Plateau Slope

Another important characteristic of a real PCI curve is the plateau slope which is usually represented by the relation [100]  

The plateau slope is not necessarily constant over the whole length of the plateau. The major cause of plateau slope can be attributed to compositional inhomogeneities [56, 101, 102], For arc-melted alloys, heat treatment could reduce the plateau slope. Usually, the pressure in the middle of the plateau is used to characterize the alloy. As with hysteresis, sloping plateaus have an important technological impact on some applications and reduction of the plateau slope is advisable. 

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There are two basic cycles for heat pump operation conventional (15) and temperature upgrading (3, J/[). It is convenient to visualize the operation of these cycles by following the changes in pressure and temperature of each alloy on a Van t Hoff plot. For ease of narration, these curves are idealized. Many engineering properties of metal hydrides must be considered in a detailed explanation (e.g., hysteresis, plateau slope, cyclic stability, etc.). The two cycles are shown in Figure 17. 

Plateau Pressure/Temperature Plateau Slope Hysteresis Heat of Reaction Hydrogen Capacity Volume Change Rate of Decrepitation Ease of Activation Kinetics of Reaction Tolerance to Gaseous Impurities Chemical Stability (Disproportionation)... 

Plateau slope is usually a function of metallurgical segregation that sometimes occurs during the production of a hydriding alloy(2, 3, 4). in some applications a sloped plateau is desired, but in most cases a reasonably flat plateau is preferred. We have learned to vary (or largely eliminate, if desired) the plateau slope by heat treatment techniques ( 2,4 ). ... 

In periodically working cyclic installations it is important to use hydride systems with the maximal contents of active hydrogen. Questions of revealing of new hydride materials are extremely important from the point of view of a ratio of the prices and efficiency. Concentration of active hydrogen depends on hysteresis Fh=Pd/Pa, a plateau slope =ln(Pci/Pcz) (Cj-C2). The hydrides most suitable to... 

HHP under other approximately identical conditions are what have a small plateau slope and a hysteresis of pressure at absorption and desorption. This position is the basic from a point of view of increase in amount of the active hydrogen circulating in HHP, and improvements of HHP efficiency. For example, the amount of hydrogen in inverse proportion also can decrease three times at changeFh with 0.9 up to 0.6. An ideal case is hydride which does not have hysteresis of pressure and plateau slope. 

The plateau in a counter should be checked frequently, e.g. weekly. A standard preparation giving some 100 or 1000 pulses/min. is used. If the plateau slope rises to above 10 % per 100 volt, the counter should be discarded. 

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