Anodizing is a process in which the surface of an aluminium product is converted into a protective oxide layer by connecting the product in an acidic solution to the positive pole of a rectifier. Due to the high electrical resistance of the oxide layer a large overpotential (10 to 30 V) is needed to obtain a reasonable high current density (500 to 3000 A/m2).
Therefore a considerable amount of heat is generated (5000 W/m2 of more) on the electrode-electrolyte interface. Traditionally, most of the produced heat is removed by forced convection of the electrolyte. This agitation is not always homogeneous but is a key factor in the overall performance of the reactor.
Elsyca has developped a theoretical model for the entire assembly of electrical circuit, anodizing tank and aluminium product and for the formation of the oxide layer at the anode. This model includes:
- fluid flow of the electrolyte due to forced convection
- temperature and heat flux distribution in the electrolyte and aluminium product
- electrical potential and current density distribution in the electrolyte and the aluminium product
- electrical resistance of wires and connections
- leackage currents and grounding
- a non-linear relation between the local surface temperature, potential and current density describing the anodizing reaction (oxide layer growth)
- heat generated in the oxide layer, aluminium and in the electrolyte.
Electrocolouring is a AC electrochemical process which fils the pores of aluminium oxide layers to give them a decorative coloured appearance. Originally colours ranged from bronze to black, but more recently a wider range of colours can be produced.
Optimizing both the process parameters and cell configuration of anodizing processes can be handled in a very fast and effective way using an in house software tool that includes all of the above features. Also the Elsy2D software tool can be used to model anodizing and electrocolouring processes (though in some less detail).