Skeptical Inquirer, organ ``Vyboru pro vedecka zkoumani paranormalnich tvrzeni'' (cleny komitetu jsou i ctyri laureati Nobelovy ceny) ve svem c. 4, rocnik 24 (2000), str. 18-19, otiskl zatim nejpodrobnejsi rozbor paranormalnosti te krakatenove blamaze. Puvodni text nasleduje:

The Czech republic has a long tradition in explosives engineering, and the infamous "Semtex" (supposedly hexahydro-1,3,5-trinitro-1,3,5-triazine, though it is still a secret and other sources speak on penterythritol tetranitrate) is a good example of the tradition. Its name is derived from a village, Semtin, where the firm Synthesia is located. The university in the nearby town of Pardubice has a department specializing in explosives; this is unusual at a university. Consequently, if a respected senior scholar from the Czech Academy of Sciences in Prague (who has no link to Pardubice or Semtin) announces in a large-scale newspaper interview: "We discovered ... a compound which is ... the strongest classical explosive known so far. It is one hundred times, possibly even one thousand times, stronger than trinitrotoluene, dynamite or nitroglycerin" you should pay your attention. This is especially true if the announcement is backed by the Academy. But the army, navy and air-force showed no interest, not because the cold war is over but because the armed services are paid for real accomplishments, not just for plays of words. What went wrong?

The play on words was really impressive in this case. The discoverer named the new species Krakatene/Cracatene (in an obvious reference to the volcano Krakatoa or Krakatau, whose eruption in 1883 is considered to be the most destructive one in recorded history). He had no experimental support for his claim, which was based solely on theoretical speculation. The formula of the species is C6. The discoverer gave only one argument in support of the claim that the substance explodes: "A ring of six carbon atoms is very rich in energy. We say that we have a compound with a very large positive heat of formation."

Small carbon clusters are not new. Otto Hahn and coworkers reported clusters up to C15 as early as 1942-1943. They have been considered as a component of the mechanism of formation of C60 and of soot. They have been characterized spectrally to some extent; they can be linear, cyclic or even non-planar. Extensive theoretical calculations have been done on them, but they were never prepared in macroscopic amounts as condensed-phase chemical species. It is also known that C4, C3, C2 and even C1 have heats of formation in the ideal gas phase at room temperature which are greater per carbon atom than that of C6. Does this mean that one should call them krakatene-4, krakatene-3, krakatene-2 or krakatene-1?

The heat of formation is a very useful quantity as it permits evaluation of the heat of reaction of any chemical process. However, it is a variable term which depends on the definitions of reference states. A stable species does not necessarily have a negative heat of formation (e.g. liquid benzene, +49 kJ/mol) but it may (liquid hexafluorobenzene, -991 kJ/mol). If you invest extra labour you can redefine the reference states and change the signs at will (however, you would create confusion in the useful data). If we are bold enough and look at the notorious explosives we shall find that the heats of formation may be positive or negative. Liquid nitroglycerin is perfectly all right with a value of -371 kJ/mol (and doesn't seem to care that it has a large negative heat of formation) but TNT jumps to +44 kJ/mol (another source gives a value of -75 kJ/mol for solid TNT). Moreover, nitroglycerin creates almost twice as large a cavity in a standard lead block test of explosive strength as the same mass of TNT.

In fact, energy contents are not good predictors of explosive strength. Conventional explosives have a lower energy output, by one order of magnitude, than common fuels. The detonation of nitroglycerin yields about 6 kJ/g. (Usually, explosives do not need atmospheric oxygen; i.e. explosion stoichiometry is not identical with that of combustion. However, the combustion of nitroglycerin yields a similar amount of energy.) Burning one gram of graphite or gasoline gives 33 and 47 kJ, respectively. Still, no one tries to use coal in place of dynamite, though porous charcoal with liquid oxygen or simply coal dust would work. However, the energy produced is essentially the same in all the three carbon species. What really matters are kinetics and reaction rates; the energy and hot gases must be released in a relatively short time. Indeed, the time for complete reaction is shorter in explosions, by five orders of magnitude, than in the burning of fuel. Therefore, pressures developed are higher by four to six orders of magnitude. Hence, if someone tries to "invent" new explosives using pencil and paper, he/she should estimate reaction rates, not heats of formation! All this is certainly not new: C. N. Hinshelwood and N. N. Semenov received the Nobel prize for such work in 1956, and they explained the kinetics of some explosions as early as the 1920's and 1930's.

But even before we discuss any kinetics, and before we ask what are the expanding gases in the Krakatene case, we have to realize that potential explosives must be stable under ordinary conditions in order to be fabricated, stored, transported or even smuggled, and they should explode only upon activation. It must be possible to produce it readily in large quantities. This is certainly a basic requirement, but C6 can only be prepared in small amounts in the gas phase or on inert-gas matrices. There are two stability domains for carbon clusters: C60 and some larger aggregates, and soot. We certainly do not know all the thermodynamic and kinetic details of the complex system but we know what the final products are.

Not everybody cooks fullerenes in an oven. Let us consider a system as trivial and innocent as N2, and let us consider a higher excited electronic state of it, say a quintet located some 900 kJ/mol above the ground state. The heat of formation of N2 is zero by definition, and the quintet has its heat of formation 900 kJ/mol or about 33 kJ/g. This is considerably higher than the assumed heat of formation of C6. Now, one could rise his/her voice, wave his/her hands dramatically or jump happily - Super-Krakatene! Hardly any chemist would pay attention to the hand-waving arguments, since we cannot produce the quintet in large amounts or store it for a long time. Therefore, there is no need to bother with the kinetics of the energy release from the quintet back to the ground state.

Last, but not least, it is virtually impossible to publish such a polemic within the Czech scientific community. People are afraid that it would further lower the shaky image of science in the eyes of the general public. (This is supposedly a reason why the Semtin/Pardubice people never publicly commented on the Krakatene story.) Nevertheless, science is, in one way or another, a self-correcting institution, and this is its vital feature. Let us, finally, quote J. P. Joule who apparently anticipated that people would have problems with work-heat conversions for decades, if not centuries, to come and stated it as an error-dissipation law: "The way to make no errors is to write no papers".

Zdenek Slanina

A partial bibliography of the Krakatene/Cracatene explosive discovery: Young Front (March 20, 1993); J. Mol. Struct. (Theochem) 313 (1994) 335, esp. p. 341; THEOCHEM - J. Mol. Struct. 119 (1994) 335, esp. p. 341; Chem. Listy 86, 162 (1992), esp. p. 164; General Chemistry, Karolinum (1994), esp. p. 211.