What is the difference between nuclear fusion and cold fusion?

Asked by: Robert Hernandez

Answer

Nuclear fusion can produce energy when the nuclei of lighter elements come together (fuse), creating larger nuclei. Energy is liberated when the total mass of the end products is slightly less than the mass of the lighter nuclei going into the process, with that difference in mass being converted to energy via Einstein's famous E=mc² relationship.

Because the protons in nuclei are all positively charged, and like charges repel, nuclei need some convincing to get them to fuse. That convincing ordinarily involves high temperature and pressure, such as exists at the core of a star or under conditions created by a fission bomb.

Cold fusion is an attempt to get fusion to occur under less extreme conditions, possibly as a result of chemical reactions. Despite the flurry of publicity several years ago, cold fusion remains unrealized speculation for now.
Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor

Cold fusion, if it worked, would be a form of nuclear fusion.

Although many nuclei can be fused, this subject normally refers to fusion of hydrogen isotopes deuterium or tritium to form helium. When this happens energy is released. Unfortunately, the hydrogen nuclei are positively charged and repel one another -- very strongly so at short distances. This makes fusion difficult to achieve. In the Sun very high levels of heat and pressure overcome the repulsion. On Earth fusion can also be forced this way, but so far not with more energy being released than what went into building the neccessary heat and pressure.

Early in 1989 two chemists, Prof. G. Stanley Pons and Prof. Martin Fleischmann were experimenting with electrolyzing heavy water, (which contains tritium), using palladium electrodes. Hydrogen in all its forms has a very strong affinity for palladium. From their measurements, Pons and Fleischmann calculated that more energy was being released from the process, as heat, than was being put into it as electricity. They speculated that somehow tritium nuclei were being forced close together enough to cause fusion. This would account for the apparent excess heat being released. The process was called cold fusion because the temperatures involved were far lower than any at which fusion had been known to occur.

Today it is believed by most scientists familiar with the facts of the case that the procedures of Pons and Fleischmann were flawed and their conclusions mistaken.
Answered by: Craig Busse, B.S., Process Engineer, Lucent Technologies, Whippany NJ