Capillary impregnation

Capillary impregnation is mainly characterized by its exothermicity, by the capillary pressures developed in pores and by the speed with which the pore space is filled. 

The role of adsorption kinetics and the diffusion of surfactants is especially important in controlling capillary impregnation. According to studies by N.N. Churaev, the solution impregnating the capillary quickly loses its dissolved surfactant due to adsorption of the latter on capillary walls, so the rate of impregnation may be limited by the diffusional transport of surfactant from the bulk of the solution to the menisci in the pores. 

For large-scale manufacture the so-called incipient wetness impregnation (also called pore volmne, or dry or capillary impregnation) is the most advantageous method. In this approach the support is brought into contact with a solution the volmne of which corresponds to the total pore volume of the solid and which contains the appropriate amoimt of precmsor compound. The principle of this method is shown in Figme 6-3. 

The simplest way to execute impregnation is by contacting a previously dried support, of pore volume Vpj, with a volume V = Vpj of solution containing the precursor of the active phase. The solution is drawn into the pores by capillary suction (hence capillary impregnation ) [12-14]. In the case of proper wetting no excess of solution remains outside the pore space and the procedure is also called dry or incipient wetness impregnation. 

During impregnation, the precursor is deposited on the support from a liquid solution, which in most cases is water-based. If the support surface is hydrophobic or if hydrolysis of the support must be avoided, a nonaqueous solution is used [11]. Typically, the support is immersed in a solution that contains the inert precursor as a metal salt. In the case of capillary impregnation, the support is initially dry, whereas during diffusional impregnation, the support is initially filled with the liquid solvent... 

The evaluation of the usability of a refractory product in a defined industrial context is a difficult technical procedure. The characteristics of the material must be known and its effect on the in-service behavior must be evaluated. Acquiring knowledge about the service properties of the material starts with its raw materials in fact, a refractory retains through the very nature of its manufacturing process, the memory of its raw materials. Insofar as the behavior of the refractory is mainly governed by phenomena of corrosion and capillary impregnation, the chemical composition, open porosity (volume and distribution into pore sizes) and microstracture ate essential parameters. The arrangement of the different constituents needs to be taken into account ... 

Figure 10.6. Capillary Impregnation of a magnesia chromite refractory by a calcic slag...

The main origin of multidimensional chromatography lies in planar chromatography. The development of paper chromatography, i.e. the partition between a liquid moving by capillary action across a strip of paper impregnated with a second liquid... 

The selective deposition of catalyst particles on the inner or on the outer walls of CNTs is the prerequisite for the investigation or utilization of the confinement effect, as discussed in Section 15.2.3. Wet chemistry methods making use of the capillary effect are most effective however, they depend on surface functionalization and tube diameter. In any case, CNT caps as well as radial carbon sheets and walls blocking parts of the inner CNT cavity have to be removed prior to impregnation, e.g., by mild oxidative treatment. The impregnation of this material with a limited amount of liquid can lead... 

In the supported liquid membrane process, the liquid membrane phase impregnates a microporous solid support placed between the two bulk phases (Figure 15.1c). The liquid membrane is stabilized by capillary forces making unnecessary the addition of stabilizers to the membrane phase. Two types of support configurations are used hollow fiber or flat sheet membrane modules. These two types of liquid membrane configuration will be discussed in the following sections. 

In this technique, commonly called Gas phase chromatography (GPC), the mobile phase is a gas and the stationary phase is a liquid. The liquid can be immobilised by impregnation or bonded to a support, which, in the case of capillary columns, is the capillary inner surface (the partition coefficient K is also involved). 

Over 100 stationary phases of various types have been described in the literature for packed columns, which are slowly being abandoned. However, for bonded phase capillary columns the choice of stationary phase is limited because the generation of the film at the surface of the column requires a different principle than impregnation. Generally, two families of compounds are used to modify the polarity polysiloxanes and polyethylene (silicones) glycols. Very special phases such as cyclodextrins can be used for enantiomeric separations. Stationary phases can be used between a minimum temperature under which equilibrium is too slow to occur and a maximum temperature above which degradation of the polymer occurs. The maximum temperature depends on the film thickness and the nature of the polymer. 

This technique represents the transposition of classical polyacrylamide or agarose gel electrophoresis into a capillary. Under these conditions, the electro-osmotic flow is relatively weak. In this approach, the capillary is filled with an electrolyte impregnated into a gel that minimises diffusion and convection phenomena. In contrast to its use for proteins that are fragile and thermally unstable, CGE is ideal for separating the more rugged oligonucleotides. 

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