X-Message-Number: 1505
Date: Thu, 24 Dec 92 01:14:29 CST
From: Brian Wowk <>
Subject: CRYONICS: storage temps

Edgar Swank:
 
> The interest in LN2 is for long-term storage. Referring to Hugh
> Hixon's article from CRYOMSG 15, -80xC is clearly too warm for
> long-term storage (1 second of body temp decay takes 17 minutes).
 
> I would guess -164xC (L Methane) is the warmest useable (1 sec at body
> temp = 42 years) long-term storage temp.  LN2 is overkill (24 Million
> yrs.),  but is used because it's economical.
 
        The variation of reaction rate with temperature depends on the 
activation energy of the chemical reaction (see the Arrhenius equation).  In 
particular, if reaction A takes place 1000 times slower if we lower the 
temperature by a given amount, this does not mean reaction B will also slow 
by a factor of a 1000.  Reaction B might slow by a factor of 1,000,000 if its 
activation energy is higher than A's.
 
        As it turns out, Hugh Hixon chose one of the fastest chemical 
reactions known in nature as the benchmark for his article, "How Cold is Cold 
Enough?"  This was a conservative thing to do, but it can also be misleading.  
Practically all chemical reactions will slow by a much greater factor than 
the "1 second of body temp decay takes 17 minutes" (at -80'C) figure quoted 
by Mr. Swank.  Furthermore, at -130'C *all* chemical reaction rates go 
identically to zero inside cells.  At this temperature (TG, or the "glass 
transition temperature"), even the Arrhenius equation fails because any 
remaining liquid water inside cells becomes as solid as glass, rendering all 
reactants immobile.
 
        I agree with Edgar that -80'C is probably not good enough for 
centuries of storage.  (Believe it or not, at this temperature traces of 
unfrozen liquid water still exist inside cells.)  However, -130'C will do 
quite nicely for a very long time.
 
                                                --- Brian Wowk

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