Materials science, an interdisciplinary field of R & D, certainly benefits from the cooperation of engineers, chemists andphysicists. An example is in the synthesis and applications development of organometallic polymers. Their structures are being optimized through employing different monomers, polymer blending, and post-treatments to render them suitable as precursors for non-oxide advanced ceramics like S i c , Si,N,, AlN, BN or TiN. Pyrolysis transforms these polymers into the ceramic state. Since these inorganic polymers have unique processing advantages (solubility and fusibility) over classical ceramic powder or metallurgical processing, a vast array of novel applications, e.g., ceramic coatings, binders, impregnations or spun fibers are possible. -[*] Dr. M. Peuckert, Dr. T. Vadhs, M. Briick, Materialforschung, Hoechst AG Postfxh 80 03 20, D-6230 Frankfurt am Main 80 (FRG) [**I The authors wish to thank b: Aldinger, P. I.ble.v, H.-L Kkiner, K. Kiihlein and G. Siegemund for many interesting discussions and continuous support ofthe work. For the NMR measurements we owe thanks to H. K/uge.Silicon Carbide Pol ysilazanes Processing ( 0 VCH Verluggr~sells~hufi mhH, D-6940 Weinheim, 1990 0935-964H~90j0909-0398 $3.50 t .25/0 Adv. M a w . 2 (1990) No. 9
The pyrolysis of organoelemental polymerss provides a powerful route to high‐ppurity, high‐performance ceramics. The various factors influencing the production of low‐oxygen‐content ceramic fibers from polymeric silazanes are examined and the possibility of controlling the composition of the fibers by varying the pyrolysis atmosphere resulting in stable, amorphous phases is described. The fibers have great potential in the reinforcement of metal and ceramic matrix composites.
Complex ceramic miniaturized structures that have much smaller dimensions and better precision than that which has been reported previously were prepared by a combination of X‐ray synchrotron lithography, casting, and pyrolysis processes. Poly(methyl methacrylate) and poly(tetrafluorethylene) miniaturized structures were prepared with high precision via a combination of X‐ray synchrotron lithography, electroplating, and molding (the German Lithographie, Galvanoformung, and Abformung (LIGA) process). Casting of a solution of a preceramic polymer, poly(vinylsilazane), in these miniaturized structures was performed for the first time, similar to the slurry‐casting technique of macroscopic bodies. Subsequent pyrolysis led to nearly perfect, complementary bodies of the original structures because of the high smoothness of the pyrolyzed ceramics. This was demonstrated by the complex spool and meander‐like miniaturized structures with internal dimensions <2 μm and an aspect ratio as high as 5. To evaluate optimal process parameters for the preparation of these complex ceramic miniaturized structures, the pyrolysis process of poly(vinylsilazane) was investigated using Fourier transform infrared spectrometry, X‐ray diffractometry, atomic force microscopy, and scanning electron microscopy. The first step of pyrolysis involved dehydrocoupling of –CH and –NH groups and nucleophilic substitution of the Si–CxHy groups, which led to the elimination of the CxHy substituents and the formation of an amorphous silicon carbonitride (Si:C:N) at 800°C. The residual hydrogen content, which was chemically bonded as Si‐H, decreased as temperatures decreased from 800° to 1400°C. Heating to 1500°C converted the amorphous structure to a semicrystalline phase‐separated ceramic composed of α‐Si3N4 crystals embedded in a carbon‐silicon amorphous matrix. The amorphous phase could be partially etched with a KOH solution. Because of the absence of grains, the amorphous material revealed a much smoother surface than that of the crystalline material or that possible by conventional slurry processes.
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