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As promised last week this weeks topic is cold fusion. Cold fusion is loosely defined as the fusion of two atomic nuclei to form a single more massive nucleus at temperatures and pressures at or near normal atmospheric conditions at sea levels.
First off we need to look at what really happens in nuclear fusion and why it is so had to achieve. Nuclear fusion is all about the balance between to fundamental forces of nature, the strong nucleic force and the electromagnetic force. In this instance the electromagnetic force is the repulsive force that two likely charged nuclei exhibit and is governed by the inverse square of the distance between the two nuclei. Put simply if you halve the distance between the two nuclei the force pushing them apart will double. The strong nucleic force is an attractive force and only acts over extremely short distances. The strong nucleic force is what holds the nucleus of the atom together. The problem is that you need to overcome the electromagnetic repulsive force and get the two nuclei close enough together in order for the strong nucleic force to take over and fuse the two nuclei together. The distances involved are extremely short and since the electromagnetic repulsion gets greater as the separation decreases overcoming it requires the expenditure of a great amount of energy.
Generally the temperature and pressure of a substance are a measure of the energy that the atoms that make up that substance possess. Relate this, to the energy that is needed to get nuclear fusion to take place and it reveals that you need extremely high temperatures and pressures to give the individual nuclei enough energy to overcome the repulsive electromagnetic force. Temperature and pressure are however an average measurement of the energy of all the particles that make up a sample and if you look at all the individual particles you will find that there is a range of energies that the individual particles actually exhibit. The concept is that while the average energy is way to low for fusion to take place on a large scale some individual nuclei within a sample may possess enough energy to overcome the repulsive electromagnetic force and allow fusion to take place.
As we saw in last weeks discussion whether or not you get back more energy from the fusion process than you expend getting it to take place, depends on the number of protons in the two small nuclei to start with. As the atomic number increases the number of protons increases and this increases the amount of energy that needs to be expended in order to gent the two nuclei close enough together to allow fusion to occur. In general if the atoms possess more protons than nickel or iron the amount of energy that is required to overcome the electromagnetic repulsive force is greater than the energy that will be returned from the fusion process. Ultimately this means that fusion between nuclei that create new nuclei with less protons than nickel or iron will give you a net gain in energy while the opposite is true for nuclei that produce nuclei with a greater number of protons. This is why fission reactions of heavy atoms like uranium releases energy while the reverse process of fusion, between tritium and deuterium also releases energy.
The debate over cold nuclear fusion was started in 1989 when Fleischmann and Pons reported anomalous experimental results that they attributed to nuclear fusion. If plain water is electrolyzed in a closed cell that is surrounded by a calorimeter the total amount of energy input and heat released can be explained using standard and well understood physics and chemistry. However, if the water is replaced with heavy water, D2O, and the cathode is made of pure palladium there appears to be a surplus of energy that can't be explained by conventional physics and chemistry. It is this surplus that Fleischmann and Pons attributed to nuclear fusion.
There has been considerable debate over the claims of Fleischmann and Pons and to date there is no real consensus one way or the other. The lack of the appropriate fission byproducts and gamma ray emissions would seem to indicate that nuclear fusion not taking place. Considering that the results are not always repeatable, one must at least that there is something going on that is not yet fully understood. Whether this is nuclear fusion is or not another question entirely and to date it has remained unanswered..
Now there are other techniques that do actually produce nuclear fusion at relatively low temperatures and pressures but they all consume more energy than they produce and are therefore not suitable as a source of energy.
After nearly two decades the repeatability of so called cold fusion is still inconsistent and there is still considerable debate over whether there is in fact nuclear fusion taking place. Until the process is both regularly repeatable and fully understood there is no way to even conclude that cold fusion is taking place let alone using it at commercial levels to produce power.
You can read more about cold fusion with these links:
How do you see cold fusion? Do we really understand how nuclear fusion takes place or is cold fusion just poor science and a waste of time, money and effort?
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Re: Future Energy Sources 1.9.2.2 Cold Fusion
