AgSnO2 Contact Material Research Articles

The effects of oxide additives on the mechanical characteristics of Ag–SnO2 electrical contact materials

The effects of oxide additives such as WO3, Cu2O, In2O3, etc. on the mechanical characteristics of Ag-8wt.%SnO2 contact materials were investigated. The tensile tests of the Ag–SnO2 materials prepared by powder metallurgy method were carried out on a MZ.Ms tensile machine. The fracture morphologies of the tensile samples were studied by a Scanning Electron Microscope (SEM). The fracture mechanism was simulated and analyzed utilizing ANSYS software. The results revealed that the addition of oxide additives increased the ultimate strengths and elasticity moduli of the Ag-8wt.%SnO2 contact materials. The maximum strength was achieved on the sample with addition of Cu2O, which reached up to 134.6 MPa. The stress concentration around SnO2 particles was relaxed with adding oxide additives. The initiation and propagation of the intergranular cracks in Ag–SnO2 contact materials were inhibited. Accordingly, the plasticity and creep resistance of the prepared materials were markedly improved. It was interesting that no visible intergranular cracks were generated in the Ag-8wt.%SnO2 contact materials when the SnO2 particles were decreased to about 70 nm. The mechanical properties of the Ag-8wt.%SnO2 nanocomposites were dramatically improved by adding In2O3. The mechanism was quite different from the Ag–SnO2 materials containing micron-sized SnO2 particles.

Study on DC arc performance of doped AgSnO2 contact materials

In this paper, AgSnO2 contact materials doped with Bi2O3, CeO2, La2O3 and TiO2 were prepared by powder metallurgy. The arc time, arc energy and welding force of the four contact materials were measured, and the arc combustion images and surface microstructure were photographed, which were used to investigate the effects of different additives on the arc properties of contact materials. The JF04C electrical contact material testing system was used to measure arc parameters, high-speed camera and scanning electron microscope were used to capture arc image and surface morphology, respectively. The obtained image was processed using an image processing method based on mathematical morphology. The arc area change was obtained by arc image processing, and then the arc combustion process was analyzed. Combined with arc parameters, arc area and microstructure analysis, the advantages and disadvantages of the four-contact materials doping with different additives against arc erosion were investigated. The results show that the AgSnO2/Bi2O3 and AgSnO2/CeO2 contact materials have strong arc erosion resistance among the four contact materials.

Properties of Ag-SnO2 Contact Materials for Low-Voltage Electrical Appliances with Different Doped Particle Sizes

In this paper, the relationship between additive particle size and properties of Ag-SnO2 contact materials was studied. La2O3 and Fe2O3 were selected as additives for contact materials, and the proportion of additives were determined by wettability experiment results; Ag-SnO2 contact materials were successfully fabricated by the powder metallurgy method, and the physical and electrical contact properties of Ag-SnO2 contact materials with five additive particle sizes were investigated. The results show the influence of additives on the properties of Ag-SnO2 contact materials are disparate, the contact resistance and arc energy are smaller and more stable when the additive particle size is about 500 nm. For further proving this conclusion, the arc-eroded surface morphologies of the doped AgSnO2 contact materials were investigated by scanning electron microscopy (SEM), which indicated that the properties of two kinds of Ag-SnO2 contact materials could be improved significantly by selecting appropriate additive particle size.

Properties of doped Ag–SnO2 electrical contact materials with different SnO2 particle sizes

It is believed that the particle size inevitably affects properties of contact materials due to the effects of microstructure. The Ag–SnO2/CuO and Ag–SnO2/Bi2O3 contact materials with six different SnO2 particle sizes were successfully fabricated through powder metallurgy method. The physical and electrical contact properties of two kinds of Ag–SnO2 contact materials with different SnO2 particle sizes were investigated. The results showed that with the increase of SnO2 particle size, the electrical conductivity of two kinds of Ag–SnO2 contact materials significantly increased first and then decreased, the density and hardness of Ag–SnO2/CuO decreased first and then increased, and the Ag–SnO2/CuO increased first and then decreased. It was found that the contact resistance and arc energy were smallest and most stable when the SnO2 particle size was about 800 nm, which indicates that the properties of two kinds of Ag–SnO2 contact materials can be improved significantly by selecting appropriate SnO2 particle size.

Effect of sintering temperature on the physical properties and electrical contact properties of doped AgSnO2 contact materials

AgSnO2 electrical contact materials doped with Bi2O3, La2O3, and TiO2 were successfully fabricated by the powder metallurgy method under different initial sintering temperatures. The electrical conductivity, density, hardness, and contact resistance of the AgSnO2/Bi2O3, AgSnO2/La2O3, and AgSnO2/TiO2 contact materials were measured and analyzed. The arc-eroded surface morphologies of the doped AgSnO2 contact materials were investigated by scanning electron microscopy (SEM). The effects of the initial sintering temperature on the physical properties and electrical contact properties of the doped AgSnO2 contact materials were discussed. The results indicate that the physical properties can be improved and the contact resistance of the AgSnO2 contact materials can be substantially reduced when the materials are sintered under their optimal initial sintering temperatures.

Impact of convection-diffusion and flow-path interactions on the dynamic evolution of microstructure: Arc erosion behavior of Ag-SnO2 contact materials

Arc erosion behavior of Ag-30SnO2 (wt.%) composite and its microstructural evolution is complex due to the interaction of gravity segregation with liquid evaporation. This paper was focused on understanding the dynamic microstructural evolution of Ag-30SnO2 materials in the arc erosion systems. The microstructures and arc erosion characteristics of Ag-30SnO2 materials were investigated. Further, the movable and stationary contacts were selected as the models by phase identification and microstructure analysis. The arc erosion behaviors of Ag-SnO2 contact materials were studied using the computational fluid dynamics (CFD) method. Mathematical models and simulation results indicated that the dynamic microstructural evolution of movable and stationary contacts were strongly influenced by the convection-diffusion and the flow-path ((cl/ll)+(cg/lg)). In stationary contact, the convection-diffusion can cause the much more fluctuation of ∇(∇CAg) and ∇(∇CSnO2) at the concavity of “pyramid-like” concentration curves. Thus, this flow-path with nearly linear, which led to the serious SnO2 enrichment in the surface of molten pool. In contrast, in movable contact, the relatively mild fluctuation of ∇(∇CAg) and ∇(∇CSnO2) were induced by convection-diffusion in the “pyramid-like” concentration curves, as a result, the serious Ag enrichment can be formed in the surface of molten pool due to the flow-path with gradually fluctuation.

Effect of CuO additives on the formation of SnO2-rich layers in Ag-SnO2 materials

In order to investigate the effect of CuO additives on the formation of SnO2-rich layer in Ag-SnO2 contact materials, the laser rapid melting experiment was carried out on Ag-SnO2 contact materials for the purpose of simulating the rapid melting process of an instantaneously arc melted surface layer during arc erosion. The microstructure of laser melted and arc eroded Ag-SnO2 materials were investigated using scanning electron microscopy (SEM). The experimental results were also theoretical analyzed with two models dealing with the particle-dendrite interaction during solidification process. It was found that the Ag-SnO2 materials with CuO additives have found no SnO2-rich layer in the re-melted area and the SnO2 particles still stayed in Ag matrix because of the increasement of dragging force between Ag matrix and SnO2 particle. As the dragging force increase, the advance speed of SnO2 particles in front of S/L interface was lowered and SnO2 particles were apt to be engulfed by Ag matrix during solidification, so the CuO doped SnO2 particles were more difficulty to be pushed out of the Ag matrix than pure SnO2 particles. These results indicated that the effect of CuO additives on the formation of SnO2-rich layer in Ag-SnO2 contact materials was enhanced the wettability of SnO2 particles in Ag melt pool and restrained the SnO2 particles rise to the contacts surface.

Study on properties of AgSnO2 contact materials doped with rare earth Y

SnO2 in the AgSnO2 contact material is a kind of high hardness and almost insulated wide bandgap semiconductor material. In the process of use, the contact resistance is large and the temperature raise is great, so that the contact reliability is reduced and the electrical life is shortened. In order to improve the comprehensive performance of AgSnO2 contact materials, based on the first principle of density functional theory, the electrical and mechanical properties of Y with different ratios doped SnO2 contact materials are calculated. Through the analysis of energy band, density of state and elastic constant, the results show that when the doping ratio of Y is 0.167, the conductivity is the best; the hardness decreases, and the universal elastic anisotropy index is the smallest. Finally, in the experiment, SnO2 powders with different doping ratios are prepared by sol-gel method, AgSnO2 contacts with different doping proportions are prepared by powder metallurgy, and arc energy, contact resistance, density and hardness are measured. and the final simulation and experimental results are well matched.

Analysis of the influence of Ti doping on the electrical properties of SnO2

The electronic structure, energy band and density of states (DOS) were calculated from the density function theory (DFT) for pure SnO2 and Ti doped SnO2 of various concentrations. The results reveal that: the 3d electronic state of Ti atom has a great contribution to the conduction band at the Fermi level, as a result, the conduction band shifts to the lower energy level, the forbidden bandwidth is smaller and the electrical conductivity is improved than that of pure SnO2. With the decreases of Ti doping concentration, the forbidden bandwidth decreases gradually, in other words, the electrical performance is gradually improved, and when the doping concentration of Ti is 6.25%, the forbidden bandwidth is at the lowest level, that is 0.148 eV. According to the semiconductor theory, the relative electron hole number and the electron hole effective mass of Ti doped system were calculated. The results show that with the decreases of Ti doping concentration, the relative electron hole number increases and the electron hole effective mass decreases. When the doping concentration of Ti is 6.25%, the hole effective mass is 0.242 m0, the relative quantity of hole is 0.5355. At last, the experiment verification reveals that when the doping concentration of Ti is 6.25%, the experimental value of electric conductivity is the largest, that is 58.09%IACS. In summary, when the doping concentration of Ti is 6.25%, the SnO2 material has better electrical properties. This research provides theory and data support for further study on AgSnO2 contact materials.

Improved Workability of the Nanocomposited AgSnO2 Contact Material and Its Microstructure Control During the Arcing Process

There are two major weaknesses for the AgSnO2 contacts used in the low voltage switch devices. One is poor workability, which causes the AgSnO2 materials to hardly deform into the required shape. Another is the increased contact resistance after arcing, which, in turn, causes an unfavorable temperature rise in the switches. In this article, the nanocomposited AgSnO2 materials were developed to overcome the weaknesses. The nanosized SnO2 powders with or without CuO additive were prepared by the chemical precipitation method. The SnO2 powders and Ag powders were high energy milled together to obtain AgSnO2 composite powders, which were then sintered, hot pressed and extruded. It was found that the SnO2 particles mainly distribute in the interior of Ag grains with Ag film on the grain boundary. The hardness of AgSnO2 composites and the wetting angle of Ag melt on SnO2 particles decreased with the addition of a small amount of CuO. By the combining effect of Ag film on grain boundary and the addition of CuO, the elongation and workability of the AgSnO2 materials improved. The experiments of rapid solidification revealed that more SnO2 particles with CuO addition were engulfed in the Ag matrix than those without CuO, which inhibited the redistribution of SnO2 particles on the contact surface during the arcing process. The industrial type test in the 45A contactor suggested that the nanocomposited AgSnO2 materials are suitable to be used as contacts in low voltage switches.

Arc erosion behaviors of AgSnO2 contact materials prepared with different SnO2 particle sizes

To clarify the effect of SnO2 particle size on the arc erosion behavior of AgSnO2 contact material, Ag–4%SnO2 (mass fraction) contact materials with different sizes of SnO2 particles were fabricated by powder metallurgy. The microstructure of Ag–4%SnO2 contact materials was characterized, and the relative density, hardness and electrical conductivity were measured. The arc erosion of Ag–4%SnO2 contact materials was tested, the arc duration and mass loss before and after arc erosion were determined, the surface morphologies and compositions of Ag–4%SnO2 contact materials after arc erosion were characterized, and the arc erosion mechanism of AgSnO2 contact materials was discussed. The results show that fine SnO2 particle is beneficial for the improvement of the relative density and hardness, but decreases the electrical conductivity. With the decrease of SnO2 particle size, Ag–4%SnO2 contact material presents shorter arc duration, less mass loss, larger erosion area and shallower arc erosion pits.

Contact resistance characteristics of Ag–SnO2 contact materials with high SnO2 content

The contact resistance and surface morphologies characteristics of Ag–SnO2 contact materials with high SnO2 content was investigated in make-and-break operations. The microstructure and arc eroded surface morphologies of Ag–SnO2 samples were researched by Scanning Electron Microscopy (SEM). The surface profiles and average surface roughness Sa of arc eroded Ag–SnO2 samples were also analyzed by Scanning Laser Microscope (SLM) 3D surface technique. With the SnO2 content increase from 15wt.% to 30wt.%, it was found that contact resistance of Ag–SnO2 materials increased by 33% and stabilize in 5mΩ when contact force over than 70N. The surface morphologies of arc eroded Ag–SnO2 samples were stable and uniform compared with the original samples. The theoretical analysis and experimental results of contact resistance characteristic indicated that contact force is the predominant factor for the contact resistances of Ag–SnO2 materials with high SnO2 content and contact resistance of high SnO2 content Ag–SnO2 materials can be reduced significantly by increasing the contact force.

Preparation of rod-like SnO2 powder and its application in Ag-SnO2 electrical contact materials

In this study, rod-like SnO2 particles with a diameter from 1 to 4 μm and the length from 5 to 50 μm were successfully prepared by chemical precipitation method. Then, SnO2 particles were mixed with silver powder by wet ball milling. After hot pressing, hot-extrusion and drawing, Ag-SnO2 electrical contact material was fabricated. The microstructure, mechanical properties and material transfer of Ag-SnO2 contact material were studied. The results showed that this kind of Ag-SnO2 electrical contact material has good performance, that is, homogeneous microstructure, high hardness HV117·55, low electrical resistivity (2·227 μΩ × cm) and low material transfer.

A study on the uniformity of silver coatings on nanometer SnO<SUB align="right">2 particles through chemical plating

The dispersion of AgSnO2 contact materials could be improved by using silver coated SnO2 particles as the starting powders in the powder metallurgy (P/M) process. For that purpose, nanosized SnO2 particles covered with silver coatings were prepared through chemical plating in this study, and the stability of the chemical plating solution and the uniformity of silver coatings were studied. The results showed that by dropping reduction fluids into ammoniacal silver solution, the self-decomposition of the electroless plating bath were completely inhibited, and by adjusting the dropping speed, the uniformity of silver coatings on SnO2 particles could be improved relatively.

Influence of Rare Earth on the Wetting Ability of AgSnO2 Contact Material

Abstract AgSnO 2 is a most potential substitute contact material for AgCdO. In practice, however, it has some congenital defects. This paper, is to focus whether wetting ability of AgSnO 2 contact material can be improved and its defects can be decreased when rare earth elements are added. Young's equation has proved that the smaller the wetting angle is, the better the material wetting ability. So, rare earth elements La and Ce were selected as additives in the present experiment. And three Ag-based contact materials were prepared with different ratios of SnO 2 to La or Ce. Then, wetting angles of the contact material were measured by the sessile drop method. They were compared with the wetting angle of the AgSnO 2 contact material. The measurement results show that La can improve the wetting ability of AgSnO 2 contact material obviously. For further proving this conclusion, the simulation arc tests for AgSnO 2 and AgSnO 2 La 2 O 3 contact materials were carried on. And their microstructures were analyzed. The results prove that AgSnO 2 La 2 O 3 contact material has better wetting ability than AgSnO 2 .

Study on New Types of Environmental Protection AgSnO<sub>2</sub> Electrical Contact Materials

AgSnO2contact materials have begun to replace toxic AgCdO materials in switching devices such as contactors and circuit breakers since 1970s [1,, which is partly due to the fact that AgSnO2materials have shown higher service lives, better welding resistance and less arc erosion in contactors of larger size [. Furthermore, the growing awareness of environmental problems makes it desirable to replace AgCdO contact materials [. However, these materials suffer from an inadequate welding behavior compared with AgCdO [. It was observed that AgSnO2made by traditional metallurgical process exhibited high overtemperatures attributed to high contact resistance caused by surface layers of accumulated SnO2, which was due to the poor wettability of SnO2grains in the silver melt in combination with their high thermal stability [6,7]. Another important point was the large size and high hardness of SnO2particle prepared by traditional process, which reduced the workability of AgSnO2contact materials [8]. In this work, the authors prepared Ti4+-doped SnO2using sol-gel technique and investigated the microstructure, size, distribution and crystallization of Ti4+-doped tin oxide grains as well as the doping effects on the electrical conductivity of these materials.

Comparison of properties of silver-metal oxide electrical contact materials

Changes in physical properties such as density, porosity, hardness and electrical conductivity of the Ag-SnO2 and Ag-SnO2In2O3 electrical contact materials induced by introduction of metal oxide nanoparticles were investigated. Properties of the obtained silver-metal oxide nanoparticle composites are discussed and presented in comparison to their counterparts with the micro metal oxide particles as well as comparable Ag-SnO2WO3 and Ag-ZnO contact materials. Studied silvermetal oxide composites were produced by powder metallurgy method from very fine pure silver and micro- and nanoparticle metal oxide powders. Very uniform microstructures were obtained for all investigated composites and they exhibited physical properties that are comparable with relevant properties of equivalent commercial silver based electrical contact materials. Both Ag-SnO2 and Ag- SnO2In2O3 composites with metal oxide nanoparticles were found to have lower porosity, higher density and hardness than their respective counterparts which can be attributed to better dispersion hardening i.e. higher degree of dispersion of metal oxide in silver matrix.

Arc erosion of AgSnO2 electrical contacts at different stages of a break operation

Arc erosion studies are conducted on AgSnO2 contact materials at different stages in the break operation. A resistive load arrangement is used with up to 42 V DC at 24 A and a constant contact opening velocity. The arc current is terminated at different stages as the arc is drawn between the contacts enabling a study of the arcing phenomena up to that point. Surface profiling of the contacts is conducted to determine the extent of erosion at the different stages as the arc is drawn. Spectral analysis is also conducted on the arc and then related to the extent of erosion. The results show that particular features occur at different stages as the arc is drawn. As the arc is initially established, it goes through an “Arc Generation” regime where the arc roots are small and immobile on both the anode and the cathode. Material transfer occurs mainly from anode to cathode. The spectral analysis indicates that Sn and O species dominate the arc followed by the Ag species. As the arc is drawn further and enters the “Arc Degeneration” regime, the anode undergoes significantly larger erosion than the cathode. Also, both contacts indicate that multiple arc roots have formed, which are highly mobile in the later stages of the discharge. The spectral analysis indicates that Ag and N species are in high concentrations compared to other species. The mechanisms of erosion and deposition are discussed in relation to the species within the arc discharge. For the complete break operation, it is found that the anode undergoes major erosion, and it is thought that the gaseous ions species do not dominate the arc under these conditions of short arcs and voltage <42 V to cause cathode erosion.

Study on the failure mechanism of Ag-Ce contacts in DC level

Nominal contact resistance, minimum erosion and material transfer are required with low cost materials working in a wide currents range for DC relays. Ag-Ni contact materials have low contact resistance, but the erosion and material transfer are large at high current level. Ag-SnO2 contact materials have good anti-welding properties and resistance to arc erosion, but they have large contact resistance during working and are easily block SnO2 from flocking together on the surface at low current level. In this paper, the failure mechanisms of Ag-Ce contact material were studied. The surface morphologies of the contacts after electrical endurance test for Ag-Ce contact material were compared with that of Ag-Ni and Ag-SnO2 contact materials. The effect of Ce on the surface morphologies of the contacts after electrical endurance test was analyzed.

Linear elastic contact of the Weierstrass profile

A contact problem is considered in which an elastic half–plane is pressed against a rigid fractally rough surface, whose profile is defined by a Weierstrass series. It is shown that no applied mean pressure is sufficiently large to ensure full contact and indeed there are not even any contact areas of finite dimension — the contact area consists of a set of fractal character for all values of the geometric and loading parameters. A solution for the partial contact of a sinusoidal surface is used to develop a relation between the contact pressure distribution at scale n − 1 and that at scale n . Recursive numerical integration of this relation yields the contact area as a function of scale. An analytical solution to the same problem appropriate at large n is constructed following a technique due to Archard. This is found to give a very good approximation to the numerical results even at small n , except for cases where the dimensionless applied load is large. The contact area is found to decrease continuously with n , tending to a power–law behaviour at large n which corresponds to a limiting fractal dimension of (2 − D ), where D is the fractal dimension of the surface profile. However, it is not a ‘simple’ fractal, in the sense that it deviates from the power–law form at low n , at which there is also a dependence on the applied load. Contact segment lengths become smaller at small scales, but an appropriately normalized size distribution tends to a limiting function at large n . † The authors dedicate this paper to the memory of Dr J. F. Archard, 1918–1989.