Steel-Recycling Innovation Includes Aluminum to Control Impurities
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duced a composite material from a series of thin copper rings and ordinary copper wire strung parallel to the rings. The composite is among a new class of materials called “metamaterials,” so called for the way in which the mixing or arrangement of two or more materials at a very fine level can affect the electromagnetic properties of the resulting composite. This class of materials has the ability to reverse properties such as the Doppler effect, which is the change in the observed frequency of a wave as the source moves relative to the observer. In ordinary materials, the Doppler effect is manifested as an increase in the frequency of emitted radiation as a source approaches. Maxwell’s equations, which describe the relationship between magnetic and electric fields, suggest that microwave radiation or light would show the opposite effect in this new class of materials, shifting to lower frequencies as the source approaches. Similarly, Maxwell’s equations suggest that a lens made of such materials, instead of dispersing electromagnetic radiation, would focus it as it passes through.
MRS BULLETIN/JUNE 2000
Schultz said, “If these effects turn out to be possible at optical frequencies, this material would have the crazy property that a flashlight shining on a slab can focus the light at a point on the other side.” The scientists demonstrated the ability to reverse these properties by beaming microwave radiation through the composite material. Their results verified that the composite had negative electric permittivity and negative magnetic permeability. In most known materials in nature, these qualities are positive.
Steel-Recycling Innovation Includes Aluminum to Control Impurities When steel producers recycle steel scrap, tin from tin-plate scrap and copper from domestic incinerator scrap accumulate in the steel, posing a major problem for the steel industry unless controlled properly. Such impurities have harmful effects on ductility, causing defects in the worked material. Scientists at Leeds University have discovered that the controlled addition of aluminum to molten steel during
recycling forms alloys with the tin and/or copper, rendering both harmless. The method is simple, cheap, and environmentally friendly. The source of aluminum can be pure metal, an alloy, or a compound capable of dissociation at the operating temperature. However, one source is aluminum cans, currently recycled separately from steel cans. “Why go to the trouble of separating them when they contain the very ingredient we want to add?” said team leader Bob Cochrane. “An obvious extension of our process would be to charge mixed loads of scrap, saving on sorting costs.” The addition of a metal as an alloying agent is a radical departure from conventional treatments, which extract the unwanted metals by chemical or electrochemical methods in de-tinning plants. These methods are expensive and use environmentally unfriendly chemicals. De-tinning plants also have limited capacity, and environmental considerations are increasingly putting co
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