Influence of molybdenum on thermal properties of CMCs

Aluminum nitride (AlN) has received considerable attention in recent years because of its high thermal conductivity. AlN is currently used in thermal management applications. AlN single crystals have a thermal conductivity as high as 320 W{center_dot}m{sup {minus}1}{center_dot}K{sup {minus}1}, whereas the thermal conductivity of polycrystalline AlN varies from 80 to 200 W{center_dot}{sup {minus}1}{center_dot}K{sup {minus}1}, depending on the microstructure and composition of the sintered ceramic. Conventional AlN ceramics, however, do not exhibit thermal conductivity as high as expected because of their relatively low purity and sinterability. Purity, particle-size distribution, oxygen content and specific surface area affect sinterability and thermal properties of AlN. It is difficult to produce pure AlN powder and dense, sintered AlN materials that are free from oxygen impurities. The effect of adding a ductile metallic phase (aluminum) to improve the mechanical behavior of AlN is therefore studied. Aluminum, because of its low melting point, degrades the mechanical properties of AlN at high temperatures. A refractory metal with high thermal conductivity is the best choice as a second phase additive. The influence of molybdenum addition on the thermal properties of AlN has been studied.