11/7/2023 0 Comments Liquid iron and nickel![]() These advanced simulation methods are not only important to obtain a better understanding of Earth's magnetic field, they also provide new insights into the electronic scattering processes in different materials. ![]() We also had to take imperfections and irregularities into account, which made the computer simulations even more challenging," says Karsten Held. "Together with our colleagues from Würzburg, we did not only have a look at iron and nickel, but also at alloys of these two materials. The many-particle-calculations were performed by Andreas Hausoel (University of Würzburg), some of them on the Vienna Scientific Cluster (VSC). To obtain these results, different metallic structures had to be analysed in large-scale computer simulations, and the behaviour of their electrons had to be calculated. As a result, convection currents have to emerge, which eventually build up Earth's magnetic field. As a consequence, the thermal conductivity of nickel and, thus, the thermal conductivity of Earth's core is much lower than it would be in a core consisting only of iron." Due to the significant proportion of nickel, the heat of the high-temperature earth core cannot flow towards the planet's surface by means of the motion of the electrons alone. "At high pressure, the electrons in nickel tend to scatter much more than the electrons in iron. But as it turns out, nickel plays a crucial role: "Under pressure, nickel behaves differently from iron," says Alessandro Toschi. For a long time, this fact was not considered to be particularly important. However, our planet's core also contains almost 20% nickel. "Then, earth would not have a magnetic field at all." "If Earth's core consisted only of iron, the free electrons in the iron could handle the heat transport by themselves, without the need for any convection currents," says Karsten Held. Up until now, however, nobody could really explain how these convection currents emerge in the first place: iron is a very good heat conductor and at high pressure its thermal conductivity increases even more. "When electrical currents are created in such a system of flows, they can cause a magnetic field which in turn increases the electrical current and so forth - and finally the magnetic field becomes so strong that we can measure it on the surface of Earth," says Alessandro Toschi. In combination these effects produce a complicated spiralling flow of hot material. At the same time, Earth's rotation leads to strong Coriolis forces. Hot material rises up to the outer layers of the globe, creating convection currents. The heat of Earth's core has to find a way to escape. "It is hardly possible to recreate these conditions in a lab, but with sophisticated computer simulations, we are able to calculate the behaviour of metals in Earth's core on a quantum mechanical level." "Under these extreme conditions, materials behave in a way which may be quite different from what we are used to," says Karsten Held. There is a pressure of hundreds of gigapascals - that is comparable to the pressure which several railway locomotives would exert if they could be balanced on one square millimetre. As it turns out, it is crucial for the dynamo effect that Earth's core contains up to 20% nickel - a metal, which under extreme conditions behaves quite differently from iron.Įarth's core is about as big as the moon and as hot as the surface of the sun. Giorgio Sangiovanni (Würzburg University) has now published calculations in the journal " Nature Communications," which show that the theory of the geodynamo has to be revised. ![]() But with iron alone, this effect cannot be explained.
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