Thin porous

Filtration may also serve as the preparatory step for the operation following it. The latter stages may be drying or incineration of solids, concentration or direct use of the filtrate. Filtration equipment must be selected on the basis of their ability to deliver the best feed material to the next step. Dry, thin, porous, flaky cakes are best suited for drying where grinding operations are not employed. In such cases, the cake will not ball up, and quick drying can be achieved. A clear, concentrated filtrate often aids downstream treatment, whereby the filter can be operated to increase the efficiency of the downstream equipment without affecting its own efficiency. 

Through these processes dissolved substances and/or finely dispersed particles can be separated from liquids. All five technologies rely on membrane transport, the passage of solutes or solvents through thin, porous polymeric membranes. 

In most of its uses, e.g. the external surfaces of tinplate cans, tinned steel has only to resist condensed moisture. In the absence of pollution of the atmosphere by unusually large amounts of sulphur dioxide or chlorides, or of several days of continuous wetting, tinned steel remains unrusted even the thin porous coatings on the common grades of tinplate remain bright and unmarked over the periods involved in the commercial handling and domestic storage of cans, and the domestic use of kitchenware. When... 

Sheet steel is normally prepared for application of enamel by a sequence of operations including thorough degreasing, acid pickling and neutralisation. A nickel dip stage is often included to deposit a thin, porous layer of nickel applied at about 1 g/m especially when conventional groundcoat is not used (see Section 13.7). 

Figure 7. Cyclic voltammogram of 7% w/w FePc dispersed on Vulcan XC-72 carbon. The specimen was prepared by mixing the carbon with an FePc solution In pyridine and subsequently removing the solvent by boiling It off. The sample was then heat treated at 300°C In flowing He to remove coordinated pyridine. The cyclic voltammogram was obtained with the material In the form of a thin porous coating In 1 M NaOH at 25 C. Sweep rate 5 mV s (19).

Several mechanisms have been proposed to explain the activation of carbon surfaces. These have Included the removal of surface contaminants that hinder electron transfer, an Increase In surface area due to ralcro-roughenlng or bulld-up of a thin porous layer, and an Increase In the concentrations of surface functional groups that mediate electron transfer. Electrode deactivation has been correlated with an unintentional Introduction of surface contaminants (15). Improved electrode responses have been observed to follow treatments which Increase the concentration of carbon-oxygen functional groups on the surface (7-8,16). In some cases, the latter were correlated with the presence of electrochemical surface waves (16-17). However, none of the above reports discuss other possible mechanisms of activation which could be responsible for the effects observed. 

Aspekt-Modifikator-U Single-use agent which produces a thin porous film capable of retaining lubricant on the surface of engine and transmission components. Reduces noise, wear, varnish formation and fuel consumption and improves detergency. 

Alternative forms of sorbent bed have been developed. These include thin porous glass-fibre or PTFE disks in which sorbent particles are embedded, and disposable plastic pipette-tips fitted with small sorbent beds. 

Fig. 1 shows the cyclic voltammetry of an FePc/XC-72 dispersion, heated at 280°C in an inert atmosphere, in the form a thin porous Teflon bonded coating electrode in a 1 M NaOH solution. A description of the methodology involved in the preparation of this type of electrode may be found in Ref. 3. As can be clearly seen, the voltammetry of this specimen exhibits two sharply defined peaks separated by about 330 mV. The potentials associated with these features are essentially identical to those found by other workers for the reduction and oxidation of films of iron oxy-hydroxide formed on a number of host surfaces, including iron and carbon.(5)... 

Fig. 1. Cyclic voltammetry of 7% w/w iron phthalocyanine, FePc dispersed on Vulcan XC-72 carbon, after a heat treatment at 280°C in a flowing inert atmosphere. The measurement was conducted with the material in the form a thin porous Teflon bonded coating in 1 M NaOH at 25°. Sweep rate 5 mV/s. (Reproduced with permission from ref. 3. Copyright 1985 Elsevier.)...

The dependence of the PL spectra on temperature is again quite complicated. The change from a Gaussian-shaped PL spectrum at RT to a multi-peak spectrum at 5 K for low excitation energies was initially interpreted in terms of an interference effect in the thin porous layer [Ho3]. Later work, however, showed that the peak positions are independent of PS layer thickness, excitation wavelength and sample rotation [Ke3]. The spacing of the peaks is about 61 meV. The origin of this fine structure is still controversial [Ro4],... 

A thin, porous, and highly vascularized epithelium with high total blood flow per cubic centimeter, which ensures rapid absorption and onset of therapeutic action... 

Inorganic membranes employed in reaction/transport studies were either in tubular form (a single membrane tube incorporating an inner tube side and an outer shell side in double pipe configuration or as multichannel monolith) or plate-shaped disks as shown in Figure 7.1 (Shinji et al. 1982, Zaspalis et al. 1990, Cussler 1988). For increased mechanical resistance the thin porous (usually mesoporous) membrane layers are usually supported on top of macroporous supports (pores 1-lS /im), very often via an intermediate porous layer, with pore size 100-1500 nm, (Keizer and Burggraaf 1988). 

Initially devised to measure interactions in single soap films (air/water/air) [8], the TFB technique has been progressively improved and its application has been broadened to emulsion films (oil/water/oil) [ 12] and asymmetric films (air/water/oil or air/water/solid) [13,14]. In a classical setup, a thin porous glass disk is fused on the side to a capillary tube and a small hole is drilled in the center of the disk. The liquid solution fills the disk, part of the capillary, and a thin horizontal film is formed across the hole. The disk is enclosed in a hermetically sealed box, with the capillary tube exposed to a constant reference pressure Pr. Under the effect of the pressure difference AP between the box and the reference, the... 

Additionally, they have been used as porous layer beads (PLB) (10, i I), in which case a thin porous adsorbent layer is coated onto a fluid impervi-(Mi> core, snch ns solid glass bends. The thickness of (he porous Inyci is generally 1-3 pm, i.e., to of the particle diameter, and the par-... 

There are other secondaiy standard electrodes, and one that is often used as a secondaiy standard is the Ag-AgQ electrode. It consists of an Ag wire that has been made an anode in a chloride-containing solution. The resulting evolution of Cl2 forms a thin porous film of AgCl on the silver wire. The wire and its layer are immersed in a standard KC1 solution and the electrode is reversible with respect to Cl- on the grounds of reasoning similar to that presented for calomel. The potential of this electrode is 0.222 V versus the standard H2 electrode. 

Figure 25-10 shows a rapid separation of proteins on superficially porous particles, which consist of a 0.25-p.m-thick porous silica layer on a 5-pm-diamctcr nonporous silica core. A stationary phase such as Clg is bonded to the thin, porous outer layer. Mass transfer of solute into a 0.25-p.m-thick layer is 10 times faster than mass transfer into fully porous particles with a radius of 2.5 pm. enabling high efficiency at high flow rate. Superficially porous particles are especially suitable for separation of macromolecules such as proteins, which diffuse more slowly than small molecules. 

The adsorbents in HPLC are typically small-diameter, porous materials. Two types of stationary phases are available. Porous layer beads (Figure 3.14A) have an inert solid core with a thin porous outer shell of silica, alumina, or ion-exchange resin. The average diameter of the beads ranges from 20 to 45 fim. They are especially useful for analytical applications, but, because of their short pores, their capacities are too low for preparative applications. 

Ion Engines. Saunders (Ref 6a) reports successful usage of porous W platelets for ionizing the N2 working medium in exptl ion-powered rocket engines. Thin, porous W platelets were developed by sintering compacted 1-micron powder at 2750°F for 20 hrs in a H2 atm... 

A single-cell sensor based on the measurement of the limiting current can function properly only if the rates of the electrode reaction (1) and its inverse are higher than the rate by which O2 molecules arrive at the electrode by diffusion. The ability of an electrode to support reaction (1) and its reverse is conventionally expressed(fi) by the so-called exchange current density Jg, which is of the order of 1 A/cm2 for thin porous Pt electrodes at T > 600 C. 

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