D.J. van Ooijen

Electrical resistance of hydrogen-charged iron wires

Abstract Pure iron wires were supersaturated with hydrogen by cathodic charging in sulphuric acid. It was found that the hydrogen precipitates at the crystal boundaries, building up high gas pressures. Microscopic cracks are thus formed, accompanied by cold working of the surrounding metal. An increase of the electrical resistance of the wires due to the cracks and an increase due to coldworking, could be measured as two distinctly different effects. No change in the resistance due to interstitial solution of hydrogen could be detected.

Superconductivity of NbSn2

In the course of investigations on the Nb/sub 3/Sn phase diagram, a new superconductive intermetallic compound was found with the composition NbSn/sub 2/ and having a critical temperature of 2.60 deg K. A short description is given of the preparation of NbSn/sub 2/, and the results of measurements of the resistance transition and critica1 field are preserted. (H.D.R.)

ANALOGON OF BARKHAUSEN NOISE OBSERVED IN A SUPERCONDUCTOR

To investigate the mechanism of the destruction of superconductivity by a magnetic field, an experiment in which the field penetration is heard as a noise similar to that observed by Barknausen during the magnetization of a soft ferromagnetic material was performed. A superconducting wire was surrounded by a pick-up coil and placed in a solenoid. Experiments were performed on soft annealed lead and lead-20.4 wt% indium wires. Explanations for the observed noise were presented. (C.E.S.)

Influence of cold-rolling at 78°K on the superconducting transition of lead

Lead wires were rolled at 78 deg K to 120% increase of length and the superconducting transition was measured at 4.2 deg K in a longitudinal magnetic field at several current densities (j). The critical field (H) was defined as the field that restores half the normal resistance to the wire. The wire was annealed at six different temperatures and after each annealing the j- H characteristic at 4.2 deg K was determined. The resistivity decrease as the sample is annealed at various temperatures was also measured. (H.D.R.)

INFLUENCE OF NEUTRON-IRRADIATION AT 78 K ON THE CRITICAL FIELD OF SUPERCONDUCTING LEAD

Measurements on the critical field of neutron-irradiated lead are given. Lead wires, soft-annealed for 2 hours at 200 un. Concent 85% C in vacuo, were encapsulated in an evacuated silica tube and subsequently irradiated in a low flux reactor for a period of eleven days at a temperature of 78 un. Concent 85% K. The integrated flux was about 10/sup 18/ fast neutrons cm/sup -2/. Values of the residual resistivity measured before irradiation and after recovery for 20 minutes at 353 un. Concent 85% K are listed. (C.E.S.)