Attempts to obtain high critical temperature superconductors by means of organic or related superconductor models are reviewed. These attempts may be classified into five types: (1) Little's model and its modification (2) Ginzburg's model and its modification (3) Perlstein's model and its modification (4) attempts based upon electrically conductive polymers (5) attempts by means of biochemical preparation. None of them have yet been successful, but in many respects progress is being made. These attempts seem to try to find new mechanisms for synthesizing superconductors, e.g. the exciton mechanism, which differ from the already known phonon-electron interaction machanism.
Niobium is drawing attention as the principal material of superconductor. It has been used as an additive in steel for these about twenty years. In many well-known fields, Niobium is now beeing extensively used as industrial material. This paper is intended to introduce an outline of the raw materials, metallurgical processing, production and uses of Niobium based, as much as possible, upon statistical data.
Mechanical properties and microstructural changes of 18wt%Cr-8wt%Ni stainless steel deformed at 4.2°K. were investigated. The elastic limit and tensile strength of 18wt%Cr-8wt%Ni stainless steel annealed at 1, 050°C for 1hr were 45kg/mm2 and 155kg/mm2, respectively. Serrated stress-strain curve was observed and several stages in work hardening were experimentally distinguishable. The first stage is characterized by the pseudo-easy glide of γ phase, the second stage shows a rapid increase in work hardening by the martensite transformation. These two stages are linear hardening, but the third stage is parabolic hardening. α′ phase is formed in ε phase at least in the first stage and the process of γ phase to α′ phase transformation is appeared by γ→ε→α′. The relation between grain diameter and elastic limit was given by the “Petch” formula. Lattice constants of α′ and ε phase formed at 4.2°K are a=2.87Å for α′ phase, and a=2.55Å and c=4.01Å for ε phase.
A simple calibration method of thermocouples is described. An apparatus was constructed and Constantan vs. Chromel thermocouple was used. Its handling and temperature-emf curve are mentioned. The apparatus is a continuous flow cryostat and temperature in sensor is controlled by flow rate of liquid N2 (or He) and heater. Absolute values of temperature were determined with vapor pressure thermometer. Both junctions of thermocouple thermometers were soldered with silver solder without twisting. Wood's metal solder was used to install dissimilar junctions on sensor. Liquid nitrogen is useful as the reference junction point because of the stability in its boiling temperature. Temperature region of calibration is below 80K. In calibration and application, the same measuring intruments were used. Obtained emfs are a little less than the NBS-data. And temperature deviation from obtained curves is ±0.5K at 20K. But when we applied those with vapor pressure thermometer, indicated temperatures between two thermometers were almost the same. It is, therefore, considered that calibrated thermocouples have reproducibility. Formulation of data will make it possible to record temperatures automatically.