SYNTHESIS AND PROCESSING OF META-STABLE NEGATIVE THERMAL EXPANSION MATERIALS, ZIRCONIUM TUNGSTATE AND ZIRCONIUM PHOSPHOTUNGSTATE (ZRW_2O_8 AND ZRWP_2O_(12))

摘要

Synthetic routes and Direct Current Sintering wereinvestigated to form core-shell structured materials orpellets of negative thermal expansion materials, ZrW_2O_8and Zr_2WP_2O_(12) to be used as a radionuclide wasteform.The solution synthetic routes, while successful in thegrowth of additional phase pure ZrW2O8 on the surface ofthe ZrW2O8 seeds, did not completely encapsulate them.Via Direct Current Sintering, a narrow temperature bandof phase stability for ZrW_2O_8 was identified from 650-700C at a pressure of 60 Mpa. The pellet was partiallysintered, showing some void spaces by SEM. Zr_2WP_2O_(12)necessitated much higher temperatures to maintain phasepurity, at 1400 C and produced a dense pellet.