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Pressure absorption isotherm

Fig. 1. Absorption isotherms of hydrogen in palladium within a large range of temperatures and pressures of hydrogen gas. Numbers denote temperature in °C. Hydrogen pressure is given in the logarithmic scale. Broken line closes the area of the two-phase o + region of the Pd-H system. Different shapes of experimental points denote different authors data, cited by Scholten and Konvalinka (9). After Scholten and Konva-linka (9). Fig. 1. Absorption isotherms of hydrogen in palladium within a large range of temperatures and pressures of hydrogen gas. Numbers denote temperature in °C. Hydrogen pressure is given in the logarithmic scale. Broken line closes the area of the two-phase o + region of the Pd-H system. Different shapes of experimental points denote different authors data, cited by Scholten and Konvalinka (9). After Scholten and Konva-linka (9).
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... [Pg.115]

Figure 5.23 Pressure composition isotherms for critical temperature 7. The construction of the hydrogen absorption in atypical metal (left). The van t Hoff plot is shown on the right. The slope of solid solution (a-phase), the hydride phase the line is equal to the enthalpy of formation (p-phase) and the region ofthe coexistence ofthe divided by the gas constant and the intercept with two phases. The coexistence region is the axis is equal to the entropy of formation... Figure 5.23 Pressure composition isotherms for critical temperature 7. The construction of the hydrogen absorption in atypical metal (left). The van t Hoff plot is shown on the right. The slope of solid solution (a-phase), the hydride phase the line is equal to the enthalpy of formation (p-phase) and the region ofthe coexistence ofthe divided by the gas constant and the intercept with two phases. The coexistence region is the axis is equal to the entropy of formation...
Absorption pressure-composition isotherms were established by metering fixed amounts of hydrogen into the system and determining the pressure after equilibrium. In each case, the sample chamber was isolated before hydrogen... [Pg.322]

Figure 1. Pressure-composition isotherms for the Dy2Co7-H system. Hydrogen concentration is expressed as atoms of H per formula unit of Dy2Co7. X designates absorption O designates desorption. Figure 1. Pressure-composition isotherms for the Dy2Co7-H system. Hydrogen concentration is expressed as atoms of H per formula unit of Dy2Co7. X designates absorption O designates desorption.
P-C-T Determinations Low Pressure Studies. Absorption isotherms obtained for the reaction of hydrogen with TiMo are shown in Figure 3 for 590°-392°C. These temperatures are above the decomposition temperature of /J-TiMo (see Figure 2) consequently, decomposition of the solid solution plays no role here. These data follow Sieverts Law only in the very dilute region—to hydrogen-to-metal ratios (H/M) of about 0.02. Thereafter, deviations in the direction of decreased solubility are observed. Data in the region of Sieverts Law can be used to determine the relative partial molar enthalpy and entropy at infinite dilution (47). From Sieverts Law (Equation 1), where Ks is a tempi/2 = Ksn (1)... [Pg.360]

The absorption isotherms of acetone in nitrocellulose containing 11.6 and 13.5% N respectively at 40°C have been studied by Desmaroux [41]. Acetone was dissolved in castor oil. In a separate series of experiments, Desmaroux has established the vapour pressure of acetone dissolved in castor oil, hence the activity of acetone vapour, defined as the ratio of acetone vapour pressure of the respective solution to the vapour pressure of pure acetone. Curves illustrating the relationship between the number of acetone equivalents absorbed by one anhydroglucose unit (Q) equivalent of nitrocellulose, and the activity of the acetone vapours are shown in Fig. 90. [Pg.249]

Vinyl Chloride/Polyethylene Absorption Isotherms. The absorption isotherms have been determined by adding increasing quantities of vinyl chloride to an aqueous suspension of polyethylene. After saturation of the polyethylene, there is no further increase in the pressure with increasing quantities of vinyl chloride. The principal characteristics of the various polyethylenes examined are shown in Table I. [Pg.149]

Figure 2 shows that this absorption increases considerably with temperature. The maximum pressure reached by these absorption isotherms is higher than the value that could be explained by the vapor pressures of vinyl chloride and water. This increment is caused by residual inert gases present in the autoclave. [Pg.150]

Into a 5-liter autoclave, continuously stirred at a speed of 450 rpm, water, a dispersing agent, and polyethylene (powder or pellets) are introduced in the proportions set forth in Table II. After introduction of the initiator, the vinyl chloride is injected in such a quantity that, at the polymerization temperature, the vinyl chlorides partial pressure is lower than the vapor pressure of pure vinyl chloride at the same temperature. The vinyl chloride quantities compatible with this condition are easily determined by the absorption isotherms. When the pressure has dropped to at least half of its maximum value, the nontransformed vinyl chloride is removed. After filtering, washing, and drying, the product is collected. [Pg.152]

Figure 2.2 Typical shapes of the absolute adsorption isotherm and excess absorption isotherm. The inflection of the excess adsorption isotherm can occur at high pressures. Figure 2.2 Typical shapes of the absolute adsorption isotherm and excess absorption isotherm. The inflection of the excess adsorption isotherm can occur at high pressures.
Similar effects have been found in pressure composition isotherms of LaNi5Hx measured volumetrically [11]. Figure 4 shows variations of the absorption pressure with time to execute an entire measurement loop. As clearly visible, even after a measurement time of one week per cycle, changes in the plateau pressures are observable. [Pg.189]

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... [Pg.464]

A close set of equations was formulated in Ref. 16, related to the capillary pressure isotherms determined by the method of standard porosimetry [60], In the latter procedure, the equilibrium amount of the wetting liquid is measured in the porous sample under study. Simultaneously, the amount of the wetting liquid is measured in the standard specimen with a genuine porous structure, in which the capillary equilibrium is established. The standards are kept in thermodynamic equilibrium with the sample. The comparison of the amount of wetting liquid in the membrane with the pore-radius distribution in the standards, enables one to record (with a minimum of theoretical assumptions), the volume-size and surface-size distribution curves, specific pore-space surface area, and absorption isotherm in the membrane of interest, for various wetting liquids. [Pg.465]

Figure 7.1 demonstrates the importance of using compressibility in the calculation of hydrogen uptake at even modest pressures by contrasting the calculated absorption isotherms for the LaNi5-D2 system at room temperature with and without correction for the deuterium compressibility. Even at pressures of a few bar the error is significant over the breadth of the absorption plateau. Once pressures of several hundred bar are reached, the uncorrected isotherm is completely misleading. [Pg.176]

Pressure-composition isotherms may be constructed under an isochoric constraint by adding hydrogen aliquots to the system and measuring the hydrogen absorption or desorption stepwise, or under an isobaric constraint by actively controlling the pressure over the sample to a constant value while the sample absorbs or desorbs. [Pg.177]

Minimal Sieverts (isochoric) hydrogenator. To record an absorption isotherm, gas prepared at measured pressure and temperature in l/ ef is admitted to the sample cell via valve S. The absorbed amount is calculated from the final pressure in the system and the temperatures of the gas in 1/ref and Vceii using Eq. (7.6). [Pg.180]

An absorption isotherm is obtained (after initial activation cycles), and the sample chamber is sealed at a temperature ri(°C) with p phase hydride at H/M = 1. Then the sample temperature is increased to a temperature, T2, which is associated with pressure increase, and generally one observes a loss of hydrogen capacity (the magnitude of which varies from alloy to alloy) as shown in Fig. 12.7(b). The start of the aging time is referred to as to, shown in the schematic on the right. If the hydrogen pressure increases, then the H/ M in the sample decreases as a function of time. [Pg.328]

An hysteresis phenomenon is observed when the plateau pressure determined for an absorption isotherm is higher than the plateau pressure measured at the same temperature for the desorption process. Hysteresis is caused by the large stresses associated with the metal to hydride transformation which give rise to internal defects such as dislocations and stacking faults. Hysteresis decreases with increasing temperature as thermally activated stress relaxation processes set in. It is in general important to eliminate or at least minimize hysteresis for most applications. [Pg.544]


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See also in sourсe #XX -- [ Pg.305 , Pg.306 , Pg.316 ]




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