Tuesday, 23 July 2013

Cold Fusion- A Modern Heresy

Fusion is a hot topic these days. The stakes are higher than ever for a source of sustainable energy and many still want a piece of the action. But like most feats, it's fallen on the wayside of fringe physics as a modern-day heresy. The basic idea is whether it may be possible to recreate the power of the sun (which undergoes fusion of atomic nuclei at 10^7 K) at or near room temperature. In 1989, Fleischmann and Pons claimed they could create such a process on earth at room temperature using a simple electrolysis cell experiment. Using heavy water (D2O), where hydrogen atoms have been replaced by hydrogen's heavier isotope, deuterium; they applied a palladium cathode as an electrode and passed a current via the water, allegedly causing large quantities of heat to be produced. Such a 'cold fusion' reaction is nothing short of miraculous: firstly, there is a positive charge produced by the nucleus of every deuterium atom, prohibiting the atoms from coming close enough to fuse (Coulomb barrier). The sun overcomes the Coulomb barrier by the enormous temperatures that sends atoms accelerating at great speeds and colliding to fuse and release energy; even more miraculous, the Fleischmann-Pons experiment didn't produce lethal doses of radiation, as often expected from fusion reactions. To explain away their phenomenon, it was proposed that neutrons were being exchanged between the atomic nuclei (and releasing heat in the process), others believed that deep within the lattice of palladium atoms, an exotic clustering of electron clouds allowed the deuterium nuclei to come close enough to fuse. Another proposal was that spontaneous fractures in the palladium cathode effectively fired the deuterons together. The experiment itself was quantitatively measured in terms of  the current put in to the cell compared with loss of heat and temperature rise during the entire set-up; but was this really cold fusion? Apart from the lack of experimental reproducibility, a strong theoretical argument can be made as a final 'nail in the coffin' against the feasibility of cold fusion; Leggett and Bayem maintained that in calculating  the maximum degree to which the Coulomb barrier can be lowered (presuming maximum entropy/equilibrium) in addition to the binding energies of electrons in both hydrogen and helium, one can also consider the affinity of the metallic lattice for an atom (the energy released when an atom is put in the crystal and permitted to occupy the lowest energy-state). Such nuclear parameters are well defined, except for the final one because there is no precise measurement of the affinity of palladium or titanium for helium, but it can be rest assured that the value must be small due to the fact that helium releases readily from such metals at room temperature. Other cold fusion scenarios such as a deuteron-metal apparatus in a transient state but under thermodynamic equilibrium are questionable in their efficacy.

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