Current Activated Pressure Assisted Densification (CAPAD) Processing of Ceramics Doped with Rare Earths for Functionality

Department of Mechanical Engineering
Advisor: Professor Javier Garay

Abstract: The performance of Solid Oxide Fuel Cells (SOFCs) and Lasers are important to both society and science. With  the  aim  of  improving  the  performance  of  these  devices  through  materials  improvement,  aluminum  nitride (laser   host   material)   and   cerium   oxide   (SOFC   electrolyte) with   rare   earth   dopants   Gd₂O and   (RE)₂O₃ (RE  =  Sm,Yb,Gd)  respectively  were  densified  using  the  current  activated  pressure  assisted  densification  (CAPAD) process.    To  achieve  performance  improvements  in  electrolyte  materials  it  is  necessary  to  improve  oxygen  ion conductivity. This was done by maintaining  small  grain  sizes  and  doping  to  create  oxygen  vacancies.  For  laser  host materials  transparency  and  the  ability  to  accept  rare  earth  dopants  are  both  important.  Both  AlN  and  ceria  samples were consolidated to near full density. Samples were processed with CAPAD, using direct current ranging from 1600A to  2900A,  at  pressures  of  105MPa  and  141MPa  with  total  processing  times  ranging  from  400-800  seconds. Processing  temperatures  ranged  from  1000-1700 ̊C.    Translucency  was  achieved  in  both  doped  and  pure  AlN samples. The grain size of the doped ceria samples was maintained below 600nm.