Newsgroups: sci.space
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: The great light bulb debate
Message-ID: <1990Nov13.035815.10203@zoo.toronto.edu>
Organization: U of Toronto Zoology
References: <9011092213.AA05755@cmr.ncsl.nist.gov>
Date: Tue, 13 Nov 90 03:58:15 GMT

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