Pore tailoring

Kharitonov et al. [59] have shown that direct fluorination of the polyimide Matrimid is possible, hence the resulting membrane should have a nice potential for use in harsh environment. Perfluorinated materials were also studied by Hagg [60] for chlorine gas purification, and were shown to be exceptionally stable in these harsh environments. The selectivity was however too low. In a later publication on chlorine purification [31] it was suggested to use perfluorinated monomers as surface-modifying compounds for pore tailoring of glass membranes for chlorine gas separation. 

The CMS membranes may be prepared in two different ways, and in both cases the pore tailoring is the focus for the final membrane ... 

The CMS membranes are prepared by carbonizing (under pyrolysing conditions) the precursor membranes in a high temperature tube furnace, as shown in Figure 15.4. The step-by-step method (several dwells) most commonly used as the protocol for the carbonization process is described elsewhere. Many researchers report different carbonization conditions in their research works illustrating very well that each precursor will need different protocols in order to be pore tailored for specific applications. " The carbonization process is the most important step for fabrication of CMS membranes and is used to tailor the pore size and structure of the carbon membranes. Therefore, how to control the carbonization conditions is crucial for the resulting CMS membrane performance. Su and Lua reported that the statistical 2" factorial... 

The large majority of activated alumina products are derived from activation of aluminum hydroxide, rehydrated alumina, or pseudoboehmite gel. Other commerical methods to produce specialty activated aluminas are roasting of aluminum chloride [7446-70-0], AIQ calcination of precursors such as ammonium alum [7784-25-0], AlH2NOgS2. Processing is tailored to optimize one or more of the product properties such as surface area, purity, pore size distribution, particle size, shape, or strength. 

Industrial carbon anodes and artificial graphites are not a single material but are rather members of a broad family of essentially pure carbon. Fortunately, artificial graphites can be tailored to vary widely in their strength, density, conductivity, pore structure, and crystalline development. These attributes contribute to their widespread applicability. Specific characteristics are imparted to the fmished product by conti ollmg the selection of precursor materials and the method of processing [19]... 

Activated carbon is an amorphous solid with a large internal surface area/pore strucmre that adsorbs molecules from both the liquid and gas phase [11]. It has been manufactured from a number of raw materials mcluding wood, coconut shell, and coal [11,12]. Specific processes have been developed to produce activated carbon in powdered, granular, and specially shaped (pellet) forms. The key to development of activated carbon products has been the selection of the manufacturing process, raw material, and an understanding of the basic adsorption process to tailor the product to a specific adsorption application. 

As RO membranes become looser their salt rejection falls (see Section 31.8.1). Eventually a point is reached at which there is no rejection of salts, but the membrane still rejects particulates, colloids and very large molecules. The membrane pore size can be tailored to a nominal molecular weight cut-off. The resulting filtering process is called ultra-filtration. 

For L=NH3 (1) and L=Pr2NH (3), the isotherms are of type II as expected for non-porous materials [27]. Sample 2 shows a significant uptake at 0.6

narrow particle-size distribution which results in a more regular packing with interparticle pores of size similar to that of the particles [27]. The latter shows that the ligand-assisted synthesis does not only allow one to affect the total surface area and particle size, but also the size distribution which is an important tool for tailoring the particle properties. 

To overcome the limitations of natural zeolites a whole range of synthetic zeolites have been manufactured since the 1950s. These have tailored pore sizes and tuned acidities, as well as often incorporating other metal species. The basic synthesis involves mixing a source of silica, usually sodium silicate or colloidal Si02, with a source of alumina, often sodium aluminate, and a base such as sodium hydroxide. The mixture is heated at temperatures up to 200 °C under autogenous pressure for a period of a few days to a few weeks to allow crystallization of the zeolite. 

For many years, research efforts in materials chemistry have focused on the development of new methods for materials synthesis. Traditional areas of interest have included the synthesis of catalytic, electronic, and refractory materials via aqueous methods (sol-gel and impregnation) and high-temperature reactions [1-3]. More recent strategies have focused on the synthesis of materials with tailored properties and structures, including well-defined pores, homogeneously distributed elements, isolated catalytic sites, comphcated stoichiometries, inorganic/organic hybrids, and nanoparticles [4-13]. A feature... 

Figure 41.6 illustrates the typical capabilities in tailoring Si-TUD-1 pore diameter using different hydrothermal treatment times (10). The pore diameter can be varied from 4 to 19 nm by increasing the hydrothermal heating time from 0 to 48 hours. The sample with 48 hours of hydrothermal treatment still had an appreciable surface area of400 m /g. 

Improved characterization of the morphological/microstructural properties of porous solids, and the associated transport properties of fluids imbibed into these materials, is crucial to the development of new porous materials, such as ceramics. Of particular interest is the fabrication of so-called functionalized ceramics, which contain a pore structure tailored to a specific biomedical or industrial application (e.g., molecular filters, catalysts, gas storage cells, drug delivery devices, tissue scaffolds) [1-3]. Functionalization of ceramics can involve the use of graded or layered pore microstructure, morphology or chemical composition. 

This research has given insight to a very unique bicontinuous blend system. It has also shown that the pore structure and release rates from EVAc matrices are not only dependent on particle size and loading but also on the blending technique. It becomes apparent that it is possible to tailor these systems not only for release rates but also for initial time of release of insoluble biologically active agents. 

Vertical media with very high coercivities can be produced by plating into alumina pores [112], Some of these media are too hard to be easily written with present heads. Tailoring of the pore size can be used to obtain structures with the desired Hc [115, 116], however. Recording characteristics of disks have been determined [112-114, 116] such media show excellent promise as vertical recording media. In addition, structures with electrodeposited Fe in the pores were tested in life-tests at elevated temperatures and humidity and in corrosive atmospheres. They were found to perform satisfactorily. 

---