40TH ANNIVERSARY TABLE I Compositions of early varieties of first generation SiC fibres TABLE II Compositions, Youngs moduli and densities of first gener- produced by Nippon Carbon ation commercialised SiC fibres hemical composition Nippon Carbon Ube Industries Elemental composition %owt Fibre name Nicalon 200 Tyranno LOX-M C SiO, C Precursor PCS Cured by Oxidation xidation NLP10160 Si(wt%) NLM-1025 C(wt%) 31.6 NLP20254 O(wt%) 117 Ti(wt%) C/Si 1.31 1.36 group with the evolution of Co gas and forming a Si-c Young s modm ys (Pa bond. The nascent B-SiC grains, formed at slightly lower temperatures increased in size and the amorphous struc- ture evolved into a semi-crystalline structure consisting of nano sized B-SiC grains surrounded by a much less ordered phase made up of silicon, carbon and oxygen. [12]. The Tyranno fibres could be made with diameters Heating to 1500 C produced large grain growth, the evo- half that of the Nicalon fibres. The precursors of these first lution of carbon monoxide and the disintegration of the Tyranno fibres were also crosslinked in air. Ube Industries fibr used a code to indicate the oxygen content of the fibres The first fibres of this first generation, which were so that the fibre which was commercialised was known as made available by Nippon Carbon around 1982, were Tyranno LOX-M, with the letter M, which is the thirteenth the Nicalon 100 series but were replaced after about four letter in the alphabet, representing an oxygen content of years by the Nicalon 200 series which became the standard approximately 13%by weight grade for much of the ceramic matrix composite studies By the end of the 1980s the two Japanese companies subsequently undertaken. These fibres had diameters of were producing first generation fine diameter Sic around 15 um but showed variability in diameter along fibres and their compositions and densities are shown their length because of the difficulties of spinning the pre- in Table Il. The details of the composition and the cursor fibres, as can be seen from Fig 4. Table I shows nomenclature used to describe the fibres have changed the approximate chemical composition of these fibre slightly since their initial introduction so that the nicalon Yajima and his colleagues had considered several routes fibres mentioned in Table I are now grouped under the to making SiC fibres and one included the addition of simpler heading of Nicalon 100 or 200 series. Bulk Sic titanium to the PCS so as to give polytitanocarbosilane is however the second hardest material known and is (PTC)[11]. This precursor was obtained by the grafting crystalline, it possesses a Youngs modulus of around of titanium alkoxide, Ti(OR)4, in which=CnH2n+l, onto 400 GPa and a density of 3. 15 g/cm and can be used in the PCS chains. This linked the polymer chains together, air up to 1600oC. At this temperature passive oxidation of increasing molecular weight and its spinability. In 1987, the surface to Sio2 protects it from further degradation another Japanese company, Ube Industries announced the Table II reveals that the properties of the first generation production of Tyranno fibres made from PTC precursors of fine Sic fibres were not those of the bulk material and reported that they had better thermal and chemical This has been shown to be due to the non stoichiometric stability compared with the then-existent Nicalon fibres composition of the fibres, which are rich in carbon and contain oxygen, as shown in Tables I and Il. An alternative approach to producing polymer derived SiC fibres, similar to the first generation fibres which have been developed commercially, has been described by university researchers. In contrast to the manufactur ing technique described above, it has been shown that such fibres could be produced from precursor filaments made 864 from high-molecular-weight PCS [13]. The infusible PCS was prepared by pressure pyrolysis of polydimethylsilane Fine fibres were formed by the dry spinning of concen- trated PCs-based polymer solutions which were then py 78910111213141516118192021 rolised in an inert atmosphere in the temperature range of 1000 to 1200C. The fibres produced in this manner were Figure 4 Range of diameters observed with Nicalon NLM 202 fibre taken reported as possessing very similar properties to those of from the same tow [43 the commercialised first generation fibres [14] 82540TH ANNIVERSARY T A B L E I Compositions of early varieties of first generation SiC fibres produced by Nippon Carbon Elemental composition %wt Chemical composition %wt Fibre type Si C O SiC SiO2 C NLP-101 60 27 13 69 24 7 NLM-102 54 34 12 63 21.5 15.5 NLP-202 54 37 9 66 17 17 group with the evolution of CO gas and forming a Si–C bond. The nascent β-SiC grains, formed at slightly lower temperatures increased in size and the amorphous struc￾ture evolved into a semi-crystalline structure consisting of nano sized β-SiC grains surrounded by a much less ordered phase made up of silicon, carbon and oxygen. Heating to 1500◦C produced large grain growth, the evo￾lution of carbon monoxide and the disintegration of the fibre. The first fibres of this first generation, which were made available by Nippon Carbon around 1982, were the Nicalon 100 series but were replaced after about four years by the Nicalon 200 series which became the standard grade for much of the ceramic matrix composite studies subsequently undertaken. These fibres had diameters of around 15 µm but showed variability in diameter along their length because of the difficulties of spinning the pre￾cursor fibres, as can be seen from Fig. 4. Table I shows the approximate chemical composition of these fibres. Yajima and his colleagues had considered several routes to making SiC fibres and one included the addition of titanium to the PCS so as to give polytitanocarbosilane (PTC) [11]. This precursor was obtained by the grafting of titanium alkoxide, Ti(OR)4, in which R=CnH2n+1, onto the PCS chains. This linked the polymer chains together, increasing molecular weight and its spinability. In 1987, another Japanese company, Ube Industries announced the production of Tyranno fibres made from PTC precursors and reported that they had better thermal and chemical stability compared with the then-existent Nicalon fibres 0 2 4 6 8 10 12 14 16 18 20 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 24 25 Diameter (µm) % Figure 4 Range of diameters observed with Nicalon NLM 202 fibre taken from the same tow [43]. T AB L E I I Compositions, Young’s moduli and densities of first gener￾ation commercialised SiC fibres Producer Nippon Carbon Ube Industries Fibre name Nicalon 200 Tyranno LOX-M Precursor PCS PTC Cured by Oxidation Oxidation Si (wt%) 56.6 54 C (wt%) 31.7 31.6 O (wt%) 11.7 12.4 Ti (wt%) 0 2.0 C/Si 1.31 1.36 Young’s modulus (GPa) 200 185 Density (g/cm3) 2.55 2.37 [12]. The Tyranno fibres could be made with diameters half that of the Nicalon fibres. The precursors of these first Tyranno fibres were also crosslinked in air. Ube Industries used a code to indicate the oxygen content of the fibres so that the fibre which was commercialised was known as Tyranno LOX-M, with the letter M, which is the thirteenth letter in the alphabet, representing an oxygen content of approximately 13% by weight. By the end of the 1980s the two Japanese companies were producing first generation fine diameter SiC fibres and their compositions and densities are shown in Table II. The details of the composition and the nomenclature used to describe the fibres have changed slightly since their initial introduction so that the Nicalon fibres mentioned in Table I are now grouped under the simpler heading of Nicalon 100 or 200 series. Bulk SiC is however the second hardest material known and is crystalline, it possesses a Young’s modulus of around 400 GPa and a density of 3.15 g/cm3 and can be used in air up to 1600◦C. At this temperature passive oxidation of the surface to SiO2 protects it from further degradation. Table II reveals that the properties of the first generation of fine SiC fibres were not those of the bulk material. This has been shown to be due to the non stoichiometric composition of the fibres, which are rich in carbon and contain oxygen, as shown in Tables I and II. An alternative approach to producing polymer derived SiC fibres, similar to the first generation fibres which have been developed commercially, has been described by university researchers. In contrast to the manufactur￾ing technique described above, it has been shown that such fibres could be produced from precursor filaments made from high-molecular-weight PCS [13]. The infusible PCS was prepared by pressure pyrolysis of polydimethylsilane. Fine fibres were formed by the dry spinning of concen￾trated PCS-based polymer solutions which were then py￾rolised in an inert atmosphere in the temperature range of 1000 to 1200◦C. The fibres produced in this manner were reported as possessing very similar properties to those of the commercialised first generation fibres [14]. 825