Abstract
Electrolysis of aluminum under A. C. in alkaline solutions containing metallic salts, organic acid salts, and fluorides were conducted. Concentrations of additives were as follows: alkali carbonate (sodium carbonate and ammonium carbonate): 0.3-0.8mol, metallic salts (silver, copper, ferric iron, nickel, and antimony): 0.02mol, organic acid salts (tartrate and citrate): 0.05-0.2mol, and fluorides (ammonium fluoride and sodium fluoride): 0.15-0.2mol. Colored films (about 4-5μ in thickness): were prepared by electrolysis under A. C. of 2-3amp/dm2 at 20±1°C for 30min. In sodium carbonate solution, a yellowish green film was formed in a bath containing copper salts, a brown film in a bath containing iron salts, and blackish brown film in a bath containing nickel salts. On the other hand, in ammonium carbonate solution, a yellowish brown film was formed in a bath containing silver salts, a black film in a bath containing nickel salts, and a blackish brown film in a bath containing antimony salts. Experiments results of the properties of the above colored films showed that acid resistance (to 10% H2SO4) and alkali dropping test (10% NaOH) were equal or superior, but hardness (by Martens' scratch hardness tester) was inferior to those values of anodized films of nearly the same thickness prepared in H2SO4.
