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

Excerpt

Abstract: ZnAl ₂O ₄ spinel precursor powders (mole ratio ZnO : Al ₂O ₃ = 1 : 1) doped with 0.5-2.0 mass-% Zr ⁴⁺ 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 ZnAl ₂O ₄ ceramics doped with different concentrations of Zr ⁴⁺ were investigated. Sintered density above 97 % of the theoretical density of pure ZnAl ₂O ₄ ceramics was achieved with the addition of 2.0 % Zr ⁴⁺ . The residual flexural strength of the sintered body was as high as 120 kg.cm ^-2 for the highest addition of Zr ⁴⁺, and it was higher than that of the Ti ⁴⁺ doped ZnAl ₂O ₄. The powder XRD patterns of sintered compacts revealed that besides ZnAl ₂O ₄ spinel as the major crystalline phase, a minor amount of tetragonal ZrO ₂ 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 Zr ⁴⁺-doped ZnAl ₂O ₄ compacts. …