Nickel oxide with gallium

Fig. 25. Differential heats of adsorption of carbon monoxide at 30°C on fresh (A) or oxygenated (B) samples of a gallium-doped nickel oxide. Reprinted from (63) with permission J. Chim. Phys.

Thermochemical Cycles Testing the Formation of Gaseous (Cycle 1) or Adsorbed (Cycle 2) Carbon Dioxide by the Interaction of Carbon Monoxide with Oxygen Preadsorbed on Gallium-Doped Nickel Oxide ... 

Fig. 26. Differential heats of interaction of carbon monoxide at 30°C with a sample of gallium-doped nickel oxide, containing a limited amount (0.4 cm3 02 gm l) of preadsorbed oxygen.

Gallium-doped nickel oxide contains more metallic nickel than pure or lithiated nickel oxides (Table X). Concentrations of metal deduced from magnetic susceptibility measurements (23) are, moreover, in agreement with the results of chemical analyses (30). The following mechanism of incorporation explains these results (80) ... 

The calorimetric study of interactions on the surface of gallium-doped nickel oxide therefore yields results which are similar to those obtained on pure Ni0(250°), although the incorporation of trivalent ions changes somewhat the surface affinity toward oxygen. In both cases, two reaction mechanisms for the production of gaseous carbon dioxide are probable. In mechanism II, a reaction intermediate, C03-(ads) is formed whereas, in mechanism I, gaseous carbon dioxide is produced directly by the interaction of carbon monoxide with adsorbed... 

Figure 13.19 The conversion of insulating oxides into semiconductors, (a) (i) Nickel oxide (NiO) doped with hthium oxide (Li20), making it a p-t)fpe semiconductor, and (ii) the energy-band structure of Li+-doped NiO. (b) (i) Zinc oxide (ZnO) doped with gallium oxide (Ga203), making it an n-type semiconductor, and (ii) the energy-band struemre of Ga -doped ZnO...

Because of the potential importance for industrial-scale catalysis, we decided to check (i) whether an influence of a semiconductor support on a metal catalyst was present also if the metal is not spread as a thin layer on the semiconductor surface but rather exists in form of small particles mixed intimately with a powder of the semiconductor, and (ii) whether a doping effect was present even then. To this end the nitrates of nickel, zinc (zinc oxide is a well-characterized n-type semiconductor) and of the doping element gallium (for increased n-type doping) or lithium (for decreased n-type character) were dissolved in water, mixed, heated to dryness, and decomposed at 250°-300°C. The oxide mixtures were then pelleted and sintered 4 hr at 800° in order to establish the disorder equilibrium of the doped zinc oxide. The ratio Ni/ZnO was 1 8 and the eventual doping amounted to 0.2 at % (75). 

Students construct an electrochemical cell with a nickel wire cathode and a copper plate as the anode. One side of an aluminum oxide filter with 20 nm diameter channels is exposed to a nickel plating solution when attached to the copper electrode. Gallium-indium eutectic paint is applied to the other side of the filter in order to maintain electrical contact with the electrode. Students connect the electrodes to a 1.5 V battery for approximately 30 minutes as the nickel cations are reduced to nickel metal within the filter pores. Nickel nanowires grow at a rate of approximately 1 micrometer per minute. 

While the spatial resolution of AES, XPS and SIMS continues to improve, atomic scale analysis can only be obtained by transmission electron microscopy (TEM), combined with energy dispersive X-ray spectroscopy (EDX) or electron energy loss spectroscopy (EELS). EDX detects X-rays characteristic of the elements present and EELS probes electrons which lose energy due to their interaction with the specimen. The energy losses are characteristic of both the elements present and their chemistry. Reflection high-energy electron diffraction (RHEED) provides information on surface slmcture and crystallinity. Further details of the principles of AES, XPS, SIMS and other techniques can be found in a recent publication [1]. This chapter includes the use of AES, XPS, SIMS, RHEED and TEM to study the composition of oxides on nickel, chromia and alumina formers, silicon, gallium arsenide, indium phosphide and indium aluminum phosphide. Details of the instrumentation can be found in previous reviews [2-4]. 

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