Hydrogen gas pressure and

Palladium is a special case in the Group 10 metals in contrast to Ni and Pt it forms bulk hydrides under mild conditions. The schematic Pd-H phase diagram is shown in Figure 10.7. At low hydrogen concentrations the atoms occupy a small fraction of the interstitial octahedral positions in the palladium fee lattice (the diluted PdH or a-phase), up to about 0.015 H per Pd atom at room temperature. With increasing hydrogen gas pressure (and below the critical temperature T, which is 295 °C for... 

As we mentioned, the cell voltage depends on the activities of all the ions and compounds in the cell reaction in this case it depends not only on the hydrogen gas pressure and but on acu ao,2+ as well. Standard conditions is defined as u = 1 for all products and reactants in the cell reaction, and so if the hydrogen electrode is operating under SHE conditions (uh2( ) = /njfe) = 1 bar), the copper electrode is pure Cu (acu(s) = 1) and the cupric ion concentration and activity coefficient are adjusted to give 00,2+ = 1, the ceU voltage will be the standard cell voltage, S°. 

Recombination of hydrogen atoms at MnS inclusions in front of the crack tip, leading to the formation of brittle cracks at the inclusion-matrix interface, which propagate imder the action of hydrogen gas pressure and triaxial tensile stress. 

Relationship between the residual aromatics content, the hydrogen partial pressure, and the chemical hydrogen consumption (for a SR gas oil). 

PL-3.13.3 Control and Limiting of Hydrogen Gas Pressure in High-Pressure Steel Distribution Systems... 

Austenitic steels are the most resistant to hydrogen embrittlement among the stainless steels and have been successfully used in high-pressure hydrogen gas piping and pressure vessels. Austenitic stainless steels generally provide the best performance of any structural metal in hydrogen gas service. 

A-2.8.1 Pressure and Temperature. An important general trend is that structural metals become more susceptible to hydrogen embrittlement as hydrogen gas pressure increases. An example of this trend is the measured threshold stress intensity factor, Km, as a function of gas pressure for low-alloy steels. Kjh decreases as gas pressure increases. Increasing hydrogen gas pressure enhances the concentration of dissolved hydrogen in materials, which promotes hydrogen embrittlement. 

Figure 2. Description of the initial and boundary conditions for the hydrogen diffusion problem in the pipeline. The parameter / denotes hydrogen flux and C,(P) is normal interstitial lattice site hydrogen concentration at the inner wall-surface of the pipeline in equilibrium with the hydrogen gas pressure P as it increases to 15 MPa in 1 sec. At time zero, the material is hydrogen free,...

Figure 5. Description of (a) boundary conditions for the elastoplastic problem and (b) initial and boundary conditions for the hydrogen diffusion problem at the blunting crack tip in the MBL formulation. The parameter bCl denotes the crack tip opening displacement in the absence of hydrogen. The parameter C, (P) denotes NILS hydrogen concentration on the crack face in equilibrium with hydrogen gas pressure P. and / is hydrogen flux.

We solved the transient hydrogen diffusion initial/boundary-value problem coupled with the large strain elastoplastic boundary value problem for a pipe of an outer diameter 40.64 cm, wall thickness h = 9.52 mm, and with an axial crack of depth 0.2/i on the inner wall-surface. We obtained the solutions under hydrogen gas pressure of 15 MPa, material properties for an X70/80 type steel, and... 

Figure 5. Isotherms of hydrogen gas (pressure p atm) in equilibrium with absorbed hydrogen in LaNi5 (concentration H atoms/LaNi5). Notice the alpha-region is where hydrogen is in solid solution, the (alpha+beta)-region is made-up of both solid solution hydrogen and hydrides, and the beta-region is...

The ideal gas law should be corrected by the Van der Waals equation for the volume of gas molecules and molecular interactions at higher hydrogen gas pressures. 

Consider the diffusion of hydrogen through a composite wall comprising Ni and Pd of identical thicknesses at 400°C. The hydrogen gas pressure in contact with the Ni is 1.0 atm, and that in contact with the Pd is 0.1 atm. The following data on each metal are provided ... 

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