AgSnO2 Contacts Research Articles

Designing sandwich-structured Ag–SnO2 contact materials: Overcoming the trade-off between erosion resistance and mechanical properties

Designing a second-phase enhancement system for SnO2 microstructures always plays a major role in improving the electrical contact performance of Ag–SnO2 contacts. This study fabricated sandwich-structure Ag–SnO2 contacts to overcome the trade-off between the erosion resistance and mechanical properties of Ag–SnO2 contacts via electrospinning with spark-plasma sintering; subsequently, the influence of SnO2 interlayers on the arc-erosion behaviour and mechanical characteristics of the contacts was investigated. The sandwich structure facilitated a reduction in the hill-and-valley morphology of the contact surface during repetitive erosion; fibrous SnO2 restricted the fluid evaporation of Ag, while SnO2 interlayers dispersed molten bridges, thereby improving the erosion resistance of the system. In parallel, 3D models of the sandwich-structured Ag–SnO2 contacts were reconstructed to investigate the evolution of their mechanical characteristics. Experimental and simulation indicated that the dispersion of stress concentration and reduction in surface deformation induced by the interface effect were the mechanical enhancement mechanisms, while the improvement of impact and wear resistances was attributed to the intensified support provided by the SnO2 interlayers on the matrix surface. Moreover, the synergistic interactions between Ag and SnO2 interlayers mitigated crack initiation and fracture propagation, thereby improving the fracture resistance of the contact matrix. These insights led to a feasible strategy for designing the microstructures of Ag-based contact materials.

Properties of AgSnO2 Contact Materials Doped with Different Concentrations of Cr.

As an important component carrying the core function and service life of switching appliances, the selection and improvement of electrical contact materials is of great significance. AgSnO2, which is non-toxic, environmentally friendly and has excellent performance, has become the most promising contact material to replace AgCdO. However, it has deficiencies in machinability and electrical conductivity. The property of AgSnO2 contact material was improved by doping element Cr. The relationship between the mechanical and electrical properties of AgSnO2 contact materials and doping concentrations were investigated and analyzed by simulation and experiment. Based on the first principle, the elastic constants of supercell models Sn1−xCrxO2 (x = 0, 0.083, 0.125, 0.167, 0.25) were calculated. The results show that the material with a doping ratio of 25% is least prone to warp and crack, and the material with a doping ratio of 12.5% has the best toughness and ductility and the lowest hardness, which leads to molding and is subsequently easier to process. The Cr-doped AgSnO2 contacts with different doping proportions were prepared by the sol–gel and powder metallurgy method. Additionally, their physical performance and electrical contact properties were measured in experiments. The results show that the doped SnO2 powders prepared by the sol–gel method realize integration doping, which is consistent with the crystal model constructed in the simulation calculation. Sn0.875Cr0.125O2 has lower hardness, which is beneficial to process and form. Doping helps to stabilize the arc root, inhibit the ablation of contact by arc, reduces arc duration and arc energy, improves the resistance to arc erosion of AgSnO2 contact material, and makes electrical contact performance more stable. The contact material with a doping concentration of 16.7% has the best arc erosion resistance.

Effect of Ni, N Co-Doped on Properties of AgSnO2 Contact Materials

The first-principles method based on density functional theory was used to analyze the impurity formation energies, energy bands, density of states, electron overlap population and elastic modulus of SnO2, SnO2–Ni, SnO2–N and SnO2–Ni–N. SnO2 powders with different additives were prepared by the sol-gel method, and then X-ray diffraction experiments and wettability experiments were carried out. The powder metallurgy method was used to prepare AgSnO2 contacts with different additives. The simulation experiments on hardness, electrical conductivity and electrical contact were carried out. The simulation results show that the conductivity of Ni–N co-doped SnO2 is best, and more impurity levels are introduced into the forbidden band, thereby increasing the carrier concentration, reducing the band gap, and improving the conductivity. The experimental results show that Ni, N doping does not change the structure of SnO2, so doped SnO2 still belongs to the tetragonal system. Ni–N co-doping can better improve the wettability between SnO2 and Ag, reduce the accumulation of SnO2 on the contact surface and reduce the contact resistance. Ni–N co-doped SnO2 has the smallest hardness, improving ductility, molding and service life of the AgSnO2 contact material.

Effect of Cu, N co-doping on conductive properties of AgSnO2 contact

The structure, impurity formation energy, energy band and density of states of SnO2-N,SnO2-Cu and SnO2-Cu-N were studied and analyzed theoretically by using the first- principles method based on the density functional theory in this study. AgSnO2 contacts with different additives were prepared by using sol-gel method and powder metallurgy method, and a series of experiments were carried out on the samples. The simulation results show that the impurity formation energy of Cu,N co-doped SnO2 is the smallest, and its structure is the most stable compared with other doping systems. In the vicinity of Fermi energy level, there is a strong hybridization between Cu atoms and N atoms, and more impurity energy levels are introduced into the forbidden band, which increases the carrier concentration, decreases the band gap and enhances the conductivity. The experimental results show that the doping does not change the structure of SnO2, so the doped SnO2 still belongs to the tetragonal crystal system. And the Cu,N co-doping can greatly improve the wettability between SnO2 and Ag, so that the aggregation of the SnO2 on the contact surface can be effectively prevented, and the contact resistance is reduced. Among the four kinds of AgSnO2, AgSnO2-N, AgSnO2-Cu, AgSnO2-Cu-N contacts, the conductivity of AgSnO2-Cu-N contact is maximum, which is 56.18%IACS, and the contact resistance, arc duration, arc energy and welding force are the smallest, which are 0.946 mΩ, 1.90 ms, 174.31mj and 28.05cN, respectively. Therefore, Cu,N co-doping can fully combine the advantages of Cu single doping and the advantages of N single doping to make up for the shortcomings of AgSnO2 contact, which further improves its conductivity. Moreover, Cu,N co-doping also improves the arc corrosion resistance and anti-welding behaviour of the contact.

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.

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.

The Preceding Voltage Pulse and Separation Welding Mechanism of Electrical Contacts

In order to obtain a better understanding of the welding mechanism in contact separation, electrical endurance tests were conducted with AgSnO2 and AgNi contacts on a simulation test device. Waveforms of contact displacement, contact voltage, and current were recorded with LabVIEW during the tests, and changes in a contact gap and heights of pips with increases in operation cycles were observed through charge-coupled device cameras. The resultant test results show that welding in separation is accompanied with a preceding voltage pulse which represents arc rather than contact bounce arc.

The Effect of Transverse Magnetic Field on Making & Breaking Arc Durations of Electrical Contact

Application of transverse magnetic field (TMF) is one of the most important ways to improve electric life and breaking capacity of DC relays. For better understanding of dependence of arc durations on transverse magnetic field, a series of experiments were conducted under an external transverse magnetic field with 12 pairs of AgSnO2 contacts in a DC 28V 60A/30A/5A circuit, respectively. By using permanent magnets, the transverse magnetic field was obtained and the magnetic flux density at the gap center was varied from 13 to 94mT. The results show that breaking arc duration is decreased monotonically with increases in the magnetic flux density, but making arc duration isn't decreased monotonically with increases in the magnetic flux density. In addition, both the magnetic flux density and the breaking arc duration have threshold values Bl and Tbmin, respectively, which means the breaking arc duration is almost stable with the value Tbmin even if the magnetic flux density is higher than Bl.

Effect of Axial and Transverse Magnetic Fields on the Arc Duration and Material Transfer

Axial and transverse magnetic fields are widely used in many kinds of switches to decrease the arc erosion. In this paper, the influence of these two kinds of magnetic fields on the arc phase transition was studied particularly for AgSnO2 contacts breaking a 28V/25A circuit. The experiments were carried out under resistive and inductive loads in an atmospheric environment. The relationships between flux densities ranging from 0 to 200mT and the arc duration were obtained. It was found that the transverse magnetic field was more efficient in balancing the arc phases and decreasing the arc erosion. The results can be used to guide the design of arc extinguishment systems in DC high power relays.

General properties of high current switching under 36 V DC for Ag and AgSnO 2 contacts

This study presents a study concerning the contact opening under DC voltage in the case of high-intensity currents (a few hundred amperes) for Ag and AgSnO2 contacts. The application fields are mainly automotive and aeronautical systems. An experimental device has been designed in order to study the opening of contacts under various conditions. The influence of several parameters (opening velocity, arc current intensity, nature of the circuit load and so on) on contact opening is studied. The measured parameters characterising the opening phase are: the arc duration, the arc energy and the arc voltage. Moreover, the study of the contact erosion under the electric arc action is achieved with the help of a 3D profilometer enabling the measurement of mass transfer and, for instance, of the amount of molten or eroded metal.