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 Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=1505