The Thickness of Anodic Films on Aluminium

The thickness of the anodic film produced on aluminum in anodizing is intimately connected with some of the most important properties of the films such as corrosion resistance absorptive power insulation resistance etc.And is therefore of great interest (1,2). Napier and Westwood(3)have determined thicknesses of Adonic films obtained on anodizing in sulphuric acid baths of various strengths and at several temperatures .these Experiments were conducted at constant current and therefore the results are of little practical importance since all the commercial processes are conducted at constant voltage and not at constant current. Bradshaw and Clarke (4)Have collected similar data at constant voltage but their work was limited to the investigation of a sulphuric acid electrolyte of 20% -vol .concentration.In view of the non –availability of explicit Information about the conditions of anodizing in sulphuric acid which would yield films of maximum thickness, the present investigation was undertaken.