Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!dimacs.rutgers.edu!aramis.rutgers.edu!athos.rutgers.edu!nanotech From: neufeld@aurora.physics.utoronto.ca (Christopher Neufeld) Newsgroups: sci.nanotech Subject: Re: Diamonds? Keywords: diamonds, bones Message-ID: Date: 12 Apr 91 20:34:49 GMT Sender: nanotech@athos.rutgers.edu Organization: University of Toronto Physics/Astronomy/CITA Lines: 70 Approved: nanotech@aramis.rutgers.edu In article erich@eecs.cs.pdx.edu (Erich Stefan Boleyn) writes: > > Anyway, These deposition methods are still energy expensive. >Even supposing that you have high amounts of energy available that would not >damage your nanotech machinery (energy high enough to establish the carbon- >carbon pi sigma bonds are also high enough to pose possible danger to the >strutural integrity of your device ?), that is still a lot of energy to >direct locally. > > [stuff deleted] > >How would >the energy feed be done for a nanomachine? Chemically? It would have to >provide a good punch, so to speak... current biological-chemical reactions >don't tend to be too high-energy... (this is where I don't know what the >comparative energy levels would be, I'll check up on it). > Recall that the carbon atoms -> diamond synthesis is exothermal, so the nanomachine doesn't have to channel the energy to form the bond, it just has to stand out of the way. "Bond energies" refer to the binding energy of the bond, or the energy which is released when the bond is formed, not the energy required to make the bond. If that were the case, every compound you see would realize that it could get to a lower energy state by atomizing and the world would dissolve to gas. The nanomachine would just have to be designed not to absorb the energy, which will be primarily thermal energy released when the lattice rebounds from the new carbon bond. Very little of that energy is likely to find its way back to the nanomachine, if just because of acoustic impedance mismatches between the crystal and the surrounding medium. >> The point of all this is that diamond would make a pretty good bone >>material. It isn't going to transform spontaneously into graphite inside >>a person's legs. I don't think there is much in the way of biological >>impediments to the evolution of diamond bones. > > Moving around molecule subunits is easier than moving atoms, and calcium >has always been abundant as a free ion in cells, not to mention being used >by many other things. One of the main problems would be to work with raw >carbon, and how to isolate that from the rest of the body. Making bones is >a sloppy operation. > Now I'll stray far from my field. The diamond atoms in the crystal form bonds with their four nearest neighbours in a tetragonal geometry, akin to sp3 hybridization of atomic orbitals. This is also the geometry of a methane molecule, and will be very close to the geometry of a methyl group CH3. Not ever having gone above high school chemistry, I'd design my diamond-building machines to be dominantly atomic step extenders. They would come in with a methyl group on a long stick, and would insert it at the edge of a step from one crystal plane to the other. In doing so they would trade the methyl for the hydrogen on the surface of the crystal, ie. the surface of the crystal would always be fully hydrogenated, with the crystal being built by substituting a methyl group for one or more hydrogens on the surface. Perhaps one in every million nanomachines would be atomic step creators. They would have the capacity to form a bond with the surface of a crystal plane, instead of just the edge of one. This scheme would allow each crystal plane to be manufactured to completion with fast growth along the face of the crystal, and slow growth outward, to limit the formation of voids and nanomachine inclusions. This scheme doesn't involve handling individual unbonded carbon atoms, which are notoriously reactive, just the handling of methyl groups which biological systems do all the time. -- Christopher Neufeld....Just a graduate student | Flash: morning star seen neufeld@aurora.physics.utoronto.ca Ad astra! | in evening! Baffled cneufeld@{pnet91,pro-cco}.cts.com | astronomers: "could mean "Don't edit reality for the sake of simplicity" | second coming of Elvis!"