SYNTHESIS OF AIN BY EXOTHERMIC NITRIDATION REACTION OF AI ALLOYS THROUGH DIFFUSION CHANNEL OF NITROGEN

研究了Al-Y、Al-Ca和Al-Li合金的直接氮化反应，重点考察了合金成分、反应温度和反应时间。虽然Al-Y合金和纯Al没有明显的反应，但Al-2.3wt%Li、Al-5.0wt%Li和Al-5.0wt%Ca合金在1000ﾟC下很短的时间内就完全转化为AlN，而Al-1.0wt%Li和0.5wt%Li在1000ﾟC保温5h时的转化率分别为28.2%和12.6%。Al-2.3wt%Li合金的反应可分为三种类型：表面氮化、体积氮化和分离氮化。在分离氮化过程中，产物极大地膨胀，没有显示出原始形态的痕迹。其内部由棒状、片状和球状的AlN颗粒组成。随着反应温度的升高，产物的尺寸增大。在Al-1.0wt%Li和A1-0.5wt%Li中，氮化过程中没有观察到放热反应，这与Li含量较高时的情况有很大不同。AlN-1.0wt%Li合金产物中的物相为AlN，而AlN-0.5wt%Li合金产物中的相为AlN和α-A1203。Al-Li和Al-Ca等Al-Li合金的氮化机理是基于Li向表面迁移形成的明渠中氮的扩散。

Direct nitridation of A1 alloys such as Al-Y,Al-Ca and Al-Li was investigated with particular emphasis on the alloy composition, reaction temperature and reaction time. Although no noticeable reaction was seen for A1-Y alloy and pure Al, the alloys of Al-2.3wt%Li, A1-5.0wt% Li and Al-5.0wt%Ca converted completely to AlN in very short soaking time at 1000ﾟC,and Al-1.0wt%Li and 0.5wt%Li showed conversion ratios of 28.2 and 12.6%at 1000ﾟC for 5h, respectively. The reaction using Al-2.3wt%Li alloy could be divided into three categories : namely, surface nitridation, volume nitridation and breakaway nitridation. In the breakaway nitridation, the product greatly expanded to show no trace of the original form. The inner part consisted of rod-like, plate-like and spherical AlN grains. The size increased with increasing reaction temperature. In A1-1.0wt%Li and A1-0.5wt%Li, the exothermic reaction was not observed during nitridation, which is quite different from the case of higher Li content. The phase in the product from the AlN-1.0wt%Li alloy was composed of AlN,whereas those from AlN-0.5wt%Li was AlN and alpha-A1203. The nitridation mechanism of A1 alloys such as Al-Li and Al-Ca was estimated to be based on the nitrogen diffusion through open channel formed by Li migration to the surface.