Carbonitrides, hydrogenation

Titanium Carbonitride. Titanium carbonitride (TiCJSfi.x) combines the wear properties of TiC with the low friction and oxidation and chemical resistance of TiN. It is obtained in a hydrogen atmosphere and at a temperature of approximately 1000°C by the following simplified reaction ... 

Hall, Dieter, Hofer, and Anderson (19) also studied the carburization of e-nitrides with hydrogen-carbon monoxide mixtures and the reduction of e-nitride and e-carbonitride with pure hydrogen. The rate of removal of nitrogen increased with the fraction of hydrogen in the gas as shown in Table II. For hydrogen-carbon monoxide mixtures containing less... 

The reduction of nitrides of iron in pure hydrogen was very rapid, and at 200°C. nitrogen was virtually completely removed from fused iron catalysts in three hours. The hydrogenation of carbonitrides was considerably slower than that of nitrides, and the rate varied inversely with the carbon content of the carbonitride (Table III and reference 19). In... 

Reaction of e-Carbonitrides with Pure Hydrogen (FezO t-MgO-KiO Catalyst)... 

In considering the effect of the electronic structure of catalysts on activity, Dowden (33) suggested that carbides, and similarly nitrides and carbonitrides, should be less active for synthesis than the corresponding metal since the interstitial atoms may contribute electrons to the unfilled d-shells of the metal, which are believed to be essential for the catalytic activity of transition metals in hydrogenation reactions. This hypothesis is supported by the low activity of cobalt carbide compared with that of reduced cobalt (28,29). For iron catalysts the hypothesis... 

The synthesizing of this catalyst consists of three process steps which are construction of carbon nanotubes (CNTs) on carbon fibers support, coating of polymer-derived silicon carbonitride (SiCN) on CNTs and finally decoration of transition metal on surface. The rate of hydrogen generation has been reported as 75 L mim g" [100]. 

In the present work, essentially all carbon species were removed leaving pure silicon nitride. When the deposition was conducted in hydrogen, however, Si-C bonds in the precursor were only partially ruptured, with the concomitant formation of silicon carbonitride (Fig. 6a). Since the Si-to—C ratio in methylsilazane is unity, the low carbon composition of the films, about 9%, estimated from the peak to peak height, indicates that reactive hydrogen also promotes thermal decomposition of carbon—related bonds in the precursor. The atomic composition of each elements remained uniform throughout the film thickness. The relative atomic composition does not appear to be dependent on the deposition temperatures as shown in Fig. 7. 

The chemical structure of the films and particularly the incorporation of hydrogen were studies by FTIR (Perkin Elmer 1760). Fig. 8 shows infrared transmittance spectra of silicon carbonitride films (a) and silicon nitride films (b) deposited at 1123 K. The clusters of absorption peaks that appear in both spectra in the 1300 to 1940 and 3320 to 3900 wavenumber (cm i) regions are attributed to atmospheric moisture. CO2 is also detected at around 2345 cm i. For spectrum (b), the strong band at 847 cm-i indicates the formation of amorphous silicon nitride [161. The much weaker peak at 3326 cm i which is due to a N—H stretching vibration indicates the existence of N—H bonds in the films. The Si—N band at 847 cm i appeared to be broadened near its base line around 1173 cm i. This is due to the existence of N-H bonds which exhibit another bending mode at 1170 cm l All the films displayed similar spectra, and there was no indication of an Si—H bond in silicon nitride. In addition to the stro line at 837 cm, resulting from the fundamental stretching of silicon carbonitride [17], the main difference between spectra (a) arid (b) is the presence of a weak Si—H band, which is observed to be more intense in the films deposited below 1123 K. None of the films exUbited the C—H band around 2900 cm i, which is present in the IR spectrum of the precursor. 

The refractive index of silicon nitride and silicon carbonitride thin films deposited at various temperatures is shown in Fig. 9. The re active index of silicon nitride has been well characterized and is generally reported to be between 1.8 and 2.1 [18]. The scatter in the reported values is largely attributed to variations in film stoichiometry and methods of deposition. The presence of impurities such as hydrogen, oxygen and firee silicon in particular, may also account for some of the r orted divergences. The measured refractive index of silicon nitride increased with deposition temperature from 1.82 to 1.95. Minor fluctuations in the atomic ratio of Si—to—N, that can be seen from the AES analysis (Kg. 7) may be responsible for the observed dependence of the refractive index on the deposition temperature. The refractive index for silicon carbonitride similarly ranged from 1.68 to 1.94. 

---