C. Reynaud et al. International Journal of Refractory Metals d Hard Materials 19(2001)425-435 46}|·日PB X-PA-C 102030 PFA content Fig.4. Effects of the PFA size and nature on the bulk density of green Fig. 5. Efects of the PF. and nature on the skeletal density of tape(thermocompressed). green tape. Skeletal density is calculated from Eq.(2): Pskelet a quite similar evolution between bulk density for corn starch as PFA and predicted values is shown. Corn starch leads to very low additional voids. On the op- posite, Orgasol PFA which has a similar effect intro- duces higher additional voids in the tape. The higher additional void in the tape may be attributed to the more difficult rearrangement of the ceramic and PFa particles in the organic phase during the drying of the tape, likely due to the chemical interactions between 不“A polyamide particles and tape casting additives The skeletal density of the green thermocompressed 8品号5 ape has been calculated according to eq (2) 日PAB A·· Com starch It is assumed that no casting organics are adsorbed on the PFA surface, the casting organics are entirely 30405060 distributed in the matrix. Fig. 5 shows the variation of PFA content(vol%) the green skeletal density versus PFA content. The skeletal density is quite constant for corn starch PFA Fig. 6. Effect of the PFA nature on the volumetric shrinkage during Consequently a constant volumetric shrinkage can be sintering expected for porous materials with corn starch as PFA to the annihilation of the small porosity which is ther 3.3. Sintering characteristics of monolithic block modynamically unstable, or the filling by the liquid phase of the finest porosity effects of PFa on volumetric shrinkage are Fig. 7 illustrates the evolution of the volumetric shown in Fig. 6. As expected, porous material using shrinkage during sintering of the green skeletal density corn starch as PFA exhibits a quite constant volumetric of the tape compared to the theoretical prediction in the shrinkage up to 45 vol% similar to free PFA volumetric case of a full densification of the ceramic skeleton, or shrinkage. Surprisingly, PA-C has a sligh partial densification of the skeleton(98 and 96%). The volumetric shrinkage and it is very closed to corn stard bulk density of free PFA laminar specimen reaches 97 one. On the opposite, PA-A porous materials present a 99% of the theoretical bulk density. Most of the exper- significant increase of volumetric shrinkage. This is due imental values are included between the lower and upper% &      , 3       
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