Dielectric catastrophe

Many authors have discussed a dielectric catastrophe and the Mott transition in terms of the Clausius-Mossotti relationship... 

When the condition (RIV) = 1 is fulfilled, the refractive index/ dielectric constant goes to infinity, and we have a NM-M transition. The Herzfeld criterion when applied to metal-ammonia solutions does indeed predict (67,93) that localized, solvated electrons are set free by mutual action of neighboring electrons at metal concentrations above 4-5 MPM, and measurements (Fig. 20) similarly indicate a dielectric catastrophe in this concentration range. The simple Herzfeld picture has recently been applied by Edwards and Sienko (70) to explain the occurrence of metallic character in the Periodic Table. 

The earlier theoretical prediction of a M—NM transition is that derived from the work of Goldhammer23 and Herzfeld.14 These authors considered the effect of increasing density on the atomic polarizability and suggested that there would be a divergence in the polarizability or the dielectric constant causing the release of bound electrons. The Herzfeld criterion for dielectric catastrophe is given by. 

These experimental findings for low-frequency electromagnetic response are in contrast with the expectations for the Anderson IMT [99] in which electronic behavior is controlled by disorder. In the dielectric phase, electrons are bound by fluctuations of the random potential. On the metallic side of the transition, free carriers have short scattering times. In the metallic phase near the transition s is positive because the disorder causes dynamic polarization due to slowing diffusion due to localization effects. When approaching the IMT transition the localization effects increase and s diverges (dielectric catastrophe [120]). 

Even though this contribution is always negative, the total capacity must be positive - otherwise the capacitor would accumulate charge spontaneously. Thus Eq. (17.4) is only valid if f > rjm, so that there is no electronic overlap between the two plates. Similarly the use of a macroscopic dielectric constant in Eq. (17.5) presupposes a plate separation of macroscopic dimensions, and again the total capacity is positive. Only unphysical models or bad mathematical approximations can produce negative interfacial capacities, which enjoyed a brief spell of fame under the name of the Cooper-Harrison catastrophe [2]. 

Break down voltage (BDV) describes the highest voltage that can be applied to a capacitor without destroying the dielectric by a catastrophic breakdown. 

The dielectric strength can be defined as the voltage that will produce a catastrophic decrease in the resistance of an insulator divided by the thickness of the specimen, so that it has units of volts/length. It is affected by a variety of factors, including the polymeric structure, the specimen geometry, and the testing conditions. 

Another important advantage of MR fluids is their relative insensitivity to temperature changes and contamination. This arises from the fact that the magnetic polarization of the particles is not influenced by the presence or movement of ions or electric charges near or on the surface of the particles. Surfactants and additives that affect the electrochemistry of the fluid do not play a role in the magnetic polarizability of the particles. Further, bubbles or voids in the fluid can never cause a catastrophic dielectric breakdown in an MR fluid. 

Real-world experience has shown that the eventful failure of electrical equipment is frequently catastrophic. In particular, there is no doubt that transformer fires do produce askarel oxidation products in significant quantities. Studies have indicated that the breakdown of askarel transformer dielectric systems due to multi-stress aging may produce toxic products at concentrations of concern. The yield and distribution of products can be expected to depend upon the availability of oxygen. The major quantity of toxic products will undoubtedly be derived after the failure of the transformer has resulted in a fire situation. 

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