X-Message-Number: 4749
Date: Wed, 9 Aug 1995 17:09:12 +0200 (MET DST)
From: Eugen Leitl <>
Subject: Why Florine is Evil & stuff

> CryoNet - Tue 8 Aug 1995

cold start: kinetic inhibition at low temperature is
an advantage, not something undesirable. Hence oxygen/hydrogen
is a much better system than H_2/F_2.

Keith F. Lynch wrote on Mon, 7 Aug 1995:
> 
> What about monatomic oxygen and/or monatomic hydrogen?  I'm sure
> either substance will react with the other, or with itself, at that
> temperature, releasing lots and lots of energy, and nothing toxic.

No method of storage of monoatomic species is currently known, apart
from argon matrix at 0.1 K, may be. I'd rather be handling solid
ozone: enthalpy of formation is _very_ large, at least one order
of magnitude higher than any chemical reaction known. In fact, the
hydrogen plasmatrone derives some of the heat from metal-catalyzed
heat of hydrogen recombination on the metal surface. At such energies
heat of combustion is negligeable, as compared to the recombination
enthalpy. (This isn't a nuke though, just one small step in the right
direction).
 
> What I'm not sure of is whether either substance can be kept stable at
> that temperature.  Perhaps if the individual atoms were constrained
> in a latticework of some relatively inert element such as gold?

Using atomic oxygene is the best way to make gold oxide from Au bulk:
you can watch surface tarnishing real fast. Argon matrix at about 0 K and 
massive dilution is probably the only containment possible for free
radicals.

> (If nanotechnology can use diamonds, why not gold?)

Because carbon is ubiquitous, and gold is not. Because carbon is versatile
and gold is not. Etc. There might be some limited uses for Au in nanotech,
though. Catalysts or 1d metals as columnar complexes, probably.

> Alternatively, why not simply use RF heating?  A low frequency will
> penetrate evenly to all parts of the brain, with no hot spots from
> shielding, focussing, reflection, diffraction, or any other mechanism.

The problem is power: you'd need several kW RF to heat even a modest
organ as Fahy says. I don't think RF is viable for whole-body defrosts, 
due to extreme power requirements though it may be optimal for 
neuropatients retrieval.

Concerning shockwaves: you might be getting some if you'd use MW or
GW RF power. (Consider using the Nova Laser at Livermore for tissue
rewarming instead, then you'll sure get shockwaves ;).

Concerning F_2 and HF storage: F_2 is stable in dry glass containers,
one is making xenone fluoride in quartz containers to allow short
wave (from sunlight or UV) in in period of some days. (Hydrolysis
to xenone oxide is usually done in teflon capillaries in _small_
quantities. Otherwise you might need some new lab equipment after
watching some teflone aerosol and possibly a new operator.. 
Giant holes.)

Steel surfaces undergo oxidation, presenting an inert metal fluoride 
surface. However, if you make a spot hot enough, the fluoride will
melt off, exposing a clean surface, which will react with fluorine...
provided, the rate is high enough, you'd get a nice explosion, since
the reaction is autocatalytic. For room temperature this storage works good,
though. For above reasons, it is highly unsafe transporting (warm) fuming 
nitric acid in titanium or aluminum container and than scratching the 
inner surface... don't do that.

There isn't any diamond fluoride, but one can substitute hydrogen
on diamond surface by fluorine, thus making it much more inert.
However, the layer being monoatomic, can be breached with species
of high enough energy, exposing a hot (radical) spot on the surface.
PTFE (teflone) is essentially a hydrocarbon with all hydrogens
substitued by fluorines.

Free fluorine, as ozone, ignites any organic substance instanteously
(chlorine does this only rarely), free carbon (as carbon black) and
HF is released. Warmed water burns in fluorine with a pale flame, 
oxygene I think, too. Bricks will burn if dripped onto with NF_3, in fact 
thus the porous membranes for gaseous uranium hexafluoride (which is 
nasty stuff on its own right) isotope separation by diffusion was 
achieved in Los Alamos (they used other methods, too).

The product of fluorine/hydrogen combustion is HF, which is a (very
nasty) fluid at about 18 deg C, gaseous HF is not anything I'd recommend
breathing to the average mammal. HF solved in water is hydrofluoric
acid, diluted solutions of which are used for glass etchings in art.
With concentrated HF solutions, silicates can be converted to thin
air (silicon tetrafluoride, SiF_4), if treated repeatedly in a lead
crucible (?). Simplest way to make HF is to pour conc. sulfuric
acid upon calcium difluoride and heat the mess. (Don't do that at home, 
either).

Toxicity: hydrofluoric acid (especially hot) makes really spectacular 
burns which don't heal for months, since it grabs calcium ions from 
tissue. Apart from being corrosive, HF is damn toxic on its own right,
so beware.

(I hope above passage has convinced you why free fluorine is Evil.)

Concerning Will Wares coolin' gizmos proposal: unfortunately there
ain't no endothermic reaction which could cool down tissue at such
concentrations measurably. Some heat flow and Carnot loss will
have to be dealt with, unfortunately.

The highest cooling rates for tissue
known is based on bringing a tiny slice into direct contact with
a copper block at liquid He temperature _very_ rapidly, a relatively
recent EM specimen preparation technique (End-80's Nature?).

This produces good water glass at a minimum of artefacts real
fast (I think they did neurotransmitter vesicle dynamics for
a demo, though I might be inventing things here).

-- Eugene


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