Aspects of electrical breakdown of liquid insulating material I

Summary The electrical breakdown strength of insulating oil depends on the size of foreign particles which may form bridges in a place of maximum electric stress. This theoretical relation was verified with colloid suspensions of particles of known radius. Mineral oils may deteriorate if the particles unite by the process of flocculation, the occurrence of which depends on the relative magnitudes of the attractive London-Van der Waals forces acting between the particles and the repulsive forces between their ion atmospheres. The possibility of using a mineral oil as an insulator depends on the existence of an upper limit of the size of particle complexes due to the rapid fall-off of the L.-v.d.W. forces at diameters exceeding 500 Å. The latter value of 2r corresponds to a breakdown strength of 1 kV/mm. If acids are being formed, the upper limit of 500 Å will shift towards larger values, and correspondingly the breakdown strength may drop below 1 kV/mm.     

Measurement and analysis of the infrared reflection spectrum of semiconducting SnS

The infrared reflection spectrum of p-type SnS single crystals was measured between 2 and 25μ. The observed dispersion was ascribed to the combined effects of lattice vibrations and free holes. An analysis gave for the index of refraction n₀ = 3.6 ± 0.1, the dielectric constant = 19.5 ± 2, and the effective charge on the atoms e^* = 0.7e₀.

The effective mass of holes is isotropic in the plane perpendicular to the c-axis, with m^* = 0.20m₀; the effective mass parallel to the c-axis is much larger: m^* m₀.     

Breakdown of liquid insulating and dielectric material

Summary One of the possible causes of long-time breakdown of low-frequency impregnated paper capacitors and cables is known to be the long-time formation of a conducting bridge between the electrodes, followed by a short-time thermal breakdown. Such a bridge may consist of polarizable particles, ions or colloidal contaminants of high dielectric constant, particularly conducting material. These particles flow towards a place of maximum stress because of the action of transverse quadratic gradient-E-forces in a nonuniform field, thus forming a conducting path for the short-time development of gas and the subsequent breakdown by ionization. From a long-time breakdown strength of 50 kV/mm there follows a particle diameter of about 40 ?.     

Varying the Lewis base coordination of the Y2N2 core in the reduced dinitrogen complexes {[(Me3Si)2N]2(L)Y}2(μ-η2:η2-N2) (L = benzonitrile, pyridines, triphenylphosphine oxide, and trimethylamine N-oxide)

The effect of the neutral donor ligand, L, on the Ln(2)N(2) core in the (N═N)(2-) complexes, [A(2)(L)Ln](2)(μ-η(2):η(2)-N(2)) (Ln = Sc, Y, lanthanide; A = monoanion; L = neutral ligand), is unknown since all of the crystallographically characterized examples were obtained with L = tetrahydrofuran (THF). To explore variation in L, displacement reactions between {[(Me(3)Si)(2)N](2)(THF)Y}(2)(μ-η(2):η(2)-N(2)), 1, and benzonitrile, pyridine (py), 4-dimethylaminopyridine (DMAP), triphenylphosphine oxide, and trimethylamine N-oxide were investigated. THF is displaced by all of these ligands to form {[(Me(3)Si)(2)N](2)(L)Y}(2)(μ-η(2):η(2)-N(2)) complexes (L = PhCN, 2; py, 3; DMAP, 4; Ph(3)PO, 5; Me(3)NO, 6) that were fully characterized by analytical, spectroscopic, density functional theory, and X-ray crystallographic methods. The crystal structures of the Y(2)N(2) cores in 2-5 are similar to that in 1 with N-N bond distances between 1.255(3) ? and 1.274(3) ?, but X-ray analysis of the N-N distance in 6 shows it to be shorter: 1.198(3) ?.     

Dimensionality selection in a molecule-based magnet

Gaining control of the building blocks of magnetic materials and thereby achieving particular characteristics will make possible the design and growth of bespoke magnetic devices. While progress in the synthesis of molecular materials, and especially coordination polymers, represents a significant step towards this goal, the ability to tune the magnetic interactions within a particular framework remains in its infancy. Here we demonstrate a chemical method which achieves dimensionality selection via preferential inhibition of the magnetic exchange in an S=1/2 antiferromagnet along one crystal direction, switching the system from being quasi-two- to quasi-one-dimensional while effectively maintaining the nearest-neighbor coupling strength.     

X‐ray diffraction,differential scanning calorimetry and evolved gas analysis of aged plutonium tetrafluoride (PuF4)

Journal of Radioanalytical and Nuclear Chemistry - A 30 year-old PuF4 sample consisting of brown powder (PuF4-b) and pink granules (PuF4-p) was analyzed. X-ray diffraction shows the bulk...     

Testing the electric strength of liquid dielectric or insulating material

Summary Starting from the assumption that electric breakdown of liquid hydrocarbons takes place in general far below the intrinsic breakdown strength owing to irremovable and filterable contaminants flowing towards a place of maximum stress where a conducting bridge may be formed, the authors attempt to combine the theory they propose with earlier experimental results. Hydrocarbon oil of rather poor quality was purified by means of an electrostatic Cottrell-filter. This filter removed most of the foreign particles of high dielectric constant, by which the one-hour breakdown strength was increased from about 10 kV/mm to 60 kV/mm.     

Dipoles and electric breakdown

Summary It is shown that breakdown of insulating or dielectric material may be caused either by polarizable particles or permanent dipoles. Induced dipoles as well as permanent dipoles may gather at a place of maximum stress and form a bridge. Bridges consisting of permanent dipoles may cause the gap between the valence energy band and the conduction energy band to be filled by impurity or imperfection levels. The low ionization potentials of electrons attached to permanent dipoles may facilitate breakdown. An attempt is made to reconcile Crowe's results with ours.