Absorption-desorption isotherms

Figure 2. Static hydrogen absorption/desorption isotherms for HY-STOR Alloy...

Figure 9.15 Equilibrium absorption-desorption isotherms generated in CmH24 slurry, corrected...

Benham, M.J. and Ross, D.K., Experimental-determination of absorption-desorption isotherms by computer-controlled gravimetric analysis, Zeitschriftfur Physikalische Chemie Neue Lolge, 1989, 163 p. 25-32. 

Conventionally, the moisture sorption characteristics of fibers are depicted by absorption-desorption isotherms. In practice, it is difficult to compare isotherms of different fibers over the whole range of RH and temperature values. It is often sufficient to compare their regains at the standard conditions of 65% RH and 21°C (70°F). Table 8.9 gives absorption regains for a few fibers, together with the difference between absorption and desorption regains. 

Homogeneous and isotropic liquid pressure is warranted for high connectivity of the network of water-filled pores. This requirement, which would be indicated experimentally by the absence of hysteresis effects in water absorption/desorption isotherms, is a prerequisite for the proposed mechanism of pore swelling. 

Fig. 3. Water absorption-desorption isotherms for several MWX samples, showing the relationships between relative humidity, pore size, and capillary pressure. ...

While for macroporous structures the inner surface can be calculated from the geometry, meso and micro PS layers require other methods of measurement First evidence that some PS structures do approach the microporous size regime was provided by gas absorption techniques (Brunauer-Emmet-Teller gas desorption method, BET). Nitrogen desorption isotherms showed the smallest pore diameters and the largest internal surface to be present in PS grown on low doped p-type substrates. Depending on formation conditions, pore diameters close to, or in, the microporous regime are reported, while the internal surface was found to... 

The Li-Mg-B-N-H structure possesses storage capacity of more than 10 wt.% at around 150-200 "C. However, the reversibility of the hydrogen sorption characteristics was determined using pressure-composition isotherms as shown in Figure 6. From this study, we found reversible hydrogen absorption-desorption behavior (-3-4 wt.%) of the new complex hydride Li-Mg-B-N-H. The improvement in temperature and reversible hydrogen storage capacity were unaffected even after ten... 

The thermodynamics of Reaction 5.43 are comparable to those of other metallic, ionic and covalent hydrides. NaAlH4 exhibits typical low hysteresis and a two-plateau absorption and desorption isotherm. 

Figure 1. Ideal absorption and desorption isotherm for a metal-hydrogen system (1)...

Figure 2. Absorption and desorption isotherms for the ZrMn2- H2 system.

As mentioned above for 245°C the hydrogen absorption isotherm was obtained (see Fig. 2 and Fig. 5). Comparing the absorption and desorption isotherms one could see that hysteresis of the enthalpy values is absent in practice even for the range of H concentrations 1.8reference data [8, 9] AHdes. > AHabs.. ... 

The absorption and desorption isotherms for milled 2.5 LiH + Si mixtures measured by Vajo et al. shotv ttvo plateaus. Figure 7.13 shows the Van t Hoff plots of the lower and upper plateaus from the LiH-Si-H system as well as the pure Li-H... 

X-ray powder diffraction patterns were obtained on oriented film specimens [7] (2 to 45° 2 , Philips PW 1120, monochromatized CuKa radiation, continuous peak registration). BET surface area and the pore volume distribution were determined from Nj adsorption-desorption isotherms at 77 K (degassing at 393 K, lO" mbar, 5h Sorptomatic 1900, Carlo Erba Instruments). The IR-spectra were recorded on KBr wafers [4] with a Specord 80M spectrometer. The XPS (X-ray photoelectron spectroscopy) spectra were obtained with VG ESCALAB 200 MKII spectrometer equipped with a twin anode AIKa source (1486 eV). The thermogravimetric (TGA) analyses were carried out with a Setaram TG 85 thermobalance at a heating rate of 6 K min in a helium flow of 30 ml min . The chromium content of the samples was determined by EPMA (JEOL 840 scanning electron microscope) with energy dispersive spectrometer (EDS, Tracer Northern) and by AAS (atomic absorption spectroscopy, Perkin Elmer 3030) analyses. 

Pore-radius distributions and ab-/ desorption isotherms are important structural characteristics of generic porous media [80, 88]. The absorption isotherm provides a relation for the liquid uptake of a porous medium under controlled external conditions, viz., the pressure of an external fluid. Within a bounded system, such as a cylindrical tube, a discontinuity of the pressure field across the interface between two fluid phases exists. The corresponding pressure difference is called capillary pressure, Pc. In the case of contact between gas phase, Pg, and liquid water phase, P1, the capillary pressure is given by... 

The characterisation of the colloids both in the free and in the embedded state was first performed using transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and atomic absorption spectroscopy (AAS). In addition, nitrogen adsorption-desorption curves at 77 K, H2-chemisorption measurements, solid state Si-NMR, XRD, SAXS, XPS, MAS-NMR, NH3-FTIR, and Au Mossbauer spectroscopy were applied. For the embedded triflates, the catalysts were characterized by nitrogen adsorption-desorption isotherms at 77K, TG-DTA, H, C, and Si solid state MAS-NMR, XRD, TEM, SEM, XPS and, FTIR after adsorption of NH3. 

The vanadium content in the catalysts was determined with a Perkin-Elmer Mod. 3030 Atomic Absorption Spectrometer. The surface areas of the catalysts and of the corresponding supports were determined by nitrogen adsorption/desorption isotherms on a Micromeritics Mod. 2000 ASAP. 

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