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C. Reynaud et al. International Journal of Refractory Metals d Hard Materials 19(2001)425-435 Table 3 Characteristics of sintered monolithic materials Pore forming agent or ceramic material PA-A P PA-C Corn starch ure Sic (free PFA) PFA contents(PFA volume/volume of fully dens ape i.e. SiC+ casting organics+ PFA) Domain of linear shrinkage during sintering (% l8-25 l8-25 l8-25 l8-20 18-19 Linear domain of pfa content versus final 040 0-45 porosity(vol%) Slope of the linear domain 0.68 0.9 Maximal porosity of sintered materials(vol%) 0±2 31.5±1.5 4士1 41.5±1.5 porosity versus pore size for porous material usin corn starch. illustrates this behaviour. The channel size between two pores in contact can be 100 estimated according to the eq. 3)derived by Zok et al. [15] 中四m=(1-LS)×GS×12m-1 where linear shrinkage(LS)is taken as 0.2, and grain size(GS) is taken as I um. The calculated values, listed in Table 4, are somewhat higher than the experimental 3.5. Porosity control The porosity control can be mainly affected by the thermodynamic stability of pores and the pore filling by the liquid phase The thermodynamical stability of pores is directly PFA contentⅳo%) linked to the dihedral angle in solid phase sintering Fig. 9. Open and closed porosities versus different PFA (corn starch [16]. This value of dihedral angle o determines the and PA-C)contents. value of the critical pore coordination number Nc. If Fig. 10. Porous microstructure obtained after liquid phase sintering of a laminar composite composed of same layers elaborated by tape casting 40 vol% of PFA PA-C was incorporated in the slurry, and a volume fraction of porosity of 33 vol% was reached;(b)25 vol% of corn staro corporated in the slurry led to 21. 5 vol% of porosity. / / , , 9& '>+ B3 ;" < " 5 ) % ) " > , 3 '5+ 3 ! / ')+ 3 " $ , 1 ' + 0 M & 3 ;"A< E "! & 6 ' + $! . % %* , >> . , # ' + . * " . > %*% %*@ %* ' %+ % '% = J J %+ '.+ -$ -$ -$! - ! O 3 '.+ "8- "8- "8- "8- ! "8-"C 5 % M '.+ !- !-$! !-> !-$ !A8 !7 !C !8 1 '.+ ! >" " >$ " $" " C 2 0 % ' %*+ "+ 1 % 2 3 "3+ 4 5 67 869 ':' $>"