Preparation of yttrium aluminium garnet (YAG) via reactive sintering using heterogeneous nucleation

This article presents a new method of obtaining yttrium-aluminium garnet, which uses reaction sintering with nucleation using heterogeneous nanometric α-Al2O3 particles. The first step was to obtain alumina and yttria precursors by precipitating them from nitrate solutions (aluminium and yttrium, respectively) with ammonium carbonate followed by calcination of the yttrium oxide precursor at 700 °C, while the aluminium oxide precursor was hydrothermally treated at 130 °C for 2 h. Two stoichiometric mixtures with respect to Y3Al5O12 of the obtained powders were homogenized for 30 minutes in an environment of pH = 12, then they were dried. In one mixture, 10 vol.% of the hydrothermal aluminium component was replaced by α-Al2O3 nanopowder to induce nucleation. Homogeneous powder mixtures were pressed at a pressure of 300 MPa and sintered in a cycle consisting of natural sintering at temperatures of 1130-1675 °C and additional HIP densification at 1600 °C in the case of samples sintered at the highest temperature. The phase composition of the produced powders and sinters was determined by XRD analysis, while the microstructure of the latter was shown in SEM images. In addition, DSC-TG analysis of the obtained precursor powders was performed. The solid state reaction between the yttrium oxide and alumina precursors led to the yttrium-aluminium garnet. The use of heterogeneous nucleation allowed for a higher density of obtained materials than for non-nucleated samples, both during free sintering and after hot isostatic pressing, and production of fully dense material.