Sintering of Porous Silver Compacts at Controlled Heating Rates in Oxygen or Argon

E.A. OLIBER,; C. CUGNO,; M. MORENO,; M. ESQUIVEL,; N. HABERKORN,; J.E. FISCINA ,; C. GONZALEZ OLIVER

Santiago, Chile.

Congreso; Sociedad Argentina de Materiales; 2003

Sociedad Argentina de Materiales

Submicronic (~0.4µm grain size) spherical silver particles were pressed into pellets and pre-fired at 235ºC for 4 hours in static air. These porous silver compacts were densified in a dilatometer at heating rates (hr) of 2, 4 and 10ºC min-1 (up to ~ 600ºC) under Ar or O2 . The total lineal densification ranged from 8 to 12% giving bodies of relative density near 0.80. After a small densification (stage (i)) each curve showed a clear Ti (ºC) at which the densification (AD(T)) exhibited a rapid increase (jump; stage (ii)), and had a characteristic peak in densification rate (DR(T)). Then the AD continued by another mechanism (stage (iii)), related to grain growth, till the densification rate started to decrease probably due to densification (stage (iv)) of closed pores located at 4-grain corners. For every atmosphere the Ti increased with heating rate, and the Ti values for O2 were 79-105ºC lower than those for Ar. From DR kinetics analysis it is concluded that under O2 stage (ii) is due to grain boundary diffusivity (gb) whereas for stage (iii) the volume (vol) diffusion is the main process. From detail densification fits it is shown for stage (iii) there is an initial contribution to densification coming up from an initial stage controlled by (gb) diffusion, and that the main process is still the intermediate stage with simultaneous grain growth controlled by volume self-diffusivity. For the Ar case the whole densification range appears to be controlled by (gb) diffusivity. Some impurity contamination of the Ag could produce a (gb) contamination under Ar gas such as for stage (iii) the controlling mechanism could become the (gb) process instead of volume diffusion.