Microporous sintered membrane

Figure 1.1 SEM of a microporous sintered membrane prepared from a PTFE-powder.

In the particulate-sol method a metal alkoxide dissolved in alcohol is hydrolyzed by addition of excess water or acid. The precipitate that results is maintained as a hot solution for an extended period during which the precipitate forms a stable colloidal solution. This process is called peptization from the Greek pep—to cook (not a misnomer many descriptions of the sol-gel process have a strong culinary flavor). The colloidal solution is then cooled and coated onto the microporous support membrane. The layer formed must be dried carefully to avoid cracking the coating. In the final step the film is sintered at 500-800 °C. The overall process can be represented as ... 

Zinc is electrodeposited from the sodium zincate electrolyte during charge. As in the zinc/bromine battery, two separate electrolytes loops ("posilyte" and "nega-lyte") are required. The only difference is the quality of the separator The zinc/ bromine system works with a microporous foil made from sintered polymer powder, but the zinc/ferricyanide battery needs a cation exchange membrane in order to obtain acceptable coulombic efficiencies. The occasional transfer of solid sodium ferrocya-nide from the negative to the positive tank, to correct for the slow transport of complex cyanide through the membrane, is proposed [54],... 

In general, UHMWPE is difficult to process because the resin does not flow when melted. However, there are alternative techniques to process this material, i.e., sintering, compression molding, ram extrusion, or gel processing. Microporous membranes can be made... 

The slip coating-sintering procedure can be used to make membranes with pore diameters down to about 100-200 A. More finely porous membranes are made by sol-gel techniques. In the sol-gel process slip coating is taken to the colloidal level. Generally the substrate to be coated with the sol-gel is a microporous ceramic tube formed by the slip coating-sintering technique. The solution coated onto this support is a colloidal or polymeric gel of an inorganic hydroxide. These solutions are prepared by controlled hydrolysis of metal salts or metal alkoxides to hydroxides. 

Another example of the use of XRD in material characterization is shown in Figure 4.2. The XRD pattern of a sintered opal membrane covered with a molecular sieve is shown. The membrane was prepared with the opal sample 81C [47] afterward, the produced membrane was covered with an AlP04-5 microporous molecular sieve synthesized on the surface [41],... 

Unfortunately due to time limitations, there was no time to coat these steam stable mesoporous membranes with a microporous silica toplayer. Microporous (doped) silica membranes have, however, been applied on conventional mesoporous Y-AI2O3 membranes which were not stable under SASRA conditions. On these membranes permeance measurements have been performed which showed that these membranes could be prepared with a very high selectivity under cleanroom conditions. Stability measurements on (doped) silica bulk material sintered at a high temperature (600-800°C) showed no change in the specific surface area during SASRA treatment. This is an indication that it should be possible to prepare a silica membrane that shows complete stability towards SASRA conditions. 

In contrast to dense inorganic membranes, the rate of advances toward industrial-scale applications of porous inorganic membranes has been rapid in recent years. In the early periods of this century, microporous porcelain and sintered metals have been tested for microfiltration applications and, in the 1940s, microporous Vycor-type glass membranes became available. Then in the mid-1960s porous silver membranes were commercialized. These membranes, however, have not seen large scale applications in... 

FIGURE 6.9 Microporous membrane structures (a) resulting from packing and sintering of ceramic nanoparticles and (b) ultramicroporous channels in the crystalline structure of a zeolite. 

Membrane symmetric or asymmetric microporous. Ceramic, sintered metals, or polymers with pores 0.2 to 1 pm. Symmetric polymers have a porosity of 60 to 85% asymmetric ceramic membranes, porosity 30 to 40%, are used for high pressure and higher temperature <200°C. 

The membrane nanoporous layers are proposed to be formed by laser sintering of nanopowders deposited onto the surface of microporous structure by sol-gel sedimentation/centrifugation technique. In principle, the method of laser sintering is well known [1], However, there is no wide application in practice of nanopowder processing up to date. A number of constraints defines what quality of sintered stmcture may or may not be achieved by this technique. On the whole, the comprehension of nanopowder sintering mechanisms by laser radiation is rather low. 

Fig 3 A sandwich-type reagent degasser. A, B, plastic blocks D. sintered metal disk M, microporous membrane and G, engraved groove [12]. 

The FIP microfiltration membranes were permanent microporous titanium dioxide (Ti02) membranes formed on the inside of 1.6 cm I.D. sintered stainless steel tubes with a membrane area of 0.029 m supplied by Du Pont Separation Systems, Seneca, SC. Membrane permeability was expressed as permeate flux divided by applied pressure (m s bar l). All membranes used in this study had an initial permeability of pure water of at least 9.8 m s" bar" at 37°C. The average pore diameters in the titanium dioxide layer are normally about 0.15 pm. 

Membrane symmetric or asymmetric microporous. ceramic, sintered metals or polymers with pores 0.2-1 gm. Symmetric polymers have a porosity of 60 to 85% asymmetric ceramic membranes, porosity 30 to 40%, are used for high pressure and higher temperature < 200 °C. Pressure 0.03-0.35 MPa. Pressure 0.3-0.5 MPa for ceramic. Hydraulic permeability. A 70 to 10000 g/s m MPa, capacity/unit 0.001-1 L/s. Liquid permeate flux 0.001-0.2 L/s m with the perme-... 

---