H. Morozumi et al 2 EXPERIMENT Table 1. The properties of the ToNEN poysilazanes Molecula Density 2. 1 Matrix precursor (mPas)at30°c Perhydropolysilazane(PHPS) and methylhydro PHPS 800 1.1-1.2 1050 SNC 11-1.2 4080 oligosilazane (SNC) were used as matrix pre- cursors. PHPs was synthesized by ammonolysis of a dichlorosilane pyridine adduct. SNC was Table 2. The properties of the toNEN fibres synthesized by coammonolysis of a dichlorosilane- SNF pyridine adduct and a monomethyldichlorosilane- pyridine adduct. 3 The properties of PHPs and Tensile strength(GPa) SNC are shown in Table 1. These polymers are Tensile modulus(GPa) 200 200 Density transparent liquids with low viscosity, and have a Typical composition si 596 thermosetting property. By heating to 100-300 C. ( % a thermal crosslink BNcO 37.1 328 oceeds, and glass- like hard 4 solids are obtained By firing to 800-1500oC in 2.7 7.6 nitrogen or inert gases, the cured products convert to amorphous silicon nitride based ceramics with 70-90 wt% yield. The yield is extremely high in nation, curing and firing processes were performed preceramic polymers(e.g. repeatedly polycarbosilane lastylene, etc. ) that have 50-60 wt% yield. The differences between PHPS 2.3.2 2D(Cross-ply composites) and SNC are shown in the composition. The SNC was used as a matrix precursor, because the H NMR spectrum of SNC exhibits a peak cor- UD composite, SNF/SNC, showed higher flexural responding to SiMe due to the addition of a strength than the SNF/PHPS. SNF and SNBF monomethyldichlorosilane. SNC consists mainly of were used as reinforcement. 2D(cross-ply)compo- structured units of SiH,NH and SihMeNH sites were fabricated as follows. A unidirectional fibre aligned preform w d by windi 2.2 Ceramic fibre strand. which was infiltrated with snc. on to a drum. To obtain a UD prepreg, the preform was Two kinds of ceramic fibres, produced by pressed to a thickness of 0. 2 mm ToNEN, were used as reinforcements. SNF The prepreg was then cut and stacked in the derived from perhydropolysilazane SNBF is derived structure of [0/90/90/012. The stacked prepregs from polyborosilazane. 10 The properties of both were cured in a n2 atmosphere with a pressure of fibres are shown in Table 2. The surfaces of these 0.05-0. 1 mPa at 100-300 C for 1-3 h. The cured fibres were coated with a C-rich layer by chemical body was then fired in a n2 atmosphere to 1350.C vapour deposition(SiClg-CHa gases system). The To densify the products the same repeating process purpose of this fibre coating is not only to prevent as in the Ud composites was performed reaction between fibre and matrix, but also to give adequate interface shear strength. The thickness of 2. 4 Characterization the coated layer was about 0. I um. The densification of the fired material in the repeat- 2.3 Fabrication procedure ing proccss was monitored by mcasuring bulk dcn sities. The products were characterized by SEM 23. I Ud(Unidirectional fibre reinforced AES, X-ray diffraction analysis, and a three-point composites bending test at room temperature.( For cross-ply PHPS and SNC were used as matrix precursors. composites, the high temperature strength was UD composites, SNF/PHPS and SNF/SNC, were measured at 1250%C in a n2 atmosphere. The three fabricated as shown in Fig. 1. A unidirectional point bending test was performed in accordance SNF aligned preform was prepared by winding a with JIs R1601 except for thickness of sample strand, which was infiltrated with precursor, on to Samples were cut into 1.0-1. 2 x 4 x 40 mm bars a mandrel. The preform was pressed to a thickness and tested with a span length of 30 mm at a cross of 5 mm, and cured in a n2 atmosphere with a head speed of 0.5 mm/min JIS R1601 is not always pressure of 0.050. 1 MPa at 100-300C for 1-3 h. advantageous to continuous fibre reinforced com- The cured body was then fired in a n2 atmosphere posites which show non-brittle failure, since this to 1350C. To densify the product, the impreg- method shows a complex fracture mixed with tensile180 H. Morozumi et al. 2 EXPERIMENT Table 1. The properties of the TONEN poysilazanes 2.7 Matrix precursor Molecular weight (A&) Density Viscosity (mPa+) at 30°C Perhydropolysilazane (PHPS) and methylhydro￾oligosilazane (SNC) were used as matrix pre￾cursors. PHPS was synthesized by ammonolysis of a dichlorosilane-pyridine adduct. SNC was synthesized by coammonolysis of a dichlorosilane￾pyridine adduct and a monomethyldichlorosilane￾pyridine adduct. l3 The properties of PHPS and SNC are shown in Table 1. These polymers are transparent liquids with low viscosity, and have a thermosetting property. By heating to 10&3OO”C, a thermal crosslinking proceeds, and glass-like hard solids are obtained. By firing to 800-1500°C in nitrogen or inert gases, the cured products convert to amorphous silicon nitride based ceramics with 70-90 wt% yield. The yield is extremely high in comparison to other preceramic polymers (e.g. polycarbosilane, polysilastylene, etc.) that have 50-60 wt% yield. The differences between PHPS and SNC are shown in the composition. The ‘H NMR spectrum of SNC exhibits a peak cor￾responding to SiMe due to the addition of a monomethyldichlorosilane. SNC consists mainly of structured units of SiHzNH and SiHMeNH. 2.2 Ceramic fibre Two kinds of ceramic fibres, produced by TONEN, were used as reinforcements. SNF is derived from perhydropolysilazane. SNBF is derived from polyborosilazane. lo The properties of both fibres are shown in Table 2. The surfaces of these fibres were coated with a C-rich layer by chemical vapour deposition (SiC14-CH4 gases system). The purpose of this fibre coating is not only to prevent reaction between fibre and matrix, but also to give adequate interface shear strength. The thickness of the coated layer was about 0.1 pm. 2.3 Fabrication procedure 2.3.1 UD (Unidirectionaljibre reinforced composites) PHPS and SNC were used as matrix precursors. UD composites, SNF/PHPS and SNF/SNC, were fabricated as shown in Fig. 1. A unidirectional SNF aligned preform was prepared by winding a strand, which was infiltrated with precursor, on to a mandrel. The preform was pressed to a thickness of ~5 mm, and cured in a N2 atmosphere with a pressure of 0.05-0.1 MPa at 10&3Oo”C for l-3 h. The cured body was then fired in a N2 atmosphere to 1350°C. To densify the product, the impreg￾PHPS 800-I 000 1.1-1.2 1 O-50 SNC 800-I 000 1.1-1.2 40-80 Table 2. The properties of the TONEN fibres SNF SNBF Tensile strength (GPa) 2.2 Tensile modulus (GPa) 200 Density 2.5 Typical composition Si 59.6 (%) B - N 37.1 : 0.4 27 2.2 200 2.5 48.0 3528 5:4 7.6 nation, curing and firing processes were performed repeatedly. 2.3.2 20 (Cross-ply composites) SNC was used as a matrix precursor, because the UD composite, SNF/SNC, showed higher flexural strength than the SNF/PHPS. SNF and SNBF were used as reinforcement. 2D (cross-ply) compo￾sites were fabricated as follows. A unidirectional fibre aligned preform was prepared by winding a strand, which was infiltrated with SNC, on to a drum. To obtain a UD prepreg, the preform was pressed to a thickness of ~0.2 mm. The prepreg was then cut and stacked in the structure of [O/90/90/O]2. The stacked prepregs were cured in a N2 atmosphere with a pressure of 0.05-0.1 MPa at IOO-300°C for l-3 h. The cured body was then fired in a N2 atmosphere to 1350°C. To densify the products, the same repeating process as in the UD composites was performed. 2.4 Characterization The densification of the fired material in the repeat￾ing process was monitored by measuring bulk den￾sities. The products were characterized by SEM, AES, X-ray diffraction analysis, and a three-point bending test at room temperature. (For cross-ply composites, the high temperature strength was measured at 1250°C in a N2 atmosphere.) The three￾point bending test was performed in accordance with JIS R1601 except for thickness of sample. Samples were cut into 1.0-1.2 x 4 x 40 mm bars and tested with a span length of 30 mm at a cross￾head speed of 0.5 mm/min. JIS R1601 is not always advantageous to continuous fibre reinforced com￾posites which show non-brittle failure, since this method shows a complex fracture mixed with tensile