X-Message-Number: 25989 From: "Basie" <> Subject: Rotating cryostat Date: Fri, 8 Apr 2005 23:15:48 -0400 I wonder how long it would take for the ice in the body to migrate to the head in a cryostat. It would be expensive and risky but ideally the patient should slowly rotate. Basie This is a quote! "Another way to slow chemical activity is by lowering the temperature. The problem here is that some materials go through a significant phase change as temperature is lowered, water being the most obvious example. Not only does water freeze to sharp-edged ice crystals, but these expand to a larger volume than that occupied by the original water. Also, over time, the crystals - as crystals do - consolidate, moving water molecules from one place to another. So you eventually wind up with a dehydrated material having a few large pieces of ice dispersed through it. There would be, of course, major changes in the texture and perhaps of the chemistry of the preserved material during this process. The lower the temperature the slower this migration. At cryogenic temperatures it is pretty much - though not completely - stopped. Still, material stored in liquid helium would probably keep a long time before this process caused a significant amount of damage. The problem is that - on Earth, at least - maintaining such low temperatures requires a highly technical infrastructure. If you really want to preserve something a long time by freezing, you'd have to leave the planet. (The Antarctic ice caps are only a few million years old at most. Even without warming periods melting them, the pressure of new snow on top slowly squeezes the lower ice, causing physical deformation. Much of the ice is eventually pushed out onto the ocean by slow creeping due to the weight of ice above it and further inland.) For really long term storage you definitely want cryogenic temperatures, whatever else you may do to preserve your material. Burying something in an icy planetesimal well out in the Oort Belt or Kuiper cloud would do for at least a few hundred million years. The temperature would be a few Kelvins, plenty cold enough. But there's one small problem. When other stars pass by, every few million years, their gravity affects the orbits of these bodies, sometimes sending one or more careering through the inner solar system. The chance of any one particular body having this happen is remote, but still... Even using a free body, one which orbits the galaxy independently of a parent star, runs this risk. And there's also a chance of collision, as well as cosmic rays. If you want to keep something frozen for billions of years this just won't do. Interestingly, there's a place much nearer to Earth where a low-maintenance cryogenic facility capable of holding a very low temperature for a few billion years and providing better protection from cosmic radiation could be built. Find a crater at one of the Moon's poles. Dig a narrow, vertical shaft. Insulate the bottom and sides with multiple, waffled layers of something appropriate. (Aluminized or silverized mylar, for instance.) Place your object there. The deeper the shaft the lower the rate of micrometeoroid impacts and the lower the amount of outside radiation (including thermal) which makes it to the bottom. However, the Moon does generate some internal heat, so the hole can't be too deep. Half a kilometer or so should work fine. With the object insulated from the surrounding rock and open to empty space in a vacuum, temperatures will soon be down to not far above the microwave background. Devices of this type are known as Ruzic Cryostats. Of course, at the most, this will only last until the sun enters its red giant phase... No matter how hard you try, nothing lasts forever. So, let's accept and value impermanence, and appreciate things for the few billion years they'll be around." This work is Copyright 2002 Rodford Edmiston Smith. Anyone wishing to reprint this material must have permission from the author, who can be contacted at: Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=25989