Potassium Fluoride (KF) in XIN XIN QJ102 Silver Brazing Flux

     Potassium Fluoride (KF) serves as one of the core active components inQJ102 silver brazing flux.

Its functions can be broken down into keypoints based on the brazing mechanism:

      1. Oxide Film Removal (Core Function)

     During the brazing process, a stable oxide film forms on metal surfaces(especially copper, steel,

and stainless steel), such as:

     ▶CuO/Cu₂O

     ▶Fe₂O₃

     ▶Cr₂O₃ (stainless steel)

     Function of Potassium Fluoride:

     ▶Reacts with metal oxides

     ▶Generates soluble or fusible fluoride complexes

     ▶Enables the oxide film to be "dissolved" or "peeled off"

     Results:

     ▶The solder can directly wet the metal surface

     ▶Improves spreadability and bonding strength

     2. Provision of Active Fluoride lons (F^-)

     At high temperatures, potassium fluoride:

     ▶Partially dissociates and releases F^- (fluoride ions)

     ▶F^- has extremely strong chemical activity

     Function:

     ▶Attacks stubborn oxide films (especially Cr₂O₃ in stainless steel)

     ▶Improves the overall "activity level" of the flux

     Essence:

     ▶KF is the "active source" that determines the flux strength

     3. Lowering Flux Melting Point (Synergistic Effect)

     KF usually forms a eutectic system with the following components:

     ▶KBF₄ (Potassium Tetrafluoroborate)

     ▶KAlF₄/ K₃AlF₆ (Potassium Aluminate Fluoride)

     Function:

     ▶Lowers the overall melting temperature of the flux

     ▶Activates the flux at a lower temperature

     Effects:

     ▶Wider brazing window

     ▶More stable operation

     4. Improving Wettability and Fluidity

     The molten salt system formed with KF participation has:

     ▶Good fluidity

     ▶Low surface tension

     Function:

     ▶Helps solder spread

     ▶Improves weld compactness

     5. Risks and Control (Critical)

     Although potassium fluoride is effective, it also brings problems:

     Potential Risks:

     ▶Generates fluoride residues (corrosive)

     ▶May produce irritating gases at high temperatures

     ▶Not suitable for the electronics industry (corrosion risk)

     Industrial Control Methods:

     ▶Proportion control with KBF₄

     ▶Addition of corrosion-inhibiting components.

     ▶Optimization of cleaning performance (low-residue design)

     One-Sentence Summary (For Formulation)

     ▶Potassium Fluoride = the "main component" for providing activefluoride ions + breaking

oxide films

     Recommendations for Formulation Development (Key Points)

     In the QJ102 system, KF is generally:

     ▶Not used alone

     ▶Combined with KBF4 to form the main system

     Common Logic:

     ▶KF → Provides activity.

     ▶KBF₄ → Stabilizes + controls reaction rate