![]() ![]() With optical applications, black is the most popular anodizing colour to reduce internal reflections. This can be used to great artistic effect, producing aluminium parts with strikingly tasteless colours to adorn your motor bike or, more topically, telescope. The layer is then sealed and the colour appears as part of the aluminium metal itself. Coloured dye seeps into the microscopic pores of the anodized layer and colours it. The other advantage of anodizing aluminium is the potential of coloured anodizing dye. This is known as anodizing - so called because the aluminium part forms the anode in the electrolysis bath. The process involves suspending the aluminium in and acid bath and passing an electric current through the it. Using chemical processes it is possible to build a carefully controlled layer of aluminium hydroxide on the surface of the metal which is extremely hard - much harder and more durable than the rough natural oxidised layer that normally forms. Thankfully for the aluminum industry there is a technique which overcomes the inherent softness of the metal and protects against further oxidation. ![]() After a period of time the aluminium "rusts" - slowly producing a white powdery coat. This is why aluminium is known for its resilience in corrosive environments - eg car radiators or boats. However, with aluminium a rough layer of aluminium oxide forms which strongly inhibits further oxidation. Aluminium is more reactive than iron, and, as such, will rust more readily. It oxidises quite readily to produce iron oxide - or rust as it's more commonly known. We are familiar with the action of the environment on iron. "Chemically speaking, aluminium is an extremely reactive metal. ![]()
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