Direct ink writing of yttrium barium copper oxide and iron silicon
Additive manufacturing has introduced new technologies to manufacture complex and intricate components. A sub-process of the additive manufacturing process, material extrusion is direct ink writing. Direct ink writing is able to process ceramic and metallic materials that are too brittle to be processed traditionally. Two materials of interest were iron silicon and yttrium barium copper oxide. Iron silicon powders with a silicon content of 3 wt%, 6 wt% or 15 wt% were formulated into a paste using the screen printing medium, System 3. These were the commercially available iron silicon’s at the time. A solid loading of 89 wt% was found to be printable for the 3 wt% and 6 wt% iron silicon powders. The addition of 0.1 wt% of fumed silica enabled the 15 wt% Iron Silicon powder to have a 90 wt% solid loading. Components were printed at a speed of 5 mms−1 through a nozzle diameter of 410 µm. Post processing consisted of drying at 80 ◦C and binder removal at 500 ◦C in air. Components were finally sintered between 1050 ◦C and 1300 ◦C in a 5 % hydrogen, 95 % argon atmosphere to reduce oxidation and remove any ferrous oxide phases. Yttrium barium copper oxide was synthesised through the solid state reaction method. An optimal calcination temperature of 900 ◦C was obtained through X-ray diffraction and magnetometery characterisations. The resultant powder was formulated into a shear thinning paste with a solid loading of 90 wt% using an oil based binder of 45 wt% ICP solvent and 55 wt% linseed oil. Components were printed at a speed of 5 mms−1 through a nozzle diameter of 254 µm. Components were post processed through drying at 80 ◦C and binder removal at 600 ◦C. The components were then sintered at 900 ◦C between 24 and 120 hours. Electrically superconducting transitions were observed in the additively produced components previously unreported in literature. Fluorine impurities were found to have doped the yttrium barium copper oxide crystal i and produced an insulating outer shell of barium fluoride. Despite these impurities, a transition temperature of 87.4 K and a lower critical field of 0.148 T was observed. Alterations to the tool path of the extruded material showed no significant changes in the superconducting properties of YBCO components. It was shown that bulk yttrium barium copper oxide components can be produced cheaply and effectively without the need for expensive laboratory equipment. Further post process was performed at 900 ◦C for 48 hours in an oxygen atmosphere. Significant improvements of the electrical properties were seen for samples sintered for shorter times. The critical current density and the magnetisation greatly improved after annealing in oxygen
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NotesA Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of the degree of Doctor of Philosophy at Loughborough University.
Supervisor(s)Mark Everitt ; Daniel Engstrom ; Kelly Morrison
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