Silicon Nitride Derived from an Organometallic Polymeric Precursor: Preparation and Characterization

Abstract

Partially crystalline Si3N4, with nanosized crystals and a specific surface area greater than 200 m2/g, is obtained by pyrolysis of a commercially available vinylic polysilane in a stream of anhydrous NH3 to 1000°C. This polymer does not contain N initially. Crystallization to high-purity wSi3N4 proceeds with additional heating above 1400°C under Nz. The changes in crystallinity, powder morphology, infrared spectra, and elemental compositions, for samples annealed from 1000" to 1600°C under N,, are consistent with an amorpbous-to-crystalline transformation. Although macroscopic consolidation and local densification occur at 1400"C, volatilization and accompanying weight loss limit bulk densification. The effect of temperature on specific surface area is examined and related to the sintering process. These results are applicable to pyrolysis, decomposition, and crystallization studies of ceramics synthesized by polymeric precursor routes. [Key words: silicon nitride, precursor, polymer, pyrolysis, surface area.]

Evolution of structural features and mechanical properties during the conversion of poly[(methylamino)borazine] fibers into boron nitride fibers

“…Although the ability of specific polymers to be converted into covalently bonded ceramics (polymerderived ceramics, PDCs) is known for a long time [1], much attention has been focused recently on the preceramic polymer route for the production of shapecontrolled ceramics [2][3][4][5][6]. One significant advantage of this method is that ceramic fibers with fine diameters can be elaborated from tractable polymers after spinning and pyrolysis steps [4,7].…”

Aluminum-27 and Silicon-29 Solid-State Nuclear Magnetic Resonance Study of Silicon Carbide/Aluminum Nitride Systems: Effect of Silicon/Aluminum Ratio and Pyrolysis Temperature

“…The use of polymer precursors provides the potential for more control of composition, decreased impurity levels, and the ability to shape or mold the final ceramic, as well as a reduction in manufacturing costs . SiC and Si 3 N 4 have been prepared from polysilanes, polycarbosilanes, and polysilazanes, as well as other precursors. − SiC/AlN solid solutions have been prepared by copyrolysis of two separate precursors. Czekaj et al pyrolyzed dialkyl aluminum amide compounds with either polycarbosilane or vinylic polysilane.…”

Pyrolytic Conversion of Spherical Organo‐silica Powder to Silicon Nitride under Nitrogen

“…30 In this work, it can be said that the spherical powder that formed after the initial weight loss, which consisted of a mixture of fine free carbon and silica particulates, was so porous that the powder could accept nitrogen gas into an internal portion of the powder to produce Si 3 N 4 via carbothermal reduction and nitridation. In the previous studies on the pyrolytic conversion on nitrogen-free polymers 18,19 (polycarbosilane and polysilane) to Si 3 N 4 , ammonia was used as an external nitrogen source because ammonia has been known to be an active reaction source. In those cases, amorphous Si 3 N 4 was formed at low temperatures (1000°C 19 or 1200°C 18 ) under an ammonia atmosphere, followed by the formation of crystalline Si 3 N 4 at higher temperatures (1400°C 19 or 1500°C 18 ) through an amorphous-to-crystalline transformation under an ammonia or nitrogen atmosphere.…”

“…Recently, conversion of a polysilazane precursor to carbon-free Si 3 N 4 has been reported by Arai et al 16 and Schwab et al 17 On the other hand, several researchers have synthesized nitrogen ceramics, including Si 3 N 4 via the pyrolysis of nitrogen-free preceramic polymers with the use of ammonia as an external nitrogen source. Burns et al 18 and Schmidt et al 19 obtained amorphous or partially crystalline Si 3 N 4 via the pyrolysis of polycarbosilanes and polysilanes under an ammonia atmosphere at temperatures of <1000°C. Crystalline Si 3 N 4 was produced by additional heating above a temperature of 1400°C.…”