Hydrogen charging

Not all metal.s and alloys can be persuaded to fracture in an intergranular manner by impact at low temperature. However, a whole group of metals and alloys will fracture in that mode if they are first embrittled by charging with hydrogen. Some will then fracture intergranularly by impact, but others require to be fractured by a slow tensile pull. This group includes the au.stenitic stainless steels [4], nickel [12], the nickel-base superalloys [14] and nickel aluminum alloys [45]. 

As described in Section 2.1.2, irradiation can therefore alter dramatically the level of segregants at grain boundaries. The mechanism responsible is the inverse Kirkendall effect, and in a nickel-base alloy such as PEI6 the boundaries could be depleted in chromium and iron and enriched in nickel 1.16.17]. Once the effect of radiation had been removed by annealing at 871 K for I h the alloy was able to return to its original. state. 

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T boron Carbon Heteroatom Extra hydrogens Charge Total Ref. 

Pressure rise curve for X52 steel during high-pressure hydrogen permeation measurement. The measured pressure is normalized to the charging pressure on the upstream side. Here, the hydrogen charging pressure is 510 psi and the test temperature is 165°C. 

Hydrogen diffusivity as a function of temperature. The effective diffusivity data of X52 and X65 pipeline steels obtained under gaseous hydrogen charging conditions are compared with the compiled results for the literature. (After Alefeld, G. and Volkl, J. Hydrogen in Metals I—Basic Properties, Springer, New York, 1978.)... 

Figure 5.36 The NRT bond orders bm (circles) and how (squares) and terminal-hydrogen charge Qw (crosses) along the intrinsic reaction coordinate for the H2 OH- -> H HOH proton-transfer reaction.

Experimentally, trans 1,2-difluorocyclopropane is more stable than the cis isomer372. Fluorine and hydrogen charges for cis and trans 1,2-difluorocyclopropane as calculated by the CNDO/2 method are shown below ... 

Figure 6. Thermoelectric power coefficient as a function of H atoms/LaNi5 for hydrogen charged LaNij at room temperature (green) and 190°C (blue).15...

Reversibility of hydrogen charging was very good at room temperature. This is because the hexagonal lattice of the metal host, like this of LaNi, does not undergo major transformation as hydrogen is inserted interstitially. This was the first AB -type interstitial hydride in which hydrogen is stored between metal atoms. 

Those rare-earth AB -type hydrides were quickly utilized in rechargeable nickel metal hydride batteries where electrochemical hydrogen charging and discharging take place at ambient temperature. Such electrochemical hydrogen storage is reversible, when the negative hydride electrode (anode) is combined with the positive Ni electrode (cathode) in the battery cell.. 

B (oxygen centered) Oxygen charge Hydrogen charge... 

In subsequent work by the same authors, non-neutrality of the standard atoms was allowed by addition of a transferable PD valence-shell monopole population, with neutrality being maintained by a slight adjustment of the hydrogen charges, and k parameters refined after the transfer (Pichon-Pesme et al. 1995b). 

Equation (14.5) conveniently eliminates explicit calculations of hydrogen charges from the general expression for Yi ki qk + F. 

Direct estimates using the appropriate SCE potentials at the nuclei suggest 181 kcal/mol [141]. The CC and CH parameters are treated the usual way. A general formula is developed as follows. The hydrogen charge variations are expressed relative to q = —W.l me. Charge normalization, (X) c +... 

Figure 8. Maximum hydrogen solubility as a function of atom % alloy partner exhibited by V/Cr and Ti/Mo alloys. Data obtained at 40°C for a hydrogen charging pressure of 60 atm. (O) V/Cr, Ref. 52 (a) Ti/Mo, Ref. 56 (A) Ti/Mo, this work.

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