Katsuyoshi Hotta

SUPERCONDUCTIVE FILMS BY LASER POST-TREATMENT OF THERMAL-SPRAYED FILMS

Abstract In an attempt to produce a thick superconductive film of large area, an experimental study was conducted on the preparation of the film through laser post-treatment of thermal-sprayed oxide ceramic film. The ceramic powder of Bi-(Pb)-Sr Ca-Cu-O system was used as raw material. The powder was sprayed onto a stainless steel substrate using two types of spraying systems, conventional plasma spraying system and lower temperature hypersonic spraying system both followed by CO2 laser beam irradiation with oxygen gas flow to remodify the superconductive crystals in the films. The results showed that, though laser post-treatment can produce superconductive crystals in both sprayed films, higher critical temperature Tc (end) was obtained for the film prepared by the hypersonic spraying system.

Improvement of superconductive characteristics by laser surface treatment

Abstract The effect of laser beam irradiation onto the surfaces of superconductive materials of Bi system is discussed. Results of SEM observation, XRD analysis and measurement of critical temperature of laser treated surfaces indicate that the treatment can improve crystal conditions of the system.

Possibility of connecting bulks of Bi system by the laser irradiation

Abstract Laser treatment has been successful in rapidly realizing superconductors of Bi system. We applied this to easy connection between two bulks and obtained indication of successful result.

Behaviour of the superconductivity characteristics of the Bi system during water soaking

Samples of a bulk Bi-Pb-Sr-Ca-Cu-O system and a thick film of the Bi-Sr-Ca-Cu-O system are soaked in distilled water and the change in the superconductivity characteristics is measured. For the bulk samples, the maximum magnetization in the magnetization curve and the critical current density increase for the first 18 hours of soaking and then decrease during the subsequent soaking time. The critical temperature shows monotonic decrease throughout the soaking. A thick-film sample is almost the same as a bulk sample, i.e. the critical current density of the thick film first tends to increase for a short time due to its greater surface area then tends to decrease during the subsequent soaking. The critical temperature of the film sample also shows a slight deterioration as a result of the water soaking.

Preparation of superconductive films using plasma spraying technique with laser post-treatment

In an attempt to produce superconductive films of large area, a study was made on the preparation of the films through laser post-treatment of plasma-sprayed oxide ceramic films. The ceramic powders of Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O systems were used as raw materials. Each ceramic powder was sprayed onto a stainless steel substrate followed by CO2 laser beam irradiation with oxygen gas flow to remodify the composition and provide superconductive crystals on the film. The results showed that laser post-treatment can recover superconductive crystals on both films and can provide the transition temperatures Tc(on) on both systems and the critical temperature Tc(end) on the Bi-Sr-Ca-Cu-O system.

Basic Characteristics of the Single Layer Type Microwave Absorber in X Band Using Superconductor Powder

The purpose of this study is to examine the basic characteristics of the single layer type microwave absorber in X band. Samples were produced from Bi system (2223) superconductor powder and metallic powder and inserted into a wave guide system where the complex reflection intensity was measured (The short circuit method) by using the vector network analyzer[1]. As the result, at the room temperature (300K), the reflection loss is apt to increase with increasing the content of the Bi system superconductor powder. Furthermore, the measured value of the reflection loss agreed with the value calculated from the complex permittivity εr* . At liquid nitrogen temperature (77K) where the superconductor powders are in the superconducting state, some differences occurred between the calculated value and the measured one of the reflection loss. For the metallic powders, copper powder showed good agreement between the calculated and the measured of reflection loss. For the magnetic material, it was concluded that the theoretical formula under consideration of complex permeability μr* should be derivated.

Laser cutting of superconductive plate

Abstract This study deals with the possibility of high quality laser cutting of superconductive plate i.e., possibility of cutting which does not ruin superconductive characteristics on the cut surface of the plate. After all, it is found that such combination of parameter values as output power of 450W and cutting speed of 100 mm/min can yield a superconductive cut surface successfully.

Laser modification of the end of thin metal tube

Thin metal tubes used for catheter, nozzle and/or filter require smoothly-rounded ends. To produce the tube, it is cut at an appropriate length first and then the end is polished mechanically. The smaller the diameter, the more difficult it becomes to finish it. Then, a basic study on the modification of the end of thin metal tube using laser technique is conducted. Thin stainless steel and copper tubes of diameters nearly 0.5 mm and 1.0 mm with thicknesses nearly 0.15 mm are used as the specimens. A pulsed YAG laser is irradiated at the end of the tube to modify the sharp edge. Results show that suitable combinations of laser irradiating conditions can create smoothly-rounded ends. It was also found that smooth capping of the end can be carried out by the technique.Thin metal tubes used for catheter, nozzle and/or filter require smoothly-rounded ends. To produce the tube, it is cut at an appropriate length first and then the end is polished mechanically. The smaller the diameter, the more difficult it becomes to finish it. Then, a basic study on the modification of the end of thin metal tube using laser technique is conducted. Thin stainless steel and copper tubes of diameters nearly 0.5 mm and 1.0 mm with thicknesses nearly 0.15 mm are used as the specimens. A pulsed YAG laser is irradiated at the end of the tube to modify the sharp edge. Results show that suitable combinations of laser irradiating conditions can create smoothly-rounded ends. It was also found that smooth capping of the end can be carried out by the technique.

Possibility of producing a superconductive layer of large area on the bulk prepared by press forming of Bi system superconductive powder by laser surface melting method

A bulk prepared by press forming of Bi system superconductive powder never shows superconductive characteristics. To yield superconductive characteristics on the bulk, heat treatment of the bulk in an electric furnace is an essential process. This process, however, has such problems as that the size of the bulk is limited by the size of the furnace and that the process requires time as long as several ten hours. To overcome the problems, a method using laser technique has been applied. This method melts the surface of the bulk by a laser, without strict control of irradiation conditions, to yield a superconductive layer underneath the melted layer. This paper deals with the possibility of producing a superconductive layer of large area on the bulk by CO2 laser surface treatment.

Application of Laser Technique on the Formation of Superconductive Layer on the Bulk of Press Formed Bi System - Evaluation of Mechanical Properties of the Treated Bulk

In the study of the application of a laser technique on the bulk of press formed Bi system, the authors have reported that a superconductive layer can be obtained underneath the laser melted layer. In a continuing series of this study, this paper deals with the mechanical properties of the bulk laser treated. Superconductive powder of Bi system, 2223 phase was pressed to form a disk specimen of 2 mm thick and 10 mm at 29 MPa to 196 MPa. Then a CO2 laser beam of output power 6 W to 9 W was scanned linearly in air to melt the surface of the specimen to be subjected to the evaluation of hardness and fracture strength. The experimental results showed that the values of microvickers hardness of superconductive layer and melted layer are 135 and 105 respectively while that of the specimen as press formed is as low as 45. The fracture strength of the laser treated specimen was increased to 34 N from 15 N. The mechanical properties obtained deserve non sensitive handling in a practical use of the treated bulk.