Made available in DSpace on 2014-10-09T12:32:34Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:10:06Z (GMT). No. of bitstreams: 1 03209.pdf: 3814458 bytes, checksum: 2c10a4330417ae0715e500a18b636f05 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Fisica, Universidade de Sao Paulo - IF/USP

Made available in DSpace on 2014-10-09T12:32:34Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:10:06Z (GMT). No. of bitstreams: 1 03209.pdf: 3814458 bytes, checksum: 2c10a4330417ae0715e500a18b636f05 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Fisica, Universidade de Sao Paulo - IF/USP

The diploma thesis deals with the design modification of the circulation circuit of inert atmosphere in the 3D printer SLM 280HL. The aim of the proposed modifications was to increase the efficiency of condensate and flue gas removal and thus increase the quality of the production process. Based on experimental measurements of the velocity field at a height of 12 mm, it was found that in the original configuration of the build chamber, there are sites with reduced flow velocity. The test subsequently confirmed the increased porosity of the samples in the given localities. Subsequently, with the help of CFD simulations, a lower flow distributor was designed, which had the most significant effect on the porosity. Furthermore, an additional outlet and flow deflector were designed, which had the task of streamlining the drainage of condensate and fumes from under the protective glass of the laser. The designed components were manufactured and experimentally verified, which was able to prove the flow improvement and reduce the porosity on the platform. A test was also performed with a magnesium-based material, which proved more efficient removal of condensate and flue gases. The work managed to prove the influence of the flow velocity on the porosity of the component at differences in flow velocities above 0,3 ms^-1.

This master´s thesis dealing with study of influence of inert atmosphere on the wettability of soldered surfaces. The theoretical part is discussed the issue of the soldering, solder joint, oxidation, and inert atmosphere. The glass cover with internal inert gas preheating for the wetting balance testing was prepared in the practical part. With this adjustment were realised tests, in which was examined the effect of the inert gases on the wettability of different materials combination. Further experiments were focused on plasma surface cleaning as possible flux substitution. The evaluation of these experiments were discussed in the end of this master´s thesis. Some of topics were designed for further experiments.

An induction setup for levitation studies of molten metals was built. The setup was used to levitate and heat stainless steel samples of 2.00 g to 1600 °C and subject them to different atmospheres. Changes in shape and temperature were recorded by video and infrared thermocouple. Oxide films forming on the droplets during levitation were observed. It was possible to notice an immediate surface reaction when the reaction gas was introduced. This reaction is concluded to influence the surface and bulk composition, and therefore have an effect on the shape evolution of the droplet. A more oxidizing atmosphere resulted in a more conical droplet shape; this is thought to be an effect of lowered surface tension and the conically shaped volumetric force caused by the magnetic field. Changes in temperature after the sample is molten are thought to be an effect of changes in emissivity, caused by surface oxidization. Post mortem analysis show a difference in surface morphology for samples subjected to different gases, as well as a difference in amount of oxidization.

The topic of this work is the passivation of the active layer of perovskite solar cells with an inverted structure. The work is divided into theoretical and experimental part. The theoretical part describes in particular the passivation and modification of the perovskite layer as well as the characteristic properties of perovskite, including structure and stability. The experimental part deals with the preparation of photovoltaic cells with an inverted structure. For the characterization of photovoltaic cells, reference samples were prepared and their active layer was modified by plasma. The most used deposition technique for the preparation of layers was the spin coating method. From the performed experiments it can be concluded that the preparation of samples and their subsequent modification under laboratory conditions does not lead to the improvement of the final parameters of photovoltaic conversion. By transferring the sample preparation and passivation of the active layer to an inert atmosphere, it was possible to produce cells with higher efficiencies (compared to the reference sample), around 10 %. Another advantage of this plasma treatment of the active layer is that it also improves the stability of the prepared structures, which even after a few days in air show almost 80 % of the original efficiency.