salt hydrolyzes easily in water to form aluminum anode gel, which is an amorphous colloidal hydrated aluminum anode. Aluminum anodic gels, once formed, dissolve easily in water. If the temperature is higher than 25℃, the aging process occurs and the gel is transformed into a boehmelike inorganic compound structure. However, if the gel is immediately dried at room temperature once formed, dehydration occurs and the water solubility after dehydration remains unchanged.

In contrast, the fine powder-like oxides formed on the surface after anodic oxidation, which have been observed by scanning electron microscopy (SEM), are bom-like bodies with poor solubility of spicelike structures [381].

The reaction of aluminum salts formed in micropores of anodic oxide film is as follows:

(1) Aluminum salt is hydrolyzed by cleaning water at the opening of micropore to produce aluminum anodic gel. The gel dissolves easily in water and therefore dissolves.

(2) After a period of time, some of the aluminum anodic gels are transformed into water insoluble boehm - like bodies.

(3) If the temperature is maintained above 25℃, the conversion of anodic aluminum gel will be accelerated to form water insoluble boehm like body.

(4) Once the water is dried at room temperature, the boehm-like changes do not occur, and the existence of water-soluble aluminum anode is maintained.

In light of the above facts, it seems that the best course of action is to take a long cold water rinse. Experimental work has shown that a high-quality appearance without surface oxide dust can be obtained if the anodized workpiece is dried naturally and then cleaned again with water.