Solid contact

An inner filling solntion and internal reference electrode are used in macro ISEs due to a very good stability of the potential at the inner membrane-solution interface in such a setup (see Fig. 4.4). However, the presence of a solution inside a sensor could be a serious limitation for development of microelectrodes and may be nndesired for a variety of other reasons, inclnding ionic fluxes in the membrane and limited temperatnre range of sensor operation. There are several requirements for snch an inner contact. First of all, a reversible change of electricity carriers ions-electrons must take place at the membrane-substrate interface. The potential of the electrochemical reaction, ensuring this transfer, has to be constant, stable, and must not depend on the sample composition. At last, the snbstrate mnst not inflnence the membrane analytical performance. 

The first and very simple solid contact polymeric sensors were proposed in the early 1970s by Cattrall and Freiser and comprised of a metal wire coated with an ion-selective polymeric membrane [94]. These coated wire electrodes (CWEs) had similar sensitivity and selectivity and even somewhat better DLs than conventional ISEs, but suffered from severe potential drifts, resnlting in poor reproducibility. The origin of the CWE potential instabilities is now believed to be the formation of a thin aqueous layer between membrane and metal [95]. The dominating redox process in the layer is likely the reduction of dissolved oxygen, and the potential drift is mainly caused by pH and PO2 changes in a sample. Additionally, the ioiuc composition of this layer may vary as a function of the sample composition, leading to additional potential instabilities. 

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Gas-Solids Contacting Terms used in this section to describe the method by which gas may contact a bed of solids are the following ... 

Gas flow and solids flow are usually cocurrent, one exception being a countercurrent-flow spray diyer. The method of gas-solids contact-... 

FIG. 12-101 Alternative chambers and gas solids contacting methods in spray dryers. 

FIG. 18-89 Reactor-clarifier of the high-rate solids-contact type. (EIMCO Process Equipment Co.)... 

Softening lime-soda (high-rate, solids-contact clarifiers) 3.7... 

If a solids-contact clarifier is required, the surface-area requirement must exclude the area taken up by the reaction chamber. The reaction chamber itself is normally sized for a detention time of 15 to 45 min, depending on the type of treatment and the design of the unit. 

Even when solid surfaces are protected by oxide films and boundary lubricants, some solid-to-solid contact occurs at regions where the oxide film breaks down under... 

Figure 11. Solids contact clarifier without sludge blanket filtration. ...

Operation of slurry-recirculation solids contact units is typically controlled by maintaining steady levels of solids in the reaction zone. Design features of solids contact clarifiers should include ... 

Fluid coking is very insensitive to poor gas-solids contacting, but has one problem not faced by cat cracking or hydroforming. If the heavy residual oil is fed too fast to the reactor, the coke particles will become wetted and stick together in large unfluidizable lumps. Correct control of feed rate is necessary to prevent this bogging. 

Permissible gas velocities are usually set by entrainment, and for a given throughput the vessel diameter is thus determined. The amount of catalyst or other bed particles is set by reaction kinetics and the bubble-solids contacting expected. Very often there is a scale-up debit involved in fluid bed reactors. As mentioned earlier, small reactors... 

Reactor type Sampling and analysis Isothermality Solid contact Fluid- decaying catalyst Ease of construction... 

Fig. 47—Load-carrying and shearing behavior of confined ILs thin film. Liquid volume is decreased from volume 1 to volume 6 corresponding to a decreasing thickness of ILs films. The confined thin film of ILs exists at the contact area under a normal load of hundreds of MPa and undertakes shearing stress like a solid-solid contact.

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