Nitrides surface composition

Composition Nitridation temperature (K) Nitridation Surface area time (h) (m2.g-l) Total N (wt.%) Surface N (wt.%)... 

When controlled nitridation of surface layers is required, as for example in the modification of the chemical properties of the surface of a support, the atomic layer deposition (ALD) technique can be applied." This technique is based upon repeated separate saturating reactions of at least two different reactants with the surface, which leads to the controlled build-up of thin films via reaction of the second component with the chemisorbed residues of the first reactant. Aluminium nitride surfaces have been prepared on both alumina and silica supports by this method wherein reaction cycles of trimethylaluminium and ammonia have been performed with the respective supports, retaining their high surface areas." This method has been applied to the modification of the support composition for chromium catalysts supported on alumina." ... 

For quenching experiments, which were necessary to freeze-in the equilibrium states between the phase bands, the samples were reheated in a vacuum furnace under 500 mbar N2 to the original annealing temperature and dropped onto a copper plate kept below 470 K (200°C). With this treatment the Group 5 transition metal nitrides underwent a slight change in surface composition because it was impossible to adjust the appropriate nitrogen pressures. This, however, did not influence the compositions at the interface boundaries inside the diffusion couples. 

In the case of TiC, further work on substrates with well characterised bulk and surface compositions is needed to elucidate the diverging results of the literature. Whatever the explanation, it has to be recognized that the wettability of TiC and TiN, and probably of other stable and oxidizable carbides and nitrides such as ZrC, ZrN, HfC and HfN, is very sensitive to the furnace atmosphere. 

Surface area and surface compositions of the nitrided 12.5% M0O3/AI2O3 catalyst at reaction temperature of 573 K... 

Characterize nitride layer microstructure and composition by x-ray diffraction, electron probe microanalysis, scanning electron microscopy, and transmission electron microscopy. Use this information in a feedback loop to modify alloy chemistry and nitridation processing conditions to optimize the protectiveness of the nitride surface layer. 

In the case of glass, however, no great variations in behaviour between different types are expected because of their very similar structure and surface composition. Chemical vapour deposition reactions had already been tried by the last century, for instance in the refinement and deposition of silicon by reduction of SiF4 and SiCU with alkali metals [71] and in the refining of Ni using Ni-carbonyl in the Mond process [72,73]. The major impact of chemical vapour deposition on thin-film technology took place, starting some 60 years ago, when refractory compounds such as metal carbides, nitrides, silicides, borides and oxides as well as mixed phases of... 

Fig. 4.17. The process flow used in [79]. The hrst three layers are deposited using conventional blanket deposition techniques and are patterned using the digital lithography process shown in Fig. 4.16. The metal layers are thermally evaporated and the nitride/oxide composite layer is deposited using PECVD. After treatment of the stack with octadecyltrichlorosilane to passivate the surface the semiconductor is deposited additively using a jet printer from solution and dried.

Surface composition, including oxygen and oxynitride concentration, is important information required for nonoxide powder processing. In a recent study, several commercial silicon nitride powders were analyzed for total oxygen at high temperatures, and the surface oxygen was measured by AES. The bulk oxygen was then calculated based on these data [52]. Commercial SiC... 

The surface composition can differ from the bulk after heat treatment processes such as decarburization, nitriding, surface oxidation with diffusion of dissolved oxygen into the metal (often observed in titanium alloys), or depletion of an alloying element at the surface, can give the surface very different properties to the bulk material. In such cases it must be decided whether the properties of the modified surface or the bulk material are of interest. 

This chapter will describe the processing and properties of an oxide fiber reinforced ceramic matrix composite with a silicon oxycarbide matrix based on a PDC technology, introduced by AlliedSignal (now Honeywell International) under the trademark of Blackglas ceramic. The oxide fiber in this CMC system is the Nextel 312 fiber (3M, Inc.) that has been treated to form a boron nitride surface coating. The information that follows was primarily developed from Low Cost Ceramic Matrix Composites (LC ) program funded by DARPA from 1991-1997. 

Dandu et al. (2011) found for different pH values between 2.0 and 9.5 in the filtrates of ceria slurries a direct correlation of UVA is absorbance in the spectral region of the Ce ions at 300 nm and the nitride CMP RRs. Furthermore, they deduced from a peak shift to 320 nm — which is suggested to be characteristic for Ce " /SiOjc composites (Dandu et al., 2010c) or Ce ions (Tolstobrov et al., 2000), respectively — the evidence of Ce—Si formed by interaction of Ce " " ions in the supernatant and the native suboxide at the Si nitride surface (Dandu et al., 2011). 

AES is the other method used extensively in the studies of carbide and nitride surfaces. AES results available now are mainly concerned with the study of shape of the spectra of specific phases, depending on their synthesis conditions, composition, structure, stoichiometry, in order to find the relationships between AES and the character of the interatomic interactions in the near-surface layers. 

Reaction spraying is also being widely explored. In this case new compositions or particle surface reactions providing enhanced coating properties, eg, nitrides for wear resistance, are achieved while the particle is in transit. 

This reaction is catalyzed by iron, and extensive research, including surface science experiments, has led to an understanding of many of the details (72). The adsorption of H2 on iron is fast, and the adsorption of N2 is slow and characterized by a substantial activation energy. N2 and H2 are both dis so datively adsorbed. Adsorption of N2 leads to reconstmction of the iron surface and formation of stmctures called iron nitrides that have depths of several atomic layers with compositions of approximately Fe N. There is a bulk compound Fe N, but it is thermodynamically unstable when the surface stmcture is stable. Adsorbed species such as the intermediates NH and NH2 have been identified spectroscopically. 

Composition, nitridation temperature and time, surface area and nitrogen content of the "AlPONs"... 

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