S. Lowell

Hysteresis, entrapment, and wetting angle in mercury porosimetry

Abstract Intrusion—extrusion hysteresis in mercury porosimetry is shown to be due to the extrusion wetting angle differing from the intrusion angle. When correct extrusion wetting angles are used, second-cycle intrusion—extrusion curves are coincident and first-cycle intrusion—extrusion curves reflect only the fact that mercury is permanently entrapped. The distribution of the entrapped mercury volume as a function of pore radius is given for two samples. The work corresponding to the entrapment of mercury, the work associated with the change in wetting angle, and the work of extrusion are determined. These work terms were also identified with regions of hysteresis on first-and second-cycle intrusion—extrusion curves.

A method for the determination of ambient temperature adsorption of gases on porous materials

Abstract Adsorption on a variety of micro- and mesoporous materials has been measured for very slight surface coverage using nitrogen, oxygen, and krypton above their critical temperatures. The results show that the quantity of gas adsorbed is a function of the surface area of the adsorbent and the polarizability of the adsorbate.

Influence of pore potential on hysteresis and entrapment in mercury porosimetry: Pore potential/hysteresis/porosimetry

Abstract The concept of a pore potential is used to explain certain phenomena in mercury porosimetry, such as hysteresis, entrapment of mercury, and contact angle changes between intrusion and extrusion. The pore potential is determined from the work of entrapment and the work associated with changing the contact angle during an intrusion-extrusion cycle and can be altered by impregnation of porous samples with both polar and nonpolar materials.

Surface Area Analysis from the Langmuir and BET Theories

The Langmuir [1] equation is more applicable to chemisorption (see chapter 12), where a chemisorbed monolayer is formed, but is also often applied to physisorption isotherms of type I. Although this type of isotherm is usually observed with microporous adsorbents, due to the high adsorption potential, a separation between monolayer adsorption and pore filling is not possible for many such adsorbents.

Pore Size and Surface Characteristics of Porous Solids by Mercury Porosimetry

The experimental method employed in mercury porosimetry is presented in detail in chapter 18. It involves filling an evacuated sample holder with mercury and then applying pressure to force the mercury into interparticle voids and intraparticle pores. Both applied pressure and intruded volume are recorded.

Interpretation of mercury porosimetry data

The experimental method employed in mercury porosimetry, discussed more extensively in Chapter 20, involves the evacuation of all gas from the volume containing the sample. Mercury is then transferred into the sample container while under vacuum. Finally, pressure is applied to force mercury into the interparticle voids and intraparticle pores. A means of monitoring both the applied pressure and the intruded volume are integral parts of all mercury porosimeters.

Chemisorption: Site Specific Gas Adsorption

When the interaction between a surface and an adsorbate is relatively weak, only physisorption takes place via dispersion and coulombic forces (see Chapter 2). However, surface atoms often possess electrons or electron pairs that are available for chemical bond formation. Resulting chemical adsorption or chemisorption has been defined by IUPAC [1] as “adsorption in which the forces involved are valence forces of the same kind as those operating in the formation of chemical compounds” and as “adsorption which results from chemical bond formation (strong interaction) between the adsorbent and the adsorbate in a monolayer on the surface” [2].

Langmuir and BET theories

The success of kinetic theories directed toward the measurements of surface areas depends upon their ability to predict the number of adsorbate molecules required to exactly cover the solid with a single molecular layer. Equally important is the cross-sectional area of each molecule or the effective area covered by each adsorbed molecule on the surface. The surface area then, is the product of the number of molecules in a completed monolayer and the effective cross-sectional area of an adsorbate molecule. The number of molecules required for the completion of a monolayer will be considered in this chapter and the adsorbate cross-sectional area will be discussed in Chapter 6.

Mercury Porosimetry: Non-wetting Liquid Penetration

The method of mercury porosimetry for the determination of the porous properties of solids is dependent on several variables. One of these is the wetting or contact angle between mercury and the surface of the solid.

Langmuir and BET theories (kinetic isotherms)

The success of kinetic theories directed toward the measurements of surface areas depends upon their ability to predict the number of adsorbate molecules required exactly to cover the solid with a single molecular layer. Equally important is the cross-sectional area of each molecule or the effective area covered by each adsorbed molecule on the surface. The surface area, then, is the product of the number of molecules in a completed monolayer and the effective cross-sectional area of an adsorbate molecule. The number of molecules required for the completion of a monolayer will be considered in this chapter and the adsorbate cross-sectional area will be discussed in Chapter 6.