Name: WAGNER GARCIA FERNANDES
Publication date: 17/12/2020
Advisor:
Name |
Role |
|---|---|
| CARLOS AUGUSTO CARDOSO PASSOS | Advisor * |
Examining board:
| Name |
Role |
|---|---|
| CARLOS AUGUSTO CARDOSO PASSOS | Advisor * |
| JAIME ALBERTO SANCHEZ CACERES | External Examiner * |
| MARCOS TADEU DAZEREDO ORLANDO | Internal Examiner * |
Summary: In this dissertation, samples of SmBa2Cu3O7-δ (Sm-123) polycrystalline ceramics were prepared by solid-vapor reaction. For this purpose, the Sm2O3, BaCO3 and CuO reagents were mixed in the stoichiometric ratio of 1:2:3. The material was mixed in an agate grail for one hour and compacted into a cylindrical shape with a diameter of 8 mm. The tablets were made in a compaction matrix and a 3.0 ton uniaxial pressure was applied for 5 minutes. After that, they were subjected to two heat treatments in an isostatic oven. In the first heat treatment (calcination process) two isotherms, 930 ºC and 960 ºC for 40 hours and cooling by the inertia of the oven thermodynamics, were used. Then, the samples were macerated, compacted again and submitted to the second heat treatments (sintering process) with isotherms of 960ºC and 1060ºC for 72 h. Then, the samples were cooled to 520ºC and kept at that level for 24 hours. In this process, the speed of temperature decrease was -5ºC / min. The sintering step occurred under a constant flow of oxygen. Then, the samples were characterized by measurements of apparent density, X-ray diffraction and electron microscopy. The diffractogram results indicated the predominance of the Sm-123 phase with two crystalline structures: tetragonal and orthorhombic. In addition, purging phases arose that resulted from incomplete reaction and / or excessive burning. Through scanning electron microscopy images, grain size distribution, pores were observed and some samples showed microcracks. The micrographs also revealed that the ceramic samples doped with oxygen present clusters of particles in regions close to the contours of grains and pores. In our opinion, these particles can be precipitated from intermediate phases and/or unreacted products during the sintering of electroceramics.
