Synthesis of AlN by Direct Nitridation of Al Alloys

Abstract

Direct nitridation of Al-alloys such as Al-Y, Al-Ca, and Al-Li was investigated with particular emphasis on the alloy composition, reaction temperature and reaction time. The alloys Al-2.3wt% Li, Al-5.0wt% Li and Al-5.0wt% Ca converted completely to AlN in very short soaking time at 1000°C. For Al-1.0wt% Li and Al-0.5wt% Li conversion ratios at 1000°C for 5h were 28.2 and 12.6%, respectively. On the other hand, no noticeable reaction was seen for Al-Y alloy and pure Al. The product from Al-Ca alloy was difficult to crush, which seemed to be a disadvantage for AlN powder synthesis. The reaction using Al-2.3wt% Li alloy could be divided into three categories: namely, surface nitridation, volume nitridation and breakaway nitridation. In the surface nitridation, the conversion ratio was very low, indicating the thickness of AlN layer was several tens of micron meters. In the volume nitridation the conversion ratio was in the extent of about 10%, and AlN porous surface layer formed. In the breakaway nitridation, complete conversion to AlN was attained, and the product greatly expanded to show no trace of the original form. The AlN product in the breakaway nitridation consisted of rod-like, plate-like and spherical grains. The size increased with increasing reaction temperature.