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A globar is a heated silicone carbide rod used as a thermal radiation device with emissions in the middle infrared (IR) frequency range. A globar is used in conjunction with a dichroic or interference filter to emit IR radiation in the middle IR spectrum. This emitted IR radiation is used in infrared spectroscopy as a diagnostic and measurement tool in research, industrial, and forensic analysis applications. Due to the lack of oxidization of the rod in air, globars need not be enclosed in vacuum tubes as is the case with alternate IR light sources.
All heated matter emits thermal radiation to varying degrees. Thermal radiation is not the same as thermal energy which is felt as heat but rather electromagnetic emissions in the infrared spectrum of invisible light. Different materials all reflect or absorb this radiation differently depending on the exact wavelength of the emissions and the type of material involved. These known factors allow infrared radiation to be used as a diagnostic tool in the science of spectroscopy. When paired with a interference filter, a globar emits thermal radiation in the middle spectrum of the IR range at approximately 4 to 15 micrometer wavelengths.
The heated material used in a globar is silicone carbide in the form of a small rod typically 0.2 to 0.4 inches (5–10 mm) in diameter and 0.8 to 1.2 inches (20–50 mm) in length. To start the radiation process, the rod is electrically heated to between 1,832° to 3,002° Fahrenheit (1,000° - 1,650° Celsius). Due to the lack of oxidation of silicone carbide in air at these temperatures, there is no need for the rod to be enclosed in a vacuum tube. If it is enclosed, it is simply as a safety measure. An interference filter is placed between the globar and the test sample which produces a specific, know IR wavelength used to conduct the tests.
Alternate middle IR emitters used in infrared spectroscopy include chrome nickel alloy coils, high pressure mercury lamps, and older Nernst lamps. The globar is, however, one of the more practical and efficient sources of mid range IR radiation particularly in the new generation of portable spectroscopy equipment. The name globar is also a trademark of a range of silicone carbide resistors produced by several companies. Technically the term correctly refers to the IR emitter application, however, and the globar resistor reference is merely a trade name.
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