June 2004 Preparation of Si-Ti-C-0 Fabric/Mullite Filler/ Polytitanocarbosilane Laminates by PlP Method Youngs modulus of 186 GPa(Ube Industries, Ltd, Y amaguchi Japan). Excess suspension overflowed outside the mold The dried, green, laminated composites were calcined for I h at 1 100oC in an argon atmosphere. The characteristics of the lami nated composites are shown in Table I. In some samples,a pressure of 39 MPa was applied during the calcination to decreas the porosity of the composite before the PIP process. The fraction 10 of mullite powder filler in the calcined composite was 25-40 vol%, except for sample F. No filler was inserted into the fabric of sample F. The fiber fraction was in the range of 21-33 vol% 010203040506 (2) PIP Process with PTC Solution and Mechanical Polvtitanocarbosilane/ mass Properties of Densified Composites Figure I shows the viscosity of the xylene solution containing Fig. 1. Viscosity of the PTC-xylene solution used for the impregnation PTC of molecular weight 15 000(chemical composition(mass%) into the laminated porous composite of 44 S1, 2 T1, 42 C, 9 H, and 3O(Ube Industries )). The viscosity gradually increased to 30 mass% of the polymer and then rapidl creased at higher fractions of the polymer. In the present PIP process, precursor solutions containing 20-50 mass% polymer calcination of the laminated composites with a similar fiber fraction provided no increase of the packing density(samples A, nder vacuum to understand the concentration effect of the B, C, and D). The weave density affected the porosity of the polymer on the densification of the composites. The infiltrate laminated composite. The plain-weave fabric(17 yarn/2.54 cm x polymer was heated to 170C in air to cure the polymer, and it was 17 yarn/2. 54 cm, 800 filament/yarn) gave a lower porosity com- thermally decomposed at 1000C in an argon atmosphere to form posite than the satin-weave fabric (20 yarn/2.54 cm X 20 yarn/2.54 an inorganic residue. This PIP sequence was repeated eight times cm)at a similar fiber content because of the high packing to decrease the porosity. The density of the PIP-processed com- characteristic of mullite filler in the plain-weave fabric(samples E posite was measured using the Archimedes method with kerosene and G) The microstructures of the densified composites were observed The pore volume(Po) of the composite was important using optical microscopy and scanning electron microscopy in decreasing the porosity usil process In our previous (Model SM300, Topcon Technologies, Inc, Tokyo, Japan). The paper, we derived Eq.(1) porosity (P)after n PIP mposites were cut using a diamond wheel to test samples 4 mm sequences. ide, 6 mm high, and 38 mm long and were polished using Nos 600 and 2000 SiC papers. The flexural strength of each sample was P=Pol1-y-C easured at room temperature using the four-point flexural ethod with an upper span of 10 mm and a lower span of 30 mm and a crosshead speed of 0.5 mm/min( Model AGIOTA, Shimadzu where y is the ceramic yield of solids-to-polymer (y =0.88 for Seisakusho, Ltd, Kyoto, Japan). Two or three samples per PTC), D, the density of the polymer(1. 192 g/cm), Ds the density processing condition were tested. The appearance of the compos- of the solid formed (1.982 g/cm), and Cn the polymer concentra ites during bend testing was photographed using a digital camera. where I', is the volume of polymer and y, the volume of xyl Equation(1)indicates that(i) pore elimination efficiency (dP/dn) II. Results and discussio decreases as the number of PIP sequences increases, (ii)decreased Po and increased Cn effectively decrease the porosity for a given () Densification of the laminated Composites Using PIP The fractions of the fibers and the mullite filler laminated composites after the impregnation of PTC are shown in porosity Table I. The incorporation of the mullite filler in the laminated Figure 2(a) shows the decrease of abric greatly influenced the porosity before the PIp process. N fabric/mullite composite(sample B)with increasing Hp C-o mullite filler(sample F) resulted in 70% porosity. The high quences. In sample B, 20, 30, and 40 mass% polymer solutions fraction(46 vol%) of mullite filler in sample e decreased the were used in the first PIP sequence, the second through fourth PIP porosity to 33%. Samples A, B, C, and D with 31-33 vol% sequences, and fifth through eighth PIP sequences, respectively Si-Ti-C-O fabric contained 26-27 vol% mullite filler and 41-44 The solid line represents the porosity of open pores, calculated vol% porosity. The application of pressure of 39 MPa during the using Eq (1). The porosity from Eq (1)explains the trend of the Table I. Phase Compositions and Mechanical Properties of the Laminated Composites of the Si-Ti-C-O Fabrie-Mullite-PTC System after the Eighth PIP Sequence Fiber(vol%) 31.l( plain)30.8 32.9(plain) 32.9(plain) 21.2 (plain) 29.9(plain) 21.7( satin) Mullite filler(vol%) 25.5 ure during calcination 0 0 39 (MPa) PTC-derived solid(vol% 26.6 29.1 15.5 38.4 21.2 Closed pore(vol%) Young's modulus at elas 40±4 30±4 32±6 15±1 19±3 13±1 deformation(GPa) eda30m1223 3=13 111±2 69.1 12 7.2-7 03 139±2Young’s modulus of 186 GPa (Ube Industries, Ltd., Yamaguchi, Japan)). Excess suspension overflowed outside the mold. The dried, green, laminated composites were calcined for 1 h at 1100°C in an argon atmosphere. The characteristics of the lami￾nated composites are shown in Table I. In some samples, a pressure of 39 MPa was applied during the calcination to decrease the porosity of the composite before the PIP process. The fraction of mullite powder filler in the calcined composite was 25–46 vol%, except for sample F. No filler was inserted into the fabric of sample F. The fiber fraction was in the range of 21–33 vol%. (2) PIP Process with PTC Solution and Mechanical Properties of Densified Composites Figure 1 shows the viscosity of the xylene solution containing PTC of molecular weight 15 000 (chemical composition (mass%) of 44 Si, 2 Ti, 42 C, 9 H, and 3 O (Ube Industries)). The viscosity gradually increased to 30 mass% of the polymer and then rapidly increased at higher fractions of the polymer. In the present PIP process, precursor solutions containing 20–50 mass% polymer were impregnated into the porous green composites for 40 min under vacuum to understand the concentration effect of the polymer on the densification of the composites. The infiltrated polymer was heated to 170°C in air to cure the polymer, and it was thermally decomposed at 1000°C in an argon atmosphere to form an inorganic residue. This PIP sequence was repeated eight times to decrease the porosity. The density of the PIP-processed com￾posite was measured using the Archimedes method with kerosene. The microstructures of the densified composites were observed using optical microscopy and scanning electron microscopy (Model SM300, Topcon Technologies, Inc., Tokyo, Japan). The composites were cut using a diamond wheel to test samples 4 mm wide, 6 mm high, and 38 mm long and were polished using Nos. 600 and 2000 SiC papers. The flexural strength of each sample was measured at room temperature using the four-point flexural method with an upper span of 10 mm and a lower span of 30 mm and a crosshead speed of 0.5 mm/min (Model AG10TA, Shimadzu Seisakusho, Ltd., Kyoto, Japan). Two or three samples per processing condition were tested. The appearance of the compos￾ites during bend testing was photographed using a digital camera. III. Results and Discussion (1) Densification of the Laminated Composites Using PIP The fractions of the fibers and the mullite filler in the green laminated composites after the impregnation of PTC are shown in Table I. The incorporation of the mullite filler in the laminated fabric greatly influenced the porosity before the PIP process. No mullite filler (sample F) resulted in 70% porosity. The high fraction (46 vol%) of mullite filler in sample E decreased the porosity to 33%. Samples A, B, C, and D with 31–33 vol% Si-Ti-C-O fabric contained 26–27 vol% mullite filler and 41–44 vol% porosity. The application of pressure of 39 MPa during the calcination of the laminated composites with a similar fiber fraction provided no increase of the packing density (samples A, B, C, and D). The weave density affected the porosity of the laminated composite. The plain-weave fabric (17 yarn/2.54 cm 17 yarn/2.54 cm, 800 filament/yarn) gave a lower porosity com￾posite than the satin-weave fabric (20 yarn/2.54 cm 20 yarn/2.54 cm) at a similar fiber content because of the high packing characteristic of mullite filler in the plain-weave fabric (samples E and G). The pore volume (P0) of the starting composite was important in decreasing the porosity using the PIP process. In our previous paper,38 we derived Eq. (1) for the porosity (P) after n PIP sequences: P
P0
1 Y Dp Ds Cp n (1) where Y is the ceramic yield of solids-to-polymer (Y 0.88 for PTC), Dp the density of the polymer (1.192 g/cm3 ), Ds the density of the solid formed (1.982 g/cm3 ), and Cp the polymer concentra￾tion (vol%) in the xylene solution (Cp Vp/(Vp  Vx) Vp/P0, where Vp is the volume of polymer and Vx the volume of xylene). Equation (1) indicates that (i) pore elimination efficiency (dP/dn) decreases as the number of PIP sequences increases, (ii) decreased P0 and increased Cp effectively decrease the porosity for a given polymer, and (iii) a polymer with a high Y value (low loss of mass during pyrolysis of the polymer) is desirable for decreasing porosity. Figure 2(a) shows the decrease of porosity in the Si-Ti-C-O fabric/mullite composite (sample B) with increasing PIP se￾quences. In sample B, 20, 30, and 40 mass% polymer solutions were used in the first PIP sequence, the second through fourth PIP sequences, and fifth through eighth PIP sequences, respectively. The solid line represents the porosity of open pores, calculated using Eq. (1). The porosity from Eq. (1) explains the trend of the Fig. 1. Viscosity of the PTC–xylene solution used for the impregnation into the laminated porous composite. Table I. Phase Compositions and Mechanical Properties of the Laminated Composites of the Si-Ti-C-O Fabric–Mullite–PTC System after the Eighth PIP Sequence Property Value ABCDE FG Fiber (vol%) 31.1 (plain) 30.8 (plain) 32.9 (plain) 32.9 (plain) 21.2 (plain) 29.9 (plain) 21.7 (satin) Mullite filler (vol%) 25.9 25.5 25.9 26.5 45.9 0 28.0 Applied pressure during calcination at 1100°C (MPa) 0 0 0 39 39 0 0 PTC-derived solid (vol%) 26.6 29.1 24.4 22.2 15.5 38.4 21.2 Open pore (vol%) 11.0 9.6 13.7 14.9 9.2 31.7 24.8 Closed pore (vol%) 5.4 5.0 3.1 3.5 8.2 0 4.3 Young’s modulus at elastic deformation (GPa) 40  4 30  4 32  6 15  1 19  3 20  1 13  1 Strength (MPa) 312  17 264  14 227  9 111  2 172  2 69.1  0.3 139  2 Energy of fracture at 3.0 mm of displacement (kJ
m2 ) 19.4–22.3 9.9 18.5 10.2 12.8 7.2–7.4 4.4 June 2004 Preparation of Si-Ti-C-O Fabric/Mullite Filler/Polytitanocarbosilane Laminates by PIP Method 997