THE EFFECT OF TEMPERATURE AND UNIAXIAL PRESSURE ON THE DENSIF1CATION BEHAVIOR OF SILICA AEROGEL GRANULES

摘要

Materials are being developed in the U.S. for the removal and immobilization of radioiodine from the gas streams in a nuclear fuel reprocessing. Silver-functionalized silica aerogel is being investigated because of its high selectivity and sorption capacity for iodine and its possible conversion to a durable silica-based waste form. In the present study, we investigated the effect of pressureless isothermal sintering at temperatures of 900-1400 °C for 2.5-90 min or isothermal hot-pressing at 1200 °C for 2.5 min on densification of raw and silver-functionalized silica aerogel granules with nitrogen sorption and helium pycnometry. Rapid sintering was observed at 1050 and 1200 °C. Pressureless sintering for only 15 min at 1200 °C resulted in almost complete densification: the macropores disappeared, the specific surface area decreased from 114m~2/g to 25 m~2/g, pore volume from 7.41 × 10~(-3) m~3/kg to 9×10~(-5)m~3/kg, and adsorption pore size from 18.7 to 7 nm. The skeletal density of sintered granules was similar to the bulk density of amorphous silica (2.2 × 10~3 kg/m~3). Low-pressure hot-pressing accelerated the sintering process, decreasing significantly the pore size and pore volume.