MadSci Network: Chemistry |
Tommy, I should first point out that a blackbody radiation spectrum extends over the entire range, from a wavelength of "zero" up to "infinity". The idea is simply that the peak of the curve shifts to lower wavelengths as the temperature increases. The overall amount of radiated power also increases, so that (for example) the amount of UV light emitted by an object increases dramatically as the temperature increases, up to the point that the UV emission can become a safety issue long before reaching a temperature like 8500 C. Note that since UV light is invisible, UV emissions can significantly damage or destroy your eyesight very quickly, since you don't instinctively look away, blink or contract your pupils. So please be careful before you start messing around with UV emitters. Now, as far as everyday materials are concerned, 8500 C is an astoundingly high temperature. As far as I know, even very durable materials (e.g., diamond, metallic tungsten or alumina (a ceramic)) melt or sublimate long before reaching 4000 C. So a material that is solid at 8500 C seems improbable, and perhaps flatly impossible, to me. That said, there are other ways of generating UV radiation. Are you interested in 8500 C because you need to generate broadband radiation in that range, or do you just want to generate SOME light SOMEWHERE within that particular wavelength band? If all you want is to generate some UV light, and you don't really care about whether it is broadband emission or just a few sharp emission lines, then I suggest using a mercury-vapor discharge tube. These are rather easy to obtain from a scientific supply company, and shouldn't be very expensive ($10-$20, if I recall correctly). Some higher-end units will come with their own power supply, so that you won't have to purchase a separate supply to get the discharge going. Please also keep in mind the fact that mercury (and especially mercury vapor) is poisonous, and so you need to be very careful with the glass tube. If you are insistent upon generating broadband UV radiation in the 300-400 nanomenter wavelength range, then I'm not certain how you should proceed. As it turns out, 8500 C is tremendously hot for ordinary materials, but is actually a very cold temperature in plasma physics -- note that the photosphere of the sun (its cold (!) outer edge) has a temperature in the neighborhood of 6000 C. Experimentally, the biggest problem in generating (and sustaining) a plasma at a temperature of thousands or even low ten-thousands of degrees Celsius is that the plasma will be very susceptible to impurity radiation. In other words, rather than getting the atoms/ions in the plasma to collectively radiate as a blackbody, you'll most likely end up with lots of low-charge-state atomic and ion radiation. Consider the discharge in a fluorescent tube, for example -- the electrical discharge in the tube excites a few high-energy emission lines, and those photons then excite the fluorescent material lining the tube, producing a broad-band spectrum we perceive as nearly-white light. Well, I'm not sure what else to say right now. If you have further questions or would like clarifications, please feel free to ask. Good luck! Sincerely, Aaron J. Redd
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