Re: We're stuck with each other

From: Robert J. Bradbury (
Date: Wed Jan 23 2002 - 13:01:41 MST

On Wed, 23 Jan 2002, Eliezer S. Yudkowsky wrote:

> Nanotechnology produces diamond as a waste product. If you convert carbon
> in its other forms into diamond, you get a large amount of energy *out* of
> the chemical reaction.

Actually, I don't think that's true Eliezer. According to the Handbook
of Chemistry and Physics Chapter 5: Selected Values of Chemical Thermodynamic
Properties, going from carbon to diamond, the delta-H is 0.45 and the
delta-G is 0.69 (at STP). So the reaction is endothermic and non-spontaneous
according to:

So you do not get energy out of making diamond (at least from graphite).

> That's why diamonds are so hard - you have to expend that amount of energy,
> add it back in, before you can break the molecular bonds.

If I understand what you are saying that isn't really true. The hardness
of a material is determined by the bond strength, the orientation of interatomic
bonds and the bond density of the material. Diamond and BN are two of the
hardest materials known because they have the smallest atoms and the greatest
bond density. In contrast, I've been told that solid H2 is about as soft
as butter.

  C + O2 --> CO2
C has a delta-H of 0.45 and a delta-G of 0.69.
O2 has a 0 delta-H and delta-G
CO2 had dH and dG of ~-94.
So the reaction will be exothermic.

  C + 2H2 --> CH4
H2 has a dH and dG of 0.
CH4 has a dH of -15.9 and a dG of -12.1.
So this reaction will be exothermic as well.

  CH4 + O2 --> CO2 + 2H2

 dH_products - dH_reactants = dH_rxn
  (-94 + 0) - (-15.9 + 0) = -78.1
So, you get more energy out of burning diamond in oxygen (~-94)
than you get out of burning methane in oxygen (~-78).

What I believe, Eli meant was that the production of diamondoid from
"hydrogen-rich feedstock" such as methane, is exothermic, e.g.
  CH4 (methane) + O2 --> C(diamondoid) + 2H2O
  (0.45+0) - (-15.9+0) = 16.35

Well, that isn't exothermic(!), so Eric is getting his 400 maJ per
atom (Nanosystems, pg 398) out of changes in the entropy in the
system (2 gases being converted into a solid and a liquid).
  (0.57+18.2) - (44.5+49) = -74.7 (this is using the delta-S's)

> Along with the concept of a diamondoid space suit goes the
> concept of diamond, not as expensive rocks dug up out of the ground, but
> as a waste material produced by exothermic and exoergic nanotech
> manufacturing processes.

Cough... But where did the hydrogen rich carbon feedstock come from?

Yes, I know -- ultimately from sunlight. But Eric does kind of gloss
over that detail in Nanosystems. If you want this to be renewable
you don't want your hydrogen-rich feedstock to be coming out of the

> What you do have with nanotechnology is the diamondoid recycling problem.
> As I pointed out at the last Foresight Gathering when the topic of
> recycling came up, "a diamond is not forever", but it's probably more
> efficient to disintegrate it - take the energy output of a power plant or
> a solar mirror and run the diamondoid material through en masse - rather
> than disassembling it atom-by-atom, as I've heard proposed.

You don't have to add power, you just have to ignite it and it should
burn fine. That is why sapphire nanobots are much more dangerous than
diamondoid nanobots -- sapphire doesn't burn, except perhaps in a
hydrogen rich atmosphere.

> Speaking of which, Robert, are you sure that it's possible to consume
> diamond and oxygen as a fuel?

Funny you should ask. Nanomedicine, Table 6.1, pg 141 lists diamond
as having the "highest known oxidative chemical storage density,
possibly surpassed only by fullerene materials" (I question question
that since fullerene bond density is lower).

It goes on to say, "an injection of ~0.7 cm^3 of diamond colloid (the most
energy-dense chemical fuel known--it has been used as rocket fuel)
encapsulated in trillions of suitable submicron-scale biocompatible carrier
devices provides an energy resource equal in size to the entire serum
glucose supply..."

Too bad there isn't any citation on who was using diamond dust to power
rockets. :-(

> Are you sure you aren't thinking of a rocket-suit that got you into
> orbit by turning something else, maybe acetylene, into the diamondoid suit?

Nope. I'm fairly sure what Eric had in mind was burning the contents
of the fuel tank, then burning the tank, then burning the rocket engines
themselves one by one (presumably one remains). As the discussion
above shows, from a dH point of view diamond dust makes a great fuel.
Since its a solid + a gas going to a gas, there shouldn't be significant
entropy losses.


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