Porosity evolution during sintering in cold isostatically and filter pressed compacts of nanozirconia powders

摘要

The nanopowders 3 mol% Y_2O_3-ZrO_2 with different size of crystallites and degree of agglomeration were tested. Two nanopowders were obtained by a co-precipitation technique together with the controlled crystallization of the resulting sediment under hydrothermal and calcination conditions. They had a crystallite size of 8 nm and 20 nm (D_(111他）). respectively, and showed a respective modal particle size (D_(50)) of 7.3 nm and 1640 nm. The third submicron powder (D_(111t) = 25 nm, D_(50) = 1700 nm) was of commercial origin. The nanopowders were formed by isostatic and filtration pressing, and then pressureless-sintered in the air. The basic properties of powders were characterized, and their behaviour during heat treatment was investigated in the range from room temperature to 1600°C. Changes in phase composition, porosity, pore size and relative density as a function of temperature were determined. A significant effect of the morphology of the nanopowders on the beginning and maximum temperatures of the shrinkage of the samples as well as on the temperature at which open pores closed was found. A transient increase in the size of open pores in the sintered samples was observed, depending on the initial morphology of the nanopowders. The temperature of the beginning of the growth of the pore size and its scale was dependent on the initial pore size in the compacts, which was controlled by the crystallite size of the powder and its agglomeration state. The energy of activation of the processes responsible for the sintering shrinkage of the studied nanopowders was estimated.