Chapter 16. Mechanisms for Promoting Firing-Sag Resistance by Control of Clay Particle Size and Feldspar Alkali Content

  1. William Smothers
  1. Jerry Weinstein and
  2. Victor A. Greenhut

Published Online: 26 MAR 2008

DOI: 10.1002/9780470318799.ch16

A Collection of Papers Presented at the 1981 Fall Meeting and the 84th Annual Meeting of the Whitewares and Materials & Equipment Divisions The American Ceramic Society: Ceramic Engineering and Science Proceedings, Volume 3, Issue 11/12

A Collection of Papers Presented at the 1981 Fall Meeting and the 84th Annual Meeting of the Whitewares and Materials & Equipment Divisions The American Ceramic Society: Ceramic Engineering and Science Proceedings, Volume 3, Issue 11/12

How to Cite

Weinstein, J. and Greenhut, V. A. (2008) Mechanisms for Promoting Firing-Sag Resistance by Control of Clay Particle Size and Feldspar Alkali Content, in A Collection of Papers Presented at the 1981 Fall Meeting and the 84th Annual Meeting of the Whitewares and Materials & Equipment Divisions The American Ceramic Society: Ceramic Engineering and Science Proceedings, Volume 3, Issue 11/12 (ed W. Smothers), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470318799.ch16

Author Information

  1. Dept. of Ceramic Science and Engineering, Rutgers University, Piscataway, NJ 08854

Publication History

  1. Published Online: 26 MAR 2008
  2. Published Print: 1 JAN 1982

ISBN Information

Print ISBN: 9780470373996

Online ISBN: 9780470318799

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Keywords:

  • pyroplastic;
  • orthoclase;
  • vitrification;
  • aluminous;
  • crystalline

Summary

An experimental sanitary-ware composition was examined at various firing temperatures using a high temperature torsion instrument to determine apparent viscosity and a standard sag-bar test. The type of alkali in the feldspar portion, Na vs K, and the particle size of the clay portion, coarse vs fine kaolin, were varied while other characterizing body features were maintained constant. Except at initial low firing temperatures, K feldspar provided increased torsional viscosity and showed decreased pyroplastic sag. Viscosity data and scanning electron microscopy microstructural studies indicated that sag resistance resulted from formation of a stiffer glassy phase and development of an interlocking-mullite structure. Finer-clay fractions resulted in increased torsional viscosity and decreased pyroplastic sag at all firing times and temperatures studied. Examination of microstructures showed isolated glassy-phase regions separated by kaolinite and quartz regions in fired bodies using a fine-clay fraction. On firing a body containing a coarser-clay fraction, a quasi-continuous glassy phase was produced which would result in lower viscosity and greater pyroplastic sag in contrast to the structure of the finer-clay-body composition.