Author: Eduard Chyhyrynets

Author: VLADA PASTUSHENKO ; Type of thesis: Master Thesis
Abstract: A solar collector is an apparatus that collects the sunlight energy, and then alters this energy into a more usable or storable energy form. The absorber surface used in thermal solar collectors requires high absorptance in the solar spectrum and low emittance. Several techniques, such as vacuum techniques, are currently used to produce solar absorber surfaces. However, the desired characteristics of the solar absorber coating may be better controlled by direct electrodeposition. Other electrodeposition advantages are basically rapidity, low cost, free from porosity and industrial applicability. Copper substrate was chosen due to its use in a large variety of domestic and industrial piping as a thermal and electrical conductor. Black chromium is an important coating material used in solar thermal systems as a spectrally selective surface. This coating is usually obtained by electrodeposition from sulphate free chromium (VI) aqueous solutions which represent a health and environmental hazard due to the presence of Cr (VI), a known toxic and carcinogenic agent. Recent developments in green chemistry have shown that ionic liquids can be used as electrolytes, allowing the deposition of a wide range of materials with negligible environmental and health impacts. Continue reading →

Author: DANIEL ADRIEN FRANCO LESPINASSE ; Type of thesis: Master Thesis
Abstract: THIS THESIS IS PROTECTED BY TRADE SECRET. IF YOU WANT TO CONSULT IT, You need to contact the Master Director

In this research, an innovative source was built and were performed the preliminary tests to study a magnetron sputtering configuration in order to deposit quarter wave resonator cavities (QWRs) .This project is based on the deposition of niobium onto copper cavities that will be used for the development of an ion accelerator. To do this, it was required the development of the vacuum chamber using a rotating magnetron , a test cavity and a test cathode, both of them made with stainless steel. The methodology was established depositing stainless steel onto quartz substrates placed along the cavity in order to observe the uniformity of the coating. The results are focused on thickness measurements. In addition to the sample thickness measurements was realized the film stripping test in order to see differences in deposition rates, all over the resonator wall. Were studied three groups of test changing the configuration of the magnetic field and other parameters like sputtering pressure, power and also time of deposition. Finally was found that the vacuum system was successfully assembled and is available for thin film deposition. Preliminary deposition tests with SS were performed and different thicknesses were observed along the cavity. Thickness values are higher on the internal region of the cavity where the target is closer and lower thicknesses are in the top where might be holes in the magnetic field. Also, the appropriate pressure found to reduce differences in thickness along the cavity was 8×10-3 mbar and the stripping test shows that the deposition rates are different on the top of the cavity probably due to the absence of magnetic field. Nowadays, we are modifying the configuration of the magnetron in order to improve the plasma on the top of the cavity. Continue reading →

Author: OLGA CHERENKOVA ; Type of thesis: Master Thesis
Abstract: A nuclear reactor is a system that contains and controls sustained nuclear chain reactions. Reactors are used for generating electricity, moving aircraft carriers and submarines, producing medical isotopes for imaging and cancer treatment, and for conducting research. Fuel, made up of heavy atoms that split when they absorb neutrons, is placed into the reactor vessel (basically a large tank) along with a small neutron source. The neutrons start a chain reaction where each atom that splits releases more neutrons that cause other atoms to split. Each time an atom splits, it releases large amounts of energy in the form of heat. The heat is carried out of the reactor by coolant, which is most commonly just plain water. The coolant heats up and goes off to a turbine to spin a generator or drive shaft. So basically, nuclear reactors are exotic heat sources.
Cyclotrons continue to be efficient accelerators for radio-isotope production. In recent years, developments in the accelerator technology have greatly increased the practical beam current in these machines while also improving the overall system reliability. These developments combined with the development of new isotopes for medicine and industry, and a retiring of older machines indicates a strong future for commercial cyclotrons. For both systems, efficient cooling is required. Nowadays liquid metals are in wide use for this purpose. Liquid metal cooled reactors were first adapted for nuclear submarine use but have also been extensively studied for power generation applications. Liquid metals have safety advantages because they have high heat transfer characteristics, due to high boiling point, no high vapor pressure, and they allow a much higher power density than traditional coolants. Cooling by liquid mercury, sodium, NaK, lead has been studied and used. But due to numerous imperfections of these coolants (such as toxicity, high vapor pressure, not appropriate melting/boiling points, corrosion etc) it is necessary to develop new cooling systems for research and industrial purposes. Thus after choosing the new coolants (liquid metals with desirable properties) for target cooling we will develop the protection coatings for tubes taking into account factors which influence corrosion such as solution pH, oxidizing agent, temperature, velocity, stresses, impurity content. So we can conclude that development of new protective thin films, coatings, claddings are required and mandatory for protection. For its development we propose to use the magnetron sputtering which is a very perspective method for obtaining of thin films. One feature of magnetron sputtering which explains its wide use for the coatings is the low charged particle fluxes reaching a substrate. By this method we can obtain coatings on conductive materials as wellas on nonconductive, also on materials with low melting points. Sputtered films typically have a better adhesion on the substrate than evaporated films. Thereby the producing of protective coatings from liquid metals coolants embrittlement used for nuclear reactors and target cooling in the radiopharmaceutical sphere has been under development within the bounds of this project. Continue reading →

Author: ANDREA CAMACHO ; Type of thesis: Master Thesis
Abstract: This works deals with the A15 compound synthesis on niobium samples and over the internal surface of niobium cavities by means of induction heating. Specifically, three compounds were studied: Nb3Ga, Nb3Al and Nb-Al-Ga. As for the preparation of the niobium samples, they were treated with BCP solution in order to polish the surface. The niobium cavities were treated with centrifugal tumbling, BCP solution and high pressure water rising. Subsequent, the samples, or cavities, were placed into an inductor controlling the voltage, time, sample position, temperature, type and pressure of gas used. The highest critical temperature
obtained was 18 K and Tc 0,35 K, in Nb-Al-Ga#1 sample by inductive measurement. Mapping analysis showed the uniform diffusion of aluminum into the niobium, and the gallium diffuses creating channels into niobium. The composition was measured by EDS obtaining (82±1)% wt. Niobium, (11,3±0,9)% wt. Gallium, (4,7±0,2)% wt. Aluminum and (1,9±0,1)% wt. Oxygen. Finally, RF test confirmed that the cavities obtained after the annealing were normal conductive indicating that the preparation parameters must still be optimized. Continue reading →