Availableonlineatwww.sciencedirect.com SCIENCE DIRECT E噩≈3S ELSEVIER Journal of the European Ceramic Society 25(2005)123-127 www.elsevier.com/locate/jeurceramsoc a new type of precursor for fibers in the system Si-C J. Clade, E Seider, D. Sporn Fraunhofer-Institut fiir Silicatforschnung ISC, Neumerplat: 2, 97082 Wir=burg, Germany Available online 18 September 2004 Abstract Ceramic fibers with compositions in the system SiC have a great potential for high-temperature applications. In recent years, our efforts have been dedicated to the development of polymers consisting of polysilanes suitable to spin fibers and build up matrices for CMC as well The polysilanes are synthesized via disproportionation of the so-called disilane fraction [Richter, R, Roewer, G, Bohme, U, Busch, K Babonneau, F, Martin, H.-P. et al, App. Organomet. Chem., 1997, 11, 71(and references cited therein)). A further thermal treatment yields materials which are soluble in organic solvents, and these solutions can be dry-spun to give fibers which are subsequently pyrolyzed. Solubility and high c yield make this precursor a promising candidate for matrix infiltrations, too. The chemistry and the adjustment of y d solubility to the requirements of the fiber processing as well as the conversion of the dried fibers to pure SiC fibers by thermal O 2004 Elsevier Ltd. All rights reserved Keywords: Polysilanes: Si-C, CMC, Fibers 1. Introduction manufacture of SiC ceramic fibers via melt-spinning; the cur- ing of the green fibers by heating them in air is usually re- SiC fibers have been of great interest for high tempera- quired ture applications for the last 20 years. Yajima et al. -al Many other methods for the preparation of prece- ready obtained polymer-derived SiC fibers in 1975, when ramic polycarbosilanes have been reported, for exam- they heated dodecamethyl cyclohexasilane(already reported ple the Wurtz-like coupling of pheny methyldichlorosilane/ by Burkhard in 1949 )in an autoclave, extracted low molec- dimethyldichlorosilane mixtures> and of r2SiClz/ ular proportions with acetone, dissolved the high molecular RSiCl3 mixtures, 6 the hydrosilylation of vinylsilanes7-19 portion with xylene, dry-spun the solution and pyrolyzed the and the ring-opening polymerization of 1, 3-disilacyclobutane green fibers. A more simple approach, during which the use derivatives with Pt catalysts 20-22 They have been summa of an autoclave could be avoided, was invented by the same rized in several review articles. 23-25 group of researchers, leading to a polycarbosilane which Unfortunately, the fibers commercially available so far was meltable and could thus be spun via the melt-spinning(Nicalon, Hi-Nicalon, Tyranno, etc. )either show insufficient process. 4, 6-8 Since the green fibers obtained in this process stabilities against oxidation or thermal creep due to their were still meltable, they had to be cured by heating in air up rather high oxygen content, or are only available at very high to 200C. This leads to a considerable oxygen content in the costs due to expensive processing steps such as electron beam SiC ceramic fibers Verbeek and Winter applied the synthesis of polycar- sCe g(e.g Hi-Nicalon), which prevents their use at a large bosilanes via a radical polymerization of monosilanes for Disilane mixtures forming as a high-boiling fraction a patent, a reaction which was first described by Fritz et during the Muller-Rochow process- as well as their base- al.0-2 The patent of Verbeek and Winter also describes the catalyzed disproportionation into monosilanes and polysi lanes are well-known. 27-30 Extensive studies of the use off these polysilanes as preceramic polymers were reported by Corresponding author. Baney31-33 as well as roewer and co-workers4(see also 0955-2219/S- see front matter 2004 Elsevier Ltd. All rights reserved doi: 10.1016/j-jeurceramsoc. 2004.07.009Journal of the European Ceramic Society 25 (2005) 123–127 A new type of precursor for fibers in the system Si–C J. Clade∗, E. Seider, D. Sporn Fraunhofer-Institut f ¨ur Silicatforschung ISC, Neunerplatz 2, 97082 W ¨urzburg, Germany Available online 18 September 2004 Abstract Ceramic fibers with compositions in the system Si–C have a great potential for high-temperature applications. In recent years, our efforts have been dedicated to the development of polymers consisting of polysilanes suitable to spin fibers and build up matrices for CMC as well. The polysilanes are synthesized via disproportionation of the so-called disilane fraction [Richter, R., Roewer, G., Bohme, U., Busch, K., ¨ Babonneau, F., Martin, H.-P. et al., Appl. Organomet. Chem., 1997, 11, 71 (and references cited therein)]. A further thermal treatment yields materials which are soluble in organic solvents, and these solutions can be dry-spun to give fibers which are subsequently pyrolyzed. Solubility and high ceramic yield make this precursor a promising candidate for matrix infiltrations, too. The chemistry and the adjustment of viscosity and solubility to the requirements of the fiber processing as well as the conversion of the dried fibers to pure SiC fibers by thermal treatment will be reported. © 2004 Elsevier Ltd. All rights reserved. Keywords: Polysilanes; Si–C; CMC; Fibers 1. Introduction SiC fibers have been of great interest for high tempera￾ture applications for the last 20 years. Yajima et al.1–4 al￾ready obtained polymer-derived SiC fibers in 1975, when they heated dodecamethyl cyclohexasilane (already reported by Burkhard in 19495) in an autoclave, extracted low molec￾ular proportions with acetone, dissolved the high molecular portion with xylene, dry-spun the solution and pyrolyzed the green fibers. A more simple approach, during which the use of an autoclave could be avoided, was invented by the same group of researchers, leading to a polycarbosilane which was meltable and could thus be spun via the melt-spinning process.4,6–8 Since the green fibers obtained in this process were still meltable, they had to be cured by heating in air up to 200 ◦C. This leads to a considerable oxygen content in the SiC ceramic fibers. Verbeek and Winter applied the synthesis of polycar￾bosilanes via a radical polymerization of monosilanes for a patent,9 a reaction which was first described by Fritz et al.10–12 The patent of Verbeek and Winter also describes the ∗ Corresponding author. manufacture of SiC ceramic fibers via melt-spinning; the cur￾ing of the green fibers by heating them in air is usually re￾quired. Many other methods for the preparation of prece￾ramic polycarbosilanes have been reported, for exam￾ple the Wurtz-like coupling of phenylmethyldichlorosilane/ dimethyldichlorosilane mixtures13–15 and of R2SiCl2/ RSiCl3 mixtures,16 the hydrosilylation of vinylsilanes17–19 and the ring-opening polymerization of 1,3-disilacyclobutane derivatives with Pt catalysts.20–22 They have been summa￾rized in several review articles.23–25 Unfortunately, the fibers commercially available so far (Nicalon, Hi-Nicalon, Tyranno, etc.) either show insufficient stabilities against oxidation or thermal creep due to their rather high oxygen content, or are only available at very high costs due to expensive processing steps such as electron beam curing (e.g. Hi-Nicalon), which prevents their use at a large scale. Disilane mixtures forming as a high-boiling fraction during the Muller-Rochow process ¨ 26 as well as their base￾catalyzed disproportionation into monosilanes and polysi￾lanes are well-known.27–30 Extensive studies of the use of these polysilanes as preceramic polymers were reported by Baney31–33 as well as Roewer and co-workers34 (see also 0955-2219/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2004.07.009