Oxygen active elements

Our recent study (Ref. 31) on the internal oxidation of Ag-I.2 at% Mg and Ag-0.25 at% Mg-0.25 at% Ni showed that the clustering of oxygen active elements, R, with oxygen atoms O, varied with the ratio r = (0/R). The lower amount of R in the alloy has higher r-values Temperature dependent r-values indicated that lower temperatures showed higher r-values. Therefore, we can apply these phenomena in the oxygen-charging step or the CVD process. 

The development of CVD films for high-temperature corrosion protection of ferrous alloy has focused on methods with and without addition of oxygen-active elements. CVD processes, which employ vapor-transport and heat treatment of a stabilized alloy substrate to... 

As in many other cases, scale adherence and oxidation resistance are improved by microalloying with oxygen active elements, e.g. Y, Zr, Hf, Ce, or La (Mrowec... 

During the last few decades, efforts have been made to develop wear-resistant alloys by adding alloying elements such as Mo, Cr, Ti, W and V, (which are able to form carbides to enhance wear-resistance).They also incorporated oxygen active elements such as Si, Pd, Y and Ce into the alloy to develop corrosion-resistant wear materials. 

Zhang TC, Li DY (2000b) Beneficial effect of oxygen-active elements on the resistance of aluminide coatings to corrosive erosion and dry erosion . Surface and Coatings Technolog/, 130, 57-63. 

In phase-fluorimetric oxygen sensors, active elements are excited with periodically modulated light, and changes in fluorescence phase characteristics are measured. The delay or emission (phase shift, ( ), measured in degrees angle) relates to the lifetime of the dye (x) and oxygen concentration as follows ... 

Although the epoxidation by nitrous oxide proceeds over non-zeolite catalysts, they also include iron as an active element One may think that in all these cases a special oxygen species generated by N20 plays an important role, similar to the a-oxygen on FeZSM-5. 

Tribochemical reaction The formation of an iron sulfide tribofilm may be displaced by other surface active elements such as oxygen, where the oxide of the iron heat of formation AHf = -2.82 eV is thermodynamically more stable than the sulfide AHf = -1.04 eV. Using the data from Table 5.11, compare the heat of formation of molybdenum oxide and molybdenum sulfide. 

An interesting example of oxygen activation by onium salts of nontransition elements has been claimed. Sulfonium salts were found to be especially effective,211 and it was proposed212-214b that dioxygen complexes of sulfonium compounds can initiate autoxidations via hydrogen transfer with hydrocarbons, e.g.,... 

Antimony is a moderately active element. It does not combine with oxygen in the air at room temperature. It also does not react with cold water or with most cold acids. It does dissolve in some hot acids, however, and in aqua regia (a mixture of hydrochloric and nitric acids). It often reacts with materials that do not react with either acid separately. 

Calcium is a moderately active element. It reacts readily with oxygen to form calcium oxide (CaO) ... 

Niobium metal is resistant to attack by most common chemicals. It does not combine with oxygen or most other active elements except at high temperatures. It does not react with most strong acids unless they are hot and concentrated. 

Nitrogen gas is used where an inert atmosphere is needed. An inert atmosphere is one that does not contain active elements. Ordinary air is not an inert atmosphere. It contains oxygen. Oxygen tends to react with other elements. 

Rubidium is one of the most active elements. It catches fire when exposed to oxygen in the air. For that reason, it must be stored completely submerged in kerosene. Rubidium also reacts vigorously with water. It produces hydrogen gas that catches fire and burns. Rubidium combines violendy with the halogens (fluorine, chlorine, hromine, and iodine). 

Sodium is a very active element. It combines with oxygen at room temperature. When heated, it combines very rapidly, burning with a brilliant golden-yellow flame. 

Thallium is a fairly active element. It reacts with acids and with oxygen in the air. When exposed to air, it forms a thin coating of thallium oxide (TI2O) that peels off easily. As the coating drops off, a new layer forms in its place. 

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