Porous casting surfaces

The results for the removal of PAHs from the 5 surface substrates are summarized in Table 16. In general, the 23 PAHs listed in the table averaged removal rates around 90% from the smooth surfaces and over 80% for the porous cast magnesium surface. In contrast, supercritical fluid extraction studies using CO2 for the removal of PAHs from soils for environmental applications have shown relatively poor removal efficiencies for many of the compounds listed in the table often requiring the addition of secondary solvents to the C02. However, it appears that from the results on the removal of the PAHs shown in Table 16, surface contamination is... 

Slurry or slip casting provides a relatively inexpensive way to fabricate unifonn-thickness, thin-wall, or large cross section shapes [4o, 44, 45, 46, 42 aiid 48]. For slip casting, a slurry is first poured into a porous mould. Capillary suction then draws the liquid from the slurry to fonn a higher solids content, close-packed, leather-hard cast on the inner surface of the mould. In a fixed time, a given wall thickness is fonned, after which the excess slurry is drained. 

Another type has several flat plates manifolded into a plastic header. The surface of the laminate is suitable for dip-casting membranes, whereas the interior is several orders of magnitude more porous. Permeate collects in the center of the laminate and drains into the header. 

Cellulose acetate films, specially cast to have a dense surface and a porous substmcture, are used in reverse osmosis to purify brackish water (138—141) in hollow fibers for purification of blood (artificial kidney) (142), and for purifying fmit juices (143,144) (see Membrane technology). 

The scale can also be removed by shot blasting using abrasive grits such as dry sand, less than I mm (p. This method is more suited for components not suited to the dip method and cast iron components, in which the acid may become trapped in the porous surfaces. For sheet-metal components and complicated shapes and crevices, the dip method alone is recommended. 

A process for making hollow articles from latex. A heat-sensitised compounded latex is poured into a hollow non-porous mould which is then rotated about several axes until the latex has gelled on the surface of the mould. See Rotational Moulding. Similar to slip casting of ceramics. Ketones... 

In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity-hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H20 wt% in the pervaporate in the range 83-92 and a water selectivity, aH2o, of 250 at 25 °C) is higher than that of the non-treated one (aH2o = 19) as well as that of the acrylic acid treated membrane (aH2o = 22). 

In addition to the criticisms from Anderman, a further challenge to the application of SPEs comes from their interfacial contact with the electrode materials, which presents a far more severe problem to the ion transport than the bulk ion conduction does. In liquid electrolytes, the electrodes are well wetted and soaked, so that the electrode/electrolyte interface is well extended into the porosity structure of the electrode hence, the ion path is little affected by the tortuosity of the electrode materials. However, the solid nature of the polymer would make it impossible to fill these voids with SPEs that would have been accessible to the liquid electrolytes, even if the polymer film is cast on the electrode surface from a solution. Hence, the actual area of the interface could be close to the geometric area of the electrode, that is, only a fraction of the actual surface area. The high interfacial impedance frequently encountered in the electrochemical characterization of SPEs should originate at least partially from this reduced surface contact between electrode and electrolyte. Since the porous structure is present in both electrodes in a lithium ion cell, the effect of interfacial impedances associated with SPEs would become more pronounced as compared with the case of lithium cells in which only the cathode material is porous. 

Along this line, sol-gel materials based on Si02find increasing use in solid-phase assisted synthesis. The sol-gel synthesis creates well ordered porous glasses which retain a rigid and exposed surface area (300-1000 m g ) [56]. Gelation occurs after a sol is cast into a mold so that the monolithic samples can be tailored to a desired size or shape [57]. 

An early generation of composite membranes, developed by Riley, et al. (21), was based on cellulose triacetate (CTA) cast in an ultrathln coat from chloroform on the finely porous surface of a cellulose nitrate/cellulose acetate substrate. These membranes did not reflect a need for a hydrophllic-gel Intermediate layer. Yet, this membrane substrate is much more hydrophilic than the rejecting CTA layer, and high flux as well as high separation were concurrently obtained. This is not the case if the porous substrate is highly hydrophobic. A rejecting layer deposited on such a surface would yield an extremely poor productivity due to the loss of... 

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