Palladium hydrogen embrittlement

The method is more useful with titanium, and the effect of alloying titanium with a small amount of palladium is described in Section 5.4. The use of platinum in the prevention of hydrogen embrittlement in tantalum. 

Hydrogen has a low solubility in solvents for example, at ambient conditions, only 0.018 and 0.078 mL of gaseous H2 dissolves into each milliliter of water and ethanol, respectively. However, the solubility is much more pronounced in metals. Palladium is particularly notable in this respect, which dissolves about 1000 times its volume of the gas. The adsorption of hydrogen in steel may cause "hydrogen embrittlement," which sometimes leads to the failure of chemical processing equipment [4],... 

The content of this chapter is closely related to permeation, which is the transport of a solute across a layer of solvent (or membrane) under the action of a difference in activity. For example, the permeation of hydrogen through a metal foil has been studied, particularly for palladium [F.A. Lewis (1967)] and iron [J. P. Hirth (1980) H. H. Johnson (1988)]. One reason for studying the permeation of hydrogen through iron is to understand the hydrogen embrittlement of steel. 

The hydrogen permeation process is influenced by the surface topography, the purity of the metal and its defect structure (e.g., grain boundaries and dislocations). Within the metal, the hydrogen occupies octahedral interstitial sites. At high hydrogen concentrations, above 20°C, the a phase of palladium hydride exists, and one of the problems associated with pure palladium as a membrane is hydrogen embrittlement and the distortion of the metal by repeated adsorption/desorption cycles of exposure. 

It follows from the work of Darling and others that formation of the beta phase palladium hydride must be avoided to prevent embrittlement, cracking and delamination of thin catalytic films of unalloyed palladium used on composite membranes of Nb, Ta, Ti, V, and Zr. This also holds true for alloys of palladium susceptible to hydrogen embrittlement. Likewise, transformation of Nb, Ta, Ti, V and Zr substrates into brittle hydrides at low temperatures or at high hydrogen partial pressures must also be avoided. 

The most important problem associated with the use of pure palladium membranes is the hydrogen embrittlement phenomenon. When the temperature is below 300°C and the pressure below 2.0 MPa, the ]S-hydride phase may nucleate from the... 

The most important problem associated with the use of pure palladium membranes is the hydrogen embrittlement phenomenon. When the temperature is below 300 °C and the pressure below 2.0 MPa, the 3-hydride phase may nucleate from the a-phase, resulting in severe lattice strains (see Figure 13.3), so that a pure palladium membrane becomes brittle after a few cycles of oc (3 transitions. Such a problem can be overcome by using Pd-alloy containing another metal, such as silver. The palladium alloys have a reduced critical temperature for the oc-P phase transition. Pd-Ag membranes can operate in hydrogen atmosphere at temperatures below 300 °C without observing... 

Silica is another interesting material for the preparation of inorganie membranes for H2 separation. In particular, these are less expensive and also do not undergo hydrogen embrittlement like palladium membranes. They are generally prepared by chemical vapor deposition (CVD) or sol el ... 

Pure palladium becomes brittle in the presence of hydrogen during thermal cycling due to dimensional changes caused by a transformation between two phases (a and ft) of palladium hydride around 300°C. To avoid metal embrittlement and resulting membrane cracking or distortion, pure palladium membrane should not be exposed to hydrogen at temperatures below 300°C. To increase resistance to embrittlement, Pd is alloyed with... 

Some 100 years after Cavendish s discovery of hydrogen, and only 3 years after it was realized that hydrogen sorbed from chemical or electrochemical sources causes blistering and embrittlement to steel vessels, Graham [29] observed the ability of palladium to absorb hydrogen and wrote in Philosophical Transactions of the Royal Society of London ... 

R.E. Buxbaum, R. Subramanian, J.H. Park, and D L. Smith, Hydrogen Transport and Embrittlement for Palladium Coated Vanadium-Chromium-Titanium Alloys, Journal of Nuclear Material, Part A, 233-237, 1996, pp.510-512. 

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