A simple method for synthesis of acicular beta-Si_3N_4 seed crystals

摘要

Acicular silicon nitride (beta-Si_3N_4 ) seed crystals have been synthesized using a moderately low temperature heat-treatment process, with the aid of a low volume fraction of multiple sintering aids (i.e. MgO and CaO, in combination with either Y_2O_3 or Nd_2O_3). The effects of the heat-treatment cycle and the additive composition on the alpha- to beta-Si_3N_4 phase transformation were examined, for both cold-isostatically pressed pellets and simple packed powder. In the case of the packed powder, full transformation was achievable following heat-treatment at 1625 deg C for four hours, in approx 0.1 MPa nitrogen. The use of multiple oxide additives allows seed liberation from the heat-treated materials using a simple dilute HF soak at room temperature. The resulting beta-Si_3N_4 seed crystals exhibit a narrow size distribution, with mean aspect ratios of approx 4:1.