Sponge-like pores

Efforts to overcome the limitations of the fragile membranes (as delicate as soap bubbles) have evolved with the use of membrane supports, such as polycarbonate filters (straight-through pores) [543] or other more porous microfilters (sponge-like pore structure) [545-548]. 

Figure 2.4.1 Electron microscopy picture of biocoal, which was made by hydrothermal treatment of oak leaves. The sponge-like pore structure with structural elements in the 20-50 nm region is nicely seen.

Ti-SBA-15 Sponge-like pore structure TBOT TEOS Postsynthesis method (Ti added to SBA-15) 100 °C, 2 days Wu, 2002 (46)... 

Ti-TUD-1 Sponge-like pore structure TBOT TEOS TEA TEA, Ti fi-butoxide, TEAOH and aging and heating dry gel in autoclave Room temperature, 1—4 days Shan, 2001 (47)... 

For example, the capillary forces mentioned in Chapter 1 become extensively involved in the movement of water through a sponge. Sponges consist of many interconnected capillaries. An oil reservoir can be considered a simplified model of a sponge. If the reservoir is finely pored and sponge-like, then oil recovery is very poor (less than 30%), while if the pores are of large diameter, then recovery will be very high (over 60%). 

This so-called "active" layer has characteristics similar to those of cellulose acetate films but with a thickness of the order of 0.1 micrometer (jjm) or less, whereas the total membrane thickness may range from approximately 75 to 125 ym (see Figure 1). The major portion of the membrane is an open-pore sponge-like support structure through which the gases flow without restriction. The permeability and selectivity characteristics of these asymmetric membranes are functions of casting solution composition, film casting conditions and post-treatment, and are relatively independent of total membrane thickness. 

As an example of hybridization of zeolites with cellulose derivatives, self-supporting zeolite membranes with a sponge-like architecture and zeolite microtubes were prepared by using CA filter membranes as a template [154]. The hierarchical structure with sub-nanometer- to micrometer-sized pores is a characteristic of great promise for a wide range of applications such as catalysis, adsorption, and separation. There was also an attempt to prepare alginate membranes incorporated with zeolites, e.g., for pervaporation separation of water/acetic acid mixtures [155]. 

Semiconductor fabrication techniques permit the feature size of Si-based devices to reach into the deep submicron regime [i]. Additionally, Si can be anodized electrochemically or chemically (e.g., in an HF-containing electrolyte) to produce a sponge-like porous layer of silicon, with pore dimensions that range from several microns in width to only a few nanometers [ii]. These properties of Si make it a useful substrate for fabricating sensor platforms, photonic devices and fuel cell electrodes [iii]. 

It has an open sponge-like morphology of interconnected Au ligaments with a narrow pore size distribution. The pore size can be controlled during the manufacturing process, ranging from 10 to 1000 nm. This medium may be an interesting alternative to silica-based materials for radiolysis studies. 

The oilseed reaches typically 112.8°C (235°F), as read by a thermometer near the die plate, and approximately 10-13% moisture. Internal pressure is 13 0 times greater than atmospheric pressure. At this pressure and temperature, all moisture, even injected steam, is compressed into the liquid phase. On release into atmospheric pressure, some of the moisture flashes to reach equilibria. This vaporizing moisture inflates the collets with internal pores and surface cracks, imparting a porous, sponge-like structure to the collet. 

The oilseed reaches 235°E at 10-13% moisture at the die plate under a pressure of 30 0 atmospheres. All the water (natural moisture, injected steam, and liquid water) is compressed into the liquid phase. When the product leaves the high-pressure interior of the expander, some of the moisture flashes to reach equilibrium at atmospheric pressure. The flashing inflates the collets with internal pores and surface cracks, giving the collets a sponge-like structure. Eigure 17 shows typical soybean collets made with expander for solvent extraction. 

Cellulose-based monoliths prepared from cross-linked sponge-like regenerated cellulose with a continuous, interconnected, open pore stmcture (50-300 p.m) are commercialized by Sepragen under the trade name Seprasorb and are available for ion-exchange chromatography. 

Fig. 1 shows the porous silicon structures formed on different silicon wafers. Porous silicon on p-type wafer is characteri d by a sponge-like structure with pore wall thickness of 2-4 nm and 5-6 rnn for wafers with resistivity of 12 and 0.03 Q cm, respectively (Fig. la,b). Porous silicon on n-type silicon (0.01 Q cm) shows a branch-like structure (Fig. lc,d). In this case mother pores branch out and form the daughter pores. The pore wall thickness is 7-10 nm for porous silicon anodized with the light exposition (Fig. Ic) and 15-20 nm for porous silicon anodized without the light exposition (Fig. Id). 

Raney nickel is a sponge-like material made up of 2.5-15 nm microcrystallites that are agglomerated into macroparticles several microns in diameter. The surface area and composition of these particles depend on the base concentration and temperature used for the removal of the aluminum from the alloy. High temperature preparations that remove almost all of the aluminum generally have a surface area of 50-80 m /g. Catalysts prepared at temperatures of 50°C or lower have more aluminum present and surface areas of 100-120 m /g. These surface areas are related to the pore diameters and pore volume of the catalysts. The more extensive the base attack on the alloy the larger the average pore diameter and pore volume of these particles and the smaller their surface area. ... 

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