Cause of browning and blacking effect on aluminium sheeting?

[Hugh O'Brien]

Hi everyone,

Not sure if this should be here or in the chemistry section. It's a question about chemical reactions in aluminium.

I work for a construction company and we have a number of aluminium sheets used for cladding and roofing. We've noticed that some of these have a blacking and browning effect on them. The sheets are on the outside of a building and the building itself is situated in a city centre.

I read on this site (and somehow managed to lose the page) a question about the possibility of mercury causing such an effect, but that question hadn't been answered (and was posted in 2004). We were wondering if this could be a factor?

Also, there is a work site near by and another thought was that it could be cementitious or limestone dust having an effect on the sheeting.

Would anyone know what could cause such effects on alluminium? I'll try and get some photographs so that you can see what I mean. If you need any more information on it, then ask away and I'll try to give as much as I can.

Thanks. :)

 

[nbryan5]

</code>The blackening and browning of aluminum sheets can be caused by a variety of factors. The most likely cause would be corrosion from the presence of certain gases and chemicals in the air. The presence of mercury or cementitious or limestone dust near the building could also be contributing to the corrosion. Additionally, poor quality paint or sealant on the aluminum surface can lead to corrosion, as well as improper application of the paint or sealant. To determine the exact cause of the blackening and browning, it is best to consult with a professional who can inspect the sheets and take samples for further analysis. In addition to the samples, photographs of the affected areas can also help in determining the cause. Once the cause is identified, appropriate steps can be taken to prevent further corrosion.

 

[oswaler]

The browning and blacking effect on aluminium sheeting is most likely caused by a process called oxidation. Aluminium is a reactive metal and when exposed to oxygen and water, it forms a layer of aluminium oxide on its surface. This layer is typically thin and transparent, but can become thicker and darker in certain environments.

In the case of the construction site, it is possible that the dust from nearby cement or limestone is contributing to the oxidation process. These materials can release alkaline substances that can accelerate the oxidation of aluminium. Additionally, pollutants in the air such as sulfur dioxide or nitrogen oxides can also contribute to the browning and blacking effect.

Mercury, on the other hand, is not likely to be the cause of the discoloration. While it can react with aluminium, it is usually in the form of an amalgam and would not cause the same type of discoloration as oxidation.

To prevent or reduce the browning and blacking effect on aluminium sheeting, it is important to regularly clean and maintain the surface of the sheets. This can help remove any pollutants or dust that may be contributing to the oxidation process. Additionally, using a protective coating or paint can also help prevent the formation of the aluminium oxide layer.