Process for producing optimized melt-textured bodies based on the high-temperature superconductor YBa2Cu3O7 (YBCO)

A process for producing melt-textured bodies comprised of the high temperatures superconductor YBa2Cu3O7(YBCO) for use in contact-free self-stabilizing magnetic bearings, comprising the following steps:

• a) preparing a base material:
• providing a commercially available powder of compounds YBa2Cu3O7-x, Y2O3 and PtO2 being ground in such a way that the YBa2Cu3O7 powder has a grain size in the range of d=10+2 μm, whereby it has a specific surface of about 1+0.2 m2/g, with an oxygen content of x<0.2% and a foreign phase content of <1%, a carbon content of at most 2000 ppm and a transition metal content of together at most 2000 ppm, the Y2O3 powder has a grain size of about d+4.5 μm, and the PtO2 powder has a grain size of about d=60 μm,
• b) providing an amount suitable for desired texturing by:
• processing the three powders for a texturing process in stoichiometric parts according to the compounds YBa2Cu3O7+0.35 mol % Y2O3+0.1 wt % PtO2 and mixing the compounds in a ball mill for a predetermined period limited by a CO2 absorption, or under an inert atmosphere until a uniform mixing state has been achieved, pressing the mixed powder uni-axially into a mold and subjecting it to a high pressure of at least 300 bar to form densified blanks of a predetermined shape, covering the surfaces of the blanks with a contamination protective cover and further densifying the blanks in a cold isostatic compression step under at least 3000 bar whereby the powder particles come into close contact with one another, and
• c) subjecting the blanks to a temperature treatment:
• by heating the blanks in a crucible from ambient temperature to 600° C. in 1.5 hrs, then heating the blanks from 600° C. to 1100° C. in 1.6 hrs, and maintaining the blanks at this temperature for about ½ hr, then reducing the temperature at a rate of 300° C./hr to a temperature of 1040° C. for about 85 hrs;
• then reducing the temperatures at a rate of about 5° C./hr from 930° C. to 850° C. and then increasing the cool down speed to 50° C./hr until a temperature of 450-400° C. is reached, then flushing the crucible with oxygen and maintaining this temperature for at least 80 hrs and finally cooling down to ambient temperature at a rate of about, 100° C./hr.