Basic Functions of the Separators

Separators serve two primary functions while having to keep the positive electrode physically apart from the negative in order to prevent any electronic current passing between them, they also have to permit an ionic current with least, possible hindrance. These two opposing requirements are best met by a compromise a porous nonconductor. 

The necessity of electronic insulation — the origin of the term separator — has to be met durably, i.e., often over many years within a wide range of temperatures and in a highly aggressive medium. Under these conditions no substance harmful to the electrochemical reactions may be generated. 

The unhindered ionic charge transfer requires many open pores of the smallest possible diameter to prevent electronic bridging by deposition of metallic particles floating in the electrolyte. Thus the large number of microscopic pores form immense internal surfaces, which inevitably are increasingly subject to chemical attack. 

Not only the electrolyte, but also the electrodes, directly or indirectly exert a chemical attack, either by an oxidation or reduction potential of the electrode material itself or by the generation of soluble oxidizing or reducing substances. 

In the older battery literature the term separator is frequently used very loosely, to include all nonmetallic solid components between the electrodes, such as supporting structures for active materials (tubes, gauntlets, glass mats), spacers, and separators in a narrow sense. In this section, only the last of these, the indispensable separating components in secondary cells, will be termed separators , distinguished from the others by their microscopically small pores, i.e., with a mean diameter significantly below 0.1 mm. 

The electronic insulation - the origin of the term separator ) - has to be durable, that is, it must be effective over many years over a wide range of temperatures and 

Handbook of Battery McOerials, Second Edition. Edited by Claus Daniel and Jurgen O Besenhard. 

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The basic function of the spectrometer is to separate the polychromatic beam of radiation coming from the specimen in order that the intensities of each individual characteristic line can be measured. In principle, the wide variety of instruments (WDXRF and EDXRF types) differ only in the type of source used for excitation, the number of elements which they are able to measure at one time and the speed of data collection. Detectors commonly employed in X-ray spectrometers are usually either a gas-flow proportional counter for heavier elements/soft X-rays (useful range E < 6keV 1.5-50 A), a scintillation counter for lighter elements/hard X-rays (E > 6keV 0.2-2 A) or a solid-state detector (0.5-8 A). 

The two most popular classic detector circuits for FM are the Foster-Seeley discriminator and the ratio detector. Other types of FM detection used today include phase-locked loop circuitry. The basic function of the discriminator is to convert the frequency swings in the FM signal back into amplitude variations for further audio processing. The discriminator is, therefore, susceptible to both amplitude and frequency variations. For this reason, the Foster-Seeley detector is always preceded by a limiter stage. The ratio detector on the other hand, acts like a limiter, and so there is no need for the use of a separate limiter stage. 

Nearly all these techniques involve interrogation of the surface with a particle probe. The function of the probe is to excite surface atoms into states giving rise to emission of one or more of a variety of secondary particles such as electrons, photons, positive and secondary ions, and neutrals. Because the primary particles used in the probing beam can also be electrons or photons, or ions or neutrals, many separate techniques are possible, each based on a different primary-secondary particle combination. Most of these possibilities have now been established, but in fact not all the resulting techniques are of general application, some because of the restricted or specialized nature of the information obtained and others because of difficult experimental requirements. In this publication, therefore, most space is devoted to those surface analytical techniques that are widely applied and readily available commercially, whereas much briefer descriptions are given of the many others the use of which is less common but which - in appropriate circumstances, particularly in basic research - can provide vital information. 

Finally, one development results from returning to a basic idea from the dawn of the lead-acid battery, wherein the functions of support for the positive active material and of the separator are combined into one component the gauntlet separator [84] consisting of a coarsely porous, flexible support structure coated with micropo-rous polyethylene material for separation. The future has to show whether this approach will be able to meet all demands. 

Stratified flow. A separated flow model for stratified flow was presented by Taitel and Dukler (1976a) in which the holdup and the dimensionless pressure drop, = (dpldz)TPl(dpldz)GS is calculated as a function of the Lockhart-Martinelli parameter only. (The results, however, differ from those of Martinelli and compare better with experimental data.) This model uses two basic approximations ... 

The dynamic mechanical behavior indicates that the glass transition of the rubbery block is basically independent of the butadiene content. Moreover, the melting temperature of the semicrystalline HB block does not show any dependence on composition or architecture of the block copolymer. The above findings combined with the observation of the linear additivity of density and heat of fusion of the block copolymers as a function of composition support the fact that there is a good phase separation of the HI and HB amorphous phases in the solid state of these block copolymers. Future investigations will focus attention on characterizing the melt state of these systems to note if homogeneity exists above Tm. 

In order to determine the force between plates as a function of their separation, one would have to perform a series of simulations with different wall separations and with the chemical potential of the fluid fixed at the bulk value. This is technically feasible, but very computationally intensive [42]. The qualitative behavior of the force law can, however, be estimated from the density profile of a fluid at a single wall using the wall sum rule and a superposition approximation [31,43]. The basic idea is that the density profile [denoted pH(z)] of a fluid between two walls at a separation H can be obtained from the density profile [denoted pj (z) of the same fluid at a single wall using... 

By combining a-aminophenylacetic acid with d-camphorsulphonic acid Betti and Mayer in 1908 separated it into its isomers. This seems to be the first case in which the basic function of an amino acid has been requisitioned for purposes of separation in all the above cases, the acidic function, by combination with optically active bases, has been made use of... 

Solute equilibrium between the mobile and stationary phases is never achieved in the chromatographic column except possibly (as Giddings points out) at the maximum of a peak (1). As stated before, to circumvent this non equilibrium condition and allow a simple mathematical treatment of the chromatographic process, Martin and Synge (2) borrowed the plate concept from distillation theory and considered the column consisted of a series of theoretical plates in which equilibrium could be assumed to occur. In fact each plate represented a dwell time for the solute to achieve equilibrium at that point in the column and the process of distribution could be considered as incremental. It has been shown that employing this concept an equation for the elution curve can be easily obtained and, from that basic equation, others can be developed that describe the various properties of a chromatogram. Such equations will permit the calculation of efficiency, the calculation of the number of theoretical plates required to achieve a specific separation and among many applications, elucidate the function of the heat of absorption detector. 

C-P-Q is converted to the charge separated diradical state C h-P -Q-. Then an electron is transferred from Q to the lipid-soluble 2,5-diphenylbenzoquinone Qs 133b yielding Qs. In the third step uncharged semiquinone QsH is formed when the latter accepts a proton from the external aqueous solution. The basic function of a proton shuttle is carried out when the semiquinone radical diffuses through the membrane in the fourth step. It is then oxidized to Qs + by the carotenoid radical cation... 

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