Processamento de ligas do tipo Gd(GeSi) aglomeradas com estanho

Abstract

The development of magnetocaloric materials are linked with the science and engineering of cooling since 1997, with the discovery of the giant magnetocaloric effect in the GdGeSi alloys, around the room temperature. Because of this new family of materials, there was an important advance in this area of knowledge. However, it becomes necessary to develop methods of processing these materials for use them in thermomagnetic machines. Based on this scenario, the objective of this study is to conduct a study of the processing of Gd5.09 Ge2.03Si1.88 alloy bonded with tin to determine a balance between mechanical and magnetic properties. This processing is based on the use of a salt of tin as a binder material in a matrix of Gd5.09 Ge2.03Si1.88 for the manufacture of tablets, which were heat treated. Thus, the tablets obtained were characterized by magnetic measurements, temperature variation, and hardness, in order to determine the influence of the binder material in the properties of the samples. The alloys were mixed with 3, 5, 10 and 15 wt.% tin, that we use to produce green compacted tablets which were heat treated at 473 K per around 10 hours. The results were a reduction of the magnetocaloric effect of about 30% in both samples with 3 and 5 wt% Sn, with and without heat treatment, while for 10 and 15 wt.% Sn we observed a decrease in the magnetocaloric effect of about 60% in indirect measurements. The heat treatments performed substantially reduced the first order magnetostructural transition of all samples, as well as the microhardness of the tablets. In the direct measurements (ΔTA), we reported a change of 2.5 K for the standard sample (as cast in bulk) with a field of 1.75 T and 1.5 K for the heat treated sample with 3 to 5 wt.% Sn. For samples with 10 and 15 wt.% Sn the ?TA was reduced to negligible values.