At present, hundreds of electrical contact materials for low-voltage electrical appliances have been developed, but only dozens of contact materials have been industrialized and applied in practice. They can basically be summarized into four series: Ag-CdO, Ag-Ni, Ag-W, and Ag-C. In other words, the vast majority of them are silver-based materials, or contain significant amounts of silver. In addition to its high electrical conductivity, thermal conductivity and high plasticity, silver also has a small affinity with oxygen. The oxidation products Ag2O and AgO can decompose at 200°C, and the resistivity of these two oxides is small and（1Ω·cm and 120Ω·cm respectively at room temperature ）. Therefore, silver can provide lower contact resistance for the contacts. When the surface of a silver-based contact is oxidized, the current contraction zone will generate heat, and the silver oxide on the surface will decompose, thereby restoring the contact between the metals on the contact.

    In frequently operated electrical devices, copper-based contacts are sometimes used: Cu-Cd, Cu-WC, Cu-W. In special point contact structures with large contact pressure, frequent operations, and friction during contact, copper-based contacts can provide good wear resistance and sufficiently low contact resistance.

    All series of electrical contact materials currently used are composite materials, and the solubility of their components in the matrix is very limited. Therefore, when producing electrical contacts based on copper and silver, powder metallurgy methods are often used.

    Through the alloying method, the performance of silver-based and copper-based contacts will not be improved, nor can this comprehensive problem be fundamentally solved, because although alloying can improve the hardness and wear resistance, it will inevitably accompanied by a decrease in melting point, thermal and electrical conductivity properties. The powder metallurgy method can obtain dispersion-strengthened materials that have the comprehensive properties of each component without reducing the electrical conductivity, thermal conductivity, and melting point, or prepare pseudo-alloys with a solid frame structure.

    As mentioned earlier, these application properties of contact materials are tissue-sensitive. The dispersion of each phase in the material, their mutual orientation, phase interface, etc., will affect the arc cathode spot state, the melting depth and electrical corrosion resistance of the material. For example, when the tungsten powder particle size increases from 2 to 8 μm, When reaching 25μm, the degree of electrical corrosion of Ag-W contacts will increase by 2 times.  Ag-CdO contact material can work well on medium-current and low-voltage electrical appliances when the components are finely dispersed; when the components are coarsely dispersed, it can be used on high-current and low-voltage electrical appliances. There are certain differences in the production processes of these materials. Therefore, research on technology is of great significance not only for improving product quality, but also for expanding the application fields of products.

    It should be emphasized that the literature on the effect of W particle size on contact arcing stability is conflicting. Some articles point out that as W particles increase from 1 μm to 20 μm, the corrosion resistance of the material increases. In composite materials with a particle size of about 20 μm, it is again observed that the amount of wear caused by the influence of capillarity and brittle damage is reduced.

    Although powder metallurgy is used to a greater or lesser extent in the preparation process of all electrical contact materials, differences in the physical and chemical properties of the components that constitute electrical materials will bring different characteristics to each type of contact material. , there are opportunities for the birth of new materials.

——The content of the article comes from the Internet