Fundamentals of Glass‐to‐Metal Bonding: VIII, Nature of Wetting and Adherence

Abstract

The sessile‐drop method for the evaluation of wetting is discussed in terms of forces acting on the liquid drop. For acute angles, or wetting of the solid, the driving force is the lowering of the solid‐gas surface energy by the liquid. Contact angles of approximately 25° and less, obtained under appropriate conditions, appear to be associated with interfacial conditions that lead to the development of a strong chemical bond (an interchange or sharing of electrons) and to good adherence. A theory is proposed whereby chemical bonding depends on the development of a balance of bond energies across the metal‐glass interface. The factors that lead to this condition are discussed. A modified Dupre's equation to take into account a strain factor and a contact coefficient is developed. Bonding of Na 2 Si 2 O 5 molten glass to platinum, gold, and iron and oxidized iron in several atmospheres is discussed.