X-Message-Number: 4184
Date: 10 Apr 95 08:32:26 EDT
From: yvan Bozzonetti <>
Subject: SCI.CRYONICS: Angel's cooling.

First a crack story: 

Some friend was interested, some time ago to build a set of 60" telescopes 
with the primary mirror made from ordinary cooked back grass. The first 
blank was heatted to 625 degree and then cooled at natural speed in the 
oven. It shatered on the first move. The second was cooled more slowly and 
broken only when a hole was cut in its center. The 3rd was lost at the 
polissage end, when many microscopic glass grains where trapped on the 
surface.

Having seen that and be interested by 80" mirrors, I wash surfaces with 
some phosphoric acid to reducethe glass powder accumulation and more, I 
apply the cooling rule given by Robert Angel, from Tucson (He spin casts 
some big mirrors up to 320" in diameter). From its charts, a ultra tin 
mirror blank 80" in diameter and 1" thick must be cooled in no less than 3 
week if we don't want to see hasardous forces in it. As a first rule of the 
tumb, cooling time expands as the thickness square. A 4" mirror would cool 
safely in : 3 x 4 x 4 = 48 weeks.

Now, if cryonics patients was made from glass and coud be thought of as 80" 
diameter disks, 4" thick, the cooling time would be near 48/3 = 16 weeks, 
taking into account the shortest temperature rage between room and LN2. Up 
to dry ice temperature, cooling could be faster and slow down beyond.

Yes, patients are not made from glass, ice is not even a glassy material, 
neverthless the real cooling time to suppress any cracking must remains in 
the same order, may be ten, may be twenty weeks... A look at Angel's law 
could suppress many problems and even the need for complicated 
cryoprotectant solutions. The experiment seems simple to do for any 
cryonics organization...

	Yvan Bozzonetti.


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