Jeremy Faludi's got another awesome overview of materials design up at Worldchanging. This time, he writes about "Metal vs. Plastic"—breaking down the pros and cons of aluminum, steel, titanium—even touching on annodizing and powder-coating. Here's the intro:
As I mentioned in an earlier post, I've been doing some green product design advice & research for a startup doing a consumer-electronics device. This post compares the impact of aluminum to two other metals, as well as plastic, and talks about the options for coating/finishing the metal.
and here's a fact-packed para on the former:
Anodization is a microns-thin layer of oxidation on the surface of the aluminum. It involves some nasty chemicals (depending on the color, these can include sulphuric acid, nitric acid, phosphoric acid, nickel acetate, and others; some use hexavalent chromium, but we will definitely avoid that), but small amounts of them (because the oxidation layer is so thin). The coating is non-toxic to the user, the concern is the waste and worker safety in manufacturing; any decent modern plant has emissions/effluent controls, but it would be better not to use toxins in the first place. The main advantage of anodization is that it does not hurt recyclability of the aluminum--it is such a thin coating (and even that coating is mostly aluminum itself) that anodized parts can be thrown right in with bare parts in recycling plants, and their value as scrap is just as high as bare aluminum (according to the three recyclers I talked to).
Now that's some info for ya. Read the entire article here; Go back and read his piece on plastics here.