Hydrogen outgassing

Rapp, D.B. and J.E. Shelby, Photo-induced hydrogen outgassing of glass.. Non-Crystalline Solids, 349, 254-259,2004. 

In some processing, apparent outgassing can result from the processing. For example, the evaporation of aluminum in a system containing water vapor can produce an apparently high hydrogen outgassing because the aluminum reacts with adsorbed water vapor to... 

Thus, hydrogenation and straining of the alloy at 680-780°C followed by final outgassing results in a very fine grain structure which is favorable for the mechanical properties of the final product. 

Fig. 10 shows that the flow stress of the hydrogen-alloyed compacts is essentially less than that of the outgassed ones at all test temperatuics. The flow stress relation between the hydrogen-alloyed and outgassed compacts depended on the strain. At equal strains at test temperatures, this ratio could achieve 2 or more. Thus, the effect of hydrogen on the properties of compacted powders is much similar to that observed on bulk titanium. 

Figure 10. Hydrogen effect in compacted powder mixtures Ti + TiH2 (8 1). Compacted at 9 kbar - y, additionally annealed in vacuum at 735°C for 10 min - A, outgassed - Q-...

Fig. 1 Change of the acid sites on Co.Mo/Si02 AI2O3 with hydrogen treatment and the following outgassing.

The recovery of the Lewis add sites and the decrease in the protonic acid sites to the original values by outgassing gas phase hydrogen are rather slow and require a high temperature. The addition of Pt/Si02 did not affect much the restoration of Ae Lewis add sites of H-ZSM-5 by outgassing gas phase hydrogen. 

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... 

Hydrogen cyanide has apKa of 9.2 (Smith and Martell 1989) therefore, solutions of cyanide compounds in water (such as from sodium cyanide and potassium cyanide) can form hydrogen cyanide at acid and neutral pHs. Alkaline solutions with pH >12 are practical for preventing significant outgassing of hydrogen cyanide. 

The simulations show that steady-state diffusion conditions throughout the wall thickness are attained in 2 hr for the case when hydrogen outgases through the OD surface and 10 hr when the OD surface is impermeable. We defined an effective time to steady state / as the time at which the hydrogen concentration at NILS at the hydrostatic-stress peak location reaches 98% of the final steady state value. We found the corresponding / values equal to 6.4 min for an outgassing pipeline and 34.25 min for an impermeable pipeline. 

Reaction of carbon with sulfur dioxide was observed by Fischer and Prauschke (131). In my laboratory it was recently found that sulfur is bound by heat-treated carbon blacks and by graphitized carbon black on treatment with hydrogen sulfide, carbon disulfide, or sulfur dioxide at low temperatures, even at room temperature. The sulfur content cannot be eliminated by outgassing at 100° or by prolonged extraction with various solvents. 

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