A simple method for synthesis of acicular b-Si3N4 seed crystals

DANIEL A. GOULD; MERVIN QUINLAN; MARIA P. ALBANO; LILIANA B. GARRIDO; LUIS A. GENOVA; KEVIN P. PLUCKNETT

CERAMICS INTERNATIONAL

ELSEVIER SCI LTD

Año: 2009 p. 1357 - 1362

0272-8842

Acicular silicon nitride (b-Si3N4) seed crystals have been synthesized using a moderately low temperature heat-treatment process, with the aida low volume fraction of multiple sintering aids (i.e. MgO and CaO, in combination with either Y2O3 or Nd2O3). The effects of the heattreatment cycle and the additive composition on the a- to b-Si3N4 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 8C for four hours, in _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 b-Si3N4 seed crystals exhibit a narrow size distribution, with mean aspect ratios of _4:1.