Processing

Direct Casting Techniques

Direct casting techniques achieve gelation of liquefied slurries without removing the dispersing agents, such as water. Ceramic particle suspensions with high solids loading (greater than 60 volume percent) are poured into dense molds and solidified by changing the colloidal stability. In this way ceramic green bodies with complex shapes can be achieved. The Sigmund Group, in collaboration with Professor Aldinger from the Max Planck Institute for Metals Research in Germany, introduced one of the simplest direct casting techniques that is based on commercially available, inexpensive compounds. This technique is referred to as temperature induced forming due to the mild increase in temperature used to coagulated the dispersed slurries. The technique is based on a combination of fundamental science from solution chemistry and colloid stability.

This novel direct casting technique has been successfully applied to alumina, zirconia, and mullite powder systems, zirconia-toughened-alumina, zirconia-toughened-mullite, yttria-stabilized-zirconia binary ceramic powder systems, and yttiria-magnesia-stabilized-zirconia ternary ceramic system. The Sigmund group studies the rheological behavior of the casting slips and has developed a novel concept to quantitatively predict the gelation and wet green strength of a gelled body via a combination of percolation and crystallization theories.

Publications on Direct Casting Techniques

  1. Yunpeng Yang and Wolfgang M. Sigmund, “Preparation, Characterization, and Gelation of Temperature-Induced Forming (TIF) Alumina Slurries,” Journal of Materials Synthesis and Processing, 9 [2] (2001) 103-109.
  2. Yunpeng Yang and Wolfgang M. Sigmund, “Effect of Particle Volume Fraction on the Gelation Behavior of the Temperature Induced Forming (TIF) Aqueous Alumina Suspensions,” J. Am. Ceram. Soc., 84 [9] (2001) 2138-40.
  3. Yunpeng Yang and Wolfgang M. Sigmund, “Estimation of the Volume Fraction Gelation Threshold for the Temperature Induced Forming (TIF) Alumina Aqueous Suspensions Using Rheological Measurement,” Journal of Ceramic Processing Research, 2 [3] (2001) 120-124.
  4. Yunpeng Yang and Wolfgang M. Sigmund, “Effect of calcium ion addition on dispersant adsorption in temperature induced forming (TIF) alumina slurry,” J. Mater. Sci. Lett., 20 (2001) 651-653.
  5. Yunpeng Yang and Wolfgang M. Sigmund, “Percolation Theory Model for the Temperature Induced Forming (TIF) Ceramic Slurries, Part I – Theoretical Calculations,” submitted to J. Europ. Ceram. Soc., (2001).
  6. Yunpeng Yang and Wolfgang M. Sigmund, “Percolation Theory Model for the Temperature Induced Forming (TIF) Ceramic Slurries, Part II – Experimental Derivations of the Equation Parameters,” submitted to J. Europ. Ceram. Soc., (2001).