Outgassing reduction

The surface of the silver reaction channels was enhanced by means of the oxidation and outgassing reduction (OAOR) process, which relies on oxidation at 250 °C using pure oxygen and subsequent reduction. An increase in surface area by a factor of 2-3 was reached as indicated by chemisorption data. 

On the contrary, n-type semiconductors tend to become opaque when oxygen deficient, as a result of chemical reduction or of simple outgassing at high temperature, as we observed for FezOs, ferrites and CuO, as well as for V3O5 and WO3 [17,18]. The optical behaviour of these... 

Dining outgassing of scrap uranium-aluminium cermet reactor cores, powerful exotherms led to melting of 9 cores. It was found that the incident was initiated by reactions at 350°C between aluminium powder and sodium diuranate, which released enough heat to initiate subsequent exothermic reduction of ammonium uranyl hexafluoride, sodium nitrate, uranium oxide and vanadium trioxide by aluminium, leading to core melting. 

To see that this is true, qualitative models of the titania surface produced following each of the three pretreatments used in this study (i.e., evacuation at 600 K, evacuation at 720 K, and hydrogen reduction at 720 K) are developed below on the basis of earlier studies of Ti02 surfaces (5-6,10-22). Surface Type I Following outgassing at about 600 K the Ti02 surface should be almost entirely free of molecular water (except on the rutile fraction), but about one half of the surface should be covered... 

Materials. Niobium metal of low oxygen content was prepared by carbon reduction of high purity niobium(V) oxide obtained from Fansteel Metallurgical Corp. The metal then was arc-melted, cut into fine turnings, and outgassed at a pressure of 8 X 10 5 mm. of Hg and a temperature of 2050° for 2 hours. 

Germanium single crystals of the four n-type samples, with 0.14-, 1.8- to 2.1-, 5.5- to 10-, and 20- to 30-ohm-cm. resistivities, were crushed in an agate mortar and stored in air for 15 days before measurements were begun. Both argon surface areas and propanol isotherms were determined after activation for 15 hours at better than 10-5 mm. of Hg at six different temperatures ranging from 25° to 500° C. Even after outgassing at 500° where oxide film is lost by reduction and subsequent evaporation, additional oxide forms instantaneously at the ordinary vacuum employed and over the relatively small surface areas in the sample tube totally about 1 sq. meter. 

Fig. 4. Schematic diagram of equipment for the determination of mercury showing (a) tube for reduction with SnCl2 and outgassing of mercury vapour (b) magnesium perchlorate desiccant (c) soda-asbestos and (d) silica-windowed cell to fit in light path of instrument.

The main advantage of polyimides is that they retain their structural strength to temperatures approaching 350 C, but they also have good outgassing characteristics in vacuum. For such applications the thermal stability of a PTFE filler is a limitation, and 5% of molybdenum disulphide may be added to a polyimide for friction reduction. The wear resistance of this material was inferior to some of the filled nylons, acetals and polycarbonates, and it would probably be chosen mainly for its high temperature stability. 

Figure 3.25 FTIR spectra of carbon monoxide adsorbed on PdO, /y-AbOs catalyst, after previous calcination in air at 673 K (upper spectra) and after reduction in hydrogen (1 atm) at 673 K (lower spectra). The first spectra in each series has been obtained in contact with lOTorr CO at 130 K for 5 min. The other spectra were recorded upon outgassing (lO Torr) on warming to 270 K. 

As deduced from the magnetic balance results commented on above, also confirmed by XAS data (205), the use of chlorine-containing metal precursors may deeply modify the redox properties of ceria. The reversible contribution plays a minor role, thus suggesting that the presence of chlorine heavily disturbs the H2-CeC>2 interaction (209). This has also been confirmed by some volumetric (209) and TPD studies (166), Likewise, the above results show the existence of a new very important contribution to the total reduction degree reached by ceria. It is specifically related to the Cr ions incorporated into the ceria lattice. Though it does not revert on outgassing, no oxygen vacancies would be associated with this third contribution (52,163,193,195). 

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