Silicon oxynitride preparation

Silicon-containing ceramics include the oxide materials, silica and the silicates the binary compounds of silicon with non-metals, principally silicon carbide and silicon nitride silicon oxynitride and the sialons main group and transition metal silicides, and, finally, elemental silicon itself. There is a vigorous research activity throughout the world on the preparation of all of these classes of solid silicon compounds by the newer preparative techniques. In this report, we will focus on silicon carbide and silicon nitride. 

This model goes a long way towards explaining most experimental results reported in the literature for ISFETs with oxide or nitride surfaces. Unfortunately, the properties of these materials prepared in different laboratories are very different. It is known that silicon nitride (really silicon oxynitride SisNztOx) forms an oxygen-rich layer at the surface, whose thickness depends on the deposition conditions. This passivation layer forms rapidly (in a matter of hours) and is very stable, even under continuous exposure to aqueous electrolyte. The hydration of this layer seems to fit the requirements and predicted behavior of the Sandifer model. Consequently, ISFETs that have been exposed to aqueous solution for more than one hour show no adsorption effects which would be expected from the SBT model. 

The hydration layer model more or less fits the behavior of all oxides and of silicon oxynitride. The latter has a great advantage over other pH-sensitive layers because it is an excellent passivation material itself that can be prepared virtually pinhole-free. On the other hand, even thermally grown Si02 has pinholes and cracks that form a leakage path. It is that leakage path that apparently served as a... 

Okamura and co-workers (18) have taken air-cured PCS polymer and, through pyrolysis in the presence of ammonia, prepared essentially carbon-free silicon oxynitride fibers (equation 13). However, if the PCS polymer fiber is cured by electron beam radiation (to prevent oxygen addition), the same ammonia pyrolysis conditions provide nearly stoichiometric quantities of silicon nitride fibers (equation 14). 

Silicon nitride has also been prepared from SiCl4/NH4 [159], SiBr4/NH3 [160], and, more recently, Si2CVNH3 [161]. Silicon oxynitride (SiON) is readily prepared by use of any of the precursors used for silicon nitride with the addition of either N2O or NO as an oxygen source [162, 163, 164]. The composition and properties of the SiO N films may be varied linearly from Si02-like to Si3N4-like by the variation of the reactant flow rates. 

SiC fibers were produced using polycarbosilanes by Yajima et al. in 1975 [1,2]. Besides SiC fibers, Si-Ti-C-O fibers prepared from a polytitanocarbosi-lane have been obtained by adding a titanium tetrabutoxide to polycarbosilane or polysilane [3]. SiC fibers (Nicalon) and Si-Ti-C-O fibers (Tyranno) are manufactured on an industrial scale. Colorless silicon oxynitride fibers and silicon nitride fibers [4] have been obtained by the nitridation of polycarbosilanes in the author s laboratory. Polymers used for ceramic precursor and the resulting ceramic fibers are listed in Table 1. 

NOVEL INORGANIC MATERIALS AND HETEROGENEOUS CATALYSIS PREPARATION AND PROPERTIES OF HIGH SURFACE AREA SILICON CARBIDE AND SILICON OXYNITRIDES... 

The present paper discusses the preparation and properties of high surface area silicon carbide and oxynitride with respect to possible application in catalysis. The synthetic work includes new routes to high surface area forms of these materials. Regarding properties, an important aspect is stability. This refers both to the stability of a pore system in a non-oxide material, on which there is very little information available, and to the stability of the surface composition in the case of the latter, oxidation to the oxide will be thermodynamically preferred in most cases. We report data on the textural stability of porous silicon carbide and on the surface stability of high surface area silicon oxynitrides. Some of the work reported in the present paper has been described at recent conferences (7,8) and in a communication (9). 

Silicon nitride is receiving considerable attention as a structural ceramic, which requires a fully dense material, but it is also of interest to consider whether it could be prepared in high surface area forms. Our work in this direction has led to a synthesis of a high surface area silicon oxynitride. We summarise here the synthetic work and then report data on the stability of the surface. 

Sakka S., Kamiya K. The sol-gel transition in the hydrolysis of metal alkoxides in relation to the formation of glass fibers and films. J. Non-Ciyst. Solids 1982 48 31 16 Sakka S., Kamiya K., Makita K., Yamamoto Y. Formation of sheets and coating films from alkoxide solutions. J. Non-Cryst. Solids 1984 63 223-235 Sakka S., Yoko T., Fibers from gels. J. Non-Cryst. Solids 1992 147/148 394-403 Scholtz H., Sporn A., Ullrich A., Schoenecker A., Martin W. Fabrication and properties of sol-gel-derived PZT-fibers for 1-3 composites. Ceram. Trans. 1995 51 751-755 Sekine M., Katayama S., Mitomo M. Preparation of silicon oxynitride glass fibers by ammonolysis of silica gels. J. Non-Cryst. Solids 1991 134 199-207 Sowman H.G. Alumina-boria-silica ceramic fibers from the sol-gel process. In Sol-Gel Technology for Thin Films, Fibers, Preforms, Electronics, and Specialty Shapes, L.C. Klein, ed. Noyes Publication, 1988... 

Preparation of Red-Emitting Eu NDoped Barium Calcium Silicon Oxynitride by Solid-State Reaction and its Luminescence Properties... 

Poly(carbosilane) fibres have been employed recently as precursors to silicon nitride and silicon oxynitride fibres. The preparation of silicon nitride fibres involves a two-stage process. The precursor fibres are first crosslinked by electron irradiation then heated in ammonia at temperatures up to 1400 °C. Electron irradiation is used to effect the crosslinking reaction without incorporation of oxygen. The nitridation reaction takes place between 500 and 800 °C. At a pyrolysis temperature of 1400 °C, essentially all the carbon in the precursor is lost, giving a composition close to that of pure silicon nitride. At this temperature, however, the fibre was extensively crystallized and the tensile strength was very low. The tensile strength of the fibre was shown to reach a maximum level of about 1.4 GPa at a nitridation temperature of 1300°C. 

Belot V., Corriu R., Leclercq D., Mutin P.H., Vioux A. Preparation of oxynitride silicon glasses. Nitridation of functional silica xerogels. J. Non-Crystalline Solids 1992 147/148 309-312... 

Mutin PH. Control of the composition and structure of silicon oxycarbide and oxynitride glasses derived from polysUoxane precursors. J. Sol-Gel Sci. Technol. 1999 14 27-38 Nomura K., Takasuka Y., Kamiya K., Nasu H. Preparation ofNbN fibres by nitridation of sol-gel derived Nb20s fibres. J. Mater. Sci., Electronics 1994 5 53-58... 

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