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From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.bio,sci.chem,sci.physics
Subject: Re: Fun With Vacuum Equipment
Summary: Oil pumps work with low-vapor-pressure oil
Message-ID: <14507@milton.u.washington.edu>
Date: 16 Jan 91 03:12:40 GMT
References: <38073@cup.portal.com>
Organization: University of Washington, Seattle
Lines: 44

In article <38073@cup.portal.com> mmm@cup.portal.com (Mark Robert Thorson) writes:
>I just acquired a vacuum oven and two old (but working) vacuum pumps,
>and I've got a few questions about using the equipment.
>
>First, I changed the old oil because I was afraid it might be crap.
>I replaced it with 30 weight single-viscosity non-detergent motor oil.

	The oil in an oil pump is not a lubricant; it is a sealant
instead.  Its main specification is for vapor pressure, and it is likely
that motor oil will not do nearly as well as pump oil.

>I want to do freeze-drying and perhaps make some aerogels.  I'm
>concerned that overloading my vacuum chamber (8" x 8" x 12") might
>put out too much vapor for the pump to handle.  Does anyone have
>tips on how to avoid this situation? 

	Contamination of the oil is the major reason for changing
it (we usually go by odor); if a lot of water vapor gets into the
oil, the stuff turns into a mayonnaise-like sludge (and pump
performance vanishes).  To prevent this, use a moisture-absorbing
filter to protect the pump (a tube packed with dessicant might suffice).
	I'm not sure about making aerogels, but the techniques
I've heard of (patents by Nicolaon and Teichner) use an autoclave
(high pressure heated vessel) rather than freeze-drying.  Since
the liquids one removes from aerogels include alcohols, a LOT
of attention to fire hazard and gasket compatibility is called for.
One large aerogel-producing facility burned to the ground a couple
or three years back because of some such problems.
	If freezing changes the density of the liquid much, it
will break the solid part of the aerogel before the liquid is
removed, so the resulting aerogel will be of inferior quality.

>Does anyone remember what year and/or month the Scientific American
>article on aerogels appeared?

No, but other articles are
	Nicolaon, G. A. and Teichner, S. J.  Bulletin de la Societe
Chimique de France, 1968, V 5, p. 1900

	Teichner, S. J. and Nicolaon, G. A., US Patent #3,672,833
(1968)


	John Whitmore