Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!sun-barr!rutgers!aramis.rutgers.edu!athos.rutgers.edu!nanotech From: dietz@cs.rochester.edu (Paul Dietz) Newsgroups: sci.nanotech Subject: Re: Diamonds? Keywords: diamonds, bones Message-ID: Date: 9 Apr 91 02:34:49 GMT Sender: nanotech@athos.rutgers.edu Organization: Computer Science Department University of Rochester Lines: 41 Approved: nanotech@aramis.rutgers.edu erich@eecs.cs.pdx.edu (Erich Stefan Boleyn) writes: >> ...So why don't living things use diamond? Or do they? If >>they don't, is this telling us something about the limits of nanotechnology? >>That is, maybe diamond can ONLY be made at high pressures and/or temperatures, >>so a molecular machine couldn't do it, unless the machine operated under those >>conditions. > > Not necessarily. Consider how diamond is produced... the intense >temperatures and pressures are necessary because there is inherently a large >energy input required to produce diamond. If you look at the chemical >reaction, the activation energy is large, but there is no product energy, >and since the energy required is so large, it is very slow. Uh, fellows... you guys *are* aware of the work over the last few years on chemical vapor deposition of diamonds, aren't you? Carbon deposited from a near vacuum in the presence of large amounts of atomic hydrogen preferentially forms diamond. The first work (in Russia and Japan) used things like microwave discharges, but they can now make it work using just an acetylene torch flame as the source. This technology is already making its way into commercial products. High pressure is *not* required to make diamond. A source of chemical energy (in this case, atomic carbon and hydrogen) is needed, but that's also true in biological systems, where energy-rich compounds are consumed so that ordered structures (proteins, DNA) can be assembled with low error. Anyway, saying that diamond does not occur in biology because graphite is the lower energy state begs the question: why doesn't *graphite* occur? Or Kevlar, or nylon, or ultrahigh molecular weight polyethylene, or some other high strength materials? Most likely because evolution is constrained to do local search, and has looked at only a very tiny region of the search space. Preexisting solutions get adapted: proteins used to make spider webs, for example, even though other materials would be stronger. Paul F. Dietz dietz@cs.rochester.edu