Sol-gel control of the matrix net-shape sintering 1481 (22%) cracks inter-fibre and libre particle pores m6A/mh个 Fig. 7. Comparison of pore diameter distribution for a composite without(dotted line) and with eight cycles of zircon on (solid line). Thermal treatment was mac 1200C. Assignment of the different kinds of pore is given 4 Zr+Alosi 8Z c/A203 0 500 1500 T(°c) d 100lb) 1200 Fig. 8. Shrinkage expansion of aluminosilicate xerogel from aluminium-silicon ester heated in vacuum reducing atmosph 1300 which is related to gas evolution(H,O and Co owing to the final dehydroxylation and to the oxi- dation of carbon residues, is observed when 4 Zr +AlOSi simultaneously, the viscosity is lowered. 9 post- infiltration with this precursor may promote good , interparticle bonding without shrinkage Strain(%) 3. 4 Mechanical properties Fig 9. Room temperature flexural stress-strain traces(a) for Figure 9 shows typical fiexural stress strain plot a CAlO,cor recorded for composites before and after post- polycondensation (HP) and 1000oC firing(8Zr)and after four infiltration. a significant increase in the strength is cycles of zirconium-propoxide post-infiltration and HP ane observed at temperatures up to 1300C. The 000C firing with a subsequent infiltration cycle using alu ultimate flexural strengths measured at room tem minium-silicon ester(4Zr+AlOSi. The stress-strain traces recorded for this last sample sintered at various temperatures perature,1200° c and I300° C are compared inSol-gel control of the matrix net-shape sintering 1481 $ interparticle I: (35%) I\ : : ; : : 1 j j i micropores 1 it J ! : i : 1200°C grains I cracks l l :: ( ‘: : [ i : : : Pore diameter (pm) Fig. 7. Comparison of pore diameter distribution for a composite without (dotted line) and with eight cycles of zirconium i-propoxide post-infiltration and subsequent in situ hydrolysis-polycondensation (solid line). Thermal treatment was made at 1200°C. Assignment of the different kinds of pore is given. 500 1000 1500 T (“C 1 Fig. 8. Shrinkage expansion of aluminosilicate xerogel from ahtminium-silicon ester heated in vacuum reducing atmosphere. which is related to gas evolution (H,O and CO) owing to the final dehydroxylation and to the oxi￾dation of carbon residues, is observed when, simultaneously, the viscosity is lowered.19 Post￾infiltration with this precursor may promote good interparticle bonding without shrinkage. 3.4 Mechanical properties Figure 9 shows typical flexural stress-strain plots recorded for composites before and after post￾infiltration. A significant increase in the strength is observed at temperatures up to 1300°C. The ultimate flexural strengths measured at room tem￾perature, 1200°C and 1300°C are compared in loo￾a) dzr+AIOSi ..-: . . . . . . . ..” ,.- : 1 2 St rain(%) Fig. 9. Room temperature flexural stress-strain traces (a) for a C/A&O3 composite before and after eight cycles of zir￾conium i-propoxide post-infiltration, in situ hydrolysis￾polycondensation (HP) and 1000°C firing (8Zr) and after four cycles of zirconium-propoxide post-infiltration and HP and 1000°C firing with a subsequent infiltration cycle using alu￾minium-silicon ester (4Zr+AlOSi). The stress-strain traces recorded for this last sample sintered at various temperatures are given in (b)