Micro- and nanostructure of the surface and the cathode capacitance aluminum aluminum foil on the sequential stages of etching

Pitting corrosion starts in the areas compact the surface of the packing defect. The preliminary heat treatment of the surface of the foil creates a cube texture, which allows to obtain the crystallographic tunnels located in direction (100). During the whole technological process of etching the pittings have pixele shape. After 30 seconds etching in a mixture of phosphoric, sulfuric and nitric acids, the topology of the original surface of the foil formed by the last technological process of rolling, is destroyed. Etching in hydrochloric acid solution, the growth of pitting occurs primarily in the interior. The deepening of the pitting goes along defective packaging, forming a tunnel etching. When packing defect are inclined to the surface of the foil, the tunnels are also formed at an angle to the surface. As a result, the etching does not change the elemental composition of aluminum foil. Etching of the surface is also along the grain boundaries, which have greater defects.
Specific capacity is determined not only by the specific surface area of the foil, quantity and depth of the formed tunnels. The main factor affecting the value of the specific capacity is the internal terrain of the tunnels — their bottom and sides. After hydrochloric acid etching is more than doubling the cathode and the specific capacity. This effect is associated with the formation of the complex bottom topography of the tunnels and multi-level structure of the walls.