Emissivity of elements of the scandium subgroup

The results of an experimental study of the normal integral emissivity of metals of the scandium subgroup: scandium, yttrium and lanthanum in a wide range of solid–liquid temperatures, including the phase transition, are presented. The study is due to the lack of data on the normal integral emissivity of metals in periodicals and reference publications. The interest in the metals under study is also related to their unique physico-chemical properties, which make them promising for use in high-temperature systems. The authors of the article interpret the presented data as obtained for the first time, and they are preliminary in nature, requiring clarification. The measurement method is radiation, the method of heating samples is resistive. The experimental error is ± 3–5%. Measurements of the solid phase of metals were carried out in a vacuum, the liquid phase was studied in an atmosphere of specially prepared gas – argon. Graphical illustrations and numerical values of the results are presented. The obtained complex data on the normal integral emissivity within each of the phases of the metal state are monotonously increasing. This behavior of the normal integral emissivity is associated with structural changes in crystal lattices due to an increase in temperature. In the region of the solid–liquid phase transition, a jump in the normal integral emissivity was detected for each of the metals studied. In this case, the jump is associated with a sharp increase in free electrons during the restructuring of the metal structure due to melting, and the magnitude of the jump as a percentage of the solid phase is individual for each metal. All the results of the study have been analyzed and discussed. Numerical simulation based on classical electromagnetic theory using the Foot approximation is carried out, the results of which are compared with experimental values. It is concluded that the theoretical calculation of the emissivity qualitatively, but not quantitatively, makes it possible to describe the behavior of the emissivity of metals, provided that the values of the specific electrical resistance of metals in a given temperature range are known.