Control of beta-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 he at-treated at 1750-1900 degrees C. After removing the glassy phase, the mor phologies of beta-Si3N4 crystals were quantitatively analyzed. The aspect r atios of beta-Si3N4 crystals doped with different lanthanide oxides increas ed in the order of La2O3 > Gd2O3 > Yb2O3 at high annealing temperatures. Th e anisotropic Ostwald ripening model successfully simulated grain growth be haviors of beta-Si3N4 with different lanthanide additives, and suggested th at the observed difference in grain growth behaviors be due to the change i n the reaction rate at the (100) interface between the beta-Si3N4 crystal a nd the Ln-Si-O-N liquid phase.