Measurement of Al Freezing-Point Temperature: Effect of Initiation Process

In CCT documents it is stated that “...for the freezing curves of the metallic fixed points, the maximum observed temperature on the plateau should be taken as the best approximation of the liquidus temperature. The fixed points should be realized with the inner and outer liquid-solid interfaces and extend past the maximum by 10 % to 20 % of the fraction frozen, to clearly establish the value of the maximum and the resolution of its determination.” Also, it is accepted that “...the inner interface is essentially static. It is the temperature of the inner liquid/solid interface that is measured by the thermometer.” The analysis of freezing curves obtained by the standard method of fixed-point realization shows that the parameters of the initial part of the freezing curve, the mean temperature value of which is usually taken as the liquidus temperature, depend on how the inner interface is initiated. Variations in the duration and intensity of initiation cause changes in the initial part of the freezing curve and in the resulting SPRT measurement. Moreover, the relation between the duration of the initial section of the plateau with a minor temperature change and the duration of its final section with a significant slope also depend on the initiation method used and on the furnace temperature. The effect of freezing initiation conditions on the measurement result is individual for each fixed point because of the differences in thermophysical properties of metals and in conditions of the heat transfer from the liquid–solid interface to the thermometer. Aluminum has a maximum value of the melting specific heat in comparison with other metals used in ITS-90 fixed points; in the present study, the effect of the intensity and duration of the inner liquid–solid interface initiation was investigated both experimentally and through calculation.     

Aqueous-solution high-voltage resistors: Development, study, and application (review)

Development, studies, and applications of resistors based on aqueous solutions of salts, acids, and their mixtures are reviewed. Aqueous-solution resistors (ASRs) have a number of advantages as compared to resistors of other types: their bulk electric strength reaches 300 kV/cm for pulses of microsecond duration, their energy dissipation in a unit mass of a solution is an order of magnitude higher than that in metals, a liquid recovers rapidly its electric strength after a breakdown, the resistance value can be rapidly adjusted by replacing an electrolyte, resistors can be shaped arbitrarily, their inductance can be as low as a few fractions of 1 nH, they can be used in circuits operating at frequencies of up to ～1 GHz, they are fire-and explosion-proof, are simple to manufacture, and are inexpensive. The electric characteristics and behavior of solutions in fields of up to 50 kV/cm are refined. A list of combinations of electrode materials and dissolved substances, which operate for a long time, is presented. Criteria are given for considering the permittivity of water in the calculation of the skin-layer depth in a solution. The moisture proofness of ASR cases made of polymer materials is examined. A set of formulas for engineering calculations of several characteristics of ASRs is presented. The procedures of preparing the components, the ASR assembly, and their testing for tightness are described. The electric and service-life characteristics are presented. Along with other ASRs, much attention is being given to the hermetically sealed high-voltage small ASRs developed at the Russian Federal Nuclear Center (VNIIEF). They are serviceable in any positions in volumes with rarefied and compressed gases and oil insulation. Heat-induced changes in the volume of the solution were compensated by the following operations: changes in the geometry of the polymer case of the ASR within the limits of elastic deformations of its walls; profiling of cavities in the electrodes’ walls, so that no gas penetrates from them into the solution at an arbitrary ASR position; and separation of the solution from a hermetically sealed vapor-gaseous cavity in the electrode by an elastic diaphragm. Versions of ASR designs and their characteristics are presented for the following situations: limitation of currents in electric circuits at voltage of up to 100 kV; simulation of high-power loads, including a current of up to 300 kA of a pulsed electron beam; damping of electric oscillations and suppression of reflected pulses; a specified distribution of an electric field along the lengths of insulators for a voltage as high as ～ 3.5 MV; measurements of parameters of pulse voltage amplitudes of up to ～2 MV; the application of ASRs as high-voltage dynamic resistive-capacitive elements in circuits of voltage-multiplying generators for reducing the delay time of their operation; etc. This information, systemized for the first time, will be useful for specialists in development, research, and application of ASRs designed for different purposes.     

Modeling of the Process of Pyrolysis of Shale Particles

Based on an analysis of experimental data on the pyrolysis of Baltic shale, a kinetic model of the process with allowance for the polydispersity of fuel particles, secondary chemical reactions, and fragmentation of the particles has been constructed.     

Clinical and functional aspects of adverse effects of toxic substance complexes in firefighters

The study covered influence of combined toxic chemicals on fire extinguishers. Acute exposure of respiratory and peripheral nervous systems was demonstrated. Consequences of the exposure were proved to include polyneuropathies, neuroses and other health disorders.     

Strain hardening and wear resistance of nitrated steels and alloys

This study considers the results of an experimental evaluation of the ability of superficial layers of nitrated steels and alloys to resist damage in the conditions of frictional deformation and superficial plastic deformation. A new approach is offered to evaluate and choose modes of nitration of parts of friction assemblies.