Effect of Zr⁴⁺ Dopant on Microstructure, Densification and Thermomechanical Behaviour of ZnAl₂O₄ Spinel

Excerpt

Abstract: ZnAl₂O₄ spinel precursor powders (mole ratio ZnO : Al₂O₃ = 1 : 1) doped with 0.5-2.0 mass-% Zr⁴⁺ ions were synthesized by the coprecipitation route. The derived powders were uniaxially pressed into cylindrical pellets and sintered at 1350 °C for 1 h. The sintering behaviour, phase assemblage and microstructure of fired ZnAl₂O₄ ceramics doped with different concentrations of Zr⁴⁺ were investigated. Sintered density above 97 % of the theoretical density of pure ZnAl₂O₄ ceramics was achieved with the addition of 2.0 % Zr⁴⁺ . The residual flexural strength of the sintered body was as high as 120 kg.cm^-2 for the highest addition of Zr⁴⁺, and it was higher than that of the Ti⁴⁺ doped ZnAl₂O₄. The powder XRD patterns of sintered compacts revealed that besides ZnAl₂O₄ spinel as the major crystalline phase, a minor amount of tetragonal ZrO₂ phase is also present when the dopant quantity is higher. The SEM micrographs of the fractured surfaces of the sintered body demonstrated a coherent and uniform microstructure with a homogeneous distribution of microfine grains with Zr⁴⁺-doped ZnAl₂O₄ compacts. …