Ceramics-Silikáty 48, (4) 165 - 174 (2004)

In this fourth paper of a series on the effective elastic properties of alumina-zirconia composite ceramics the influence of porosity on the effective tensile modulus of alumina and zirconia ceramics is discussed. The examples investigated are alumina and zirconia ceramics prepared from submicron powders by starch consolidation casting using two different types of starch, potato starch (median size D₅₀ =47.2 µm) and corn starch (median size D₅₀ =13.7 µm). The dependence of effective tensile moduli E, on the porosity φ, measured for porosities in the ranges of approx. 19-55 vol.% and 10-42 vol.% for alumina and zirconia, respectively, using a resonant frequency technique, was evaluated by fitting with various model relations, including newly developed ones. A detailed comparison of the fitting results suggests the superiority of the new relation E/E₀ = (1 - Φ)·(1 - Φ/Φ_C), developed by the authors (with the tensile modulus of the dense ceramic material E₀ and the critical porosity Φ_C), over most other existing fit models. Only for special purposes and well-behaved data sets the recently proposed exponential relation E/E0 = exp [-BΦ/(1 - Φ)] and the well-known Phani-Niyogi relation E/E₀ = (1 - Φ/Φ_C)^N might be preferable.