Diffusion welding Clause Samples

Diffusion welding. Diffusion welding makes use of the principle of solid-state diffusion. Atoms of two solid, metallic surfaces intersperse themselves over time. In addition, the welding process depends on the applied pressure and the process temperature. In figure 18 the design of a press for diffusion welding is shown which is used due to the expected high stress for the material. The press consists of two halves of aluminium, four screws and four guidance pins for the absorber foils. The lower part of the press fits to the intake of the holder in the micro dispensing system. Glass slides, borosilicate glass with dimensions of 0.2 mm × 18 mm × 18 mm, are used as separating layers during the diffusion process. Otherwise, the gold would also be welded to the press itself. For the actual diffusion welding process, the loaded press is placed in an oven, and exposed to a well-defined temperature for a fixed time. The absorber array with the radioactive material is mounted on a glass aluminium assembly and a second absorber array of the same shape and thickness but without radioactive material is placed on top of it. With the help of the guidance pins the absorber foils cannot shift against each other. The other glass aluminium assembly is put on-top of the absorber-source-absorber sandwich, and the four screws are fastened to produce a pressure. Then, the guidance pins are removed otherwise the gold could also be welded to the pins. Depending on the deposited radioactive material and the used carrier solution, suitable parameters of diffusion welding can differ significantly. To avoid melting or outgassing of the radioactive material, the parameters were adjusted. Several tests were done to identify suitable diffusion welding process parameters. For materials with high melting points of all chemical compounds, e. g. 36Cl, the following parameters were determined: Torque 2 Nm per screw Oven temperature 400°C Process time 45 min to reach 400°C and 1 hour at 400°C Cooldown 12 hours For materials with low melting points of one chemical compound, e. g. 99Tc and 14C, the following parameters were determined: Torque 10 Nm per screw Oven temperature 140°C Process time 45 min to reach 140°C and 40 h at 140°C Cooldown 12 hours After diffusion welding, the press is carefully opened because there might be broken glass slides, seen in figure 19. The broken glass is removed from the welded gold foils and collected for further tests. In case of a successful diffusion welding, the radioactive ...