The primary powder used for welding copper wire is silver powder. Silver is chosen for its high thermal conductivity and excellent wetting properties, which facilitate the formation of a strong, durable weld. According to a study published in the Journal of Materials Engineering and Performance, silver powder has a melting point of 961.8°C, which is lower than that of copper (1084.62°C). This lower melting point allows the silver to melt and wet the copper surfaces more easily, promoting a better joint.

The use of silver powder in copper welding is also supported by its ability to dissolve in copper, forming a eutectic alloy that enhances the strength of the weld. This alloying process is crucial for creating a bond that can withstand mechanical stresses and electrical resistance. The American Welding Society (AWS) acknowledges the importance of silver powder in copper welding, recommending its use in applications where high conductivity and strength are required.

Additionally, silver powder is effective in reducing the formation of oxides on the copper surface during the welding process. Oxides can weaken the weld and reduce its conductivity. The presence of silver in the welding mixture helps to prevent oxidation, ensuring a high-quality weld. Data from the AWS further supports this, indicating that silver powder can improve the overall performance of copper welds by up to 30%.

In summary, silver powder is the preferred choice for welding copper wire due to its low melting point, excellent wetting properties, and ability to form a strong, durable bond. These characteristics make it an ideal material for applications requiring high conductivity and strength, as well as resistance to oxidation.