Reliably measuring hydrogen uptake in storage materials

Generally the hydrogen concentration is represented here by the hydrogen-to-host atomic ratio  

Unless specified, absorption generally includes adsorption and hydrogen generally includes protium ( H or H and H2) and deuterium ( H or D and D2). 

Considering the absolute accuracies to which pressure, volume, temperature and mass may be practically measured, hydrogen may safely be taken to be ideal above room temperature and at pressures below a few bar. At higher pressures or lower temperatures, the need to account for its non-ideality becomes apparent. Perhaps the simplest approach, and the one used exclusively here, is to define the compressibility, Z, of the gas by  

Tabulated data of good accuracy (say better than 0.1%) for some or all of Vm. P and Z are available in a wide range of pressures and temperatures for protium and, to a lesser extent, deuterium. A comprehensive tabulated source is Vargaftik (1975). Other sources are discussed by Hemmes et al. (1986). The most recent, most comprehensive and generally most accurate source is contained in the commercially available National Institute of Standards and Technology (USA) Reference Fluid Thermodynamic and Transport Properties database (REFPROP, URLhttp //www.nist.gov/srd/nist23.htm), in which are embedded advanced equations of state for protium (Jacobsen et al., 2007) and deuterium (McCarty, 1989). 

1 Isochoric isotherms for the LaNis-D2 system recorded at 25°C with (filled circles) and without (open circles) correction applied for the compressibility of the deuterium gas. Even at a pressure of a few bar, the error is accumulating noticeably, becoming extreme at pressures of hundreds of bar. 

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Reliably measuring hydrogen uptake in storage materials 175... 

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