SPARK PLASMA SINTERING OF NEODYMIUM TITANATE PYROCHLORE FOR ADVANCED CERAMIC WASTE FORMS

摘要

Spark plasma sintering (SPS) can produce high density materials in minutes instead of hours or days by applying pressure and Joule heating simultaneously. Pyrochlore (Nd_2Ti_2O_7) is one of the major phases targeted in multiphase ceramic waste forms. Single-phase Nd_2Ti_2O_7 was synthesized by solid-state reaction prior to SPS. Effects of temperature and time of synthesis on the density and microstructure of the sintered product were studied. The reactive sintering of precursor oxides will be the topic of a future communication. The densification behavior was studied by halting the sintering at different temperatures and by holding for different amounts of time at 1140°C, chosen based on initial sintering curves at various temperatures. Sintered samples were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Near theoretical density (99%) was achieved by sintering up to a temperature of 1225°C. Preferred orientation of the (001) and (012)-type planes was seen in all samples. The initial stage of sintering was governed by bulk deformation through neck formation and growth and the later stage involved a slower mass transport process. The average grain size of samples sintered at 1250°C with no dwell time was 4.67 μm with grains ranging from 1-15 μm. These results are presented and discussed in terms of optimization of the sintering of multiphase ceramic waste forms.