What are the three stages of flux when heated?

In the context of silver brazing, understanding the stages of flux when subjected to heat is crucial for ensuring optimal joint quality. The correct answer describes the transformation that flux undergoes as it is heated.

During the heating process, flux transitions through three distinct stages: initially, it appears powdery as it is applied in a dry form. As the temperature rises, this powdery flux becomes milky, indicating that it has started to melt and become a more viscous, liquid-like state. This milky substance can help the brazing process by providing a protective atmosphere and improving wetting properties on the metals being joined. Finally, as the temperature increases further, it transitions to a watery state, which is a key part of the flux's effectiveness in removing oxides and promoting a clean joint.

This sequence illustrates the importance of properly applying flux and controlling the heating process, ensuring that it efficiently facilitates the brazing operation. Understanding these stages helps practitioners recognize how flux functions during heating and why each phase is critical for a successful brazing joint.