Diffusible hydrogen

Hydrogen embrittlement is due to the reaction of diffused hydrogen with a metal. Different metals undergo specific reactions, but the result is the same. Reaction with hydrogen produces a metal that is lower in strength and more brittle. 

Hydrogen Controlled Electrode a covered electrode which, when used correctly, produces less than a specified amount of diffusible hydrogen in the weld deposit. 

Diffusion. Hydrogen diffuses through air much more rapidly than other gaseous fuels. With a diffusion coefficient in air of. 61 cm2/s, the rapid dispersion rate of hydrogen is its greatest safety asset. 

Quintana, M.A. and Dannecker, J.R., Diffusible Hydrogen Testing by Gas Chromatography , Hydrogen Embrittlement Prevention and Control, ASTM STP... 

American Welding Society, Standard Methods for Determination of Diffusible Hydrogen Content , ANSI/AWS, A4.3-93, AWS, Miami, FL, (1993). 

Smith 11, R.D., Benson, D.K., Maroef, I., Olson, D.L. and Wildeman, T.R., The Determination of Hydrogen Distribution in High Strength Steel Weldments Part 2 Opto-Electronic Diffusible Hydrogen Sensor , AWS, Welding Research Supplement, (1997), pp. 122-126. 

A description of the trapping process may be based on the chemical potentials of the hydrogen absorbed in the metal. In the general case, the chemical potential of interstitial or diffusible hydrogen may be described by the equation... 

Under equilibrium conditions, the chemical potential of diffusible hydrogen equals the chemical potential of trapped hydrogen, i.e.. 

The nmr data for this type of motion are direct and the motion clearly involves rotation about bonds in the millisecond time scale range. However. less direct evidence for motion comes from other techniques such as fluorescence depolarization, 02 diffusion, hydrogen exchange kinetics, and nmr relaxation times (see Ref. 4). The extent of this motion is not yet easy to define, but this evidence points to motion in the nanosecond time scale range. It is tempting to see the motion in this time scale as bond oscillations rather than rotations. To put it in a different way, on this time scale the side chains have some freedom to move with respect to each other but not normally to undergo substantial bond rotation. Table IV summarizes some references for motion of different types. Additionally, nmr relaxation studies suggest that the backbone or main chain of a protein is more restricted than that of the side chains. 

The mucosal cells, which possess intrinsic mechanisms that resist injury, for example, by extruding back-diffused hydrogen ions using a basolateral carrier (e.g., sodium-hydrogen or sodium-bicarbonate exchange) (Figure 64.1)... 

The Pd technology is particularly appropriate for the Livermore site because the water table is fairly far below the surface (20-30 m deep), which makes trenching (e.g. for iron wall barriers) difficult. In addition, the rapid reaction rates and small reactors afforded by Pd catalysis permit the system to be contained within a well bore, which keeps the tritiated water at the site largely below the ground surface. The facility at the Livermore field site consists of two packed bed reactors, place in series in a well-bore. The flow rate is 4 L/min, which yields a residence time of five minutes in the first column and six minutes in the second column. A membrane is used to diffuse hydrogen gas into the influent stream prior to the first reactor. The... 

Figure 12.8 Scheme of the combination of a dehydrogenation reaction (endothermic) on one surface of a Pd-based catalytic membrane and a hydrogenation reaction (exothermic) by the diffused hydrogen on the other membrane surface. 

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