Polysilazanes offer a convenient route for preparing a variety of ceramic materials.
Polysilazanes are polymers consisting of silicon, nitrogen, hydrogen and, in the case of organopolysilazanes, carbon. Such polymers can be considered either inorganic (perhydropolysilazanes) or organic (organopolysilazanes or polycarbosilazanes) in nature and have both silicon and nitrogen atoms in their backbone. Principally due to their high pyrolytic mass yields of silicon-based ceramic material (often > 80wt%), polysilazanes have been extensively used in the past as precursors to silicon dioxide,1 silicon nitride and silicon carbide ceramics.2-8 They offer a convenient route for preparing ceramic materials such as fibers, coatings or 3-D continuous fiber-reinforced ceramic matrix composites, which often cannot be made through traditional ceramic processing methods.3
Inorganic polysilazanes are currently used extensively in the electronics industry as precursors in the manufacture of dense or porous surface coatings of pure silica. In the manufacture of semiconductor devices, these coatings are produced on the surface of a substrate, such as a silicon wafer, by coating the substrate surface with a polysilazane-containing coating solution and then converting the coating layer of polysilazane into a silica-based coating film.9 Typically, such surfaces are prepared by spin-coating and then substantially converting the polysilazane layer to a silicon-oxide-containing ceramic, such as silica. The coatings are referred to by the generic term spin-on-glass (SOG).
Recently, a body of work has focused on the ability of various organic polysilazanes to form amorphous, non-glassy silicon carbonitride (SiCN) ceramics. These ceramics are resistant to chemical degradation,10 creep,11-13 oxidation,14 thermal shock, decomposition and softening.15 Thus, they are quite attractive for a variety of structural ceramic and electronic applications.16 A viable technique to fabricate ceramic devices for micro-electro mechanical systems (MEMS) by microcasting UV-curable organopolysilazanes, for example, has recently been developed.17-21 A microfabrication technique for constructing 3-D photonic crystals by deep X-ray lithography using organopolysilazanes has also been demonstrated.22
In the structural ceramics arena, both monolithic and composite ceramic structures have been fabricated using organopolysilazane ceramic precursors. Two methods have been developed to prepare crack-free monolithic ceramics from polysilazanes. The first method involves a warm pressing technique, in which the polymer is first crosslinked to an infusible state, compacted by cold isostatic pressing or warm pressing, and then pyrolyzed at a slow heating rate.23,24 The second method involves pre-pyrolysis of the polymer to a ceramic powder. The powder is subsequently compounded with additional polysilazane, and the composition is cured during a pressing step.25-27
The first approach results in ceramics having a high fraction of open porosity, while the second method results in much less gas generation and volume shrinkage in the resulting ceramic. Porous monolithic ceramic bodies can also be fabricated using organopolysilazanes. Representative of this work is the preparation of high-surface-area catalyst supports made of macroporous SiCN produced by a capillary micromolding technique.28
Organopolysilazanes have also found utility in the joining of ceramics and as the continuous phase in formulated, high-temperature coatings. Coatings and joints from filled organopolysilazanes have been demonstrated for silicon nitride matrix composites,29 for the microwave joining of silicon carbide,30 in seals for solid oxide fuel cells,31 and as electronic adhesives for bonding integrated circuit chips to carriers or circuit boards.32 They have also been used for preform joining in the fabrication of both ceramic matrix composites and metal matrix composites.33
Several coatings companies are currently selling formulated ceramic coatings based on organopolysilazanes for under-the-hood automotive and truck applications (e.g., exhaust systems, pistons, etc.), as well as organopolysilazane-based coatings for firearms and high-temperature applications requiring substantial heat insulating characteristics. Organopolysilazanes have also been used effectively in such applications as anti-oxidation layers on carbon structures,34 carbon-silicon carbide composites,35 carbon- or silicon carbide-fiber,36 and the strength enhancement of carbon foams.37
Recent investigations have also shown that selective pyrolysis of organopolysilazanes in controlled atmospheres or in the presence of various organic polymers can result in ceramics with well-defined nanoscale structural features, including such novel structures as silicon nitride nanobelts.38 Controlled pyrolysis of organopolysilazanes has also resulted in the generation of silicon nitride/silicon carbide nanocomposite structures with ceramic grains in the 30 nm size domain.39
Mesoporous ceramic materials have also been produced based on an approach that uses an organic diblock copolymer structuring agent in combination with an organopolysilazane.40 The resulting ceramic has a lamellar nanostructure consisting of hexagonally packed cylinders with an average pore diameter of about 13 nm.
Organopolysilazanes are also useful for producing either fiber or matrices in the fabrication of ceramic matrix composites. Fibers, for example, can be produced by the melt-spinning and pyrolysis of pure polysilazanes41-43 or through the modification of polysilazanes with, for example, metal alkoxides (such as alkoxides of titanium or zirconium) followed by spinning and a subsequent pyrolysis step.44,45 In the former case, SiCN fibers are produced, while in the latter case, various oxycarbonitride compositions are obtained. Highly corrosion-resistant monolithic ceramics have also been prepared using this technique of metal alkoxide modification by the reaction of organopolysilazanes with aluminum isopropoxide.46,47
CMC matrices can also be generated from polysilazanes. Variations of the polymer infiltration pyrolysis (PIP) technique have been demonstrated over the years.48-50 Resin transfer molding (RTM) techniques into fibrous preforms with suitable organopolysilazane precursors (e.g., low viscosity, solvent-free), followed by subsequent thermally induced crosslinking and pyrolysis at temperatures greater than 1400°C, results in dense CMC materials when an iterative process of reinfiltration and pyrolysis is followed (four to six cycles).48 Organopolysilazanes also find use in the production of metal matrix composites (MMCs), where they can serve as extreme high-temperature binders for performs into which molten silicon or aluminum metals are introduced.33,36
Polysilazanes are the answer for a broad range of challenging applications that cannot be satisfied by conventional materials. These materials enable long-term, cost-effective and "user-friendly" solutions in applications where high temperature stability, corrosion resistance or long term durability are critical factors.
For more information about polysilazane precursors, contact KiON Corp. at firstname.lastname@example.org ; or Clariant Corp. at (49) 6196-757-7869; email@example.com . (215) 957-6100, e-mail firstname.lastname@example.org ; or visit http://www.kioncorp.com .
1. H. Matsuo, M. Kokubo, T. Ohbayashi, Y. Tashiro, T. Suzuki, M. Kizaki, H. Hashimoto, Y. Shimizu, T. Sakurai, H. Aoki, “Method and Composition for Forming Ceramics and Article Coated with the Ceramics,” U.S. Patent 5,747,623 (1998).
2. M. Pauckert, T. Vaahs, and M. Brueck, Adv. Mater., 2  398-404 (1990).
3. K.J. Wynne and R.W. Rice, Ann. Rev. Mater. Sci., 14 297-334 (1984).
4. R.M. Laine, Y.D. Blum, D. Tse, and R. Glaser, Inorganic and Organometallic Polymers, edited by M. Zeldin, K.J. Wynne, and H.R. Allcock,
5. D. Seyferth, G.H. Wiseman, J.M. Schwark, Y.-F. Yu, and C.A. Poutasse, Inorganic and Organometallic Polymers, edited by M. Zeldin, K.J. Wynne, and H.R. Allcock,
6. G. Pouskouleli, Ceramics International, 15 213-229 (1989).
7. W.H. Atwell, Silicon Based Polymer Science: Advances in Chemistry Series, 224, edited by J.M. Zeigler and F.W.G. Fearon, American Chemical Society, Washington, D.C., 593-606 (1990).
8. J. Wan, M.J. Gasch, and A.K. Mukherjee, “Effect of Ammonia Treatment on the Crystallization of Amorphous Silicon-Carbon-Nitrogen Ceramics Derived from Polymer Precursor Pyrolysis,” J. Am. Ceram. Soc., 85  554-64 (2002).
9. J.-H. Lee, J.-H. Cho, J.-S. Choi, D.-J. Lee, “Spin-On Glass Composition and Method of Forming Silicon Oxide Layer in Semiconductor Manufacturing Process using the Same,” U.S. Patent Application US2004/0224537 A1.
10. R. Riedel, “Advanced Ceramics from Inorganic Polymers,” pp. 1-50, Materials Science and Technology, Vol. 17B, edited by R.W. Cahn, P. Hassen, and E.J. Kramer. Wiley-VCH Verlag,
11. G. Thurn and F. Aldinger, “Compression Creep Behavior of Precursor-Derived Ceramics,” pp. 237-45 Precursor-Derived Ceramics, edited by J. Bill, F. Wakai, and F. Aldinger. Wiley-VCH Verlag,
12. R. Riedel, L.M. Ruswisch, L. An, and R. Raj, “Amorphous Silicoboron Carbonitride Ceramic with Very High Viscosity at Temperatures above 1500 oC,” J. Am. Ceram. Soc., 81  3341-44 (1998).
13. B. Baufeld, H. Gu, J. Bill, F. Wakai, and F. Aldinger, “High-Temperature Deformation of Precursor-Derived Amorphous Si-B-C-N Ceramics,” J. Eur. Ceram. Soc., 19, 2797-814 (1999).
14. R. Raj, L. An, S.R. Shah, R. Riedel, C. Fasel, and H.-J. Kleebe, “Oxidation Kinetics of an Amorphous Silicon Carbonitride,” J. Am. Ceram. Soc., 84  1803-10 (2001).
15. S.R. Shah and R. Raj, “Nanoscale Densification Creep in Polymer-Derived Silicon Carbonitrides at 1350oC,” J. Am. Ceram. Soc., 84  2208-12 (2001).
16. P.A. Ramakrishnan, Y.T. Wang, D. Balzar, L. An, C. Haluschka, R. Riedel, and A.M. Hermann, “Silicoboron-Carbonitride Ceramics: A Class of High-Temperature, Dopable Electronic Materials,” Applied Physics Letters, 78  3076-78 (2001).
17. L.-A. Liew, W. Zhang, L. An, S. Shah, R. Luo, Y. Liu, T. Cross, M.L. Dunn, V. Bright, J.W. Daily, and R. Raj, “Ceramic MEMS, New Materials, Innovative Processing and Future Applications,” American Ceramic Society Bulletin, 80 , 25-30 (2001).
18. L.-A. Liew, W. Zhang, V.M. Bright, L. An, M.L. Dunn, and R. Raj, “Fabrication of SiCN Ceramic MEMS Using Injectable Polymer-Precursor Technique,” Sensors and Actuators A, 89 64-70 (2001).
19. L.-A. Liew, T. Cross, V.M. Bright, and R. Raj, “Fabrication of Novel Polysilazane MEMS Structures by Microcasting,” Proceedings of 2001 ASME International Mechanical Engineering Congress and Exposition, November 11-16,
20. L.-A. Liew, Y. Liu, R. Luo, T. Cross, L. An, V.M. Bright, M.L. Dunn, J.W. Daily, and R. Raj, Sensors and Actuators A, 95 120-134 (2002).
21. R.A. Saravanan, L.-A. Liew, V.M. Bright, and R. Raj, “Integration of Ceramics Research with the Development of a Microsystem,” J. Am. Ceram. Soc., 86  1217-19 (2003).
22. G. Feiertag, W. Ehrfeld, H. Freimuth, H. Kolle, H. Lehr, M. Schmidt, M.M. Sigalas, C.M. Soukoulis, G. Kiriakidis, T. Pedersen, J. Kuhl, and W. Koenig, “Fabrication of Photonic Crystals by Deep X-ray Lithography,” Appl. Phys. Lett., 71 , 1441-43 (1997).
23. E. Kroke, Y.-L. Li, C. Konetschny,
24. J. Seitz and J. Bill, “Production of Compact Polysilazane-Derived Si-C-N Ceramics by Plastic Forming,” J. Mater. Sci. Lett., 15, 391-93 (1996).
25. J. Wan, M.J. Gasch, and A.K. Mukherjee, “Silicon Carbonitride Ceramics Produced by Pyrolysis of Polymer Ceramic Precursor,” J. Mater. Res, 15  1657-60 (2000).
26. J. Wan, M.J. Gasch, and A.K. Mukherjee, “Silicon Nitride/Silicon Carbide Nanocomposites Derived from Polymer Precursor Pyrolysis,” 276-9, Proceedings of International Conference on Engineering and Technological Sciences 2000 (Beijing, China, 2000), edited by J. Song and R. Yin, New World Press, Beijing, China, 2000.
27. H.-J. Kleebe, D. Suttor, H. Mueller, and G. Ziegler, “Decomposition-Crystallization of Polymer-Derived Si-C-N Ceramics,” J. Am. Ceram. Soc., 81  2971-77 (1998).
28. I.-K. Sung, M.M. Christian, D.-P. Kim, and P.J.A. Kenis, “Tailored Macroporous SiCN and SiC Structures for High-Temperature Fuel Reforming,” Adv. Funct. Mater., 15, 1336-42 (2005).
29. M. Stackpoole and R. Bordia, “Processing and Properties of Si3N4 Matrix Composites, Coatings and Joints from Filled Pre-Ceramic Polymer Systems,” Environmental Barrier Coatings Workshop,
30. P. Colombo, R. Silberglitt, and G.A. Danko, “Microwave Joining of SiC,” Advanced Industrial Materials Annual Review Meeting, Jackson Hole, Wyo.,
32. C.R. Bearinger, R.C. Camilletti, G. Chandra, T.E. Gentle, L.A. Haluska, U.S. Patent 5,904,791 (1999).
33. M.K. Aghajanian, J.W. Hinton, A. Lukacs
34. A. Kojima, S. Hoshii, and T. Muto, “Characteristics of Polysilazane Compound and its Application as Coating for Carbon Material,” J. Mat. Sci. Letters, 21, 757-60 (2002).
35. J. Bill and D. Heimann, “Polymer-Derived Ceramic Coatings on C/C-SiC Composites,” J. Eur. Cer. Soc, 16, 1115-20 (1996).
36. D.J. Landini and R.L.K. Matsumoto, “Method for Processing Silicon Carbide Preforms Having a High Temperature Boron Nitride Coating,”
37. C. Duston,
38. W. Yang, L. Zhang, H. Ji, L. An, et al., “Si3N4 Nanobelts Grown by Pyrolysis of Polyureasilazane with Iron Catalyst,” J. Am. Ceram. Soc., 466 (2005).
39. J. Wan, M.J. Gasch, and A.K. Mukherjee, “Consolidation and Crystallization of Si3N4/SiC Nanocomposites from a Poly(urea-silazane) Ceramic Precursor,” J. Mater. Res., 16 , 3274-86 (2001).
40. M. Kamperman, C.B.W. Garcia, P. Du, H. Ow, and U. Wiesner, “Ordered Mesoporous Ceramics Stable up to 1500oC from Diblock Copolymer Mesophases,” J. Am. Chem. Soc., 126, 14708-9 (2004).
41. W. Verbeek, “Production of Shaped Articles of Homogeneous Mixtures of Silicon Carbide and Nitride,”
42. G. Winter, W. Verbeek, and M. Mansmann, “Production of Shaped Articles of Silicon Carbide and Silicon Nitride,”
43. B.G. Penn, J.G. Daniels, F.E. Ledbetter IIII, and J.M. Clemons, “Preparation of Silicon Carbide-Silicon Nitride Fibers by the Pyrolysis of Polycarbosilazane Precursors: A Review,” Polymer Engineering and Science, 26 , 1191-94 (1986).
44. A. Saha, S.R. Shah, and R. Raj, “Amorphous Silicon Carbonitirde Fibers Drawn from Alkoxide Modified Ceraset™,” J. Am. Ceram. Soc., 86 , 1443-45 (2003).
45. A. Saha, S.R. Shah, and R. Raj, “Oxidation Behavior of SiCN-ZrO2 Fiber Prepared from Alkoxide-Modified Silazane,” J. Am. Ceram. Soc., 87 , 1556-58 (2004).
46. A. Dhamme, W. Xu, B.G. Fookes, Y. Fan, L. Zhang, S. Burton, J. Hu, J. Ford, and L. An, “Polymer-Ceramic Conversion of Liquid Polyaluminasilazanes for SiAlCN Ceramics,” J. Am. Ceram. Soc., 88 , 2415-19 (2005).
47. Y. Wang, W. Fei, and L. An, “Oxidation/Corrosion of Polymer-Derived SiAlCN Ceramics in Water Vapor,” J. Am. Ceram. Soc., 89 , 1079-82 (2006).
48. D.V. Miller, D.L. Pommell, and G.H. Schiroky, “Fabrication and Properties of SiC/SiC Composites Derived from Ceraset™ SN Preceramic Polymer,” Proceedings of the 21st Annual Conference on Composites, Advances Ceramics, Materials, and Structures, Cocoa Beach, FL (1997), published in Ceramic Engineering & Science Proceedings 18 (1997).
49. Z.S. Rak, “A Process for Cf/SiC Composites Using Liquid Polymer Infiltration, J. Am. Ceram. Soc., 84 , 2235-39 (2001).
50. Z.S. Rak, “Novel