Effects of Oxide-Modified Spherical ZnO on Electrical Properties of Ag/ZnO Electrical Contact Material

Since the performance of silver metal oxide (Ag/MeO) electrical contact materials directly affects the reliability and service life of switching apparatus, the related research on high-performance Ag/MeO electrical contact materials has not stopped. And with the rapid development of switching apparatus, higher and higher requirements are put forward for the performance of Ag/MeO electrical contact materials. Thanks to low and stable contact resistance, short arc burning time, good resistance to high current impulse (3000-5000 A) and good anti-arc erosion, silver zinc oxide (Ag/ZnO) more than just serves as an indispensable environmentally friendly alternative to silver cadmium oxide (Ag/CdO) electrical contact material, and has become one of the important research hotspots of Ag/MeO in recent years. Nevertheless, Ag/ZnO is suffering the increasingly serious challenges, especially the poor processability and electrical properties due to the easy segregation of zinc oxide (ZnO) during the process of preparation, which urge scholars at home and abroad to seek favorable methods to optimize the Ag/ZnO. As yet, impressive strides have been made in optimization the preparation process, nano-technology and additive modification of materials, and research on the failure mechanism of materials. Aiming to provide reference for optimizing Ag/ZnO electrical contact material, this review retrospects the research progress in Ag/ZnO electrical contact materials in recent years, and expounds the preparation methods, processing technology, modification research and failure mechanism of Ag/ZnO, and points out the future development directions of Ag/ZnO.

It is generally known that Ag-CdO electric contact material excels others in characteristics. Thus, the contact material has been widely used, regardless of current strength. However, in a view point of environment, the advanced electric contact material without environmental load element such as cadmium has to be developed. Extensive studies have been carried out on Ag-SnO2 electric contact material as a substitute of Ag-CdO contact materials. In the manufacturing process of Ag-SnO2 electric contact material, it can be mentioned that typical internal oxidation process is not suitable to produce Ag-SnO2 electric contact material because the Sn located around surface may interrupt oxidation of Sn in the middle of material. Therefore, in the present study, powder metallurgy including compaction and sintering is introduced to solve the incomplete oxidation problems in manufacturing process of Ag-SnO2 electrical contact material. The formation of the blends was manufactured by wet blending of powders of Ag and SnO2. The quantity of SnO2 powder was 15wt.%, with intent to optimize the powdering process for the minute powder of which diameter is less than 5μ m. Particle size and grain distribution of Ag powder and SnO2 powder by powder metallurgy were measured by image analyzer. In order to estimate the properties of specimen tested with a variation of mixed time, the micro-hardness measurement was carried out. The Ag-SnO2-based contact material, which was produced through this study, was actually set in an electric switchgear of which working voltage is 462V and current is between 25 and 40A, for the purpose of testing its performance. As the result, it excelled the existing Ag-CdO-based contact materials in terminal-temperature ascent and main contact resistance.

Improving mechanical and electrical contact performance of silver based electrical contact material reinforced by flower spherical zinc oxide loaded with silver nanoparticles

In situ formation and doping of Ag/SnO2 electrical contact materials

In order to improve the machinability and electrical performance of the Ag electrical contact materials. A new kind of nano-Ag/SnO2-TiO2 electrical contact materials were prepared by liquid phase in-situ chemical route. The distribution state of elements titanium in copper and their effects on the microstructures and properties have been studied. The results of SEM show that SnO2-TiO2 powders are small, uniform and with no obvious phenomenon of reunion. At last, Ag/SnO2-TiO2 electrical contact materials were prepared by powder metallurgy method and electrical performance were done. Test results show that the electrical properties of Ag/SnO2-TiO2 are superior to the electrical properties of Ag/SnO2. Hence Ag/SnO2-TiO2 may become a new contact material which can replace Ag/SnO2.

Abstract

In this study, carbon nanotubes (CNTs) and multi-layer graphene (MLG) were mixed and reinforced into copper matrix at the rates of 1, 2 and 10 vol.%. Thus, the synergistic effect of CNT $$+$$ MLG hybrid structure on copper matrix was investigated and the usability of the obtained composite as an electrical contact material was examined. In addition, changes in the properties of the composite were demonstrated with the changes in amounts of CNTs and/or MLGs in Cu matrix. In this study, both reinforcements and composites were produced under laboratory conditions. The electrical conductivity, abrasion properties, and hardness of the produced composites and their usage as electrical contact material were investigated. The obtained results were compared with previous studies, and their reasons were revealed. The electrical conductivity of the obtained composite increased first to a certain reinforcement amount with the increasing CNT $$+$$ MLG hybrid reinforcement rate and then decreased. However, the electrical conductivity of the composite reinforced with only CNTs or MLGs at the same rate was found to be higher than CNTs $$+$$ MLGs reinforced composite. The abrasion resistance of CNT $$+$$ MLG hybrid-reinforced copper matrix composite showed an increase with increasing reinforcement ratio. The increase in the amount of MLGs in the composite caused an increase in the abrasion resistance of the composite. This situation can be said to be caused by the lubricant property of MLGs. CNT $$+$$ MLG hybrid-reinforced copper matrix composites were used as an electrical contact material in an experimental set-up, and this material loss in these materials and the damages on the surfaces after 20,000 turn on/off were investigated. It can be asserted that the electrical contact properties of the composite improved with increasing amount of MLGs. MLGs distributed rapidly the heat generating during the operation of the contact and weakened the mechanical effects during the on/off states of the contacts due to their lubricant properties which helped to reduce the damage on the contact materials.

Electrical contact material is a very important material for the electric power industry. An electrical contact material should display good structural characteristics (suitable hardness, high thermal conductivity and stabilization) as well as a good functional characteristic (low electrical resistivity). It is difficult to fabricate such a contact material with all these good performing parameters by common techniques because these physical parameters influence each other. In this paper, we report a novel investigation to design and prepare silver-metal oxide composite materials according to functionally layered and graded material (FLGM) concept and meeting requirement as electrical contact material. The silver-based composite samples characterized by layered component were prepared with conventional solid-phase sintering technique. One kind of sample consists of tin dioxide and silver material, in which SnO2 exhibits a graded distribution. Another consists of two metal oxides, cadmium and zinc oxides, and silver material, in which each layer has different metal oxide. Hardness, thermal conductivity and electrical conductivity, were measured and related problems are discussed. Especially, welding resistance as an important parameter for practical application was tested. SEM analyses before and after electrical erosion were also performed. We conclude that the functionally graded material (FGM) concept as a novel designing and fabricating method has potential for electrical contact composite material.

A Novel Method for the Preparation of Ag/SnO2 Electrical Contact Materials

Ag/Ni composite contact materials are widely used in low-voltage switches, appliances, instruments, and high-precision contacts due to their good electrical conductivity and processing properties. The addition of small amounts of additives can effectively improve the overall performance of Ag/Ni contact materials. Graphene has good applications in semiconductors, thermal materials, and metal matrix materials due to its good electrical and thermal conductivity and mechanical properties. In this paper, Ag-graphene composites with different added graphene contents were prepared by in situ synthesis of graphene oxide (GO) and AgNO3 by reduction at room temperature using ascorbic acid as a reducing agent. The Ag-graphene composites and nickel powder were ball-milled and mixed in a mass ratio of 85:15. The Ag-graphene/Ni was tested as an electrical contact material after the pressing, initial firing, repressing, and refiring processes. Its fusion welding force and arc energy were measured. The results show a 12% improvement in electrical conductivity with a graphene doping content of approximately 0.3 wt% compared to undoped contacts, resulting in 33.8 IACS%. The average contact fusion welding force was 49.49 cN, with an average reduction in the fusion welding force of approximately 8.04%. The average arc ignition energy was approximately 176.77 mJ, with an average decrease of 13.06%. The trace addition of graphene can improve the overall performance of Ag/Ni contacts and can promote the application of graphene in electrical contact materials.

Mechanical characteristics of the Ag/SnO2 electrical contact materials with Cu2O and CuO additives

This comment is on the paper ‘‘Piezoresistive Effect in SiOC Ceramics for Integrated Pressure Sensors’’, by Riedel et al. The experimental method of testing the piezoresistive behavior is flawed in this paper, as explained below. A similar flaw exists in Zhang et al. which is referenced by the subject paper. Due to this flaw, the piezoresistive results are not reliable. Piezoresistivity refers to the effect of strain (which relates to the stress) on the electrical resistivity of a material. This effect allows the sensing of strain (stress) by electrical resistance measurement. The correct measurement of the electrical resistance of a specimen requires that the resistance associated with the electrical contacts that are used to probe the specimen be excluded from the measured resistance. Even though the electrical contact material may be a material of low electrical resistivity, the interface between the electrical contact material and the specimen tends to be associated with a substantial resistance. Unless the specimen resistance is so high that it overshadows the contact resistances, the inclusion of the contact resistance in the measured resistance results in inaccurate measurement of the specimen resistance. The four-probe method of electrical resistance measurement is effective for the essential exclusion of the contact resistances from the measured resistance. This method involves four electrical contacts—the outer two contacts for passing a current and the inner two contacts for measuring the voltage. This configuration results in the essential absence of current though the voltage contacts, hence the essential absence of a potential drop at the voltage contacts. The four-probe method has been previously used to study the piezoresistivity of silicon carbide fiber. There are variations of the electrical contact configuration of the four-probe method, which depend on the specimen geometry. In contrast, the twoprobe method of resistance measurement involves only two electrical contacts, each of which is for both current passing and voltage measurement. Thus, current goes through the voltage contacts, resulting in the presence of a potential drop at each voltage contact. The inferiority of the two-probe method compared with the four-probe method is well established. In the subject paper, the electrical resistance is measured by using the two-probe method. As a result, the measured resistance includes the contact resistance. Each of the two electrical contacts is in the form of a pressure contact between a metal block and dried silver paint. There is substantial resistance associated with this interface. In addition, the resistance is substantial for the interface between the dried silver paint and the specimen being studied. In other words, both metal-silver and silver-specimen interfaces contribute to the resistance of each of the two contacts. The substantial contact resistance makes the measured resistance not reliable for reflecting the behavior of the specimen. The two-probe method is reliability only when the contact resistance is negligible compared with the specimen resistance. The measured resistance (3.3 kO) is not very high, suggesting that the contact resistance is not negligible. The two-probe method suffers even more in piezoresistivity testing. The application of pressure tends to cause the contact resistance to decrease (due to the tightening of the interfaces) and this effect can be reversible upon unloading. Thus, the observed piezoresistive effect may be substantially changed by the effect of pressure on the contact resistance. As a consequence, the true gage factor that describes the piezoresistivity of the specimen is expected to be considerably lower than the value reported.

This study investigated the synthesis of Ag-SnO2-ZnO by powder metallurgy methods and their subsequent electrical contact behavior. The pieces of Ag-SnO2-ZnO were prepared by ball milling and hot pressing. The arc erosion behavior of the material was evaluated using homemade equipment. The microstructure and phase evolution of the materials were investigated through X-ray diffraction, energy-dispersive spectroscopy and scanning electron microscopy. The results showed that, although the mass loss of the Ag-SnO2-ZnO composite (9.08 mg) during the electrical contact test was higher than that of the commercial Ag-CdO (1.42 mg), its electrical conductivity remained constant (26.9 ± 1.5% IACS). This fact would be related to the reaction of Zn2SnO4's formation on the material's surface via electric arc. This reaction would play an important role in controlling the surface segregation and subsequent loss of electrical conductivity of this type of composite, thus enabling the development of a new electrical contact material to replace the non-environmentally friendly Ag-CdO composite.

A B S T R A C T A R T I C L E I N F O Cu -ZrO 2 composites can be used as electrical contact materials in relays, co ntactors, switches, circuit breakers, electronic packaging requiring good electrical and thermal conductivity as well as welding or brazing properties. In the presented work copper matrix composites reinforced with 8 mol % yttriastabilised 1 wt. %, 2 wt. %, 3 wt. %, 4 wt. %, and 5 wt. % zirconia (8-YSZ) particles were fabricated by the powder metallurgy method. Cu and Cu-ZrO 2 powder mixtures were compacted with a compressive force of 500 MPa and sintered at 900 °C for 2 h within an argon atmosphere. The results of the study on the mechanical properties of the composites showed that with increasing content of ZrO 2, the micro-hardness and compressive strength increase. The relative densities of the composites decreased from 96.1 % to 92.0 % with increasing zirconia content up to 5 wt. %. The results of the el ectrical test on the composites indicated that electrical conductivity reduced gradually with increase in reinforcement content. SEM and EDS studies showed that Cu-ZrO 2 composites have a uniform microstructure in which zirconia particles are distributed uniformly in the Cu matrix.

A novel powder metallurgy method, based on preparation of powder mixtures of copper with 0.5, 1, 1.5, 2, 2.5, 3, and 5 wt.% of nanographite particles ~50 nm in size, is used to produce Cu-nanographite electrical contact materials with flake microstructure. The dispersion of graphite nanoparticles in the Cu matrix is examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Morphology, particle size, and apparent density of flake powders are investigated. Microstructure, density, electrical conductivity, and hardness are studied for green and sintered samples. The composites reinforced with lower graphite nanoparticles content (0.5 wt.%) exhibit much lower agglomeration content, while the composites reinforced with higher graphite nanoparticles content (5 wt.%) showed higher agglomeration content. It is found out that the electrical conductivity of the sintered Cu-nanographite electrical contact materials decreased from 76.92 to 68.28 IACS by graphite nanoparticle addition. The maximal (~34) and minimal (~20) Brinell hardness is obtained for the monolithic Cu sample and 5 wt.% graphite nanoparticle reinforced Cu electrical contact materials, respectively.