Impregnation of Wet Materials

There are at least two problems in impregnating wet materials. First, water is a mechanical obstacle for permeation of the organic composition into the volume of the material. Second, water impedes the wetting of the surface of the pores of the material by the composition. If a water film exists between the cured composition and the sohd, the strengthening effect of the impregnation will be minimal. 

Ensuring selective wetting of the pore surfaces of the material by the composition in aqueous medium is not alone sufficient for displacement of water by the composition. Application of mechanical work to the phase boundary is also required. The specific mechanic d work necessary for complete water displacement by the composition on a solid surface is given by [410-412] 

Equation (8.1) shows that spontaneous (without work applied to the boundary) solid surface wetting by the composition in aqueous medium is possible for equality of surface tension values in adhesive and liquid, i.e., for = 0- The maximum attainable jc,w is advisable, however, as it is in direct proportion to thermodynamic work of adhesion. Therefore, it is impossible to ensure high-quality impregnation of porous materials with organic compositions without application of work to the composition-solid boundary, even if the thermodynamic conditions for selective wetting of material pores by the composition 

3 One-Component Organic Compositions for Impregnation of Porous Materials 

Consider isocyanate trimerization as an ex lmple. This reaction in the presence of alkah and alkahne-earth metals was described in detail earher. With crown-ether in contact with the concrete surface, it forms a crown-complex with the calcium cation of calciiun oxide 

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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... 

The capillary phenomena are by all means ubiquitous in nature and our every-day life. The penetration of fluids into thin pores, such as those present in soils, plants and rocks, the impregnation of porous materials and fabrics, the changes in the structure and mechanical properties of soils and grounds upon their wetting, are all due to the capillarity. 

Two main factors exert direct influence on the impregnation of porous materials—thermodynamic and kinetic. Whereas thermodynamic factors define the conditions of adsorption of compositions onto the surface of material pores, kinetic factors influence the speed of impregnation, which is determined primarily hy the size of the pores in the material, the viscosity of the composition, and the wetting of the pore surface with the composition. 

The standard catalyst, denoted as CHsONa/MSU-y, was prepared by wet impregnation with a methanol solution of CHsONa on a mesoporous aluminium oxide support. After impregnation, the wet material was dried in air at 60°C, compressed and sieved to form pellets with a diameter ranging from 0.5 to 1 nun. Before use in transesterification of rapesed oil with methanol, in situ activation of the catalysts was done at 200°C imder nitrogen for 3 and 6 h, respectively. 

Known amounts of salt(s) of catalytic metals are dissolved in aqueous solutions and impregnated into carrier materials. The wet mass is dried at 110°C and calcined in air at 300-500°C, releasing the decomposable salt components and depositing the metal oxide on the surface within the depths of the porous carrier. For many oxidation reactions the catalyst is now ready for use but for hydrogenation it is necessary to reduce the impregnated metal oxide or salt chemically. Usually this is accomplished by flowing H2, under conditions consistent with the maximum temperature of use for the reaction of interest. 

One of the potential ways how to improve CNT dispersion in polymer matrixes is in-situ polymerization of monomers in presence of nanotubes. Monomers have very small shear viscosity in orders of about lO -lO"3 Pa.s, compared to relatively high viscosity of polymer melts, 103-106 Pa.s. This low viscosity helps to better impregnation and wetting of CNT material, which leads to more efficient dispersion and debundling of the nanotubes aggregates, especially when ultrasound is used as a dispersing agent. 

Jiang, S.P., A review of wet impregnation an alternative method for the fabrication of high performance and nano-structured electrodes of solid oxide fuel cells. Materials Science and Engineering A Structural Materials Properties Microstructure and Processing, 2006, 418, 199-210. 

To be brief, higher alkylated, methoxy functional siloxanes are used mostly for the protection of masonry. Low molecular silanes give a good penetration depth. The main field of application is the impregnation of alkaline, poorly absorbing, still-wet materials. 

The Ni/YSZ catalyst was prepared by ball milling 50 wt.% NiO and 50 wt.% yttria (8 mol%)-stabilized zirconia (YSZ) in methanol for 24 h. The YSZ was used as a support because it is commonly used as the electrolyte/support in SOFCs. The high Ni loading is required in SOFC to facilitate electron transfer. The Sn/Ni alloy catalyst was synthesized using a sequential incipient wetness procedure with tin chloride impregnated on NiO/YSZ. After calcination of this material at 873 K, the catalyst was reduced at 1073 K under 30% H /N. [16]... 

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