Nickel oxide single crystal

The diffusion of sulfur in nickel oxide single crystals was investigated at 1000 to 1250C. The measured data were found to deviate markedly from the erfc dependence for diffusion from a constant source. The diffusivities for the faster mode were given by ... 

The importance of the latter mechanism has been illustrated in experiments where hydrogen annealing of nickel-base single crystals - and Fe-Cr-Al alloys lowered the sulphur contents to very low levels and resulted in dramatic improvements in the adherence of alumina films to the alloys. This is illustrated in Figure 5.39 where the cycUc oxidation behaviour of the Fe-Cr-Al (low S) alloy, which is the same alloy as Fe-Cr-Al (normal S) that has been desulphurized by hydrogen annealing, is comparable to that of the Y-doped alloys. 

Figure 10.16 Optical micrograph showing the cross-section of a Pt-modified aluminide coating on a nickel-base single-crystal superalloy after oxidation at 1200 °C for 20 h. The original grain structure of the /3-phase is evident and y has begun to nucleate at /6 grain boundaries as a consequence of A1 depletion.

Figure 25.15b Data from Blank, S.L. and Pask, J.A. (1969) Diffusion of iron and nickel in magnesium oxide single crystals, J. Am. Ceram. Soc. 52, 669.

Magnesium Oxide-Ferric Oxide System. In these experiments either magnesium oxide single-crystal spheres of 1 mm diameter were sintered to polycrystalline ferric oxide plates or ferric oxide polycrystalline spheres were sintered to single-crystal blocks of magnesium, oxide. In general the results were similar to those obtained in the nickel oxide-ferric oxide system. 

Different nickel deposits show a great variety of contact resistance values. This is particularly so after the deposits have been exposed to the atmosphere for an extended period of time. The differences between these values may be best explained in terms of variations in plated texture. Nickel electrodeposits with polycrystalline nature have been observed to behave as single crystals ( ) when their grains were oriented such that the (100) plane was parallel to the surface. Not surprisingly, the oxidation rate in (lOO)-oriented single crystals is self-limiting at ambient temperature. 

Ten years ago one would have predicted that Raman spectroscopy could never be used to study monolayer adsorption on metals because either (a) the sensitivity of the technique would be too low to permit detection of signals using a single reflection from a smooth metal surface, or (b) oxide supported metal surfaces are black if the metal loading is high and therefore the laser light would be absorbed. Both of the above objections have been shown to be faulty insofar as the technique has now been used to study absorption on silica-supported nickel (51, 52,53) and on single crystal nickel (54). Moreover in the special case of silver,... 

The samples prepared have a good surface area after calcination at 500°C, as can be seen in table 1. Alumina-titania mixed oxide supported samples have surface areas larger than those of the alumina and titania single oxides. As expected x-ray diffraction results show that the mixed oxide catalysts are amorphous, but alumina shows a y phase structure, and Ti02 is a well crystallized anatase phase. No nickel metal or nickel oxide was detected in any of the samples, including Ti02 sample, suggesting the metal was well dispersed, and present as small crystallites (< 50A). 

Otter (18) also obtained striking interference color patterns showing variation of rate of oxidation with face, when single crystal spheres of nickel were heated in oxygen at a pressure of 1 atmosphere and a temperature of 800°C for periods up to 15 minutes. The relative order of the rates of oxidation on the different faces and the smoothness of the starting surface were not given or discussed. 

Fio. 8. Diffraction beam intensities as a function of oxygen exposure obtained after a small anneal of the crystal subsequent to ion-bombardment cleaning. Curve 1 Typical beam, in the (110) azimuth at about 28 volts, from the clean nickel lattice. Multiply the ordinate scale by 2 to obtain intensity. Curve 2 Typical beam, in the (001) azimuth at about 58 volts, from the clean nickel lattice. Multiply the ordinate scale hy 6. Curve 3 Typical beam, in the (110) azimuth at about 17 volts, from a double-spaced, face-centered lattice. Curve 4 Typical beam, in the (001) azimuth at about 27 volts, from a single-spaced, simple-square lattice. Multiply the ordinate scale by 2. Curve 5 Typical beam, in the (110) azimuth at about 22 volts, from a nickel oxide lattice. [From Farnsworth and Madden (27).]... 

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