Dissemination of IT for the Promotion of Materials Science (DoITPoMS)


Copper in motors

Automobiles today contain many motorised components: windows, seats, CD drives… you name it, it’s motorised. These motors contain lots of valuable copper. To take each motor apart and extract the components is not economically viable, taking into account the energy already expended in dismantling the automobile itself.

However, materials science could provide an answer:-

At low temperatures, materials become more brittle . This is because the movement of dislocations that enable plastic deformation is reduced at cold temperatures. There is a difference in the crystal structures of copper and the other components of the motor (steel and polymers). Copper has a face-centred-cubic (fcc ) structure (also known as cubic close packed), and steel has a body-centred-cubic (bcc ) structure. The fcc crystal structure has more slip systems on which dislocations can move than the bcc crystal structure. Copper can still show ductile behaviour at temperatures as low as -150°C – as shown on the graph by the high impact energy absorbed relative to other materials.

Impact energy as a function of temperature for several materials, steel, nylon and copper being motor components, showing how copper is still ductile at –150°C, but steel and nylon are not.

Separation of the copper from the rest of the components of the motor is thus possible by cooling it to -150°C and then crushing it. Screening will remove the much finer steel and plastic dusts which have formed as a result of their being much more brittle at this temperature than the copper.

It should be noted that the costs of cooling components to this temperature and then separating them do not appear to be economically feasible, as well as the fact that the steel and copper may amalgamate together and sophisticated (and therefore expensive) screening techniques would have to be employed to separate them.

However, in the recycling of Japanese home appliances, this technique is sometimes used – together with using the various ductile-brittle temperatures for non-metallic components to further aid in their pre-recycling separation.

This can be illustrated with a demonstration: