Vacuum pore impregnation

Figure 4.9 Photograph and schematic of a lab-scale parallel reactor for vacuum pore impregnation.

The basic principles of impregnation are as follows When pores of solid contact with active component-containing liquid, the liquid permeates into capillary due to the roles of the capillary pressure produced by surface tension the active components in the liquid adsorb on the wall of the capillary or surface of support. In order to increase the amount of the active component adsorbed on support or depth in capillary, sometimes the gas in the pores of support is eliminated by vacuum before impregnation and increasing the temperature (reduce the viscosity) of solution and speed agitation. 

The Fe3(C0)- 2"Y adducts are prepared under argon atmosphere with the HY and NaY zeolites previously heated under vacuum at 350°C. The impregnation of the support is performed either from pentane solution at 25°C or from dry mixing of the carbonyl and the zeolite to avoid any complication from the solvent. In this last preparation the sample stands in vacuo for 2kh at 60°C in order to favour the sublimation of the carbonyl into the pores of the zeolite. 

Parts with an open coherent porosity of >20% are used in vacuum tubes and aeronautics because of refractoriness, shape stability, and chemical resistance. Examples are porous cathodes impregnated with alkaline earth oxides as electron-emitting sources in special tubes, thermoionic converters heated by nuclear energy, and ionic propulsion units with porous tungsten plates as ionic sources for Cs vapor of high temperature. Those emitter plates are made of globular tungsten powder (7 pm) density 75-85%, pore size 2-30 pm, and pore number 1.4 x 10 -8 x 10 cm . ... 

Some a-Al203-based filter discs (Schumacher, Germany) were vacuum impregnated with a solution containing appropriate amounts of nickel nitrate and urea. After the excess solution was drained off, the discs were placed in a closed vessel and kept at 90 °C for a certain period, resulting in precipitation of nickel precursor by the slow hydrolysis of urea in the pores of the discs. After reaction, the filter discs were dried at 110 °C for a few hours and calcined at 450 °C for 4 h. Then the nickel-modified ceramic filter discs were obtained. For the conventional impregnation method, other steps and experimental conditions were identical to the preparation procedure with the urea method except for the absence of urea in the impregnation solution. 

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