ALUMINIUM
Very thirsty for oxygen, it has a natural layer of alumina.
It is attacked by mineral acids, except for nitric acid. It is also attacked by bases and alkaline carbonates.
It is not attacked by organic acids, except for formic acid, oxalic acid and trichloroacetic acid.
Applications of aluminium and its alloys are based on the following properties:
- Low density, approximately one third of that of copper and steel
- Good thermal conductivity, exceeded only by silver, copper and gold
- High electrical conductivity, 62% of that of copper
- Absence of magnetism
- Resistance to distilled water, nitric acid and organic acids, rural, urban and industrial atmospheres, sulphurous atmospheres, fluorinated gases but not to chloride and methyl bromide
- A thirst for oxygen and ability to be surface formed and an artificial alumina layer due to anodising.
PRINCIPLE OF ANODISING
The anodising or anodic oxidation of aluminium and its alloys is a method of electrolytic surface treatment. It consists in producing an alumina layer by the action of oxygen on the surface of parts immersed in a suitable electrolyte, and connected to a positive pole of an electricity generator.
The alumina layer develops from the outside inwards and this results in only slight swelling. The quality of the layer obtained depends on two opposing phenomena:
- an electrolytic oxygen generator phenomenon
- a chemical dissolution phenomenon
APPLICATIONS
Anodising applications are based on the properties of the alumina layer formed. This layer is in fact:
- Transparent. For some very low alloys, the initial surface condition is met. This initial surface condition of being mechanically, chemically and/or electrolytically polished, gives rise to interesting optical properties (reflectors)
- Hard. Normal hardness is 350-400 HV. Hardness is approximately 600 HV in so-called “hard” anodising.
- Porous. The alumina layer is in fact formed from billions of small pores that are open to various degrees. It is able to absorb organic or mineral dyes, fats and molybdenum bisulphide
- Insulating. Very roughly a breakdown voltage of 100 volts per micron of thickness may be permitted.
- Protective. The alumina layer is protective if it has undergone correct buildup causing clogging of pores.
The applications of anodising are limitless …
NATURE OF ALLOY AND FINISHES
The final appearance of the product also dependson the treatment or treatments that precede anodic oxidation.
Using different methods of sandblasting, mechanical preparation methods and chemical and electrolytic satin-finishing and brightening processes it is possible to obtain:
- a bright satin finish;
- a reflectance with more or less dispersive diffusion ...
The colorations are based on mineral or organic dyes
Buildups are produced with demineralised water, bichromate or glycol polyethylenes.
For more technical information or applications please contact our technical department: