roberts@CMR.NCSL.NIST.GOV (John Roberts) (11/10/90)
Apologies if this is out of date. SPACE Digest has been down for about a week. >Date: 29 Oct 90 16:07:30 GMT >From: usc!cs.utexas.edu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca!neufeld@ucsd.edu (Christopher Neufeld) >>> On one of the shuttle missions, send up thousands of tiny glass >>>spheres with small holes in them. Once in space, expose the spheres to >>>the vacuum of space and then seal them. Bring them back to earth >>>and sell them to people. Everyone can own their own piece of space! >> > A glass ball with a vacuum inside is a bad thing to have around. If >it is broken it implodes, and the pieces fly through the centre of the >sphere, and on across the room at high speed. People doing vacuum >experiments prefer metal containers whenever possible to prevent the >formation of shrapnel. You'd need a plexiglass shield around the vacuum >sphere to make it safe. > I'd hesitate to hold even a 1mm diameter vacuum sphere in my hand. If >it shattered it would send glass into my palm, and you don't want to >consider what would happen if you held it close to your face so that you >could see the tiny sphere more clearly........ > Christopher Neufeld....Just a graduate student | "The pizza was just a .............................. >Date: 30 Oct 90 17:26:15 GMT >From: news-server.csri.toronto.edu!utgpu!utzoo!henry@rutgers.edu (Henry Spencer) >Modern light bulbs are filled with argon, not vacuum. (Expensive ones >use krypton.) As you imply, the old bulbs were evacuated. I believe the main reason for the switchover to inert gas was to reduce the rate of evaporation of the filament at a given temperature. The "inert" gas usually cited in the literature is nitrogen. Why would krypton be better than argon? Halogen lamps use a halogen gas, which absorbs the tungsten evaporated from the filament (and redeposits it?), allowing the filament to be operated at higher temperature and efficiency. >CRTs are quite dangerous to handle "naked", and people >who work with them are careful; when enclosed in a monitor, one of the >safety requirements is that the faceplate be tough enough that an >implosion would not send fragments toward the user. Safety-certification >agencies like UL and CSA test this regularly. >Chris N. is not kidding about the serious safety implications of glass >vacuum containers. However, a quick fix would be to encase them in >plastic. For instance, I believe flash bulbs pretty much always explode when fired, but the plastic coating holds the glass together. >"I don't *want* to be normal!" | Henry Spencer at U of Toronto Zoology >"Not to worry." | henry@zoo.toronto.edu utzoo!henry .............................. >Date: 30 Oct 90 14:24:53 GMT >From: thorin!grover!beckerd@mcnc.org (David Becker) >Subject: Re: A great idea on how to fund NASA! >Your average incandescent bulb holds slighlty pressurized inert gas. Glass >that thin could never keep O2 out of vacuum. The pressure is to keep >the O2 out and the filament burning. >David Becker I Dweam of Dweanie >beckerd@cs.unc.edu Then how do you account for the working of the old-fashioned bulbs? Remember the scenes from the old films, such as the encounter between W.C. Fields and the blind man, in which light bulbs break with a loud BANG? (One of my favorite scenes from "Our Gang" is the one in which the city kid gets across a busy street by breaking a light bulb. The drivers all stop to check for blown inner tubes, and the kid just walks across. :-) Fluorescent tubes also contain near-vacuum. If one obtains a burned-out tube and purely by coincidence just happens to shoot it with a pellet gun from 50 yards away, the result is a very interesting "thunk" as the tube fills with air, and fragments of glass will travel several feet. (One should then be very careful cleaning up the glass, though with the absence of beryllium in modern tubes, I suppose a cut wouldn't be quite as fatal as in the old days.) The decorative "plasma spheres" also contain a pretty good vacuum, as do radiometers. Disclaimer: Kids, don't try this at home without a signed letter of permission from your congressman! John Roberts roberts@cmr.ncsl.nist.gov
philip@beeblebrox.dle.dg.com (Philip Gladstone) (11/12/90)
In article <9011092213.AA05755@cmr.ncsl.nist.gov> roberts@CMR.NCSL.NIST.GOV (John Roberts) writes: >Modern light bulbs are filled with argon, not vacuum. (Expensive ones >use krypton.) As you imply, the old bulbs were evacuated. I believe the main reason for the switchover to inert gas was to reduce the rate of evaporation of the filament at a given temperature. In the UK (10 years ago) light bulbs contained *some* gas to about 30% atmospheric pressure. This is easy to demonstrate by following this procedure: 1) Find a light bulb -- preferably a dead one (it'll be useless if you complete the rest of these instructions). 2) Fill a bucket with water. 3) Find a compass (the drawing instrument) or other sharp spiky object. 4) Use the compass to make a small hole in the metal cap of the bulb. 5) Hold the bulb under water and push the compass into the metal cap and wiggle it around inside. If you do this just right, you will break the glass seal that was used to evacuate the bulb. 6) The water now rushes in to equalise the pressure. You can now judge what the pressure was before you broke the seal by how much water entered. WARNING: If you do this wrong you could break the envelope. For this reason wear gloves. -- Philip Gladstone Development Lab Europe Data General, Cambridge England. +44 223-67600
henry@zoo.toronto.edu (Henry Spencer) (11/13/90)
In article <9011092213.AA05755@cmr.ncsl.nist.gov> roberts@CMR.NCSL.NIST.GOV (John Roberts) writes: >The "inert" gas usually cited in the literature is nitrogen. Why would >krypton be better than argon? Nitrogen is not really inert when temperatures get high. For example, if you burn titanium in air -- 80% nitrogen, 20% oxygen, roughly -- the ash is about 80% titanium nitride and 20% titanium oxide. For applications involving incandescent metals, you want something that is really inert. (If you're being really picky, the noble gases [the preferred modern term] are not really inert either, but under these conditions they qualify.) Krypton is better than argon for the same reason that argon is better than vacuum: the denser gas slows the evaporation of the tungsten filament. -- "I don't *want* to be normal!" | Henry Spencer at U of Toronto Zoology "Not to worry." | henry@zoo.toronto.edu utzoo!henry
feg@moss.ATT.COM (Forrest Gehrke,2C-119,7239,ATTBL) (11/14/90)
In article <1990Nov13.035815.10203@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: >In article <9011092213.AA05755@cmr.ncsl.nist.gov> roberts@CMR.NCSL.NIST.GOV (John Roberts) writes: >>The "inert" gas usually cited in the literature is nitrogen. Why would >>krypton be better than argon? > >Nitrogen is not really inert when temperatures get high. For example, >if you burn titanium in air -- 80% nitrogen, 20% oxygen, roughly -- the >ash is about 80% titanium nitride and 20% titanium oxide. For applications >involving incandescent metals, you want something that is really inert. >(If you're being really picky, the noble gases [the preferred modern term] >are not really inert either, but under these conditions they qualify.) > >Krypton is better than argon for the same reason that argon is better than >vacuum: the denser gas slows the evaporation of the tungsten filament. And because of the slower evaporation there is another advantage: The tungsten filament can be operated at a higher temperature; these bulbs are significantly brighter. Halogens (usually pure iodine) are still better (although a different process is taking place). But now, due to the high temperatures being reached, quartz glass must be used for the envelop. This is expensive and their applications become more specialized, such as automobile headlights, photography, etc. Forrest Gehrke feg@moss.att.com
dant@mtdoom.WR.TEK.COM (Dan Tilque) (11/14/90)
henry@zoo.toronto.edu (Henry Spencer) writes: > >Krypton is better than argon for the same reason that argon is better than >vacuum: the denser gas slows the evaporation of the tungsten filament. Obviously we need to take this to it's logical extension. It's time to start recycling all that radon that everyone has in their houses. And I want no namby-pamby whining about radon being radioactive. In a lightbulb, that's not a bug, it's a feature. --- Dan Tilque -- dant@mtdoom.WR.TEK.COM