Fracture of Soda‐Lime Glass Tubes by Field‐Assisted Ion Exchange

The field‐assisted ion exchange of K + and Na + in soda‐lime glass tubes fdled with and immersed in molten KNO 3 was Investigated. Stress distribution deduced from photoelastic measurements agrees well with that calculated from analogy to thermal stresses. Fracture was observed when a critical exchange depth was reached. The effects of tube dimension, surface condition, temperature, electric current density, current interruption, and current reversal on the critical exchange depth were studied. Calculated stresses for fracture originating on the tensile side of tubes exchanged on one side only agree with the independently measured fracture stresses of similar tubes. Fracture originating on the compressive side is believed to be related to “spalling” under biaxial compressive stresses which were frequently observed on the compressive surface.