Control of β-Si3N4 crystal morphology and its mechanism (Part 2) -: Effect of lanthanide additives

Alpha-Si3N4 powder mixed with SiO2 and Ln(2)O(3) (Ln = La, Gd or Yb) was heat-treated at 1750-1900 degrees C. After removing the glassy phase, the morphologies of beta-Si3N4 crystals were quantitatively analyzed. The aspect ratios of beta-Si3N4 crystals doped with different lanthanide oxides increased in the order of La2O3 > Gd2O3 > Yb2O3 at high annealing temperatures. The anisotropic Ostwald ripening model successfully simulated grain growth behaviors of beta-Si3N4 with different lanthanide additives, and suggested that the observed difference in grain growth behaviors be due to the change in the reaction rate at the (100) interface between the beta-Si3N4 crystal and the Ln-Si-O-N liquid phase.