Helium is not commonly used in high-temperature incandescent bulbs due to its high diffusion rate, which allows it to escape through glass walls, making it less effective than krypton or argon. Helium's ionization difficulty and lower heat capacity compared to argon also contribute to its limited application. Additionally, the cost of helium is higher than that of argon, which is readily available from the atmosphere. Graham's law explains the diffusion rates of these gases, indicating that helium diffuses significantly faster than argon and krypton.
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rachmaninoff said:Helium can diffuse through a thin glass wall, so it would escape from a light bulb (not very useful).
I did an experiment testing this last year. It turns out that effusion rates are proportional to molar mass (Graham's law?). If helium has a molar mass of something like 4 and krypton is way way up there in terms of mass, that's a considerable difference.Facial said:I suppose, then, that it can probably diffuse through a thick glass wall, but I'll have to look that up sometime with regards as to how much slower.
ShawnD said:Does helium cost more than argon or krypton?