Q2: a) AlN is a material which based on covalent bonds, therefore it has low diffusivity and thus it requires high sintering temperatures (1600-20000C). In addition, the presence of oxides on the powder surface as well as in the lattice makes it necessary to use sintering additives in order to increase its thermal conductivity. As was proven in this article the thermal conductivity of AlN sintered without Y2O3 was exceed from 65 W/m K up to 110-140 W/m K depending on the Y2O3
wt.%. The AlN relative density was also improved almost to 100% under Y2O3 addition. The key parameter for this is the thermodynamic perspective that the greater the affinity a sintering additive has to oxygen the greater is its ability to purify the lattice [1].