First-Eutectic Features of Polar Metals in Double Systems

It is known that the dense part of any liquid metal consists of ramified clusters of almost regular tetrahedrons (triangular pyramids with atoms in their vertexes) that are connected into chains by faces. Any metal additive as a second component of liquid alloy can be both beyond these clusters as separated atoms and into them as inherent clusters. The liquid-metal alloy transfers into the second state, at the first eutectic of the solvent. This polymorphic transition of liquid matrix is discovered in the systems, Pb-K and Na-Pb, by molecular-dynamic simulating their microstructure and in experiments on scattering slow neutrons by these alloys of different compositions. In the first system, the obtained results identify both the homogeneous alloy at low concentrations of potassium in liquid lead and the alloy clustering, (Pb₄K)_n, at potassium concentrations following the eutectic, Pb_0.91K_0.09. In the second one at the concentrations of lead more than 2%, just the second state is discovered with the clusters, (Na₄Pb)_n. One can expect the same polymorphic transition in the eutectic, Na_0.93Tl_0.07, with the micro-inhomogeneity, (Na₆Tl)_n, and with the melting point of 64 C. This eutectic maintained by the oxygen-free technology and enriched by the isotope, ²⁰⁵Tl, can become the best coolant for fast nuclear reactors due to the depressed chemical activity of sodium and composition stability.