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Two years ago at this Conference we presented a paper in which it was demonstrated that the sparking potentials of simple hydrocarbon gases could be related directly to certain physical properties of the molecules of which the gases were composed(1). In order to accomplish this it was first necessary to derive an expression relating the first Townsend coefficient, α, of a gas to the pressure, P, the...
In our investigation of the mechanism of electric breakdown in liquids, we have endeavored to measure a value for the electric strength that is characteristic of the liquid itself; ideally, that value which is free from the influence of all external factors such as electrode composition, surface condition, and configuration. However, because the influence of such factors as these cannot be completely...
The physical processes operative in the development of electrical breakdown in a dielectric are often reflected in the time interval between the application of a d.c. voltage and the appearance of the spark. This time may include both the time required for a free electron to appear near the cathode (statistical time lag) and the time required for the spark to develop after such an electron begins...
A broad-band spectral analysis was undertaken of the dielectric properties of ferrites (polarization, magnetization and conduction) from d.c. to the optical spectral region. After a short description of the various measurement techniques employed, characteristic data are given of electronic conduction, space-charge polarization, infrared absorption, and ferromagnetic resonance. Various additional...
The field of science and engineering which deals with electrical insulation, its properties, and its applications, is indeed a diversified one, as is demonstrated by the table of contents of this Digest. Consequently, it is difficult to decide whether one accomplishment contributes more to our understanding of the field than another. However, the authors of the various chapters of the Digest have...
The influence of the nature of the cathode metal upon the breakdown of liquid dielectrics has been studied by many investigators. However, the sensitivity of the electron emission characteristics of a metal to the physical and chemical condition of its surface makes it very difficult to obtain reproducible results, Bragg, Sharbaugh, and Crowe (1) have attempted to bypass this difficulty by using an...
While many intensive investigations have been made on a few gases (e.g. the noble gases, hydrogen, nitrogen and air) in an effort to elucidate the mechanism of spark breakdown, little effort has been made to correlate the sparking potential with molecular structure (la). We have attempted to do this by studying a series of closely related saturated hydrocarbons from C1 through C6, including straight...
In 1951 it was reported by Salvage (1) that the electric strengths of liquid straight-chain aliphatic hydrocarbons, as measured under d.c. conditions between hemispherical electrodes, increased with increase in the chain length of the hydrocarbon molecules. Until that time, a correlation of electrical breakdown of liquids with known molecular properties had been virtually impossible because of inadequate...
For some twenty-five years the decrease in the measured electric strength of liquids with increasing electrode spacing has been an important subject of study because of its practical as well as theoretical significance. Early investigators were handicapped by the lack of reproducibility of electric strength values as well as their inability to measure accurately small electrode spacings. With the...
Franz (1) has written (in German) a detailed review article concerning the theory of “intrinsic” electric breakdown in solids. The review, fifty-five pages in length, includes twenty-three figures and sixty literature references. Franz devotes a chapter to each of the following topics: (a) theory of electronic processes in crystalline solids, including a discussion of electronic energy states and...
A crucial test of any theory of electrical breakdown is the comparison of observed and predicted temperature dependence of the electric strength. The theories of von Hippel, Seitz, and Callen give the proper temperature dependence at low temperatures (for ionic crystals) but the agreement is lost at high temperature. In order to explain the high temperature region, Fröhlich has adduced another breakdown...
It has been reported-recently by Salvage (1) that the electric strengths of liquid, straight-chain hydrocarbons increase with increase in molecular weight from n-pentane through n-nonane. The purpose of the present work is to verify and investigate more carefully this behavior, and to interpret the results, if possible, in terms of the physical properties of the hydrocarbons.
In this review a year ago a good deal of space was devoted to an extensive development by Heller (1951) of a “steady-state” theory of breakdown of solids. Almost simultaneously W. Franz developed a similar theory, reports of which appeared in German journals in January (1) and June (2) of 1952. The underlying ideas of the work of Franz are in most instances very close to those of Heller, so that the...
The electron emission characteristics of the surface of the cathode used in the study of the electric breakdown of insulators are believed to have a fundamental bearing on electric strengths observed. It has been suggested that the formation of a negative space charge is the mechanism through which this influence is exerted1.
The low frequency dielectric properties of 1-monopalmitin, 1-monostearin, 1,3-dipalmitin, 1,3-distearin and a number of long-chain triglycerides have been investigated in the solid state over a wide range of temperature, The measurements were made with the aid of an impedance bridge operating in the frequency range from 0.5 to 100 kilocycles.
The dielectric constant is a very useful tool for studying molecular freedom and phase changes in organic polar compounds. Its magnitude can be used as an indication of the degree of orientational freedom of molecules in both liquid and solid phases. Thermal behavior is another useful tool, which, when combined with dielectric constant data, can often be helpful in describing phase changes in terms...
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