Makoto Hasegawa

Formation of palladium oxides by mechanochemical reaction on Pd and Ag-Pd alloy contacts

The authors have previously reported (see Proc. 14th Int. Conf. on Electric Contacts, p.233-7, 1988) that, when Pd contacts are operated using mechanical break-make actions without switching load current in the air, palladium-oxides are formed on the contact surfaces by mechanochemical reaction caused by mechanical actions, and they cause serious deterioration of contact resistance. In the present work, the formation of the same products is reported on Ag-Pd70% and Ag-Pd50% contacts after tests involving operation 100000 times. Significant increase of contact resistance, however, was not observed. On the other hand, it is also found that the products show nonlinearity of contact resistance according to measuring current in both dynamic and static measurement. Temperature calculation shows that softening of the electrodes is not the main cause of the observed phenomenon. Thermal dissolution of the products is proposed as a possible cause. >

An investigation for the method of lifetime prediction of Ag-Ni contacts for electromagnetic contactor

Electrical contacts are widely used for telecommunication and electric power systems as a device mechanically making and breaking electrical current. In the future, they will be more indispensable. In this paper, we explored the possibilities of early lifetime prediction of Ag-Ni contacts for an electromagnetic contactor. Contact erosion often leads to the contact failure and the system fault. Especially, for heavy electrical systems, the failure can cause critical troubles. We must estimate approximate periods of the system fault to avoid the troubles. The tests of lifetime are very important for that purpose. However, the tests often require an enormous amount of time. We investigate the possibilities of lifetime prediction of contacts. In the past work, we confirmed that the mass loss could lead to the contact failure of Ag-Ni contacts and the mass loss of cathode was in proportion to total arc energy generated between the anode and the cathode. At this time we measured the mass losses of cathodes with a few making and breaking operations for more samples, and accurately predicted the mass losses after a lot of operations. We compared them with experimented results of a lot of operations.

Investigations on mass change and surface morphology of contacts in electromagnetic contactor

Electrical contacts are widely used for telecommunication and electric power as a device directly making and breaking electrical current. In the future, these will be more indispensable. The aim of this paper is to reveal the characteristics of the mass change and the surface morphology of contacts used in electromagnetic contactors. First, we focused attention on the mass change of contacts because the process of contact erosion and material transfer has not been completely understood. The contact surface was observed with a laser microscope and we evaluated the surface morphology quantitatively. The experiment was performed under different conditions. The load current was 5 A, 10 A and 20 A respectively. In this paper, we investigate the characteristics of contact resistance and arc duration. Moreover, the effect of the arc energy on the mass change and the characteristics of the change of surface morphology were discussed. As a result, the mass change is affected by the cumulative arc energy. The total mass change is found to be proportional to the cumulative arc energy rather than the operation number. Furthermore, the change of the surface morphology was quantitatively verified by the laser microscope observation.

Significant increase of contact resistance of silver contacts by mechanical switching actions

When Ag contacts were operated in mechanical break-make actions without switching load current in air (laboratory atmosphere), contact resistance increased significantly on about three quarters of the test samples. No contaminant products were detected in the contact area with AES (Auger electron spectroscopy) analysis. However, SEM (scanning electron microscopy) observation revealed an interesting relationship between the contact resistance characteristic and contact surface condition. The samples on which contact resistance increased had a mirror-like plain contact surface, while those with low and stable contact resistance had a rough surface which looked severely damaged by mechanical actions. The contact resistance characteristic was also found to be influenced by measuring current levels and contact force levels. With these experimental results, a possible hypothetical mechanism for the phenomenon is discussed considering the influence of wear types of the electrode surface.<<ETX>>

An evaluation method of the contact erosion based on the DC mode test of electromagnetic contactor

Electrical contacts are widely used for telecommunication and electric power systems as a device mechanically making and breaking electrical current. In the future, they can be still indispensable. Furthermore, the performance and reliability of electrical contacts must be more improved. Details of the mechanisms, however, have not completely been revealed yet, so that contact erosion and material transfer sometimes lead them to contact failure. We focus on two issues about contact erosion. In these years, volumetric method was proposed as the new evaluation method of surface erosion. However, few papers compare it with weighing method of measuring the mass change in detail. Hence, we investigated relationship between the number of switching operations and the amount of wear in electromagnetic contactor, and compared two methods. Furthermore, electromagnetic contactor is often used in the systems with an AC power supply. On the other hand, the DC mode test provides more fundamental data for us to investigate the electrical contacts than the AC mode test. We compared the data of the DC mode test with that of the AP mode test and described the possibility to estimate contact erosion with an AC power supply in terms of the DC mode test. The result of the DC mode agreed well with that of the AP mode in the case of low load current and a small operation number. We could also show an availability of volumetric method in early lifetime prediction.

Influence of contact materials on the formation of palladium-oxides by mechanochemical reaction

Influence of contact materials on the formation of palladium oxides by mechanochemical reaction in air are examined. Mechanical break-make actions of palladium contacts in air cause formation of powdery products of palladium oxides on the electrode surfaces, and consequently significant increase of contact resistance. The same products are also produced on Ag-Pd 50% and Ag-Pd 70% contacts, but such an increase of contact resistance is not observed. It is confirmed that contact resistance of Ag-Pd 70% contacts measured with I/sub m/=0.1 A remains low through 500000 operations, despite some palladium oxides being formed. Dissimilar materials mating tests are done and influences of contact materials on the phenomena, such as effect of material transfer due to difference of hardness, are studied.<<ETX>>

Gene transfer of human hepatocyte growth factor by the use of nanosecond pulsed laser-induced stress waves

We successfully delivered a therapeutic vector construct, which carries hepatocyte growth factor (HGF) gene, to rat skin in vivo. After HGF expression vector had been intradermally injected to rat skin, LISWs were generated by irradiating the laser target put on the rat skin with nanosecond pulses from the second harmonics (532 nm) of a Q-switched Nd:YAG laser. Concentration of HGF protein increased by a factor of four by the application of LISWs when compared with that of control samples without LISW application. We also investigated the effects of LISWs on the integrity of plasmid DNA.

Nanoprocessing of silicon substrate using surface plasmon polaritons of gold particle and polystyrene particle excited by femtosecond laser

Nanohole processing of silicon substrate using surface plasmon polaritons of nano gold excited by femtosecond laser is described in comparison with the nanohole processing with transparent polystyrene (PS) nanoparticle template. Gold particles with diameters of 40, 80, or 200 nm are spin coated on the substrate, and a 100 fs, 820 nm laser pulse is used to irradiate the samples. The produced holes are analyzed by scanning electron microscopy and atomic force microscopy. A theoretical analysis of the experimental results is conducted by FDTD (Finite Difference Time Domain) simulation. The dependence of the laser fluence and particle size on the nanohole properties is studied. The nanohole profiles correspond to the field distributions on the Si substrate at low fluence region. A highest electric field enhancement factor of about 26 is obtained for gold particles with a diameter of 200 nm.

A study of contact reliability in n-hexane with small load currents

Ag and Pd contacts were immersed in liquid n-hexane, and operated to perform consecutive break operations of inductive DC load currents up to several amps. The resultant contact performances were investigated, mainly with regard to contact resistance, arc duration, and mass changes (arc erosion). From previous results obtained through recent various experiments concerning electrical contact performances in liquid environments, the authors expected to find certain load condition(s) in which electrical contacts operated in liquid n-hexane could exhibit excellent operating characteristics, possibly better than those operated in air. Unfortunately, however, such preferable load range(s) could not be specified. Ag contacts undergoing steady arcs tend to show significant increase in contact resistance due to arc products deposited on electrode surfaces, although they suffer only minor erosion. Pd contacts, on the other hand, tend to suffer severe arc erosion, although their contact resistance can be stable with load currents up to 2 A. Some experimental data were obtained from dissimilar-materials mating operations, which support our proposed mechanism model for explaining such contact phenomena in liquid n-hexane.

Signal analysis of fiber optic probe method from Ho:YAG laser ablation bubble

We experimentally and theoretically studied interpretation of the waveform signal which was obtained by the fiber-optic probe method during Ho:YAG laser ablation. We monitored behavior of the ablation bubble which occurs at the fiber tip during the ablation by means of developed fiber-optic probe method as well as time-resolved photography to investigate the information which involves the waveform signal. We used water and agar as model materials for different purposes. We determined that the waveform signal from the fiber-optic probe method is mainly attributed to the reflection of the boundary between the water-vapor bubble and surrounding material/tissue. We also found that the intensive shockwave which is induced may be monitored by our method.