Nickel hydrogen isobars

In order to study the effect of absorption in the nickel-hydrogen system in more detail, Beeck et al. (11) have investigated the hydrogen sorption isobars between 20°K. and room temperature. As shown in Fig. 6, the solid curves represent the isobars for increasing and decreasing temperature. With increasing temperature (the part between 20 and 80°K. will be discussed later), sorption increases fast between 80 and... 

Fig. 4. Sorption isobars of hydrogen ( —196°C. to temperature of presintering, up and down) at 0.1 mm. Hg pressure on evaporated nickel films presintered at various temperatures.

Fig. 6. Sorption isobars at 0.1 mm. pressure of hydrogen on an evaporated nickel film sintered at 23°C. (To obtain the ordinate in molecules X 10 18/100 mg., divide by 9.07.)...

Fig. 7. Sorption isobars at 0.1 mm. pressure of hydrogen on an evaporated nickel...

Before leaving the nickel experiments, it may be well to refer to the experiments on hydrogen adsorption variously reported in the literature. As an example, the work of Maxted and Hassid (13) had as its main objective the measurement of the slow activated adsorption of hydrogen on reduced nickel oxide catalysts. It has been proved by the foregoing that the slow adsorption is actually absorption. When plotting their data as isobars, as was done in Fig. 9, the similarity between these isobars and those obtained with sintered nickel films is evident. 

Fig. 2. Linear isobars for chemisorption of hydrogen sulfide on nickel catalysts. 7-46 ppm, data from Alstrup et al, 0.001-0.1 ppm data from McCarthy et a 1. (I. Alstrup et al14, reproduced with the permission from Elsevier Scientific Publishing Company).

Also in 1950 a paper was published describing adsorption isobars for hydrogen on nickel films from 20 K to room temperature ( ). These results were achieved with the aid of the newly developed Collins helium cryostat. 

Fig. 83. Sorption isobars of hydrogen on nickel, showing low and high temperature sorption. Curve 1, 2 5 cm. pressure curve 2, 20 cm. pressure curve 3, 60 cm. pressure.

Chemisorption of hydrogen is a widely used method for determination of the surface area of nickel in supported catalysts. The H2/Ni is complicated because of different states of chemisorbed hydrogen. At low temperatures (-196 C), a fast uptake results in a saturation layer with H/Ni less than one [46] [381]. At higher temperatures, the chemisorption becomes activated with hysteresis phenomena in isobars — and with some of the hydrogen present in subsurface sites [389],... 

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