Microstructure Evolution of Yttria Compacts by Powder Technology

Abstract

Background: Innovation in ceramic materials relies on processing of powders. Yttria also known as yttrium oxide belongs to rare earths group, which usual form is RE2O3 (RE from La to Lu, including Sc and Y). Due to great end use of RE based materials since agriculture until astronomy, the main economies such as United States of America and European Union addressed REs as critical materials. The aim of this paper is to obtain dense compacts of yttria by powder technology, in which the effect of sintering temperature on samples microstructure is evaluated. Methods: Yttria powders (Y2O3) were used as starting material, being characterized by Photon Correlation Spectroscopy (PCS); X-ray Diffraction (XRD); Scanning Electron Microscopy (SEM). Powder compacts in cylindrical shape formed by uniaxial compaction, followed by hydrostatic compaction were evaluated by means of apparent density. Sintered samples under sintering temperatures from 1350 to 1550ºC were evaluated by SEM, XRD, apparent density, and true density. Results: Cubic C-type yttria powders exhibited mean particle size (d50) of 1.6μm, and morphology like acicular. Powder compacts (diameter x height) of 9.57mm ± 0.01 x 1.53mm ± 0.01 presented mean apparent density of 53.69% (based on free powder density). As sintered samples at 1550ºC, exhibited the most densification 65.0% related to green density and 91.0% related to theoretical density, respectively. Conclusion : Yttria cylindrical compacts with dense microstructure and symmetric dimensions were formed by powder technology from powders with mean particle size of 6.51μm, by compaction methods (uniaxial and hydrostatic), followed by sintering. The most densification of samples was achieved by the sintering condition of 1550ºC for 2h, providing samples with theoretical density of 91%. These results provide useful subsidies to advance toward full densification of ytrria based materials.