Questions asked in comments below may be added here with Answers being direct or by reference to blog pages.
Q. What is cold fusion?
A. “Cold fusion” is a popular name given to experimental results which have been interpreted by some to indicate that nuclear reactions are taking place in unexpected conditions. A more neutral name is Low Energy Nuclear Reactions (LENR), and still more neutral is the Anomalous Heat Effect. These results include, most prominently, heat, but there have been persistent expert reports of tritium production, at levels far below those expected if the reaction were ordinary nuclear fusion.
Only one nuclear product has been reliably correlated with anomalous heat: helium-4, in palladium deuteride experiments, and the ratio is consistent with that expected from the conversion of deuterium to helium. How that conversion may occur remains a mystery.
Q. How was it discovered and why did it attract so much attention?
A. Martin Fleischmann, certainly a foremost electrochemist at the time, and his colleague, Stanley Pons, knew that the view that nuclear reactions were impossible from chemistry was based on approximations and assumptions, backed by the lack of known examples. They decided to look for anomalous heat; they expected that such heat would be below what they could detect, even though they were using arguably the most sensitive calorimetry of the time.
Their idea was to load palladium metal, which soaks up hydrogen to the point that the effective pressure of hydrogen was very large, with a more fusible isotope of hydrogen, deuterium, using electrolysis to raise the loading ratio.
Then their experiment melted down. Their first announcement was missing many crucial details.
There was a firestorm of reaction, and it has been said that, for a time, half the discretionary research budget of the U.S. was being spent on attempts to replicate.
As we could now predict, almost all these efforts failed, because even Pons and Fleischmann did not understand the required conditions. A crucial fact of their successful experiments was that they involved loading and deloading of the palladium over many weeks, so not only would most palladium not work at all, the metal also needed to be conditioned, the same material would produce no heat even for months, and then a burst of heat would be observed in a loading cycle. The only difference was that the material had been stressed. And then it would stop generating excess heat.
Very few exact replications were done, most workers tried to “improve” the experiment, and found nothing. But there were, in fact, replications and confirmations, they were merely rare.
If the effect were real, and if a way could be found to gain better control, this could be a major source of energy. The research, however, was pure science, they were not pursing wealth or “free energy.”
Q. “Rare replications” sounds like the “file drawer effect. ” Do we know that the heat effect is real and not merely occasional experimental error?
A. Yes. The correlation between anomalous heat and measured helium is strong enough to support the reality of the effect. This has been independently confirmed by many research groups, and the ratio is consistent with the heat being generated by the conversion of deuterium to helium. See my Current Science paper (2015)
https://lenr-canr.org/wordpress/?p=1603 links to the whole special issue on LENR.
Q. Why was replication and control so difficult?
A. This remains controversial. For a time, the only idea widely considered was that the reaction requires a population of nanocracks in the surface of the material (Edmund Storms). However, it was discovered in the 1990s (Fukai) that palladium hydride has phases beyond the normal beta phase, which can approach a 1:1 loading ratio as a limit. These phases rearrange the metal structure, allow a higher ratio, and are metastable even if the material is deloaded. While Fukai created these super-abundant vacancy (SAV) phases using a diamond anvil press, with 5 GPa pressure and 800 C, if material is highly loaded, it is possible that small amounts of this SAV material could form and accumulate at the surface. They will remain until the material is heated to annealing temperature, about 800 C. So the reaction hot spots, observed with IR cameras, which apppear to get hot enough to melt palladium, would anneal local palladium back to normal crystal structure.
(It is known that copper hydride can form SAV material through codeposition, i.e., electroplating copper while generating hydrogen, so the plating is saturated with hydrogen. In the process of loading and deloading in standard Fleischmann-Pons experiments, small amounts of palladium dissolve into the electrolyte and are redeposited, in addition to the metal being stressed, which may also facilitate phase conversion.)