Study on Reaction Behaviour of Nitrogen-containing Rare Earth Melilite Solid Solutions

Nitrogen-contaming rare earth melilite solid solutions R2Si3-xAlxO3+xN4-x (R=Nd, Dy, x=0,0.3, 0.6, 1.0, R=Yb, x=0, 0.3) were prepared at the temperatures ranged form 1500 ℃ to 1750℃ for 2h by pressureles sintering technique. The reaction sequences of these compositions at the sintering temperatures were studied. The results showed that introgen-containing rare earth (from Nd to Yb)melilite or its solid solutions can be formed and their amounts in the sintered samples increase with increasing the temperatures. However, the formation abilities of melilite solid solutions become weak with decreasing the ionic radii of rare earth elements, i.e. light rare earth melilite solid solutions can be formed as a major phase at the temperture as low as 1500℃, however, for midium and heavy rare earth it needs to increase the temperature to 1700℃ and 1750℃ respectively. The other phases to occur in the sintered samples and the factors to affect the formation behaviour of melilite solid solutions were also discussed in the paper.