Ca stabilized zirconia based composites by wet consolidation of zirconia and high alumina cement mixtures

Y. L. BRUNI; L.B. GARRIDO; E.F. AGLIETTI

Congreso; 56° Congresso Brasileiro de Cerâmica; 2011

The use of Ca ion to stabilize ZrO2 is well known. Generally, ZrO2 and calcia powders by solid state reaction at high temperature are widely used. Milling and solid state process, co precipitation, hydrothermal treatment, sol gel are very effective methods to produce Ca-ZrO2 based composites. Recently, various porous ZrO2 ceramics were fabricated using a starting mixture of m-ZrO2 containing different mole proportions of calcium aluminate cement HAC through a conventionally powder processing that consists in uniaxial pressing and reaction sintering at elevated temperature (3). The Ca stabilized ZrO2 ceramics fabricated by this process have 40 vol% open porosity and pore sizes close to 1 μm. However, dry processing have limited possibilities on geometry of shaped composites. Also, pore size of these ceramics nearly corresponds to the mean size of particles that were used. Thus, it depends on particle size distribution of the starting powders and therefore, to increase porous structure parameters a relatively coarse powder should be used. The colloidal processing (i.e. dispersing the ceramic powder in a liquid) overcomes many of these disadvantages allowing the manufacture of components with complex shapes and fine microstructure. Moreover, strength and reliability of the final components are improved. To ensure suitable porous materials for many industrial applications, several methods exist for increasing the porosity of the bodies. One method commonly employed to fabricate porous ceramics is to add fugitive particles to an initial ceramic mixture (4). In this case, the pore size and porosity can be easily controlled by varying the particle size and the volume ratio of fugitive agent /ceramic particles. Starch as pore former is effective to increase the pore volume, mean pore size and interconnectivity of porous structure of ceramics as was previously determined by mercury porosimetry. In this study, the effect of aqueous processing and incorporation of corn starch as fugitive additive on crystalline phases and sintering behavior as well as porous structure of HAC-ZrO2 mixtures were examined.