Author: Eduard Chyhyrynets

Protocol for the preparation of alumina/metal brazed joints-Master Thesis MANUEL RAMONES

Author: MANUEL RAMONES ; Type of thesis: Master thesis
Abstract: Brazing is the joining of materials through the use of heat and a filler metal with a melting temperature above 450°C but below the melting point of the metals being joined. This technique joins parts by creating a metallurgical bond between the filler metal and the surfaces of the two materials joined. There are several factors which have direct influence on the final quality of a brazed piece:
the filler metal selection, the heating technique, the atmosphere in which the process is performed, the cleaning procedure, the assembly of pieces, etc. In metal-ceramic junctions, ceramic surfaces, especially oxides, are very stable chemically, consequently, molten metals do not wet them well. There are several techniques that allow to overcome the chemical challenge. In order to develop a procedure that ensures the conditions to achieve a successful brazing process, several techniques for metal-ceramic brazing in a controlled atmosphere (vacuum) were tested. Brazing using active filler metals and direct brazing using ceramic metallization by sputtering were studied in this work. Alumina (Al2O3) was chosen as the ceramic part, whereas stainless steel 304 and Inconel were chosen as metallic components, cylindrical samples were assembled in lap configuration and were heated by IR lamps. The pieces were cut and the cross-section was studied by Scanning Electron Microscope SEM and energy-dispersive X-ray spectroscopy (EDS, EDX) searching for evidence of filler metal uniform spread and diffusion. The samples brazed using Pallabraze 850 disc of 0.01 mm of thickness for braze Inconel and Metallized alumina with 1m of Titanium and using Argon atmosphere showed the more uniform distribution and diffusion.

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Study of the Electropolishing of 6GHz Niobium cavity in ionic liquids-Master Thesis OLGA MALKOVA

Author: OLGA MALKOVA ; Type of thesis: Master Thesis
Abstract: INFN – LNL Laboratories have been already working for several years on the problem of removing fluoride ions from a solution for polishing of niobium. Ionic liquids are one of the possible solutions for this problem. The first results of niobium polishing have already been obtained in ionic liquid – Choline Chloride with Urea. During polishing in the ionic liquid was obtained smooth shiny surface with a roughness comparable as obtained after polishing in classic electrolyte. Various additives such as sulfamic acid, ammonium sulfamate, can improve the condition of the surface.
Our task is to apply this knowledge to polish RF cavities. In our work we try to create new ionic liquid and improve one that was previously obtained. In our laboratory we built new system for electropolishing 6 GHz cavities considering the experience of previous years.

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Development of a new mechanical surface treatment for the internal finishing of 6 GHz superconducting cavities-Master Thesis GUOLONG YU

Author: GUOLONG YU ; Type of thesis: Master Thesis
Abstract: 6 GHz spun seamless Superconducting Radio Frequency (SRF) cavities are a very useful tool for testing alternative surface treatments in the fabrication of TESLA cavity. However, the spinning technique has also some drawbacks like contamination, surface damage in internal part due to the collapsible mandrel line. The first important step of the surface treatments is the mechanical polishing. For this purpose, a new, cheap, easy and highly efficient tumbling approach based on vibration was developed.
Before this approach was conceived, a few other methods, such as Turbula,
Centrifugal Barrel Polishing (CBP), custom Zigzag tumbler and “flower brush” have been studied and tested. But the result was not so satisfactory neither for the low erosion rate nor for the unstableness of the system nor for the complicated polishing process. At last, a vibration system with a simple structure, working stably was created after two experiments.
Another important task of the thesis is to update the optical inspection system for 6 GHz cavities. 3 stepper motors motor was added to move and rotate the cavity and realized auto focus of the miniature camera. A software was developed to achieve a full cavity photographed by one key operation using LabVIEW. A high-efficiency mechanical polishing system is generally judged by two aspects: one is whether the surface property satisfies the demand after polishing; the other is whether the erosion rate can reach and be stabilized at a high value which is comparable or greater than the existing products. The Radio Frequency (RF) test result indicates that the vibration system is feasible. The latest erosion rate 1 gram/hour i.e. removing 13 microns depth of inner surface materials per hour exceeds the performance of CBP, which is widely used in other laboratories in the world. The mechanical polishing process is elaborated and cavities that have been polished are listed. Several influencing factors on the erosion rate, such as tumbling time, media, signal and multi-cavities and plate direction are discussed at the end. A preliminary design of 1.3 GHz vibration system as the future development is provided for the next plan. Continue reading →