X-Message-Number: 3383 Date: Wed, 02 Nov 94 17:05:56 From: Subject: SCI.CRYONICS High Pressure Cryonics Ben Best's posting concerning high pressure cryonics contains some assumptions which could lead to consequences I don't think he anticipated. First, the reason that high pressure storage has been proposed is to bridge the gap between toxic cryoprotectant concentrations and vitrifiable cryoprotectant concentrations, using current cryoprotectants. Other cryoprotectants might not have this gap. Second, some practical engineering and physics considerations come to mind. If we assume fabrication of a pressure chamber of 22" diameter using steel at 100,000 psi yield strength and a storage pressure of 2000 atmospheres (30,000 psi), this results in a chamber with 3.3" walls. This ignores engineering practice and the question of the properties of steel (industrial strength) at liquid nitrogen temperature. Other problems are electrical and fluid feed-throughs. In a lot of ways this begins to look like a gun barrel. A recent example of this scale of fabrication was Gerald Bull's long range super cannon he was developing for Saddam Hussein! In particular the closure for this pressure vessel starts to look like a breech block. A question that come to mind at this point is: Do you store people at this pressure? In which case the cost of storage per person will be very expensive. Or, since at low enough temperatures, the high pressure forms of ice can be stored at atmospheric pressure, do you process them down to - 196C and then remove them in a metastable state and store them at atmospheric pressure in liquid nitrogen with attendant transfer complications? The crystallography of the high pressure forms of ice from X-ray diffraction studies was done this way. The ice crystals were formed at high pressure, cooled to liquid nitrogen temperature and removed from the pressure vessel at -196C in a metastable state and X-rays were taken. Unfortunately, a lot of energy is stored in the ice. There is probably somewhere an anecdotal account of dealing with "explosive ice". We can estimate the amount of energy involved in the re-expansion of the ice as follows: W = PdV thus 30,000 lb/in^2 x 0.08 in^3/in^3 = 2500 in-lb/in^3 which after appropriate conversion results in a value of 67 cal/in^3 or 4.2 cal per gm. The heat capacity of ice at low temperature is as follows: -200C 0.156 cal/gm. -150C .246 -100C .332 -40C .435 0 .492 Assuming the transition takes place at -150C, the temperature jump from the released energy will be approximately 17C. "delivered by hammer" (Try pounding a piece of iron until it gets too hot to touch!) For 14,000 atmospheres (another figure mentioned in Ben's posting), a vessel of 23" steel walls results, again ignoring engineering practice and strength vs. temperature. The bottom line is that this is not a trivial project and can have some rather novel consequences. The resources that would have to be devoted to it would almost certainly be better expended in other directions. Incidentally, I at this point do not share Bob Ettinger's confidence that cracking is not a problem for liquid nitrogen cryostasis. Although he may in fact turn out to be right, there is still work to be done in this area before we can reach that conclusion, (work which is still in progress here at Alcor). Hugh Hixon Alcor Foundation Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=3383