Chapter 7. Sources of Sintering Inhibition in Tape-Cast Aluminas
- John B. Wachtman Jr.
Published Online: 26 MAR 2008
Copyright © 1993 The American Ceramics Society
A Collection of Papers on Engineering Aspects of Fabrication of Ceramics: Ceramic Engineering and Science Proceedings, Volume 14, Issue 11/12
How to Cite
Geho, M. and Palmour, H. (1993) Sources of Sintering Inhibition in Tape-Cast Aluminas, in A Collection of Papers on Engineering Aspects of Fabrication of Ceramics: Ceramic Engineering and Science Proceedings, Volume 14, Issue 11/12 (ed J. B. Wachtman), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470314272.ch7
- Published Online: 26 MAR 2008
- Published Print: 1 JAN 1993
Print ISBN: 9780470375280
Online ISBN: 9780470314272
High-purity, lightly MgO-doped A12O3 tapes (20–200 m̈m thick) were tape cast from water- or MEK-EtOH-based slurries. Dilatometric data obtained in directions both parallel and perpendicular to the cast plane under constant-rate-of-heating conditions (5°C/min to 1600°C) were utilized to evaluate all aspects of densification behavior during sintering, including small but significant tapethickness dependencies and orientation-anisotropy effects. Importantly, two unreported types of sintering inhibition were found: one is attributed to excess amounts of organic additives (>10 wt%) in the water-based slurries; the other is associated with a phosphate-containing deflocculant used in the organic-solvent slurries. In aqueous systems, overuse of organic binders/plasticizers leads to excessive dilatation (shrinkage or expansion) at low temperatures (∼350°–500°C), thereby degrading particle-particle contacts and thus inhibiting sintering in early-intermediate stages of densification. In these aqueous-system experiments, total organic content could be reduced to as low as 6.5 wt%, yielding good tape quality and improved sintering behavior. In the organic solvent system, P2O5 from the deflocculant appears to react with Al2O3 and MgO; initially it forms liquid phases, but thereafter yields binary and/or ternary crystalline phases that inhibit late-stage sintering.