GAS-L: Ceramics, Refractories and Insulations

[Reedtb2@cs.com]

Dear Dean et al:

It is important to distinguish between Ceramics, Refractories and 
Insulations.  

"Ceramics" can refer to anything made of inorganic oxides such as clays, 
mullite, alumina, zironcia, .....   and doesn't specify the form or density.

"Refractories" typically refers to ceramics in a form to resist high 
temperatures.  

"Insulation" refers to materials which have a relatively high resistance to 
heat flow, often fibrous or particulate, relying on the (heat shield) effect 
of many surfaces to relect radiation back to  its source.  

Dense refractories are typically not very good insulators, but very wear 
resistant.  Insulators are typically not wear resistant.  Some forms of 
insulation can be "rigidized" after forming to make them relatively tough.

You can check out the conductances and densities of commercial refractories 
and insulations in Table 4.14.c in the North American Combustion Handbook 
(Vol 1), (North Amer. Mfg. Co., third Ed., 1986).....

Or you can reinvent the wheel..

Yours truly,                                TOM REED                    
CPC/BEF

In a message dated 3/17/00 12:35:28 AM Mountain Standard Time, 
dstill@epud.org writes:

<< Dear friends,
 
 I am sure that many are aware of the different types of refractory cement
 mixes available dry in 50 pound bags here in the U.S. There are many types
 of insulative mixes but they tend to be soft as well. We are working on
 various A. T. mixtures to try to replicate the industrial varieties. As soon
 as something works, we'll report to the list. I'm trying to enlist the
 companies that produce insulative refractory ceramics to help in this work.
 
 Pumice or perlite or vermiculite can be mixed with cement to reduce the
 mass.
 
 A recipe for heat resistant cement is:
 
 less than 5 gallons of water
 2 cubic feet of sand
 2 cubic feet of rock
 94 pounds of cement
 dry is better than wet
 
 We are having some success with Honduran refractory ceramic parts surrounded
 by wood ash. Wood ash is a great insulation. The refractory clay is made
 from horse manure, sand, clay and tree gum. We also love spirals of aluminum
 foil in areas below 700 degrees F.
 
 We experimented with white highly emmissive paints from NASA that supposedly
 had high R values. But, in our tests thay showed no real value in stoves.
 They did not help performance in a haybox either.
 
 Best,
 
 Dean Still
 
  >>
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