Inert atmospheres metal oxidation

Toluene and CH2CI2 (Aldrich) were dried over activated molecular sieves in inert atmosphere. The oxide supports were impregnated at room temperature under Argon atmosphere with a diluted solution of metal precursor in anhydrous solvent, obtaining a 2 wt.% metal loading for each sample. The solvent was removed in vacuo, and the sample dried overnight in vacuo. 

Eu reacts quickly with moist air and should be handled at all times in an inert atmosphere. La oxidizes slowly, but continuously in air. As discussed below, electropolishing passivates the surface of La and it will stay shiny in air for 24 hours when the surface has been electropolished. However, a filed, sawed or sheared La surface will tarnish in less than hour. Thus La can be handled in air for short periods of time, —10 minutes, without excessive tarnishing, but when stored for a long period, it should be stored in an inert atmosphere. Storage in a vacuum dessicator at 10 Torr (1.3 Pa) is acceptable, but slow oxidation still occurs. A more satisfactory method for long periods of storage is to seal the metal in evacuated Pyrex tubes sealed off with a torch. The same is true for Ce, Pr and Nd. All four. La, Ce, Pr and Nd, will oxidize completely when stored in air for long periods of time. 

Hafnium metal is analy2ed for impurities using analytical techniques used for 2irconium (19,21,22). Carbon and sulfur in hafnium are measured by combustion, followed by chromatographic or in measurement of the carbon and sulfur oxides (19). Chromatographic measurement of Hberated hydrogen follows the hot vacuum extraction or fusion of hafnium with a transition metal in an inert atmosphere (23,24). 

Nonoxide fibers, such as carbides, nitrides, and carbons, are produced by high temperature chemical processes that often result in fiber lengths shorter than those of oxide fibers. Mechanical properties such as high elastic modulus and tensile strength of these materials make them excellent as reinforcements for plastics, glass, metals, and ceramics. Because these products oxidize at high temperatures, they are primarily suited for use in vacuum or inert atmospheres, but may also be used for relatively short exposures in oxidizing atmospheres above 1000°C. 

Zirconium is a highly active metal which, like aluminum, seems quite passive because of its stable, cohesive, protective oxide film which is always present in air or water. Massive zirconium does not bum in air, but oxidizes rapidly above 600°C in air. Clean zirconium plate ignites spontaneously in oxygen of ca 2 MPa (300 psi) the autoignition pressure drops as the metal thickness decreases. Zirconium powder ignites quite easily. Powder (<44 fim or—325 mesh) prepared in an inert atmosphere by the hydride—dehydride process ignites spontaneously upon contact with air unless its surface has been conditioned, ie, preoxidized by slow addition of air to the inert atmosphere. Heated zirconium is readily oxidized by carbon dioxide, sulfur dioxide, or water vapor. 

It is pmdent to perform zone melting in a dry inert atmosphere. Oxygen causes most organic melts to oxidize slowly. Oxygen and moisture not only oxidize metals and semiconductors, but often enhance sticking to the container. Molten salts attack sUica more rapidly in the presence of moisture. Oxygen and water are considered impurities in some inorganic compounds. 

Low Oxidation State Chromium Compounds. Cr(0) compounds are TT-bonded complexes that require electron-rich donor species such as CO and C H to stabilize the low oxidation state. A direct synthesis of Cr(CO)g, from the metal and CO, is not possible. Normally, the preparation requires an anhydrous Cr(III) salt, a reducing agent, an arene compound, carbon monoxide that may or may not be under high pressure, and an inert atmosphere (see Carbonyls). 

Special low fusing porcelain veneers are appHed to pure (unalloyed) titanium dental castings. It is important that firing be done either in a vacuum or inert atmosphere to protect the metal surface from excessive oxidation. The strength of the metal-ceramic bond is apparently adequate although the bonding is thought to involve primarily a mechanical rather than a chemical component. 

When cast iron is exposed to high temperatures under oxidising conditions, oxidation of the metal results, with the formation of a surface scale. In addition, the dimensions of the component become distorted. Although such dimensional changes can occur also in inert atmospheres or in vacuum, the evidence available suggests that this growth is frequently associated with oxidation, and accordingly it is appropriate to consider it as an aspect of the corrosion of the iron. 

The coating material, usually in the form of powder, is metered into a compressed-gas stream and fed into the heat source where it is heated to its melting point and proj ected onto the substrate. In the case of refractory metals and compounds which have high melting points, spraying is carried out in an inert atmosphere to avoid detrimental chemical reactions such as oxidation. 

All of the preparation procedures for the oxide promoted catalysts (T-O shared one common feature, heat-treatment of the oxide impregnated Ft on carbon catalysts in an inert atmosphere at elevated temperature, usually around 900 C. If an "alloy" phase of Ft with the metal of the metal oxide is formed by this heat-treatment, thermal reduction would have to occur with carbon as reducing agent, e.g. 

In practice, the production of vanadium by aluminothermic reduction is also governed by some other considerations. The reduction has to be carried out under an inert atmosphere (helium or argon) to avoid nitrogen pick-up from the air by vanadium metal. The composition of the oxide-aluminum charge has to be so chosen that the thermit (metal obtained by aluminothermic reduction) contains between 11 and 19% aluminum. This is necessary for the subsequent refining step in the vanadium metal production flowsheet. Pure vanadium pentoxide and pure aluminum are used as the starting materials, and the reduction is conducted in a closed steel bomb as shown in Figure 4.17 (C). 

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