Chapter 28. Gelcast Slurry Enhancement

  1. Ersan Ustundag and
  2. Gary Fischman
  1. Ogbemi O. Omatete and
  2. Miroslav Colic

Published Online: 26 MAR 2008

DOI: 10.1002/9780470294567.ch28

23rd Annual Conference on Composites, Advanced Ceramics, Materials, and Structures : A: Ceramic Engineering and Science Proceedings, Volume 20, Issue 3

23rd Annual Conference on Composites, Advanced Ceramics, Materials, and Structures : A: Ceramic Engineering and Science Proceedings, Volume 20, Issue 3

How to Cite

Omatete, O. O. and Colic, M. (1999) Gelcast Slurry Enhancement, in 23rd Annual Conference on Composites, Advanced Ceramics, Materials, and Structures : A: Ceramic Engineering and Science Proceedings, Volume 20, Issue 3 (eds E. Ustundag and G. Fischman), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470294567.ch28

Author Information

  1. Oak Ridge National Laboratory, Box 2008, Oak Ridge, TN 37831–6087

Publication History

  1. Published Online: 26 MAR 2008
  2. Published Print: 1 JAN 1999

ISBN Information

Print ISBN: 9780470375631

Online ISBN: 9780470294567

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Keywords:

  • turbomachinery;
  • gelcasting;
  • consolidation;
  • adsorbed molecules;
  • sedimentation

Summary

The packing density of two Si3N4 powders [A-high surface area ∼ 11 m2/g (Ube E 10) and B-low surface area ∼ 3.35 m2/g (Ube E03)] were investigated in order to increase the solids loading of the gelcasting slurry. The isoelectric points of both powders were between pH 4.7 and pH 6.0; consequently, the experiments were performed at either low pH 3 or high pH 10. Initial experiments were carried out with no milling and the B Si3N4 powders consistently achieved higher packing density. However, the investigation was concentrated on the A Si3N4 powder because, although it was preferred in the fabrication of turbomachinery components, it produced slurries with unacceptably low solids loading. In addition to pH adjustments (optimal pH 9.5), several reagents: anionic, cationic, and zwitterionic surfactants, polymers, and silanes were investigated to improve the aqueous dispersion of the powders. The silanes (polyethylene gycol (PEG), gluconoamide, and aromatic) increased dispersion and shelf life of the slurries without detrimental effects on the gelcasting process. PEG silane was the most effective and its addition at between 0.1 and 4.0 wt% (based on the ceramic powder) lowered the slip viscosity, increased slip shelf life up to three months, and produced gelled parts with packing density of between 51 and 52 vol%.