Name: RAONI CAETANO BARBIERI
Publication date: 12/03/2020
Advisor:
Name |
Role |
|---|---|
| CARLOS AUGUSTO CARDOSO PASSOS | Advisor * |
Examining board:
| Name |
Role |
|---|---|
| CARLOS AUGUSTO CARDOSO PASSOS | Advisor * |
Summary: Samples of SmBa2Cu3O7−d polycrystalline ceramic were prepared by the solid state reaction method, with the purpose of producing superconducting tablets. The precursor was prepared from the calcination of a mixture of samarium oxide (Sm2O3), barium carbonate (BaCO3) and copper oxide (CuO), in the molar ratio of 1Sm:2Ba:3Cu. Several production routes with different calcination parameters were tested to study their influence on the formation of the crystalline phases of the precursor. The first experiment calcined the mixture of reagents in a tubular oven with an ambient atmosphere (open oven) for 40 hours and heating and cooling rates of 10 _C/min for five calcination temperatures (920 °C, 930 °C, 940 °C, 950 °C and 960 °C). The samples calcined in the second experiment were treated twice at temperatures of 930 °C and 960 °C with the rest of the parameters equal to the first experiment. The third experiment used a cooling rate of 1 °C/min to study the influence of cooling on the formation of the phases. Then, the precursors were pelleted under 3.0 ton uniaxial pressure for 5 minutes, sintered and oxygenated. Sintering took place in a tubular oven at 960 °C for 72 hours, while oxygenation at 520 °C for 24 hours, both under pure oxygen atmosphere and flow of 1,4 cm3/s. These samples were characterized by X-ray diffraction, energy dispersion spectroscopy, scanning electron microscopy, immersion method for density calculation and computational image analysis. No sample showed a superconducting transition up to 77 K. Regarding the phase formation, the sample calcined at 930 °C and cooled slowly proved to be the best route, presenting 63% of orthorhombic phase and 29% of tetragonal. The sintering temperature used has reduced mass loss compared to previous work. The relative density of some samples was greater than 90%, with an average of 84.8%, proving to be higher than those previously found. The synthesized tablets went through a ceramographic preparation for microscopic analysis, which affected the counting of the grain edges, but showed the pores of the material. Thus the images of the unpolished surface could be used to measure the average size of the grain edges, while the images of the polished surface allowed estimating the porosity by means of digital analysis. The sizes of the grain edges showed differences between the samples treated by the different calcination routes, demonstrating that the calcination treatment also influences the compounds microstructure.
