Oxygen gallium-doped

Preadsorption of oxygen at 30°C on the surface of a gallium-doped nickel oxide produces, for instance, a considerable increase of the differ-... 

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.

Chemisorption of carbon dioxide on doped oxides prepared at 250° was also studied calorimetrically. Initial heats of adsorption on NiO(10 Li)(250°) (27 kcal/mole) and on Ni0(10 Ga)(250°) (28 kcal/mole) are similar. The gallium-doped oxide chemisorbs at room temperature the same quantity of carbon dioxide (9.3 cm /gm) as NiO(250°) (9.7 cm3/gm), whereas the quantity of gas adsorbed on Ni0(10 Li)(250°) is larger (13.0 cm /gm). Lithia chemisorbs carbon dioxide at room temperature. However, the difference between the quantities of gas adsorbed on pure and lithiated oxides is not explained by the presence of lithia, as a separate phase, in the doped sample. It seems, therefore, that carbon dioxide, as oxygen, is chemisorbed at room temperature on anionic vacancies whose concentration is particularly large on lithiated oxides. 

Adsorption of carbon monoxide on a gallium-doped sample [NiO(10 Ga)(250°)] precovered by oxygen decreases the electrical conductivity of the solid, whose color changes from black to green. Carbon dioxide is therefore formed. It appears from cycles 1 and 2 (Table XIII) that the interaction product remains adsorbed on the most active surface sites (6 = 0) and is desorbed from less active sites (6 = J0m)-Carbon dioxide is indeed found in the cold trap (1 cm /gm). Since cycle 3 (Table XIV) is balanced neither for 0 = 0 nor for 0 = 0m, the intermediate formation of C03-(ads) is precluded. 

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... 

The modified sequence of adsorptions (oxygen, then a limited amount of carbon monoxide, and finally oxygen) was also studied on a gallium-doped sample. The initial heat of the second adsorption of oxygen... 

Silicon (Si) Silicon is a lustrous silvery gray material. Because silicon conducts electricity, but not as well as a metal, silicon is classified as a semimetal. Crystals of pure silicon that have been doped with arsenic or gallium are known as semiconductors and are used to fabricate computer chips. Silicone rubbers are polymers containing silicon, oxygen, and various hydrocarbon groups, and are used in applications ranging from sealants to breast implants. 

Elemental silicon is central to the vast industry of solid-state electronics. Appropriately doped with other elements, it forms a variety of semiconductors that constitute most transistors and integrated circuits. Other elements and compounds such as germanium or gallium arsenide have also found a niche as semicondnctors in electronics, but silicon occupies the prime position. How fortunate that it is the second most abundant element in the Earth s crust. Its compounds with the most abundant crustal element, oxygen, are equally central in many different aspects of chromatography. Silica, silica gel, glass, qnartz, fused silica, and silicones all have a remarkable variety of key roles to play in chromatography. Let us familiarize ourselves with some of their relevant properties. 

Wiedemann, B., Bethge, K., Schiitze, W, Lambert, U., Pahlke, S., Reinhold, T., Weinert, B., Flade, T. (1994) Radiofrequency spark source mass spectrometric analysis of oxygen in undoped siUcon crystals and of carbon in undoped and carbon doped gallium arsenide crystals. Fresenius Journal of Analytical Chemistry, 350, 319-322. 

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