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Creating Better Thermal-Imaging Lens From Waste Sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team has found. The team successfully took thermal images of a person through a piece of the new plastic. By contrast, taking a picture taken through the plastic often used for ordinary lenses does not show a person’s body heat.

The researchers tested the optical properties of the new lens materials and found they are transparent to mid-range infrared and result in lenses with high optical focusing power. The team's discovery could provide a new use for the sulfur left over when oil and natural gas are refined into cleaner-burning fuels. Although there are some industrial uses for sulfur, the amount generated from refining fossil fuels far outstrips the current need for the element.

The new plastic is transparent to wavelengths of light in the mid-infrared range of 3 to 5 microns — a range with many uses in the aerospace and defense industries. The new lenses also have a high optical, or focusing, power — meaning they do not need to be very thick to focus on nearby objects, making them lightweight. The "inverse vulcanization" process requires mostly sulfur with a small amount of an additive. Vulcanization is the chemical process that makes rubber more durable by adding a small amount of sulfur to rubber.

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