Papers by Keyword: Rare Earth Concentrate

Abstract: In this work, the yttrium rich rare earth concentrate (Re₂(CO₃)₃) was used as additive aiming stabilization of cubic an tetragonal phases at commercial zirconium oxide with 3% mol of yttrium oxide. The use of high purity rare earth oxide as additive is being commercially used and this work aims to demonstrate the potential use of lower cost additives to produce solid electrolyte for oxygen sensors and fuel cell applications. The powders for the additive production were synthesized by the controlled precipitation method. After synthesis, the powders were de-agglomerated using mechanical grinding and mixed to commercial zirconia to produce the compositions ZrO₂:3% Mol Y₂O₃:ƞ % Mol Re₂O₃ (ƞ=3,4,5,6), followed by uniaxial press and sintering at 1500 ⁰C in two hours. The obtained sintered densities were above 96% of theoretical. X-Ray diffractometric analysis and Rietweld refinement demonstrated the stabilization of cubic and tetragonal phases for all samples with yttrium rich rare earth concentrate additives. Finally the electric behavior of the evaluated samples was carried out with complex impedance spectroscopy, showing conductivity improvement for samples with the chosen additive. At 500 ⁰C the sample A-9% had a conductivity of 1,11E^-3 Ω^-1.cm^-1, well above of the sample without additive with conductivity 5,88E^-4 Ω¹.cm^-1, indicative that use of yttrium rich rare earth concentrate as additive increases considerably the ionic conductivity of comercial zirconium oxide. Key words: rare earth concentrate, controlled precipitation, ionic conductivity

Abstract: Silicon nitride based composite has been prepared, using a direct mixture process as alternative route. Silicon carbide whiskers were mixed directly to silicon nitride based powders containing yttrium and neodymium oxide as sintering aids. Uniaxial hot pressing was used to prepare sintered samples. Crystalline phases were identified using x-ray diffractometry. Intergranular phases were analyzed using Scanning Electron Microscopy. Some mechanical properties (microhardness and fracture toughness) were also evaluated. The obtained high values of fracture toughness were correlated to the activation of toughening mechanisms, such as crack bridging and crack deflection.

Abstract: The important factor to consider for successful ceramics composites development is the need of matching the whiskers and matrix characteristics, taking into account the chemical compatibility of the sintering aids utilized. The purpose of this work was to analyze and compare use of rare earth concentrate (CTR) and yttrium oxide, as sintering aids, and its influence in the densification and physical/mechanical properties of hot pressed and sintered Si3N4-SiC(w). The CTR powder materials present high yttrium oxide percentage and its production is cheaper than the additives usually used in ceramic materials, such as Y2O3. For physical and mechanical properties evaluation, specific mass, crystalline phases, micrographs analysis, microhardness and fracture toughness were measured, showing similar results between the two sintering aids. Therefore, this study shows the possibility of obtaining low processing cost products with the use of rare earth concentrate. Meanwhile, more characterization steps are necessary for analyzing its behavior at elevated temperatures.