Effects of Y2O3 and Al2O3 sintering additives on the hot pressing behavior of AlN ceramics

AlN plates were fabricated by hot pressing AlN-Y2O3 and AlN-Y2O3-Al2O3 powder mixtures at 1700-1900 degrees C using yttria and alumina (Al2O3 particle sizes of 3 and 10 mu m) powders as sintering additives. The physical and mechanical properties of the hot-pressed AlN ceramics were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The density, thermal conductivity, transverse rupture strength, and grain size were measured. The thermal conductivity of the hot-pressed AlN ceramics ranged between 83-92.7 W x (m x K)(-1) and decreased with the addition of Al2O3, whereas the mechanical properties improved with the addition of Al2O3, which is known to have a beneficial effect of grain size refinement. The measured density values of 3.31 to 3.34 g x cm(-3) were slightly higher than the theoretical density of 3.26 g x cm(-3). This result was attributed to the use of a carbon mold under N-2 atmosphere, which effectively removed oxygen atoms from the yttrium-aluminate phase that is expected to form at 1100 degrees C.