The structure of the pulse anodized layer

This post will explain how the structural changes of the anodized oxide layer happens during the pulse anodizing process. There are four stages which happen during the pulse anodizing process. Check out my notes on the recovery phenomenon, this will definitely help you through this explanation.

In stage 1 the forming voltage has a value of E1. Anodizing at this value will give a defined oxide structure which is dependent on the anodizing parameters. Continuing anodizing with these parameters will give a uniform oxide layer with an array of hexagonal cells of a fixed size.

In stage 2 the forming voltage is abruptly decreased to a lower value E2. This will make the electrical field across the barrier layer, which still has the thickness d1, very small. This results in a zero formation rate of oxide. The dissolution will slowly increase during this period and the barrier layer will gradually diminish to an appropriate value corresponding to the lower anodizing voltage E2.

In stage 3, the thickness of the barrier layer has reached a level where the field strength has increased enough and suddenly the current increases steeply. The new cells formed are smaller and with a barrier layer thickness d2. Continue anodizing at these parameters will formed a uniform oxide layer which depends on the anodizing parameters.

In stage 4 the anodizing process continues at the current density i2 creating a uniform oxide layer with a characteristic array of hexagonal cells until the voltage is increased again, forming an oxide layer with the characteristic of the film formed in the first stage at the anodizing voltage E1.

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